Super Bronc 8hp Tecumseh - trying to get it to start !

#1
Hey Folks,

The super bronc vt-8 I bought last month has yet to start :shrug: .

When I bought my bike it needed a few parts, brake handle, throttle assembly and cable, cable stop nut (the right tecumseh kind). I waited to get those parts on before trying to start it.

When I did try to start it the first time, I gave it some Fresh gas, and new plug. No start.

Primed the cylinder w/ a little gas. No start.

Bought spark tester...connected at night got spark once out of 7 or 8 pulls.

Read thrownrod's sticky about big block tecumseh air gap , and timing...got real scared....spoke w/ Ron Kimball about part I bought mentioned issue..Ron say's you need a NovaII electronic ignition module (to replace your points and condenser) and cure that inconsisten spark.

Installed NovaII module that Ron shipped me, more spark now, and a few blap, blap's when I primed it. No start.

Pulled carburetor, took apart and cleaned it real good, replaced float bowl gasket...o'rings looked ok. Needles weren't the prettiest but don't have new ones today. Reasembled carburetor and put back on bike.

Emptied gas tank, filled w/ fresh gas.

Primed cylinder, blap, blap, no start !!! (got a trend goin' here :doah: )

Questions finally....

How do I determine if my carburetor is getting gas at all (short of taking it apart again ?) (bowl had gas in it when i took it apart),


This bike has a 'pulse fuel pump' on it...I'm not sure how they work, so am unsure on how to test ?


And any recomendations on what to try next to bring this motor back to life ?

Thank you,

Robert
 
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delray

Well-Known Member
#2
How do I determine if my carburetor is getting gas at all (short of taking it apart again ?)
maybe just start with a spray bottle of gas and give the carb couple shots and see if it will fire and if so keep sraying litlle more in it to see if will keep running. if you get it to pop over and run with the spray bottle? then you know you got carb problems and something is plug up. for example needle,jet...etc..
 
#3
maybe just start with a spray bottle of gas and give the carb couple shots and see if it will fire and if so keep sraying litlle more in it to see if will keep running. if you get it to pop over and run with the spray bottle? then you know you got carb problems and something is plug up. for example needle,jet...etc..
Hey Delray,

Thank you for the suggestion.

I'll round up a spray bottle today, and give it a go. I think that will be closer to realistic than me putting gas in the cylinder via a syrynge squirt in the spark plug hole (too concentrated probably ?)

Like I've expressed before, I'm learning, and I'm determined...and hope with experience I'll develop more intuition.

I'll let you know how this does, thank you for the help !
 
#4
First thing I'd do is resist the temptation to "prime" the cylinder. Raw fuel in there is not going to help. Wear gloves. Hold the spark plug' treads against a good engine ground ( clean piece of metal). Have someone pull the starter and see if you have consistent good spark. If that's ok then install the plug, give the Air cleaner intake a small shot of ether (starting fluid) spray. It should run for a few seconds on the ether. If it does, you've got a fuel (carb) problem.
 
#5
Hi Robert, I'd say now since you put a new style ignition on (which I have no clue about - something new to me as I'm old school) I'd say you have a fuel delivery problem. Disasemble the carb again and take off the intake too for new gaskets. possible vaccume leak there. Check out the high speed jet look for rings of distortion on the shaft and there should be a little brass washer that goes on top of the spring and a rubber O ring on top of that that goes down into the fuel pickup tube to prevent any air from coming in around the threads on the jet. If the O ring is flat or cut or missing or the brass washer is missing - it will draw fuel improperly. On the side of the pickup tube is a small hole where the fuel goes into the jet area make sure that is clean and open.

Also check the atmospheric vent hole just to the right side of the low speed jet adjustment area make sure that hole is open by squirting carb cleaner into it and the fuel pickup tube hole where the high speed jet goes into it and the side hole in the fuel pickup tube and the low speed jet hole spray all of these areas with carb cleaner and blow out with compressed air about 10 times. Reasons I say that do that so many times carb cleaner evaporates pretty quick so be fast about blowing out the passages before it evaporates...

Thrown Rod...
 
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#6
Preset carburetor adjustments are:
Idle jet adjustment is 1 1/4 off of seat
High speed jet adjustment is 1 1/2 off of seat
Throttle stop screw is 1 turn after contacting throttle lever.

These are basically rough est. from tecumseh let the motor warm up and when adjusting jets rev and wait a while for the adjustment to take effect before fine tuning each time.

You'll find the adjustment more likely after running the motor under load conditions rather than just sitting still just move rich or lean adjustments about a 1/4 turn or less until you find it.

Beware this motor will fly at least 40 - 45 mph I remember mine when I cracked the throttle it would stand the bike straight up in the air every time and I was grabbing brakes before I blew a stop sign... Very powerfull motor
 
#7
Hey Delray, Millers1, and Thrown Rod,

Thank you very much for the suggestions. I had a weird work schedule today, so am just getting back on line to send my thanks.

I'm going to source the O-rings, and possibly new needle's, this week, and rebuild the carburetor again. This time however based on what I'm learning, I'll use compressed air right after the carb cleaner...with fast evaporation, I can see how gunk could get left in there...and that the air pressure will blow any of that residual mess out...thank you!!

Also, I'd stayed away from starting fluid when the auto parts guy started giving caution that i don't overload it and blow/burn something up ! So further input on use of starting fluid is appreciated.

I'm excited to hear this is a strong motor, looking forward to it riding it !

I'll post here as I progress, so you all will know what the scoop is.

Thanks again,

Robert
 
#8
.........This bike has a 'pulse fuel pump' on it...I'm not sure how they work, so am unsure on how to test ?.......
pulses from intake/crankcase move the diaphram back and forth to push fuel. just spinning engine over is enough to pump some fuel. using one on mine because the tank is too low and won't gravity feed to carb. if you can mount the tank high enough, remove the pump for now. once the engine is running, hook it back up to see if it works. the one line that is away from the other 2 is the pulse/diaphram. should not be able to blow through it but should hear the diaphram moving back and forth on suck/blow. the others will only suck (outlet) blow (inlet) one way.
sorry for the vulgar descriptions.
 
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#9
further research on your carburetor.

Sorry I figured you had a walbro carb so the jet adjustments were for that model of carb and since you have a walbro carb with pulse pump that's a little different.
Sometimes it helps when you give us the carb stamping numbers on the carb which is usually stamped on the side of the body or located on the mounting flanges or just plain have the numbers off the motor so I can look in the master parts manual and id for type of carb in the master mechanics manual - I suspect you have a LMH carb there is several different types of styles some with fixed high speed jets some not.

Anyway this carb has a atmospheric vent located just below the choke shutter made into the mounting flange and prior to removing the hi speed nut it is advised to take out the high speed jet first.

If you have the LMH style carb then off of seat adjustments are like these just find your type of LMH listed below some have fixed jets and have no adjustment screw.
Carb. High speed adj. Screw Idle adjustment screw
LMH-1 high speed adj 4 turns Idle adj 2 1/2 turns
LMH-1A high speed adj 1 3/8 turns Idle adj 1 3/8 turns
LMH-2A Fixed idle adj 1 1/2 turns
LMH-3 high speed adj 1 1/2 turns idle adj 1 3/8 turns
LMH-8 None idle adj 1 1/2 - 1 3/4 turns
LMH-13 high speed adj 1 - 1 1/4 turns idle adj 1 7/8 - 2 1/8 turns
LMH-17 high speed adj 1 1/4 - 1 1/2 turns Idle adj 1 - 1 1/4 turns


As far as your question about carb cleaner well yeah overload the motor with that stuff and it will get hairy. I bought a Rupp continental custom with a tech h35 walbro carb on it the fellow who owned the bike had it since he was a kid and passed on so it sat forever in his garage. It was the most stubborn bike engine I ever tried to start. I dropped a teaspoon of fuel in the spark plug hole and still it evaporated pretty quick and no fire.

So a few friends stopped by and it worked like this. One guy shot starter fluid into the air cleanner (without the filter in) the other guy pulled the starter rope and I had my hand on the high speed jet ready to adjust when it fired. The guy who pulled the roped pulled and pulled while the other guy shot starter fluid I heard it catching and said it's about to fire it was just puffing then all the sudden after more pulls it caught and ran. I adjusted the high speed and got it about right and then the carb just started to flood with gas everywhere. (I will install a tank shut off valve now for sure before I burn the bike down to the ground)
Oh well. Kind of proves they are hard to start at times after sitting for years and years in a row. It took 3 guys to prime the motor - that's kind of bad for a old stubborn Walbro carb...
 
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#10
DeeJaaa,

Thanks man. I hope to experiment with this later today (after work).

In regards to testing this fuel pump, Scott Kimball (PowerTec parts) also tells me if I remove the line that feeds the carb from the pump, and pull start enough to cycle the piston a few times, gas/ or lack of gas, produced from the carb feed line will show me if it's pumping, or not.

Good idea about moving the tank up if needed to take the pump out of the equation....that must be why you see so many of those 'peanut' tanks on some Super Bronc's.

Thanks again, I'll keep y'all posted.
 
#11
Sorry I figured you had a walbro carb...
Sometimes it helps when you give us the carb stamping numbers on the carb which is usually stamped on the side of the body or located on the mounting flanges or just plain have the numbers off the motor so I can look in the master parts manual and id for type of carb in the master mechanics manual - .
Hey ThrownRod..thank you for all the detail..I just read this, and went to the garage right away to get the numbers for you.

The carb numbers are: 770 1D22

The engine numbers are HM80 - 155 74F SER 1113D

Regarding the engine number...155 74F ... I can not tell if that space before 74F is a space or a character (there's a little ding there, and not being too familiar w/ Tecumseh's numbering standards, it's making me wonder if it was actually a space or a character ?)

Sounds like I don't have to be overly concerned w/ using starting fluid.

The start-up scenario is helpful also,...I need to round up a couple of friends and give that a try (anybody want to make a trip to the coast ?).
 
#12
Hey ThrownRod..thank you for all the detail..I just read this, and went to the garage right away to get the numbers for you.

The carb numbers are: 770 1D22

The engine numbers are HM80 - 155 74F SER 1113D

Regarding the engine number...155 74F ... I can not tell if that space before 74F is a space or a character (there's a little ding there, and not being too familiar w/ Tecumseh's numbering standards, it's making me wonder if it was actually a space or a character ?)

Sounds like I don't have to be overly concerned w/ using starting fluid.

The start-up scenario is helpful also,...I need to round up a couple of friends and give that a try (anybody want to make a trip to the coast ?).
Looks like your engine should read # HM80 - 155174F (tecumsehs use 6 #) and I did see your 770 carb# and it is a Tecumseh carb and not a Walbro

The Carb PN 632199 for the whole assembly and the carb rebuild kit is PN 632009
uhh just key in these numbers on google and maybe you'll get a exploded view of this carb.
My blowed up view of it does show 2 - O rings one for High speed jet and one for the low seed jet and both with brass washers.

Good luck firing it up
 
#13
Hello again Everyone,

ThrownRod, thank you for the additional info.

Tomorrow is payday, and I'm planning on placing the order for the parts needed for the carburetor (for my vt-8).

In addition to the standard rebuild parts I added the price of a new float and both high speed, and idle screws in there and now i'm up to over $26.

I have also seen available the complete carburetor for $73
series 770 Tecumseh 632199 / 632402 OEM CARBURETOR
FITS HM80-155174 TEC632402

In that this is only my second carburetor rebuild, (and the first one went good) I don't have the experience to make a judgement call on which makes more sense....rebuild this one w/ new bits and hope it works, or buy new, and expect it will work ?

I know we are only talking about a $45 difference, but I'd like to make the most effective use of my money. Any advice is appreciated....

Thanks.
 

toomanytoys

Well-Known Member
#14
Unless you like tinkering with it, I'd just order a whole new carb. I personally have never had great success rebuilding Tecumseh carbs. Seems like to me that they have an expiration date.
 
#15
i dont think you need to be buying new parts if everything looks as it should. Most of the time its just a matter of cleaning it out good. you may have to pull it off a few times before it cleares up. carb cleaner and an air blower usually does the trick. Make sure the float is level and not leaky and full of gas or hanging up on anything. If its low the float needle seal is probrobly swolen up and not getting you enough gas. sounds like you fuel pump could be restricting it too. and make sure you clean out both holes in the threaded part of the fuel bowl screw. there is a tiny one that is often overlooked. Dont be afraid to use starting fluid. The autoparts guy was probrobly just refering to newer cars with all the electronics in the intake tract
 
#16
Hey Folks,

I finally got to spend some more time working with my super bronc, so i finished rebuilding my carbueretor, got the linkage set up correctly, and still having issues getting it to pick up and run.

Today, I took my neighbor up on his offer to help (he used to have a small engine repair business)..after listening to it try to start, he said something is up with the timing.

Upon pulling the flywheel (which I had not ever done, and considered brain surgery level stuff...but what turned out to be a neat proceedure) we find that one of the 6 magnets is loose, and another one looks a bit oddly placed...(looks like it'd been reglued but not in the original spot).

So with that, I find i am actually still back at square one, needing to do as was suggested in Thrown Rod's coil firing thread.....the string about the magnets...

And that's where my question lies...My neighbor friend says to get a new flywheel, but I like ThrownRods advice about regluing the magnets with jb weld in the original spots !

My question regards the one magnet that is not sitting quite on it's original footprint.

I've been studying this thing, and I don't see any easy way to get the missplaced magnet loose, as it's had lots of glue used on it.

So first off, does the distance spacing between the magnets as they are placed around the flywheel matter that much :shrug: ?

(I know the polarity matters, and the n.s.n.s.n.s......orientation )...but the fact that this magnet is glued tighter than a tick leads me to ask does it matter that most of the magnets have about 3/16 inch space between them and the next one...but this one probably has a good 1/4 inch space on one end and 1/8 inch space on the other.

So that said, if the space between the magnets does not matter, then i'll just reglue the 'loose' one in it's original footprint, and get on with it....if equal space does matter, then i need to figure how to get that glued one loose ?

Thanks very much for you all's help and advice !

Robert
 
#17
i think they only have magnets all the way round when there is a lighting coil. the firing is controlled by the points but you should figure out what magnet is in play when its firing and make sure that one is correct
 
#18
Magnets...

I saw your email here so I thought the answer should be shown here.

I surmise that the magnets are symmetrical in it's location when a north magnet passes at the begining of the center leg of the coil the south magnet passes at the begining of the first leg it's setting up the field of magnetism and when the north magnet leaves the center leg then the south magnet should leave the first leg at the same time for the primary circuit and same for the secondary ciruit too the south magnet enters the center leg and the north enters the last leg at the same time and both of the magnets should leave at the same time...

The same goes for the charging circuit as well.

I would cut the glue with a saw blade of some type all around it where there is glue and get down to the metal and maybe secure the flywheel in a vice and use a block of wood and give it a smack and see what happens or maybe get something thin like a small chisel and get under the magnet and tap it and see what happens. unless you find something that might desolve the glue / expoxy ???

Just be carefull those magnets are not offered in parts stores unless you go to some place like earth magnets and cut one down to size with the correct north or south magnetism.

To be honest I don't know if it really has any bearing on the spacing situation but it may reglue the one that came loose and fire it up that will tell you if it's causing a problem or not. I'd say the two magnets that are for the ign circuit should be pretty well on the money... get the crank turned to the point of it's opening the points and put the flywheel on and take note of which two magnets are over the center leg and the last leg and those are the two your concerned about as far as firing the coil.

Good luck firing your motor !!! :thumbsup:
 
#19
To help you get a better understanding of magnetism...

Point’s are means of interrupting the current to cause the rise and fall of the magnetic field is a set of normally closed points that respond to the magnetism in the core. When the points open and discharge the field of voltage and the points close then the process is repeated. The first magnet on the flywheel is the North pole it passes the first leg of the coil then passes to the center leg the south pole magnet shows up at the first leg and this is where the primary coil windings begins to set up it’s field of magnetism when the North pole magnet enters the last leg then the south pole magnet arrives at the center leg and this sets up the secondary winding for maximum fire power.
The magnetic field is now flowing in a circle around each side of the coil (which is on the center leg) and the two outer legs form a circle of magnetism and enters in through the center laminations that the coil is mounted on inducing a field for the secondary coil windings to generate the required voltage to send to the spark plug. When the South pole magnet shows up at the center leg and the North pole magnet is on the last leg it’s completing the field then the points open at the correct Before Top Dead Center settings to fire the motor combustion chamber…

A capacitor or condenser is used across the contacts to aid in the rapid field collapse and to reduce contact arcing thus extending the life of the points. (The condenser absorbs the self-induced current of the primary winding, preventing it from opposing the rapid fall of the primary current.) Early condenser’s were made up by alternating layers of tin foil and paraffined paper, cut to the same size, like the pages of a book. Even numbered foil sheets were connected together for one polarity and odd numbered sheets were connected together for the opposite polarity. These connections were then routed to each side of the breaker points. But that is the old school way from way back when. The newer condensers made in a more updated and that tin foil set up is still used but put in a round cylinder with one lead coming out of it going to where the point’s wiring is hooked up…

So, here's how it is the points and the condenser and one of the little wires from the coil is grounded usually near the laminated plate area and this all ground s through the engine block. The engine block is actually part of the magnetic field that is set up. The positive flow of electrons has to flow to a negative even though we have north and south pole magnets that positive energy has to flow in one direction only and that is through the coil wire to ground when the points calls for a spark, initial current flows in one direction and saturates the laminations. The moving points are then pulled open and the coil discharges. Meanwhile, a SECONDARY winding made up of a great many more turns of finer wire has picked up the rapidly collapsing magnetic field. More turns means more voltage and this voltage is then delivered via an INSULATED wire to a SPARK PLUG. (Finer secondary coil wire means more room for more turns and more voltage, but its higher resistance means less current - it's a trade off. We are looking for STEP-UP transformer action here and therefore few primary turns to many secondary turns.) The spark plug circuit's return path is through the engine casting back to the other side of the secondary coil winding.

Most of these old coils can be brought back to life simply by cleaning the connections under the terminal bolts. Corrosion makes a great insulator!
The insulator inside the base of the spark plug must be kept clean because the electricity from the magneto can leak through the carbon on the insulator instead of jumping across the tang, making it hard or impossible to start the engine or making it fire irregularly. Even air in the combustion chamber sets up a resistance for the coil to overcome and jump a spark at the spark plug so the gap or heat range is very important. Too much resistance in any given area and it overloads the coil with too much voltage and melts the varnish like insulator coating on the internal wiring wraps and may short out…

A spark plug will sometimes show a spark when tested outside of the cylinder and yet fail to fire the engine when replaced in the cylinder. This shows that the plug is "leaky", because of carbon or because the porcelain insulator is cracked. A "leaky" plug will spark outside the cylinder and not inside because the spark can jump through the air easier than it can jump through the compressed charge inside the cylinder, especially when the engine is cold. Trouble is sometimes caused (especially in two cycle engines) by spark plugs that do not extend far enough into the cylinder and thus a pocket is left at the end of the plug in which dead (burnt) gas collects. Such gas can not be fired by any spark. Spark plugs so located tend to carbonize quickly because they operate at too low a temperature. If your spark plug has been exposed to a gasoline flooded motor “Heave it” it’s now a junk plug…

A condenser is (supposedly) infinitely resistant to DC. BUT, when a DC is dumped into a condenser by the opening or closing of the points, it roars into the condenser, stops, backs up, roars in again, stops, backs up, etc, like waves on a beach on an incoming tide. A condenser cushions the flow of electrons in a circuit like a spring/shock combo. Therefore, when a point makes or breaks, the coil is subjected to what seems to be AC instead of DC. The lowly condenser acts like an oscillator circuit and this combined with the step up action of the coil is what jumps up the volts and fires the plug. It is the SUDDEN collapse that causes the current in the secondary. The main purpose of the condenser is to prevent arching at the point contacts and burning up the surfaces of the contacts which will cause a slow, or un-smooth collapse, thus lowering the strength of the field collapse, and cause either a low, or no voltage to be induced.

Too big or small of a condenser doesn't do the job because condensers store energy . An ignition circuit needs a condenser that is matched to the coil, and the voltage source, and the RPM of the motor. Too much capacity acts like none at all, and too small of capacity acts like none at all. Condenser design - ignition design somehow takes into account the natural frequency of the condenser.

Usually if you see a yellow spark at the plug it means the condenser is going bad. If you are cranking over an engine without the spark plug connected, never disconnect the wire from the mag nor let the spark plug wire hang. Always ground the plug wire to the engine block. To do otherwise can cause excessive voltage in the secondary winding, and a breakdown of the insulation on the wires.
The reason for arching - the collapse in the field also induces current opposite to the original in the primary winding. It is this current that causes the arching.

A condenser is able to absorb this excess, and higher electron flow, and store it until the circuit is made again, where it is released harmlessly. Without the condenser, the current would literally "bounce" back and forth in the primary winding, prohibiting a clean collapse of the magnetic field.

I believe that condensers can go bad for at least 2 reasons. One is that they are able to absorb the electron flow quickly but discharge it slowly. The other is that they absorb the electron flow slowly but discharge it quickly. I have had condensers that can not discharge the electrons quickly. They are very frustrating because they will give you a good spark most of the time because they are either over capacitated or under capacitated.

This is a important reason about grounding a magneto. If you rebuild and repaint the engine, make sure the mounting bolts and contact area between the magneto and the engine casting are clean bare metal. Of course that goes for all other contacts and connections in the circuit as well.

This is why I stress everything must be clean - super rusty laminations should be cleaned with naval jell and mounting surfaces of the condenser must be clean and even under the points must be clean for maximum ground to ensure maximum magnetic fields to be set up for the coil to act upon. Even areas on the stator plate where it mounts must be clean. All nuts and screws must be tight and no frayed wires and no cracks in the coil wire because electricity will follow the path of least resistance effecting maximum fire power. Absolutely no oil or grease near the coil or the ignition points area or even on the wires.

I too was ashamed of myself the other day – I changed a new set of points and condenser in my H35 simple right ??? uhh no fire from the coil so I put a new one in - uhh no fire from the coil… I took out the points and set them on the table and hooked up a ohm meter and no continuity at the points and sanded them down steel polishing wool and wow it passed current. Uhh threw 20 bucks over my shoulders buying a new coil for nothing… shot carb cleaner on the points blew that out and had a nice blue spark just like the other coil did. But at least I have a spare coil now… Goes to show you even a set of new Tecumseh points sealed in a plastic bag had oxidized to the point of not passing current ..

Needless to say those points had me walking around like a man lost in a forest trying to figure out what I did wrong changing points and condenser when I’v e done it hundreds of times but I’m not here to scare the hell out of everyone with rocket science because sometimes I get confused as the next guy at times. Sometimes the answer is right in front of your face but you can’t see the forest because of the trees…
Threw a Rod… :thumbsup:
 
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#20
I have reglued and even created my own flywheels and magnets.. You have to make sure to get the flywheel and magnet very clean so it not only adheres well, BUT it doesn't raise the magnet up any higher than it belongs.. :doah:

I'd never try JB weld as it's too thick and not a very strong or bondy material.. The two part super epoxys that are sold now days do a fantastic job, it will smush rite down to almost nothing there, allows ya to slide the magnet around easily to where it needs to be.. Just all around better...

Timing and yes the polarity DOES matter... You wanna get them as close as possible to where they belong.. The points will determine WHEN the engine fires, but if the magnets aren't in the right spot, ESPECIALLY on an EIC engine where it is regulated BY the position on the magnets, it can cause piss pour spark.. Being it's a lighted wheel so it's totally wrapped in magnets, even if they were not timed rite, just being the entire wheel is lined with them will saturate quite a lot of juice into the coil and it should work regardless..

The biggest thing to watch for is ride height, so they are not up or down as apposed to the others, and you want them in the right direction..
 
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