Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Hello Moped Army community! This is my first post, but have been on the site for months now doing research, reading the Wiki, and reading the forum posts. I've learned a lot and previously knew nothing about engines/mechanics, but now feel I have a decent grasp on how these mopeds work. However, I've hit a roadblock and am desperate from the MA community before I do a complete rebuild. Here is my setup, problem, and what I've done to date, so appreciate the help in diagnosing:

Bike Setup

-1976 Puch Maxi (all stock except for clone carb)


-e50 1-speed

-14mm bing clone carb

-64 jet w/ 2.22 atomizer (stock)

-Stock intake

-Stock air box

-Stock exhaust


-Won't idle / dies when trying to idle even with idle screw all the way in

-Fouled spark plug (wet with oil)....I've burned through 3 spark plugs trying to diagnose with the same results

-Heavy white smoke from exhaust that won't go away, even after clearing the engine as described here: https://www.mopedarmy.com/wiki/Clearing_out_your_engine

-Black oil substance coming out of exhaust when WOT trying to clear out engine. Oil just keeps on coming out, but very slowly.

- Used to go 30mph no problem and have pretty good acceleration, now tops out inconsistently between 20-30mph and accelerates more slowly

- Also, all these problems occurred overnight. Rode it one day working just fine and then the next day took a turn for the worse. The only "odd" thing I did the last day it worked great was let the bike idle for like 10 min after initial startup, hence why I tried to clear out the engine due to possible oil build-up.

What I've Done

-Removed all rust from gas tank

-New Petcock

-New fuel lines and inline filter

-Totally cleaned out the carb and all components. Adjusted float needle slightly with same results.

-New O-Ring between intake and carb

-New gasket between intake and head

-Drained ATF and installed new ATF with new gaskets (ATF was pretty low and a brown/maroon color)

-Replaced spark plug 3 times (same results). Bright blue when new and after clean, but not much spark after it gets fouled up obviously. The only time I can actually get the bike to idle is with a brand new plug for the first few minutes.

-Removed head to clean piston, cylinder, crank, check & set cylinder rings, etc. (Note the crank and inside of the piston area was pretty wet with dark oil, which I believe to be the source of my consistent fouled plug)

-Removed and cleaned entire exhaust manifold, pipe, and muffler. Installed new gasket at intake to head and new gasket at intake to pipe.

-Headlight, tailight, brake lights, and horn all work just fine

My diagnosis of the problem is that I have a bad crank seal on the right/clutch side and ATF is getting sucked into the engine based on how oily my crank/piston was, my consistent white exhaust smoke, low ATF fluid, and fouled plugs. Hence the no idle, poor acceleration, and low top speed. Also, when I've tried to clear out my engine a couple times (with no results) it seems to get very hot, have a unique smell, and my brand new gasket between the intake and pipe fell apart on it's own, so something isn't right there.

The only things I haven't done yet are clean the points and adjust timing. That was actually next on my list of maintenance to do on the moped, but then this whole problem happened and I got sucked into doing everything else first.

Does anyone have any other suggestions to try first? I really don't want to have to remove the engine to get to the crank seal, but if it's my only choice I guess I'll have to. I'm sure I can figure it out with the wiki, photos, YouTube, etc., but just considering it a last resort since it's an undertaking.

Sorry for the long post, but I know you guys ask a lot of questions so trying to put it all out there initially. Please help me! Thanks MA community.

-Brad (edited)

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Overpriced Parts /

Sounds like transmission crank seal is gone but stock Puch pipe and filter is just the most restrictive piece of crap known to mankind specially if the pipe is blocked

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Alex Fredericksen /

I say trans seal as well. Trans side seal is a pain to replace. You have to split the case and pull the bearing to get to it. You could try retuning the carb first if you're not up for the challenge. Lean out the carb and just top off the trans fluid once in a while. Totally ghetto but it works.

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Look, if you’ve gotten this far just from reading Moped Army then you’re not gonna have any trouble with an E50.

Drop that engine and replace those seals, and the bearings too, and fuck it, a new crank while you’ve got it open. But no need to kit it yet, get it back on the frame and just keep riding it and improving it bit by bit. Tubes and tires. Brakes. Cables. Bearings. Rewire the whole fucking thing. Fresh points. External condenser. 12v coil. Forks. Carb. Pipe. Clutch springs. Practice cleaning your carb blindfolded. Time your ignition while standing on your head. You’re gonna be like the old zen master from Remo Williams, I can tell.

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Oh Jesus, just pop it apart and replace the seals and bearings on the crank, takes like 3 hours tops. Don't mess with anything else, you start fucking around and changing things and turning it into a big project it isn't, and you'll just waste a bunch of money and end up with a project.

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Thank you all for the help! Sounds like we all have the same consensus on the problem. I’m going to take apart the engine and get the seals and bearings replaced. I’m up for the challenge and doesn’t seem that bad of a project if you have the right tools. I probably won’t get to it for a couple weeks, so I’ll report back with how everything went afterwards. Thanks MA community!

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Hi all, just wanted to give you an update that I took apart the engine, replaced all seals, all bearings, and cleaned everything! Back up in working order, running amazing at stock specifications, no oil-foiled spark plugs anymore, and topping out at 32mph no problem. Took me awhile to get to it, and took longer than expected, but no major mishaps as I took my time and went slowly. Thanks all for your help.....guess I got myself a Christmas present. Happy Holidays everyone!

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Nice work, man —

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Excellent .

And , thanks for the update and good wishes . Happy Holidays to you , too . ;)

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

I appreciate the very detailed description of what your problem was and how you took care of it. Congrats!! And Merry Christmas!

Re: Puch Maxi Not Idling, Low Speed, Exhaust Smoke

Yes, perfect post just missing some picts.

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