Puch maxi head gasket leak

Kurt Valentine /

Long time lurker, first time poster. 1978 Puch Maxi that I have restored to basically stock condition. Only change was going from a 12 mm bing to a 15 mm bing. Starts very easily. However, you can clearly see exhaust leaking between the head and the cylinder. And when you spray carb cleaner around the gasket the engine slows down. I have read everything there is to find in the wiki and done a thorough search on this forum. I have followed the instructions for sanding down the head and the cylinder using plate glass to make sure it is flat. Problem persists. I’ve tried using a gasket, no gasket, gasket with the sealer. When I use a gasket with sealer, my cold compression goes from 120 PSI to 150 psi. However, once the engine starts running the leak returns. If I takeoff from a stop with the choke completely on it runs fine and hits about 26 mph. However, once you stop, you have to put the choke on again to get running. It’s obvious that it’s getting way too much air. I can hold my finger half over the air intake and it will run just fine. A bit hard to ride with my finger down there. I’ve also tried changing out jets, From everything down to 60 all the way up to 82. Nothing makes any difference. I’m turning to the gurus on here for help! My plan was to eventually go with a new top end set up. Should I just go ahead and do that and quit messing with the stock head and cylinder?

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Re: Puch maxi head gasket leak

The head doesn't look bad. What sandpaper grit did you end with?

You didn't show the cylinder. Also the performance head on amazon was about 30.00 Id probably start there. Also use a torque wrench to torque it to specs. I gotta do that check soon. I'm almost certain my problem is on the intake manifold.

Re: Puch maxi head gasket leak

Did you switch to a 15mm intake too?

Re: Puch maxi head gasket leak

Kurt Valentine /

Are used 150 grit sandpaper on both the head and the cylinder. And yes, I have a 15 mm intake to go with the carburetor.

Re: Puch maxi head gasket leak

Check your base gasket. That head won't seal the cylinder stud holes and air could be traveling through one and leaking into crankcase.

Re: Puch maxi head gasket leak

> Kurt Valentine Wrote:

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

> Are used 150 grit sandpaper on both the head and the cylinder. And yes,

> I have a 15 mm intake to go with the carburetor.

theres likely your issue. 150 is waaaay too coarse. You need to work your way up to at least 400 grit, in stages, to remove all fine scratches. It takes time and effort, and several sheets of sandpaper. Your final sanding should be with oiled 400 grit, and leave a shiny, mirrored finish. you'll go thru at least two sheets of each grit sandpaper. Start with 180 next, then 220, 320, 400.

Re: Puch maxi head gasket leak

Kurt Valentine /

Thanks for the tips! I’ll try resanding the cylinder and head working my way up in grit.

Re: Puch maxi head gasket leak

So once I get past 220 grit do I switch to silicone carbide or aluminum oxide sandpaper and do you lightly coat the head with 2 stroke oil for the fine sanding.

Re: Puch maxi head gasket leak

Yeah, from 220 on, switch to wet/dry sandpaper. Use it dry until the final sanding of 400 grit, then add a couple drops of oil and finish to a polish.

Re: Puch maxi head gasket leak

Kurt Valentine /

Just curious, what does the smaller hole in between the two stud holes do? I noticed my head does not have a corresponding hole in it. However, the gasket between the head and the cylinder does have a hole in it to match that smaller metal hole. Could this be causing my problems?

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Re: Puch maxi head gasket leak

Some puchs had a decomp valve. It would divert into the exhaust through that hole...

Re: Puch maxi head gasket leak

The decompression hole is useless. Tap it and plug it up with an m5 set screw. But I doubt its your problem here. My guess is you have a case leak.

Re: Puch maxi head gasket leak

Kurt Valentine /

> Daniel '' Wrote:

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

> The decompression hole is useless. Tap it and plug it up with an m5 set

> screw. But I doubt its your problem here. My guess is you have a case

> leak.

What do you mean that I have a case sleep? When I rev up the engine I can see smoke coming out between the head and the cylinder, where the gasket is. Are you saying I have a leak somewhere else?

Re: Puch maxi head gasket leak

Um you wouldnt see smoke coming out of the head, you might see a couple bubbles and possibly some gooey drips. Usually a head leak will sound chirpy. I would guess the smoke is either your exhaist leaking or stuff burning off. When I said you might have a case leak I was refering to the poor performance you were talking about.

Re: Puch maxi head gasket leak

derek from black pipes moped gang /

I second plugging the decomp hole. The head you’re using doesn’t have a mating surface to cover it so your exhaust port is just going to be open to atmosphere. I’ve never personally had this problem but it makes sense to me.

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