Hi
I am working on spark issue on my Moto 4 350. Bike had a broken clutch and I end it up swapping the engine from doner big bear350 1990. Engines swap was easy , no modifications needed it bolts right on. After the engine swap, I found no spark issue. Just to explained, I kept the original Moto 4 CDI . Could that beat problem, not using big bear CDI? Original engine Moto 4 ran fine but the clutch got mess up. I was thinking engine swap would be easier, found out , not so much. Any one came across similar issue?

 

Recently, someone on here posted a picture of a Yamaha stator with two trigger coils for the spark, so if one of your stators has, and t'other hasn't, this could be your problem.

If you can find wiring diagrams for both bikes, it will show any differences in how the ignition system works.

 

Thanks for suggestion.
Both don't have a spark with this set up. Again, I am trying to run big bear 350 1990 engine in Yamaha moto 4 1987 bike. I am changing only the engine but trying to keep all yamaha moto 4 350 1987 components. Anyone knows if this will work?

 

I have some updates about my project. It didn't work, the swap of the engine for big bear 350 1991. I found out that I need CDI and wiring harnes from the big bear 350 1991- 1994 to make it work.
So I end it up putting the original stuff back in the frame, changed the oil and filter, put a new plug and cleaned the air filter with K&N cleaner. I found a used good wet clutch on eBay for $37. Also got a spare one for $26 but I need a rolllers to make it work.
Clutch installation is pretty simple but putting the cover back on with all the clutch shift forks can be a pain. I started up the machine and ran fine but my carb was overflowing.
Next thing was to rebuilt the carb. I took it all apart and cleaned the jets, needle and seat and all small passages. Use carb cleaner spray. Worked fine. I also bend the float so can stop the overflow of the carb when the engine is not running and the petcock is in on position. I put it all back together and fired up. No change , but still ran good. Plenty of power and low end torque. The carb still overflowed.
I ordered the carb kit from eBay but the guy sent me a warrior kit instead. Warrior jets are bigger and needle and seat doesn't fit. I tried playing with original needle setting to make it run less rich-you have to raise the needle higher. Still engine was bogging and sputtering at high rpm.
I put the original jets and set the needle back to factory setting - middle slot on the needle.
Runs like a champ and the overflow I just shut of the fuel after the ride. Maybe at some point I will rebuild the carb with original stuff.

 

"to make it run less rich-you have to raise the needle higher."

I know terminology is tricky with this, but you lower the needle further into the slide to weaken the mixture, by raising the circlip into the next notch up. A dribbling carb is either float level wrong, or grit under float needle, or the float needle faulty.

 

Thanks for the comment. I am still looking for the on/of switch. I purchased already two from eBay but don't work. Looking for good, old used one. New ones from china don't work.
Here is picture of completed machine.


Yamaha moto 4 350 ERT 1987

 

You are correct about the needle setting. Machine runs fine with no issues. Having problem with my other project I was working on this summer - Yamaha Moto 4 200.
Cant make the motor to stay running longer then 20 - 30 seconds. As soon as I give a throttle, machine stalls. Just to say, the needle was set on 2nd slot from the bottom to give more flow. With needle on factory middle setting I could get the motor to run at all. Jets are all stock.
Any ideas what can be causing it?

 

First be very certain that all jets and the holes they go in are clean. What happens when you give the engine choke? A cold engine needs a wildly different air/fuel ratio to a warm one, that is what choke is for. Until you can get the engine to run long enough to warm up, you are not going to be able to set the carb. Have you tried a new plug? A faulty or sooted plug can cause similar symptoms to those you describe.

 

your moto 4 looks so clean [compared to mine], was all the plastic that shiny when you got it?