Puch M9 Tuning & Problems

Hello, i guess this belongs in the performance section. I've come across a strange yet irritating problem on my moped with a Puch M9 as the title says. It has a DIY exhaust system, 50cc Autisa cylinder, 15mm bing from ebay and a homemade HC head. It starts pulling at around 4k and starts really making power from around 6,5-7k until 9k. Spark is good and its got the stock setup with points, advanced around 2,5mm. The problem is under full acceleration on 4th or sometimes 3rd gear it pulls hard until it starts losing power if i keep the throttle open, drop it to ⅓ and it can keep going. Open the throttle even a little and it starts slowing down. Once it has happened in usually pull over and wait for a few seconds on idle until i start riding again. My first thought was an air leak, sprayed around the whole cylinder/carb area and the crankcase but no change at all. Then i thought it sucks so much fuel the float bowl empties faster than it can refill, i tried riding without a gas cap, cleaning the petcock and puting a new fuel line, nothing. Then i drilled the float needle brass fitting in the carb with a 2mm bit, which helped a bit but didn't fix the problem. So, any ideas what i could do? This started happening after i ported the cylinder and upjetted from 82 to 88. (edited)

Re: Puch M9 Tuning & Problems

2,5mm advance is much for 9k rpms. Maybe you should try colder sparkplug and 1,5mm advance.

Re: Puch M9 Tuning & Problems

Jimi Koivisto /

Yeah, i have been thinking about this too. But tbh i rarely go above 8k in normal driving and the advanced ignition really helps in the poor torque of these 50cc's :D

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