Tillotson 212 - Mikuni 22 mm or 24 mm Carb?

#21
They sent you a new driver because of the shorter shaft? What exactly did they send you that was different. Im just curious. I am running a 44 driver so I dont have that problem. But curious if I want to go to a 30 series.
 
#22
The extra drag on the rear tire is due to the TAV itself. It's caused by the belt being forced to take that tight turn around the inside of the driver pulley at idle. Not much you can do to change it but nothing is wrong with the TAV or the bike. Just something else to get used to.
 
#23
They sent you a new driver because of the shorter shaft? What exactly did they send you that was different. Im just curious. I am running a 44 driver so I dont have that problem. But curious if I want to go to a 30 series.
The Tillotson PTO shaft is 2 1/2" long. The Jiang Dong 196 engine that came on the bike has a PTO shaft that was 2 3/4" long. Using the spacers that came with the original driver and the inside stationary half sheave, there was no room left on the PTO shaft to put the hub driver. It was flush. Without the spacers, (to make the driver fit on the PTO shaft), the belt was badly out of line. My understanding was that you need at least 1/4" of PTO shaft end for the hub driver to work correctly. So, the engine supplier sent me a driver that is narrower then the original driver. The Tillotson engine supplier was standup on this issue. They originally told me that the Tillotson engine would bolt up and use the Trailmaster TAV without issue. They send me the new narrower driver and belt for free.

As a side note, IMHO the Trailmaster MB200-2 has great potential. However, out of the box it needs some serious modifications to make it a real trail runner. If I had known how lacking it was for the $, I would have probably taken a different direction. My opinion may not be totally fair as my experience is mainly with motorcycles and only mini bikes when I was a kid. However, the selling dealer of the Trailmaster told me it ripped and they were clocking it on a radar gun because it was so quick. They had no place for me to actually test it before purchase. Out of the box, you could clock it with a real clock. LOL.
 
#24
The extra drag on the rear tire is due to the TAV itself. It's caused by the belt being forced to take that tight turn around the inside of the driver pulley at idle. Not much you can do to change it but nothing is wrong with the TAV or the bike. Just something else to get used to.
Thanks for the information.
 
#25
Getting ready to install the Mikuni VM22-133. How many vent hoses should there be? The carb that I have only has one on the bowl. Thanks in advance.
 
#28
Looking for some advice/recommendations on Mikuni carbs on the following. Building a Tillotson 212 engine to use on a Trailmaster mini bike. Engine has governor removed, CS grind .265 lift cam, billet flywheel w/8 degrees advance, ARC rod, 26# valve springs, 27mm intake and 24mm exhaust valves, .010 head gasket and stock Tillotson carb running an upgraded jet and air filter. I want to move to a Mikuni carb. Trying to decide between the 22 mm and 24 mm carbs. I've done quite a bit of research. Not a lot of information out there on the Mikuni 24 mm carbs that I’ve found. I see lots of information on Mikuni 22 mm carbs improving overall performance on clone 212 engines. Anybody have any results with the Mikuni 24 mm carbs on a clone 212 engine? My concern is that the Mikuni 24 mm may be too much carb for my build. Thanks in advance for any and all information.
I mean no offense, but in my opinion, you're intent on building a racing kart engine for a mini bike. Apples and oranges. I have Tillie's on both. My advise is install a 4 degree offset key to back your ignition timing from the built-in 32 your billet flywheel has that was engineered to run @ a continuous high rpm in narrow power bands on racing engines to a more acceleration friendly 28 degrees unless you plan on racing your mini bike on an oval. Might go 30 on an engine for a broad torque curve build, depending on application, but never 32 on anything not on a track. This is static timing. No advance mechanism like a car. 32 is 32 at idle and at max rpm. You're killing your low and mid range torque with too much advance. I have a similar mini bike build to yours, live in the hills of Eastern Kentucky, climb the hills, and hit 45 on the straits with a PVL flywheel/ 28 degrees advance and the TCT carb, which I believe has increased port velocity (numbers anyone?), which pairs well with the increased piston dwell time provided by the long rod and the velocity killing hemi head. These engines can have issues with low port velocity and it can unintentionally can be made worse. Flow is important, but not at the power killing loss of velocity. Torque rules. Push your gear, don't drag it along until you hit top end at 7000+ sustained where the billet flywheel was designed to perform. Clean up your ports. Polish the exhaust only. Get a pipe to match that cam and install a filter kit. Look at your timing and gear ratio. Read up on port velocity and how to make torque. End of advice. Good luck and happy trails.
 
#29
Why do you say the hemi is velocity killing? I read this wondering as for the heads stock that I baseline the hemi stock has the highest flow. (In the interest of full disclosure I have never had one of the predator 25/27 5mm stem RTC9 heads to test) but every other type I have baselined. I just went out and setup a new hemi head I bought from Chipper on the bench with the intake valve in upside down and velocity probed the runner. Port velocity was slowest at the long side and highest at the short side which is normal. I did this at 28" H2o at the very top before the valve guide I had 220FPS in the middle 290 FPS and at the floor near short side 331FPS. (320-350FPS at 28" is considered the limit before port choke. Sticking a stock size carb is the velocity killer. While the velocity thru the carb will be very high as soon as it hits the runner it will slow way down as the runner is much larger.
 

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#31
I mean no offense, but in my opinion, you're intent on building a racing kart engine for a mini bike. Apples and oranges. I have Tillie's on both. My advise is install a 4 degree offset key to back your ignition timing from the built-in 32 your billet flywheel has that was engineered to run @ a continuous high rpm in narrow power bands on racing engines to a more acceleration friendly 28 degrees unless you plan on racing your mini bike on an oval. Might go 30 on an engine for a broad torque curve build, depending on application, but never 32 on anything not on a track. This is static timing. No advance mechanism like a car. 32 is 32 at idle and at max rpm. You're killing your low and mid range torque with too much advance. I have a similar mini bike build to yours, live in the hills of Eastern Kentucky, climb the hills, and hit 45 on the straits with a PVL flywheel/ 28 degrees advance and the TCT carb, which I believe has increased port velocity (numbers anyone?), which pairs well with the increased piston dwell time provided by the long rod and the velocity killing hemi head. These engines can have issues with low port velocity and it can unintentionally can be made worse. Flow is important, but not at the power killing loss of velocity. Torque rules. Push your gear, don't drag it along until you hit top end at 7000+ sustained where the billet flywheel was designed to perform. Clean up your ports. Polish the exhaust only. Get a pipe to match that cam and install a filter kit. Look at your timing and gear ratio. Read up on port velocity and how to make torque. End of advice. Good luck and happy trails.
No offense taken. I'm on this forum looking for information/recommendations/advice which I appreciate. I'm not an expert on these engines nor have I flowed the heads or dyno'ed any of these engines. The components that I used for this build were recommended to me by several of the primary mini bike/go kart engine builders/suppliers. In fact, the approach that I took was recommended by the engine supplier as they told me that is what they do to the Tilly engines for their Trailmaster MB200-2 mini bikes.

With that said, I believe that some of my issues are from the TAV, gearing and the Tilly carb. You can see in my above posts performance issues that I was experiencing. The Tilly engine in Stage I configuration (no governor), while riding, would not exceed 4200 RPMs @ 34 MPH on GPS. Also, had issues with the carb. With the upgraded carb jet, the engine wouldn't initially start. When it finally did, it ran extremely rough. After cleaning the carb and reinstalling the jet 3 times, it finally started to work. Pretty easy to install a jet! So, I was suspicious of the carb. Gearing issue is kind of obvious as I started with a 38 tooth rear sprocket. With the TAV, because of the shorter Tilly PTO, the engine supplier sent me a new driver unit and belt. Belt doesn't matchup with calculation for correct sized belt based on driven pulley diameter and bolt to bolt centerline spacing between jackshaft bolt and driver PTO bolt. Belt is approximately 1/2" too long.

In for a penny, in for a pound! So, I ran the mini bike the other day for a short time with the built-up engine and Tilly carb. When I originally ran the Stage I engine, I was guessing it topped out at around 4,000 RPMs. It was actually 4200 RPMs with a tach. I'm guessing now with the 50 tooth rear sprocket, I'm guessing it topped out at round 5000 RPMs. I'll install the tach again after I finish installing the Mikuni 22 carb.

Comments:

1) I'm not having an issue with low or mid-range torque. Off idle, I can easily spin the 19" rear tire on dry grass.

2) Sparkplug looks a little lean. I killed the engine while running, no idling, to check the plug.

3) Engine noses over at top end.

4) Without a muffler on the header, engine is gutless. Put a muffler on the header and with some back pressure, engine runs fine.

5) Engine supplier told me this is the best flowing mini bike/go kart engine head I could buy without having the head machined. This statement was based on their dyno testing. They claim 10hp in stock form for this Tilly engine.

6) I have several 800-1000 foot straightaways where I can get on this engine.

My plan is to finish the Mikuni 22 install and then test again, weather permitting.

Tilly!Tilly! - what mini bike are you running, specifics with gearing, TAV?, etc...? My Trailmaster weights around 165 lbs.
 
#32
***UPDATE*** Had decent weather the other day. Decided to test the mini bike. Running a genuine Mikuni VM22-133 with 17.5 pilot and 135 main jets. Torque converter - installed white garter springs on the driver unit and moved the driven unit spring to the first hole. Also, installed what I consider to be the correct length belt (1/2" shorter). WOW, what a difference! Major performance improvement. Smooth power all the way to top end. No stumbling or flat spots. Engine was still pulling at the end of a 880 foot straightaway.

Now, my issue. The longer that I ride, the more I lose idle. After initial warm-up, everything is fine. Then after about 20 minutes of riding, if I let off the throttle and let it go to idle, the engine dies. If I screw in the idle adjusting screw, it will be fine for a little while and then start again. Have to crack the throttle slightly to get it to restart. Also, a little hard starting when cold. Can't find any vacuum leaks and sparkplug looks ok for the short time I've been riding. Choke is off. Air screw is almost all the way screwed in. I've read all the online carb tuning manuals and threads in this forum that I can find. My thought is to install a 20.0 pilot jet, reset the air screw and idle screw and start the retuning process all over again. Looking for some advice from Mikuni experts. Am I on the right track. Thanks in advance.
 
#34
Same issue on my vm22-133. My idle screw was backing out due to vibrations. Take the screw and spring all the way out and put a couple washers between the carb body and the spring on the idle screw. Basically the washers make the spring more compressed and it holds the screw in place. This fixed my problem. Don’t go swapping pilot jets until you try this fix first.
 
#35
Same issue on my vm22-133. My idle screw was backing out due to vibrations. Take the screw and spring all the way out and put a couple washers between the carb body and the spring on the idle screw. Basically the washers make the spring more compressed and it holds the screw in place. This fixed my problem. Don’t go swapping pilot jets until you try this fix first.
OSU1978 - thanks for the reply. I'll take a look at your suggestion. However, I don't think that the idle screw is moving on it's own due to vibration. I have to keep raising the idle RPM to keep he engine running once it warms up. It starts with an idle around 1,300 RPMs and I have to adjust it up, by 100 RPMs at a time, up to around 1,900 RPMs to keep it running. I should have clarified this in my post. Other than this issue, the engine runs and performs well.

Any other ideas?
 
#36
Idle RPM's dropping to the point of stalling out while warming up is a sign of an overly rich condition. If your air screw is close to all the way in you are most likely running rich with the 17.5 Pilot jet. I believe most people run a 17.5 Pilot jet in these engines (196 - 212) so back the air screw out 1.5-2.0 turns and see what happens. Use the choke/enrichment circuit to get it started, especially if its chilly out.
 
#37
Idle RPM's dropping to the point of stalling out while warming up is a sign of an overly rich condition. If your air screw is close to all the way in you are most likely running rich with the 17.5 Pilot jet. I believe most people run a 17.5 Pilot jet in these engines (196 - 212) so back the air screw out 1.5-2.0 turns and see what happens. Use the choke/enrichment circuit to get it started, especially if its chilly out.
OSU1978 - thanks for your reply. I appreciate your advice. I think you may be on to something. I've been researching and thinking about this condition. How I got the air screw almost all the way screwed in is because I had a bad off idle stumble. Couldn't give it any throttle off idle and it would just fall on it's face. So, I started adjusting the air screw 1/4 turn at a time, waiting, then continuing until the idle stopped increasing. Then I would adjust the idle screw appropriately. What you are saying makes sense since I have to crack the throttle (lean it out) to get the engine to start when hot or cold. Choke/enrichment circuit seems to do nothing as it is currently adjusted.
 
#38
Then I would adjust the idle screw appropriately. What you are saying makes sense since I have to crack the throttle (lean it out) to get the engine to start when hot or cold. Choke/enrichment circuit seems to do nothing as it is currently adjusted.
I and many others always have to crack the throttle to start. The only reason you dont have to do this on a stock engine is because the governor does it for you.
 
#39
Same issue on my vm22-133. My idle screw was backing out due to vibrations. Take the screw and spring all the way out and put a couple washers between the carb body and the spring on the idle screw. Basically the washers make the spring more compressed and it holds the screw in place. This fixed my problem. Don’t go swapping pilot jets until you try this fix first.
OSU1978 - YOU WERE RIGHT AND HIT THE NAIL RIGHT ON THE HEAD!!! The idle screw was backing out due to vibration. Thank you for your suggestion! I watched the idle screw slot move (back out) when I revved the engine several times. That should be an easy fix.

Weather was good today, so, I ran the mini bike around for an hour to try some things out. Before I took it our, I checked all the things that I've recently changed, i.e,, driver/driven pulleys and bolts, belt condition, carb bolts, chain, rear sprocket bolts, etc. Ran a 1/2 hour and then killed the engine at wide open throttle to check the plug. Plug looks a slight bit lean. Not bad though. So, I played around with the air screw. I'm running a 17.5 pilot, 135 main and the needle e-clip is in middle position. If I turn out the air screw more than 1/2 turn from fully seated in position. The engine has a noticeable stumble off idle. At 2.0 turns out, engine stumbled badly. Turning in the air screw from the 1/2 to 1/4 to 1/8 position (clockwise toward fully seated position) all increase engine idle RPM. Based on this, I'm thinking that I need a 20.0 pilot jet, or at least I should try one.

Regarding the main jet, with the 135 jet, the engine is still pulling at the end of 880 feet, however, only slightly/weak pulling. In general, do you gain anything in terms of cleaner/crisper performance by dropping down to a one size smaller jet, the 130?

Thanks in advance for any and all replies and comments.
 
#40
Glad I could help. Try a 20 Pilot Jet and report back. Make sure to make adjustments when the engine is fully warmed up.

You are running a torque converter so adjustments to the unit may be all you need to gain speed. I only have experience with Hilliard clutches so someone else is going to have to help you with that portion of things. Your main jet may be dead on. The only way to find out is to keep fiddling and swapping.
 

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