New 72cc Enviromoto Probs

[king4477]

Hi Everyone!

Long time listener, first time caller

I recently picked up an Enviromoto 72cc power pack and got it all installed. It's a huge upgrade from the stock GY6 139QMB engine and I love it! Only problem is that it's been stalling on me.

I also installed the UNI air filter, #90 main jet, new NGK plug, and a new fuel filter.

After WOT, getting it up to around 40 mph, and coasting down to zero, the bike usually stalls out and wont start again for 5 or 10 minutes. I thought that perhaps it was idling low and so I upped the idle a little bit and after a couple minutes of idling it also died. I've checked the plug numerous times after it died and haven't seen any issues. I tied another plug (also NGK) and had the same issue.

Can anyone point me in the right direction? My initial thought is I need to tune the carb but I don't know where to start.

[90GTVert]

Welcome to posting! ;D

The plug never looks wet? Have you tried other main jets? Other needle clip positions?

[king4477]

Thank you, and thanks for the quick reply!

The #90 jet is the only one I've tried so far. The only other jet that I have is the one that came stock. I should also mention that the bike has about 325 miles on it and came with a Keihin carb from the dealer. I did not adjust the needle, any suggestions on how I should try adjusting it? Feel free to tell me to search for the answers myself if I'm being an annoying newbie asking annoying newbie questions :spin:

Here's a pic on the plug, I removed it a few times after stalling it or just hitting the kill switch and it always looked about the same. I also tried it will a second plug and the results were similar.




Thanks again! I'll come up with more pics of this bike and my previous ones after work this week :cheers:

[stepthrutuner]

Make sure you have no vacuum leaks. I suggest stripping out all the emission crap and going from there.

[reveeen]

My *initial thought* is the vacuum petcock.

[king4477]

Thanks everyone for the ideas!

I'm going to look over the vac and fuel hoses and the petcock to double check that those are all ok and then I'll dive into carburetor tuning and let you all know the results! I'm definitely going to adjust the needle and the idle mixture, but don't know if I'll need a new pilot jet on not.

Does anyone know if a 72cc engine will run alright with the stock pilot jet?

[Goosey]

Just a not obvious suggestion, to check for spark when it is not starting for those 10-15 minutes. And with the 4 stroke, you may want to adjust the valves, too tite will stall out when hot.

[90GTVert]

I think a 72cc will be OK with a stock pilot jet if you use the stock airbox.

[king4477]

Update:

Got it running great now.

I first checked over the vacuum hoses, fuel hoses, and the petcock and couldn't find anything wrong. I began tuning the carb, starting with the idle mix. I turned the screw all the way in and four turns out, no change... uh oh. I checked over the carb for leaks (spraying carb cleaner around the seams while the engine was running to see if the engine bogged down, and it did). There was a leak where the diaphragm seals on its cap.

I checked the diaphragm for holes and tears, nothing. I rebuilt the carb, twice, tried lots of torques, never got it to seal right. Used some Permatex gasket maker to seal it up, worked great!

The carb did need a little bit of tuning. The needle came at the middle notch (out of 5) from factory which I left as is. The idle mixture works best at 2 & 7/8 turns out with the 72cc engine and UNI air filter. Any further out and I wouldn't feel comfortable without getting a larger pilot jet, but it seems okay.

All in all, this stage 4 power pack is a fantastic kit put together by Enviromoto. Thank you Enviromoto and thanks everyone for your help and your ideas!

[90GTVert]

Thanks for the update. Glad you are getting to enjoy it now. ;D