Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

78 Motobecane 50v.

I replaced the whole ignition system and I finally get spark.

But, i only get Spark when I spin flywheel by hand, no spark when I pedal the moped.

Is it possible my clutch is bad? Or belt (belt is old, worn and oily, but thought I could at least get it started first before replacing)?

It’s like the clutch is not catching to spin.

I don’t even see the flywheel spinning on the other side when I pedal. Not sure, but isn’t it supposed to ?

Any help would be much appreciated.

Thanks

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Is the switch flipped to motor mode on the pulley? You might just be in pedal mode

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

Yes, it is. I doubled checked. And can def tell because i do get some resistance when pedaling. As opposed to when it is off, it's a lot easier to pedal.

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Are you using the decomp? The first thing to do would be to replace the belt. It's probably slipping in the front pulley. You have no spark because as you said the motor isn't actually turning over

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

Ok, the belt is def worn. I will replace that next.

I was just confused because I get a spark when i turn the flywheel by hand. and my timing is set and points are clean and set.

But once I pedal the moped, no spark.

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

> Brad Florence Wrote:

> -------------------------------------------------------

> Ok, the belt is def worn. I will replace that next.

>

> I was just confused because I get a spark when i turn the flywheel by

> hand. and my timing is set and points are clean and set.

>

> But once I pedal the moped, no spark.

>

> -Brad

Yeah but if what you said is correct and the flywheel isn't spinning the motor isn't turning so it's got the same likelihood of sparking as when you're looking at it from across the garage

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

Got it. Okay thanks.

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Pushrod Fifty /

Is the braided ground wire in good condition?

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

UPDATE:

Yes, just got done working on it. So apparently if I pedal really really fast. I mean super fast, it will actually spin the flywheel now, and I am getting a spark. But it still wont start.

So after reading a bit more, I tested for compression with my thumb over the spark plug hole, and it seems as if I have very low, or no compression. So I must have a leak somewhere? Could that be why it is not starting? And maybe my decompression is broken? The decompression cable moves, but doesn't seem to do anything or make a difference in sound (like I've heard/seen before in other videos, specifically David Fixes His S**t).

So whats my next step? Taking off the engine and checking for air leaks? Could the leak just be from my exhaust, which also looks to be not in the best shape. Ill try taking that off next and checking for threads and leaks there.

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Pushrod Fifty /

You need good compression to start and a good belt, greased variator and pedal shaft. Best to just do all of the following in shot. You can lap the decomp valve to the head, clean the piston ring grooves and the cylinder ports, check for wear and see if that improves your compression. Install all new gaskets. Replace the condenser, plug, clean the points, set the timing, clean the carb. All those add up to having a good running Moby!

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Your exhaust being loose is not going to cause you to lose compression. Have a friend pull the decomp and watch the decompression valve to see if it it moves or if it's stuck

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

okay. Sounds like I got my work cut out for me.

"You can lap the decomp valve to the head"

- Does that just mean removing it and sanding it?

I did just replace the condenser, plug, cleaned the points, set the timing, and cleaned the carb first because I thought that was the issue in the beginning.

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

Really, ok, that is good to know. I thought it was. So I am moving the decomp lever and looking at it, the cable moves, but there is no way to really tell if it is actually working or sealing inside the head.

I will try removing exhaust and see if i can see inside from there.

Also, should I just replace the decomp if it is stuck or not working, its only like $8 on treats.

Thanks so much for the help everyone.

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Pushrod Fifty /

If you do a proper leak down test with air pressure, you will see if the decomp valve is leaking or not. Even a new valve will have to be lapped to the seat. Best to use the original one unless its toasted. To lap it in, remove the head and the decomp valve. Clean the head and the valve. Put some valve lapping compound on the valve and a little oil on the valve shaft. Insert the valve back into the head and push a piece of tubing over the valve shaft. Pull on the valve slightly as you turn the tube back and forth. Check for a smooth, even fresh ground surface all around the valve and the seat with no pits.

Re: Spark when I spin flywheel by hand, no spark when I pedal.

improper leakdow test: put motor at tdc, blow in intake with mouthparts, listen for leaks, also if air just blows through, maybe something is fucked? maybe not at tdc? getting to 1st base with your engine is a good idea anyway...

Re: Spark when I spin flywheel by hand, no spark when I pedal.

i'd keep the OG decomp unless it's visually damaged. clean and inspect... the OG one is "mated" to the head. if u get a new one, do the thing with the valve grinding goo and a drill....

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

Got it. I will try soon.Thanks.

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

ok, seems most people are saying I should keep the original decompressor. I will try to take it apart and clean everything and check it out. Thanks

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Lap the original valve to the head and run it . They do wear and the result is leakage .

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

So I pretty much have to take the engine off the bike? No way of avoiding that then. Thanks again everyone. I'll update when I am done.

-Brad

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Pushrod Fifty /

Its only held on by two bolts.

Re: Spark when I spin flywheel by hand, no spark when I pedal.

Brad Florence /

Update:

I replaced all the gaskets, lapped the decompression valve (made sure it sealed), put the engine all back together, made sure I had spark, and guess what, I FINALLY got it running.

Only thing now is... on idle it keeps stalling. No matter what I do to the idle screw it keeps stalling. I think it is time to replace that old Gurtner Carb with a

dellorto SHA 14.12 carburetor, or a

dellorto SHA 15.15 carburetor.

Will either of those carbs fit on my 1978 motobecane 50V (25mph version) without any adjustments?

I have the straight intake (NOT the bendy one).

Re: Spark when I spin flywheel by hand, no spark when I pedal.

At worst case you may need a new intake to go with the sha if you go that route. But if it is not running at idle, there may still be a small air leak. Most likely at the carb. Even if you get a new carb/intake. Make sure they have the proper gaskets and such to ensure no leaks.

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