Tecumseh HS40 Won't Run

[UnorthodoxCreat]

I'm trying to get the original HS40 from my Trail Tramp running but I can't get it to do anything for the life of me. Back in the fall my dad and I tried to get it running for the first time. After adjusting the points it ran roughly for a little bit till it sheared the flywheel key because we didn't have the fly wheel bolted tight. I didn't have any extra keys so that was the end of that for the day. I got some new keys but just got around to trying to get the engine running again this weekend. For some reason we can't get it run at all. It has the original diaphragm carburetor. I rebuilt that back in the fall. We've had it apart and inspected several times to try and make sure everything is correct. We've blown air through all the ports. The plug is getting wet. The engine has spark. It seems adequate at worst when turning the flywheel over by hand. Back when we had it running in the fall we even had the twilight working off the lighting coil so I don't think the ignition is the issue. We confirmed timing is correct by pulling the head and making sure th coil was adjusted correctly at .035 before tdc. I did a leak down test tonight by putting air into the head via the spark plug hole. Air is not leaking any where. It only comes out of the valves at the appropriate times in the stroke and the flywheel is hard to turn over on the compression stroke. The piston and cylinder both look great from the top side. I also confirmed timing by pulling the head and turning the engine over by hand. It always sparks at the correct time. I pulled and reinstalled both valves. Both seem perfectly fine. The only thing I haven't done is open the crankcase. I haven't been able to get the clutch off yet but I don't knew what good that would do at this point anyways.

All of the to say is there something I'm missing or something I need to check? I can't figur this out and it's got me beyond frustrated.

 

[capguncowboy]

How is your flywheel key? If it's even slightly bent, it'll throw the timing off. If it's bent, replace it. Be sure to crank that flywheel nut back on at 450 inch-lbs.

I had a similar issue on my Rupp HS40, and it turned out I wasn't getting the nut tight enough and it was bending the key, or shearing it one time.

 

[UnorthodoxCreat]

How is your flywheel key? If it's even slightly bent, it'll throw the timing off. If it's bent, replace it. Be sure to crank that flywheel nut back on at 450 inch-lbs.

I had a similar issue on my Rupp HS40, and it turned out I wasn't getting the nut tight enough and it was bending the key, or shearing it one time.

Flywheel key in it now is brand new and I can't see any damage to the flywheel or crank from when I had it come loose. It came loose at low speed, just messing around in the garage. I'll have to bring a torque wrench home from my shop to check the torque but I've been tightening it as much as I reasonably can.

 

[minibikin']

How about ignition timing? I can tell you first hand if they aren't times correctly that sometimes won't run at all.


Sent from my Texas Instruments Speak and Spell...[emoji2]

 

[UnorthodoxCreat]

How about ignition timing? I can tell you first hand if they aren't times correctly that sometimes won't run at all.


Sent from my Texas Instruments Speak and Spell...[emoji2]

Seems correct to me. I don't have the correct dial indicator so I pulled the head and checked that per the write up capgun did. I can also turn the engine over by hand with the head off and watch a plug spark just as the piston reaches tdc.

 

[bikebudy]

Do you know the compression ? anything under 60lbs don't seem to run.

 

[UnorthodoxCreat]

Do you know the compression ? anything under 60lbs don't seem to run.

Not at this time. We tried my dad's compression gauge but it didn't register anything. I thought that was the problem at first but I then tried the same gauge on my push mower that works fine and it didn't show anything either. I'm thinking the gauge isn't really made for small engines. That is why I did the leakdown test to try and confirm it has compression. It feels like it has plenty of compression when pull starting.

 

[JohnnyTillotson]

You can use a dial indicator to check the crank. Put it against it and turn. If it comes off or pushes into it, its bent. Doubtful but worth a look.
Did you put a new spark plug on? Even if you have spark, it might not be strong enough.

 

[Tink]

A new or known good condenser and sparkplug might help. Some wet plugs simply do not perform.
Check coil and plug wire for short to grounds.
Coil itself can be suspect of generating a weak or intermittent spark. Some one with an ignition coil tester could check it.

If you have flywheel magnets , make sure they are firmly secure. Polish them with emery cloth and also the coil face where energy transfers between them. Wipe off metallic residue and recheck gap.
I've encountered multiple engines where the magnet/coil faces were tarnished/rusty and cleaning them did the trick by improving ignition spark and efficiency.

 

[UnorthodoxCreat]

You can use a dial indicator to check the crank. Put it against it and turn. If it comes off or pushes into it, its bent. Doubtful but worth a look.
Did you put a new spark plug on? Even if you have spark, it might not be strong enough.

What am I checking for? To make sure the crank is straight? The plug is used but came off another bike that runs great.

 

[Dr. Shop Teacher]

What am I checking for? To make sure the crank is straight? The plug is used but came off another bike that runs great.

Two clues: if the crank is slightly bent your air gap will change, doubtful as noted above. Spark plug: from same model engine? If not, could be a contributing issue. I've gotten in the habit of changing coils on every engine I rebuild--the ones I find usually have set out in the weather for a while. If you haven't replaced the condensor, points and plunger, I'd consider it. Mr. Pat was experimenting with a kit that eliminated the points, don't know if he actually got it working. Properly setting up the condensor and points is key, Andy's step by step is real good, glad you used it.

 

[capguncowboy]

Two clues: if the crank is slightly bent your air gap will change, doubtful as noted above. Spark plug: from same model engine? If not, could be a contributing issue. I've gotten in the habit of changing coils on every engine I rebuild--the ones I find usually have set out in the weather for a while. If you haven't replaced the condensor, points and plunger, I'd consider it.

As a general rule of thumb, when I redo and tune up an old engine, I always replace the points, condenser and coil. I know they're not always bad, but I want to eliminate as many possibilities as I can. It makes things a little easier in the long run, and doesn't cost THAT much

 

[cruhr1]

Seems correct to me. I don't have the correct dial indicator so I pulled the head and checked that per the write up capgun did. I can also turn the engine over by hand with the head off and watch a plug spark just as the piston reaches tdc.

Did you use a meter to set the timing? If you had that engine running last fall and you have verified spark, fuel and no air leaks then the timing is off. I have had the stator move ever so slightly while tightening it down and they will not run unless precisely timed. I would try to reset the timing one more time.

 

[OND]

Does it try to start ? Back fire ? Pop....or do nothing ?

 

[UnorthodoxCreat]

I was rechecking timing again tonight and I have continuity across the points whether they are open or closed. That is obviously an issue I need to fix. I wouldn't think I would have any spark if there is a short do so I'm perplexed. Does anyone have part numbers for a new coil, condenser and points for a hs40 with a lighting coil. I want to replace them and be sure I get the right thing.

 

[UnorthodoxCreat]

Does it try to start ? Back fire ? Pop....or do nothing ?

It's not even trying to start now. No popping or anything.

 

[OND]

I would suspect a firing problem then.....but I think you found the problem, maybe a grounded out wire to the points.

 

[cruhr1]

I was rechecking timing again tonight and I have continuity across the points whether they are open or closed. That is obviously an issue I need to fix. I wouldn't think I would have any spark if there is a short do so I'm perplexed. Does anyone have part numbers for a new coil, condenser and points for a hs40 with a lighting coil. I want to replace them and be sure I get the right thing.

There you go! Now you're on the right track:thumbsup:

 

[UnorthodoxCreat]

My dad came over last night and we finally got this running last night, sorta. I didn't understand that when checking for continuity across the points the the coil and condenser needed to be disconnected. I had them connected and that is why I always had continuity. Before figuring that out we pulled the stator off and checked all the wires to make sure nothing was pinched or broken. When we reassembled we had a much better spark than we saw previously. We must have knocked some corrosion off something. Seeing that better spark we did the timing correctly and put everything back together. It immediately was trying to start and with a little carb tuning it was starting, idling and revving great. We couldn't get it to move though. I'm not sure if the engine isn't revving quite high enough, the clutch is worn out or both. After we tried riding it and then it died and I couldn't get it started again. It still had good spark so I'm going to pull the carb apart and make there isn't some dirt in there or something that's messing things up.

 

[UnorthodoxCreat]

I took the carb apart again yesterday and made sure all was clean. I double-checked that the gasket and diaphragm were in the correct order. I also changed the needle back to the original needle. It had a slightly different shape than the one that came with my rebuild case and I wanted to make sure that wasn't an issue. The bike will start pretty well and idles fine but I can seem to get it to rev up now. When it comes off idle it just dies. I've adjusted the main screw in and out and it seems to make no difference. I pulled the main screw out to make sure it was ok and I couldn't see any issues. Any suggestions on what to do?