79 Moby Backfire and bog

Mr. Richard Dickrich /

I need some help with my 79 moby, can't get it running well.

Here's the deal:

After is starts it will run great and at top speed until I come to a stop sign. I will try to give it gas and it bogs down when trying to accelerate from the stop sign.

It will start again, but it takes a lot of pedaling and usually backfires when it starts. It also does not idle.

It used to start right up. The carb is super clean. There is absolute not a speck in it. I soaked it overnight and know it very well at this point.

Has anyone seen this behavior on a Moby before. Thanks much.

Re: 79 Moby Backfire and bog

did you set idle on the cold engine?

if you made no deliberate changes, did the choke or throttle linkage get out of adjustment?

Re: 79 Moby Backfire and bog

Matthew Libhart /

A backfire is almost (not always, but almost) always a points issue, either bad timing or not gapped properly. My knowledge isn't specific to a Moby, but I've seen this behaviour when the points are barely opening. Get a $3 feeler gauge if you don't already have one and check the point gap and make sure it's correct. If the gap is ok, check the timing.

Re: 79 Moby Backfire and bog

Mr. Richard Dickrich /

I wanted to add that it stalls immediately after applying the back break (stopping the tire) and the front headlight and odometer light stopped working. Seems like something goes down on this bike very day. Electrical going crazy...

Do I have a chance to rescue this bike, or is it doomed forever? I don't have much luck with mopeds.

I appreciate all the help.


Re: 79 Moby Backfire and bog

If it stalls whe the brake is applied, then you have a clutch problem.

It is not disengaging

try cleaning off the clutch pads with some sandpaper.

I have often seen a broken clutch pad wedged in a moby clutch. if you can find a broken pad, then just pull it out. it might solve your problems.

set the timing and points as well





Re: 79 Moby Backfire and bog

Mr. Richard Dickrich /

Joew- Not sure what you mean by setting the idle on a cold engine. Can you please explain?

The throttle appears to working great, and I think the choke is fine as well, but I was thinking it was the choke at first. I don't really understand this choke- on other bikes it makes more sense to me- you cut off the air with the choke.

My choke works the same as before I took it apart. The hole is closed until I squeeze the choke lever and opens as I squeeze it. Not really sure how this acts as a choke, but it is working the same.

Re: 79 Moby Backfire and bog

Mr. Richard Dickrich /

Thanks Much, I've gotten two points leads-- which I will attack and now this clutch info. I have tried to clean with sandpaper, but it didn't do much. I'll take it apart next.

I am going out of town this week, so It may be a while until I write back - plus it's 100 degrees in Portland and I have no AC - not ideal moped fixing weather.

Thanks for everyone's help.

Re: 79 Moby Backfire and bog

as i see it the carb is clean.. it runs great .. just won't idle..

If you adjust idle on a cold engine, the idle mixture will be far richer than it needs to be. It may not idle at all when warm.

the hot engine tries to idle on that rich mixture, misfires and dies ..

perhaps it misfires, unburned fuel from misfires enter the exhaust and pops (backfires) in the muffler on the next sucessful ignition stroke, or when you try to restart it.

could also be something like a high float level .. that will cause a rich idle .. richness in general.. possibly a bog.

Most mixture problems are more evident at idle when the engine is barely able to run, even when things are correct...

Re: 79 Moby Backfire and bog

Mr. Richard Dickrich /

Thanks Joew, I really think you are right. I have have been exclusively working with the carb, so this bogging and backfiring MUST be related to that... gotta be the float.

The more I read, the more I think this is running rich. It's frustrating because I play with the idle screw/throttle adjustment but it doesn't seem to do anything-except make the bike stall. I can never find that fine line where it will idle. All or nothing... Just doesn't happen.

I'll tackle the clutch after I get back to where I was prior to the carb work- starting on the first kick, but hopefully it will maintain it's top speed.

I was hoping a week away would allow me to focus, but I think I am going to be itching the get back at it all week.

Thanks again.

Re: 79 Moby Backfire and bog

Carb float may have a hole in it causing it to sink?

Re: 79 Moby Backfire and bog

could be .. could also be caused by anything that prevents the float's free movement .. anything that makes it unable to float properly...

High float level could be due to a minor float needle-valve leak..

There's a lot of possibilities.

A transparent float bowl would be nice .. look-see what's really happening. link break>

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