I've read, extensively, everything I can get on boosting the performance of this little machine. It's been great so far - none of the gutless problems reported by others - but we're spending more time in the mountains now and my son needs to be able to climb hills faster than 5-10 MPH.

I haven't increased the main jet size yet (the shops are all closed until Tuesday so I can't get different jets) but I have done the following:

1) Removed the intake restrictor (exhaust was already gone, I confirmed by disconnecting the pipe from the cylinder and looking);

2) Confirmed the throttle slide completely clears the carb throat at WOT (no adjustments were necessary);

3) Confirmed the muffler "insert" is clean and unobstructed;

4) Adjusted the needle to the richest (most retracted) position to richen up the mixture now that the intake is less restrictive;

5) Extracted the standard 2-stroke oil I was using and replaced it with AMSOil Interceptor full synthetic.

The engine starts and runs great, but still lacks what I would think of as "throttle response". Punching from idle to WOT just doesn't have the takeoff I'd like. Granted this is a small unit, but I keep reading posts that talk about full sized adults doing wheelies and that is definitely not going to happen on this machine yet.

I still have the stock 55 main jet. As mentioned, I richened the needle one position (it was on "4" and is now on "5", no more room to move). I tried opening up the airbox by leaving the lid off but it ran poorly at WOT, most likely due to being far too lean.

A few questions for those of you who have modded this machine:


1) I've read conflicting advice about changing the main jet after removing the restrictors. Some say to move to 65-75, others say the increased air velocity causes the existing 55 to be the optimum choice. What have been your experiences?

2) Are there different needles available for this Mikuni carb? I'm all the way at the richest setting, and while I'll probably back that off if I have success with larger main jets it would be nice to have other needles to try too.

3) Some have suggested modifying the exhaust, particularly the "insert" that can be pulled out after removing two screws near the end of the tailpipe. I've tried completely removing that and the only change was increased noise. Granted, this is still with the stock main jet, but is there really anything to be gained here? What do they mean by "drilling" or "cutting" the insert? Drilling holes along its main (solid) tube body? Cutting off the fancy front end and leaving the rear section? BIG QUESTION: Doesn't the exhaust system play an important role in the proper operation of a 2-stroke cylinder, and won't it mess up this relationship if I modify the exhaust?

4) Is it realistic to expect "adult wheelies" on this machine, even with mods? I don't want to do wheelies but I'm using that as a measure of off-the-line power. I don't want to install an aftermarket pipe, re-port the cylinder, mill the head, etc. I just want to increase the amount of air and fuel that can pass through the engine. Are "adult wheelies" only in the realm of significant aftermarket parts, or can that be achieved by de-restricting and proper rejetting of the stock engine?

Thanks!

 

One more question: How much load does the oil injection system really place on the engine? I've read remarks that suggest removing the injection and running premix really opens up the engine, which implies it places a pretty good load on it. Other comments about beefing up this machine say "remove it or not, your choice". Anyone have real experience on what difference, if any, it makes?

Thanks!

 

More (good) data: This morning, after the machine had sat all night, it started on the FIRST pull. Normally it has taken ~3 pulls, still great for a recoil-start engine. But it appears that removing the restrictors further improves even the startup performance of this engine.

I'm surprised no one has responded to my questions above. I've seen lots of comments here from people who have de-restricted and modified this machine. No one has anything to share on my questions?!?

 

Hi, I too have completed some of the mods. I did rejet after the restrictors removed but inorder to do this properly the air screw on the carb needs to be adjusted. The best way to this is raise the back axel off the ground and rev her to 3/4. With a philips head screw driver start adjusting the screw i/4 of a turn at a time.

These little machines have 0.5 hp. I've replaced the stock exhaust with a modified exhaust and the machine now has 1.5hp.

To get any more 'signifiicant power' out of these wee machines then skiming the head and changing the exhaust would do a lot.

Any questions give me a Shout -
Shaun
Northern Ireland

 

<div class="FTQUOTE"><begin quote>I did rejet after the restrictors removed but inorder to do this properly the air screw on the carb needs to be adjusted. The best way to this is raise the back axel off the ground and rev her to 3/4.</end quote></div>

Hmm, that's interesting. I did adjust the pilot screw but only just above idle. By the time you have the engine running at 3/4 it's my understanding that the pilot screw doesn't play much of a role - the main jet and (especially) the needle jet are the main factors at that point.

What are you using as a main jet? The stock one is 55. I'm going to pick up some larger main jets today and start experimenting. I've heard folks use up to 70. What have you found?

Did you change the needle and needle jet? To what?

Thanks!

 

I changed the Jet to a 60 or 65. It seems to run ok. It depends on altitude, climate, atmospheric pressure, so you might have to play around a bit.

I didnt change the needle. What I did do was get a carb slide from an LT 50 and put that in. Its shorter and no need for grinding.

In this forum I've seen guys talk about taking out rollers in the clutch plate on the 4 stroke LT-Z50, I don;'t know if that can be done on the LT-A50.

Good luck with the jetting- but skimming the head will give a noticeable difference.

 

Last night I tried a 62.5 jet, and moved the E clip to the center position (had been in the richest). Perked up the power noticeably. Next I will try to find the upper boundary with a 75 jet, which I expect to be too rich. Rumor has it the "ideal" jet is a 70, but I want to explore the edges first.

I'm also moving to a slightly cooler plug, a BPR5HS.

 

Latest update:

I installed a #75 main jet in an attempt to find the "too rich" end of the spectrum. It was hard to tell, and that's my largest jet on hand, but if "felt" like the engine was starting to bog.

I also switched to the slightly cooler plug, BPR5HS. Both it and the hotter OEM plug (BPR4HS) showed a nice tan color on the insulator and the metal "finger" that comes over the electrode.

Since the #75 felt a bit rich, I backed off to the #70 that everyone seems to settle on. It felt better, so that's where I'm staying for a while.

One other note: As mentioned by a few others, opening up the airbox results in the intake actually being louder than the exhaust. I don't know if an aftermarket filter from K&N, etc. would have any effect on this.

Current list of mods:

* Remove intake restrictor
* Remove exhaust restrictor
* Confirm throttle slide completely clears throttle body at WOT
* Change main jet from #55 to #70
* Drill four 1/2 inch holes in airbox cap, effectively increasing potential airflow by ~5X
* Remove muffler end cap (but leave spark arrestor/insert installed and unchanged)
* Switch to BPR5HS spark plug
* Drain el-cheapo 2-stroke oil and switch to AMSOil Interceptor all-synthetic

Results:

* Significantly increased low-end acceleration
* Somewhat increased top speed (I'll measure it this weekend)
* Better power delivery through entire throttle range
* Increased engine noise, especially from intake
* Increased size of smile on 6YO rider

No chance of adult wheelies as described by some other owners, but a definite step up and more than enough for my son at the moment. I'll report back on the speed measurement.

I'd still like to hear from anyone who has removed the oil injection....

 

By removing the oil injection, the only thing you will gain is a little less weight and the ability to premix to your needs. The factory oil injection system mixes the gas to oil a little richer than what I prefer. It really won't help on the horsepower. There is a complete performance kit for the LTA50 offered by CTracing. You could look into that for more top end. As for lowend power you may want to look into clutch mods and gearing. The LTA50 is very similar to the LTZ50 in the clutch department.

 

Have you played with the clutch, I am not real familiar with these or if they are the CVT but the suzi 50 I was looking at, at the last race had 12 gram weights in the clutch. I had him try 8's and it seem to make a difference on the snappy low end. Just alot of less wieght that you have to get spinning.