Puch Maxi slow revvs/accelerations

Hey all I have a 1980 Puch that I’m working on for a friend. It sat outside for years and needed totally gone through. I’ve got it running now but it doesn’t sound like a 2 stroke. It is really slow to rev up even when it’s on the center stand. When I’m sitting on it to take off I can give it full throttle and I won’t move. I had to replace a lot of parts so I’m hoping it’s a tuning issue but I’ve been changing jets and messing with the airbox but nothing seems to change how it runs.

It’s a 1980 1.5hp Puch Maxi. It’s got a Boss pipe and a 15mm authentic Bing carb. I’ve got jet sizes 60, 62, 64, 66, 68, and 82. It runs a little worse with the smaller jets but the 82 doesn’t seem to make it act any different then the 68. My compression is somewhere between 120 and 140. My gauges shoots up to 140 but settles on 120. I’ve taken care off all the air leaks around the carb. Also running 15mm #1 Grandpa intake. Original airbox. Has a new point setup from treatland that changes the output to 12v and the timing is set at 17 degrees before TDC. Tank is clean. Gas mixed 40:1 with oil. Fresh transmission fluid. New 3 foot clutch from treatland with blue springs set to 15lbs. New piston and rings. Replaced the seals in the bottom end.

So it’s hard to start cold. Needs full choke and a few kicks. Once it’s going it idle fine but takes a little while. It’ll rev up but will die if you just go straight to full throttle. It doesn’t rev high and sound pingy like a two stroke should.

I have been repairing vintage motorcycles for years but this is my first two stroke. Any help is appreciated.

Re: Puch Maxi slow revvs/accelerations

> Taner Cox Wrote:

> -------------------------------------------------------

> Hey all I have a 1980 Puch that I’m working on for a friend. It sat

> outside for years and needed totally gone through. I’ve got it running

> now but it doesn’t sound like a 2 stroke. It is really slow to rev up

> even when it’s on the center stand. When I’m sitting on it to take off I

> can give it full throttle and I won’t move. I had to replace a lot of

> parts so I’m hoping it’s a tuning issue but I’ve been changing jets and

> messing with the airbox but nothing seems to change how it runs.

>

> It’s a 1980 1.5hp Puch Maxi. It’s got a Boss pipe and a 15mm authentic

> Bing carb. I’ve got jet sizes 60, 62, 64, 66, 68, and 82. It runs a

> little worse with the smaller jets but the 82 doesn’t seem to make it

> act any different then the 68. My compression is somewhere between 120

> and 140. My gauges shoots up to 140 but settles on 120. I’ve taken care

> off all the air leaks around the carb. Also running 15mm #1 Grandpa

> intake. Original airbox. Has a new point setup from treatland that

> changes the output to 12v and the timing is set at 17 degrees before

> TDC. Tank is clean. Gas mixed 40:1 with oil. Fresh transmission fluid.

> New 3 foot clutch from treatland with blue springs set to 15lbs. New

> piston and rings. Replaced the seals in the bottom end.

>

> So it’s hard to start cold. Needs full choke and a few kicks. Once it’s

> going it idle fine but takes a little while. It’ll rev up but will die

> if you just go straight to full throttle. It doesn’t rev high and sound

> pingy like a two stroke should.

>

> I have been repairing vintage motorcycles for years but this is my first

> two stroke. Any help is appreciated.

If it needs full choke, seems like you may be having an issue getting gas into the engine. Keep playing around with jets, and ideally if you have a spare try a whole new carb to see if that had any impact. I know you say the tank is clean, but make sure that gas can flow through it, and check the flow out of the petcock. If there’s a clog or kink or something any of the tubing you may also be running a little lean.

I recommend you check that, and also consider manually restricting airflow with your hand and see how the rpm’s react.

Check your carbs idle screw as well, turning it in may make a slight difference.(edited)

Re: Puch Maxi slow revvs/accelerations

Run the 68 jet and no airbox and see if you notice a change. I think the stock 1.5 airbox is likely too restricted

Re: Puch Maxi slow revvs/accelerations

Overpriced Parts /

78 jet with metal mesh filter not junk stock air box ever!

I’ve thrown away over 100 I will not give or sell them away because that is the demise of a puch Moped performance!

Re: Puch Maxi slow revvs/accelerations

Ditch the airbox. Make sure fuel is free flowing. Double check that timing.

Sounds like it's restricted. Just like Ken said.

Re: Puch Maxi slow revvs/accelerations

I’ve been swapping jets and trying it with and without the airbox without much change at all. Sometimes blocking the air intake with my finger helps but it never gets that 2 stroke sound. I’ll try a more careful and calculated approach to it tomorrow. Can y’all tell me what is being restricted with the stock airbox? I read all over this forum about stock air boxes being restrictive but what is restrictive about them? They don’t seal shut and they don’t have a filter except for a wire mesh in them that has holes in it plenty big for air to go right though.

I have two sizes of atomizers as well 2,22 and 2,17. I read that a 15mm carb should only run a 2,22 atomizer. Is that the case or should I be using this as a piece of the tuning puzzle too?

Re: Puch Maxi slow revvs/accelerations

hmm, maybe a new plug or your head bolts come loose.

Re: Puch Maxi slow revvs/accelerations

I bought a 4 pack of spark plugs and have been checking them and swapping out when necessary. Head bolts are firm.

Re: Puch Maxi slow revvs/accelerations

The fuel flow is fine. Everytime I take the carb off the bowl is full and some extra leaks out the hose. I've tried restricting the airflow with my hand but can't figure out a pattern of when it helps or hurts.

Does anyone have a similar set up to this? I'm unsure if it's just a jettin issue or something else.

Re: Puch Maxi slow revvs/accelerations

Can you explain a little more about what you're saying here? I've tried with and without the airbox and can't figure out which is better. Do you have a similar set up to me that you run a 78 jet with? Wouldn't the 82 jet I have get me pretty close to running right if that's the case?

Re: Puch Maxi slow revvs/accelerations

click that tab on top that says flatview.

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