Modern Buddy

Hey guys, I just picked up a Buddy 125.

I can't get it to go past 40. It seems more gutless than it should be getting there as well.

I've done several things to it in an attempt to fix the issue to no avail:

Previous owner had replaced the whole airbox assembly with a breather. I went ahead and bought the assembly off ebay, installed it, and replaced the air filter.

I also replaced the roller weights, spark plug, new pilot jet and emulsion tube (they sent me the wrong main jet, so the original is in there).

I checked the valves and they seem to be right where they ought to be at 0.08mm.

I removed the air intake stuff and idled the bike with the back of the carb open, and looked into it with a cellphone while I gave it throttle. It looks like the slide is not moving in response to throttle input. I tried the same while holding the front brake in order to put load on the engine and had the same unresponsive slide.

I came across this post describing a very similar issue:
http://www.modernbuddy.com/forum/topic23272.html

All of this seems to point at the rubber of the carburetor diaphragm not having seated correctly on the metal lip. It is also consistent with how it looked when I was reassembling it: the rubber lip seemed to be a smidge smaller in diameter than the carburator lip. I don't know how to correct this and I was wondering if anybody had any advice. If I seat one side of it, the opposite side gets out of the lip.

Thanks.

"Previous owner had replaced the whole air box assembly with a breather. I went ahead and bought the assembly off ebay, installed it, and replaced the air filter. "

My Buddy 125 ran like crap every time I made mods to the stock air box. The stock carb does not like air box mods or pod filters without huge jets.

You seem to be doing all the right things.

The diaphragm seal is a common issue with these bikes as they rack up the years. You can try two things, and if neither work, then you just need to order a new diaphragm. First is to grease the upper and lower seats for the diaphragm. fill in the lower channel where the diaphragm should seat into, and this will help hold the rubber in place, and plug any air leaks that may be happening. Use your finger and put a little grease on the top rim of the diaphragm as well, where the upper cap seats to it. You may still have a job getting it to seat, as it'll want to pop out. What I do is to use a flat screwdriver to press the diaphragm ring into its seat, working around the perimeter as you seat the top cap.

Option two...and this is the ghetto fix. Do this only if you have no other option, and are ready to order a new one anyway, if this doesn't work.....take the diaphragm out, and spray the outer ring with carb clean. Something aggressive. What this will do is swell the rubber, and expand that ring. If you are lucky, this will expand it enough that it fits back into the seat properly, or at least close enough that you can work it into place.

I replaced the diaphragm and now the bike will do 55. Thanks.

Hooray!