Polini CP 17.5 Guidance on Puch Polini 64cc

Hi everyone. I'm fixing up my old Puch with one of these newish Polini carbs. So, I haven't found much on the tuning spreadsheets.

Out of the box the carb comes with an 80 main jet and seems to run lean. I don't know the current idle jet, but I believe it is also lean. I have ordered a range of OKO idle and main jets.

1978 Maxi Luxe

Polini 43.5 mm cylinder from 2008ish. Stock head. NGK B6HS

Polini single Reed valve

MLM 19mm intake

Polini CP17.5mm carb

Uni filter hacked and strapped

Tecno Circuit Exhaust

-Any jetting experience with this carb? Planning to jump up to around 100 and work down.

-larger jets are in the mail, but I am wondering if the minimal filter and lack of airbox are a potential issue. I believe the airbox slows the acceleration in airflow to reduce a lean bog when opening the throttle.

I'm looking for acceleration and reliability over top end. My odometer reads 7,800 miles, I probably put on a few thousand ten years ago, but it has been sitting since.

I just rebuilt everything from the base gasket up. Any thoughts on when the bottom end will become trouble? 10,000 RPM? 10,000 miles?

I appreciate recommendations and will update as the build wraps up.

P.S. looking for moped people in Long Beach, CA

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Re: Polini CP 17.5 Guidance on Puch Polini 64cc

I had a 100 main in a 17.5 on a V1 polini. Not sure on the slow jet, but I think I went up one.

I switched over to a 19mm and I'm running a 95 in it. Big improvement over the 17.5.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Cool bike! Idk about your jetting but you should probably definitely just rebuild your bottom end now rather then later when something breaks. Also check out the heavy pedders on Instagram, they’re in Long Beach too. (@heavy_pedders_mpc)

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Definitely rebuild that bottom end if you're going for 10k rpm. Make sure you've got a nice roller bearing crank too.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

First Name Last Name /

Definitely a needle crank

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

First Name Last Name /

Make sure you’re jetted to the TEE. Puch Polinis are known to shit the bed even if they’re SLIGHTLY too rich. Some of the guys here reached out to Polini and were told that they were jetting the bikes too rich and/or adding too much 2 stroke oil during break in. You want a nice caramel brown color on that plug.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Did you case match it?

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

As long as your timing is conservative, and your not running a crazy pipe, polinis are super forgiving. Air leaks + advanced timing + high compression/stock head= zoinks seize city.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Wow thank you all for the advice!

I ordered OKO jets and it turns out the main jets fit the polini carb, but not the idle jets.

I put in the largest 120 main jet and raised the needle (lowest clip).

It still seems lean and soft seized in testing. (I have done a fair amount of break in on the previous bing carb. I wasn't going WOT, but stayed in it a little over 30MPH and zing). It fired back up and limped home (what is that change in sound? Loose studs?), at home it froze and came loose pretty easily after pulling the head a little oil soaking. I don't see any major scratches or shiny new metal.

I have ordered larger main and idle jets. I may have been running it too heavy on oil. I'm going to drain it, swap in the new petcock and measure some premix. Apparently polini cylinders take 60:1 synthetic, but that sounds dry. I'll probably go 50-55.

I have a big box of treats coming so there will be more pics.

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Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Answering your questions, I haven't done any porting. The power seems ample so far. I had been thinking I could do that later and put in a trick bottom end later if need be.

I had it in my head that 12K RPM reasonable for a kitted e50. Facepalm... as if I have a tacho anyhow. Apparently 7 -8K is more reasonable goal.

I think that I will go ahead and put on a smaller 19T front sprocket that I have. That won't help my low end goals. But it beats seizing.

Will that just shift my issues from bottom end bearing heat to clutch problems?

Think I can put off bottom end work? Better to just get a newer 70cc kit with better cooling? (edited)

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Edit.

I have 16T, 18T front sprocket and my bike has a 52T rear. It's older than me, it's been places you know?

So, the larger front sprocket probably won't so me any good.

I think I will be able to do a little better in the jetting department, but is this just the reality of kitted mopeds? Should I run a tach? Do the math and know your cutoff speed? Temp gauge?

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

52 is really big for the rear. Ho with the 18 in the front and something like 45 in the back. With that circuit pipe and that kit, you should get moving pretty quick as long as you have tuned up your clutch. That is where real quickness lies.

Break in period is done while idling on the kickstand. If you dont have a temp gauge, get one. Idle the bike for 10min once it gets to normal running temps. If you cant idle your bike on the stand, then that is a problem to fix. This really helps eliminate any air leaks before you get on and rip around. After the 10 minutes, kill the bike. Re-torque the head down in case anything loosened up. Also double check the intake and exhaust bolts. Repeat this process 3 to 5 times in total. After this you can start the tuning of the carb, confident that you dont have any airleak around the cyl. Just be careful if you take the carb off and put it back, you dont create an air leak there.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Kind of a lot to unpack here

Sounds like you sorta skipped ahead on the whole build, assuming that the bottom end and everything else was sorted out. 120 might be a little on the lean side but I don’t think its way out of line. I would probably started at 140 or 130 and worked my way down but those are OKO sizes and I don’t know how the polini runs different.

I would start by pulling the top end back off, cutting new gaskets, checking the ring and piston. If the ring is stuck in the piston groove, you can probably get away with replacing it and sanding the piston and be fine. If you don’t pull it apart, you risk trashing the whole kit from the ring not making a good seal. If the ring doesn’t break in correctly and seal up, the combustion gasses go around the piston and heat it up and it will trash everything. Even if the piston is a little scuffed up chances are you can sand it up and pop in a new ring and save it.

If someone was bringing it to me like this, I would want to go through all the gaskets and make sure there are no leaks. Also keep an eye on the intake manifold bolts, you don’t want to over-tighten them. I use gasket sealant (motoseal, etc) to seal up the reeds, and blue Loctite on the intake screws and just barely get them snugged down. If you overtighten them it will warp the cylinder and that can cause a seize like you are describing.

Once you have everything back together make sure you double and triple check the timing. That will have more impact on it seizing than almost anything else. For breakin and tuning I would set it up like 15 degrees, super conservative, and as you get the carb close, then you can bump it up.

As far as the gearing goes, that doesn’t look like a 52 rear in the pic. That looks like 43 or 45, just eyeballing it. Use marty’s gearing calculator to set your top speed (guessing like 52) at 9000 rpm for that pipe. Then gear accordingly. My guess would be 20x45 not doing the math. The 19 will be close enough to get you tuned but you’ll get a bit more top speed off a bigger sprocket. Those circuit pipes do not rev out much past 9k. 10 maybe if you are perfectly tuned.

You really need to check for airleaks. And did I mention to check for airleaks. Also. CHECK. FOR. AIR. LEAKS.

The jetting you are talking about on that setup should never ever seize, shouldn’t even be close with that pipe, you either fucked up the intake manifold bolts getting them too tight (search for cornped/Maize’s youtube video on polini intake screws) or you have a huge air leak.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

I just read your first post again. 19mm intake, 17.5 carb with reeds.

I think a bigger carb would solve all your problems.

I had a 17.5 on a polini V1, no reed, and it was too small. Always too lean. A 19 opened it right up.

On my V1 BRN 90 kit, with reeds, I'm running a 23 CP. And it rips. Jetted at 110.

I know I'm comparing puchs to V1s, but it seems to me you're just over jetting a small carb when a bigger one would work much better.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Thanks again for all the great advice.

-The bike idles on the stand well and I have checked for leaks with carb cleaner. I did thorough breaking in on the old Bing 12.

-The rear sprocket has 52 stamped on it. If it's actually a 45, whoever stamped that 52 is missing out on the punchline. My front sprocket I swapped in is a 18, not 19T. So it puts me close to the stock ratio.

-I let the cylinder break in idling on the old Bing and putt putts around the block for several days. I'm still avoiding constant throttle etc.

Does one need to Run break in cycles every time after pulling the head? I have replaced all the gaskets and I think she is pretty tight. Didn't deck the head or anything, but I use a torque wrench.

-Today I mixed up and loaded some 60:1, about half the oil than I had been running during break in.

-I ordered a temp/RPM gauge, lesson learned.

It seems to sound a little better on the stand running the spec oil mixture and the taller gear. I didn't have the opportunity to test ride much, but it kind of felt like it did the trick putting redline further out of reach may have been all I needed, but waiting for the sensor.

I did some calcs and I was probably going up to 10K rpm when I had that soft seize. I'm waiting for the rpm/temp gauge to come in before giving it the beans.

Taking a closer look at the timing is on my list. With the temp sensor, if I adjust my timing, can I look for a temp difference at idle or would it only show running a route and watching temps?

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Of you're just removing the head, no break in cycle is needed. Just check the torque again after a few rides.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Break in is only needed when you install a new ring.

Something sounds very wrong, did you find the video showing the intake manifold torque/pinching thing? That's where I would look next.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Test ride success! What should my target timing be?

TEST RIDE

The 18:52 gear ratio is much better and the lighter fuel:oil mix didn't cause issues and seems to relieved some of the lean symptoms. (Oil pushes gas out of the mix right)

I took a ten mile ride to the beach and back without issue. I mostly kept it under 30 mph until I can install a temp gauge, but generally shifting the power band up seems to have done the trick and it's a fucking blast.

WHAT'S NEXT?

I can probably dial in the jetting and timing a little more. Having a temp sensor should make that pretty straight forward.

WHAT IS IDEAL TIMING FOR A PUCH-POLINI? I set my timing by hand to about 15 degrees as I heard that was the conservative move for a new "kit"

I'm looking to borrow a piston stop and timing light and really dial it in. Target timing recommendations? The plan is to let the temp gauge guide me, but I appreciate your advice.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Yeah 15 is a good start. I usually get it running good on conservative timing then jet it, then start upping the timing as it breaks in. Usually you will feel it pick up good power as you advance the timing then all of a sudden the temp will shoot up, bring it back down and you're set.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

I went up to the 140 main jet and a 44 idle. It seems too rich. I tried 130, 125 and the 42 idle.

I feel like it ran better yesterday on 120/40 and was more powerful.

I have my warnings set at 160C and 7500RPM and I didn't go much over, but it still overheated some on the last ride. Still rose home, but it died and seemed to loose some power and sounds off. Going to tear it down and look things over.

I think I need to get a smaller rear sprocket like 45/48 instead of the huge 52 on there. I'll probably review some tuning videos and go to 40 idle, raise the needle to 2nd position, and try the 125 or 120 again.

My hydraulic fork and disc brake showed up today. I'll probably work on that during the week.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Lots of tuning today, about half of which was a waste of time because I was having other fuel issues. I put a filter in the line and I think that is messing with the flow into the carb. With my mlm intake the carb sits almost at the same height as the petcock and I think it is causing issues. I took out the filter and shortened the fuel line.

Given the above, I don't think I got much "good data" during testing today. I ended up back on the 120 main and middle needle setting. I think that it is about right. 125 is real happy in the mod range, but bogs out at WOT. 120 feels great, but may be hot.

NAME THIS SYMPTOM

The bike will be running well until I take it up to 6-7k rpm for most of a block (well below 300F, but warmed up now) and on the deccel it seems to lose power or cut out until I pull the choke. It will then return to idle and sound happy for a moment, pull with throttle for 30 seconds, then you got to the the choke off. Back and forth like this.

I'm hoping it was a bad seal on the fuel filter/lack of drop into the float bowl.

I think the tuning may be almost right, but I just need to gear it up so I top out at 7K and then look into clutch tuning.

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Question: FORK BRACES. Off-road use or necessary? Double rider?

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Project update: I installed an EBR hydraulic fork and I am getting that sorted out. Lots of troubles getting the brake caliper mounted. I have been filing out the plate and got some longer spacers. Almost there.

Now that it's rolling on the new front wheel, there is some slack in the headset.😎 So I still have some work to do. I got a cheap LED light and power pack, the bike is pretty well transformed at this point.

What are your thoughts on front fenders and braces. Are the necessary for good weather riding or loading an extra rider? I know two riders is over the limit printed on the frame (with Me ~200), but the running gear is mostly upgraded. Appreciate your input.

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Re: Polini CP 17.5 Guidance on Puch Polini 64cc

"The bike will be running well until I take it up to 6-7k rpm for most of a block (well below 300F, but warmed up now) and on the deccel it seems to lose power or cut out until I pull the choke. It will then return to idle and sound happy for a moment, pull with throttle for 30 seconds, then you got to the the choke off. Back and forth like this."

Either you have an air leak, or your pilot/idle jet or air mixture screw setting is too lean. When you decelerate you go from mostly main jet, to needle/slide settings, to pilot jet at idle. So if this curve is not feeling smooth adjust those components

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

Thank you Mike. I'll give that a look, I have a range of idle jets from like 38-60, currently using the 40 idle jet.

I'll try richening the idle mixture. I had been confused in thinking that the idle air screw was more of a general air screw, impacting the main circuit etc.

I was pleased last night to find wiring up the LED was easy. Also my battery has a built in switch, finally something that is easier than expected. Down the road I'm planning to add rectifier-regulators and relays to charge the battery onboard. (edited)

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Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Also hot tip: those rubber rings on the fork dust covers are meant to hold your hydraulic brake line in place ;) (edited)

Re: Polini CP 17.5 Guidance on Puch Polini 64cc

Michael Jones /

I figured as much, but my hydraulic setup came pre assembled and filled with fluid. I'll have to crack it open and re fill and bleed the brake when I have the fit squared away.

I actually have had so much trouble with the caliper mount and axel spacing that I put my old wheel back on for now. I need to find a different bracket. I have slotted out the holes on mine a bunch, but I keep having issues with the fit.

There is plenty to continue adjusting, the fork feels great. I also installed a smaller rear change ring and adjusted the rear shocks since the last ride.

I dropped the front sprocket back to stock 16T as the 18/41T seems too high (at least without clutch tuning).

Overall the hydraulic fork and taller gear make a huge improvement. Before it was racing up to the redline and overheating. Thrilling, but I thought I would lunch my cylinder soon.

There is plenty of work to do, shorting the chain for the gears, mounting the speedo on the EBRs Etc. Hopefully the 16/41 is right on. I clocked 36 on GPS and I think under 7K rpm... Not pushing my luck.

We will see what I can sort out this week. I'm sick of disc brake fitting, it stopped very well before it loosened itself in testing repeatedly. I'll get the rest end sorted, a little more carb tuning, final wiring etc, then get back to the disc brake.

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