Rev limiter or jetting!

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Rev limiter or jetting!

Postby Joe Tisseo » Mon Aug 28, 2017 8:47 am

Hi guys got a weird problem.

Im running a polini 177, standard carb jetted to suit ( plug is nice coffee colour), plug is an 8hs, with a gianelli exhaust.

Now this little thing feels very nice to ride but in the shorter gears like first and sometimes second i hit what i can only feel like is a rev limiter. In first, every time it will get to near top of the rpm range and begin to break up, not bog but hold back and sound weird. Does it worse when cold. First gear is very short so im wondering whether i may be hitting the limiter although it feels like it wants to go more!

i also have the red ducati CDI installed, i dont think its jet related as every other gear runs lovely, ticks lovely etc. Could it be my plug?

Any questions just ask guys. Thanks. Joe
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Mon Aug 28, 2017 1:21 pm

Plug seems a bit darker than previously thought but this is not after a plug chop, a long run out though and was on the throttle...
Image

Here are my jets, 140 seems pretty rich does it not? Problem only arises WOT in first gear, maybe second.
Image
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Re: Rev limiter or jetting!

Postby rob h » Tue Aug 29, 2017 2:58 pm

Plug definitely running rich, 112,140 with be 3 sounds about right. However i was doing a 177, kit stated a wide range of jets, ended up a the leanest of the suggestions. Sometimes the smaller crank inlet of the lml is a factor! I also went with the deaded be5 as the jet i was fitting was as standard jetting. You could be too rich at low revs, as it's not as important as full throttle. Full porting or standard porting make a difference. I would go one lower and plug chop.
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Wed Aug 30, 2017 4:27 am

It does make sense that its jetting but then on the other hand why is it mainly in first gear at pretty high rpm? I find it strange that it doesnt happen in the higher gears. Not saying youre wrong just trying to work it out a bit more. I will drop a jet main wise as it looks a tad rich either way.
Last edited by Joe Tisseo on Wed Aug 30, 2017 6:19 am, edited 1 time in total.
Joe Tisseo
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Wed Aug 30, 2017 6:18 am

Also doesnt a 112 main sound a bit lean for a kitted engine? I gather that these jets all work in conjunction with each other, maybe im in fact lean at the higher rpms but im riching out in lower range hence the gunked plug. I need to do a chop really!

Also im not sure how extensive the last owner was when installing the kit. The receipts dont suggest any porting was done.
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Wed Aug 30, 2017 6:31 pm

Is the forum active anymore guys, any suggestions on where to join forum wise? Was hoping this was the place. Cheers
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Re: Rev limiter or jetting!

Postby rob h » Wed Aug 30, 2017 9:59 pm

The higher the rev range the more fuel passes through, is your air filter drilled and have you de blued the air filter. What gearing are you using, lower gearing on a kit gives first no where to go you get over rev. I think 22t is recommended on your kit. My 166 malossi used 116 on a 20mm. That was with huge ports. At 112 if you are rich, it can either be mixture, filter, exhaust or timing. Is it a performance exhaust, this would strangle the performance. Have you checked timing a long time ago my polini was 19 degrees, lml is 21degrees. Hope this helps a bit!
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Wed Aug 30, 2017 10:15 pm

Rob thankyou very much. To answer a few questions

Exhaust is a gianelli performance exhaust
Im pretty sure gearing is stock, acceleration is pretty rapid. Air filter is drilled, ive not touched mixture screw as i understood thats for the lower rev range? At leas it was when i worked on four strokes. Also i havent checked timing but will! Thankyou very much for taking time to reply.
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Re: Rev limiter or jetting!

Postby rob h » Thu Aug 31, 2017 9:49 am

Two stroke carbs can be simple, the mixture screw admits air to the mix. if you increase the jets you will need to compensate with more air. the basic setting is just about right, you can adjust by a slight bit to adjust for richness. search this site for a real good guide on carb adjustment. If you need the choke to start from cold your not far off the main setting. If you are undergeared you will have rapid acceleration, but you find the engine over revs in the gears lots of struggling noise but no more acceleration. Standard on an lml is 21 tooth, better than a vespa at 20t, some keep this setting for the acceleration but cruising speed can be noisy. First gear with the torque of the Polini can be very short, most change quickly to second as it will give you better pull away. I run 22t gearing, first is like standard but you need the power to use the gears in all weather.
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Thu Aug 31, 2017 8:30 pm

Hi rob, productive day today scoot wise. Managed a proper plug chop and it was spot on.
Image

Ended up trying the cheapest possibility first and swapped out the spark plug for a new one. I went from a br8hs to a br7hs, now it revs out nicely in first and doesnt hold back. Whether it was going cooler on thw plug or just the fact it was a new one that fixed it i dont know. Either way all good now and thanks for the replies and info!
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Re: Rev limiter or jetting!

Postby Joe Tisseo » Tue Sep 05, 2017 1:46 pm

Started happening again unfortunately. Not a clue now!
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