I haul ass, but I'm weak on the comedown

Mopedophiles,

I've got a Puch Polini 64cc running a Polini-CP17.5 carb, and Tecno Circuit pipe (for the name).

Pulls well, she does almost a half ton.

However... If I ride hard, in that sustained 3/4 to WOT range, then let off the throttle and coast or brake down to a stop or low speed, the revs drop below 1000 and it takes it's time slowly building up revs to the set idle.

I put in the largest idle jet that I have 52 and upped the idle to about 1800 (main jet is at 110 now, but still rich). I was thinking it was a lack of fuel coming down from the high RPM/temp.

But now I am thinking this is a side effect of the rich main jet. The manifold and case are soaked after those high rpm runs where I'm backing off from 4 stroking. When the rpms come down, it needs to burn off all that fuel and isn't getting enough air.

So... Continuing to lean out the main jet may solve this?

Re: I haul ass, but I'm weak on the comedown

Totally normal JBOT /

You’re too rich somewhere and it’s flooding at idle.. low idle after riding hard is often main or needle.

But it’s all a balancing act.

You might be perfect on the main and needle and need a leaner idle jet and idle mix

Re: I haul ass, but I'm weak on the comedown

Probably Fred /

Manifold and case wet has nothing to do with it will do that with correct jetting.

What reeds- reed cage you running?

Re: I haul ass, but I'm weak on the comedown

Michael Jones /

Downjetting and opening up the idle air screw seems to have done the trick. Probably going to lower the main jet a little more and reduce the idle jet back where I had it.

Thanks for the tips!

Re: I haul ass, but I'm weak on the comedown

I like to set the main jet rich and the needle lean.tht way it cools down at WOT and top speed is more like 3/4 throttle

Re: I haul ass, but I'm weak on the comedown

Yep run a rich main jet and slightly lean needle. The Polini will seize if you downjet one size too far. Running rich on the main jet will help it run cool so will low timing (hpi mini rotor ignitions such as the 210 that auto retard are best). The casting on the Polini kits are poor and very seize prone if it gets much above 380F. For breaking in keep below 340F. Use a trailtech temp gauge at all times when running this kit!

Re: I haul ass, but I'm weak on the comedown

Michael Jones /

@probably Fred. I'm running the stock polini Reed that came with the kit 15+ years ago.

I lowered the idle jet to the stock 38 and the main to 95 with a work in progress airbox. Color matched Suave Men 1L.

The 90 MLM intake sits the carb way out and makes an airbox tube too long /ugly. Any tips on an intake that is angled back more like the old Bing? I'm running a Polini cp17.5 into a MLM 19mm.

Generally, I like the lean on the needle rich on the main idea, that may be where I am at, but struggling with this airbox

Thanks. (edited)

IMG_20211028_125951.jpg

Re: I haul ass, but I'm weak on the comedown

Totally normal JBOT /

Hey I know that airbox.

Your jetting will be defined by the airbox, and from my experience 70cc kits need 3 ports for air. 2 isn’t enough. You’ll always run a bit too rich.

Try 3 air tubes then play with length or even one fully open then rejet

EDIT; haha I just saw the 3rd hole nvm lol (edited)

Re: I haul ass, but I'm weak on the comedown

Totally normal JBOT /

And your duct tape seal is a bad idea.

You really want to make the seal to the airbox with a rubber hose to plastic bottle interference fit. Like squeezing the larger hose into a slightly smaller plastic hole

Also shorten the tubes on the outside of the bottle and flare them for better flow (edited)

Re: I haul ass, but I'm weak on the comedown

Michael Jones /

JBOT! The man! I heard you on Moped Monday Podcast. I was inspired by your posts and the legendary airbox calculations thread.

After I posted last I made this.

IMG_20211029_160640.jpg

It seems to work pretty well. But my test ride was cut short by witnessing a car crash. 🙁

It seems to reduce the noise some and the adjustment works. it's a bit snappier with the third plugged and pulls more revs with em open.

I saw the trash, I saw the diameter. Some filing and hacking. Bada bing.

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