Yamaha Engine cutting out at RPM???

JoeyD23

JoeyD23

#utvunderground
I wish Weller was local but since they arent I need to do some troubleshooting this weekend. At RPM my motor wants to cough and cut out.....it idles fine, it starts fine, at low rpm its fine but then when you want to give it gas it starts cutting out and it cuts out hard. so here is what I have done so far:

-First I replaced the stock fuel pump with a new Weller Racing High Volume fuel system. New filter included. routed all lines correctly.

-The CDI I have is an older BRP Pro Comm CDI. I tried swapping it with a Pro Craft CDI and it had the same results. Tommorow I pick up a newer BRP Dynatek and will be running that from here on out.

-I pulled the carb apart and checked the float bowl tap, the needle, and made sure all the jets were clean and clear. same problem still. I then tried putting a fat jet in it....same problem so went back to the proper jet.

-I changed the spark plug although it had a brand new one in there. Same problem

-The motor dyno'd perfect. I took it to the desert and was running awesome, went through one big whoop section and this started happening???

What could it be? Rusty thinks maybe the stator is going out or is bad?

PLEASE HELP!
 
Fuel cell in the phat rod? Foam in the cell? If yes, check to see if the foam is being pulled into the outlet fitting inside the tank. Seen it more than once, very tough to diagnose.
 
Thanks chris!!! Your input is always welcomed! The Fuel Cell is a custom cell, it does nto have any foam in it. Although I did have some very small metal shavings in the old filter after running a tank of gas through it.

hmmmmm.........

If your stumped then I am in real trouble! hahaaha

I havent called Jason just yet, he said to change the CDI first, I just have a strong feeling it is beyond the CDI. Could this be a symptom of a possible wiring issue? I am essentially using the stock harness, nothing fancy?
 
Is it cuttin out like a fuel delivery problem....or like a rev limiter problem? I have seen Procom boxes cut out due to the reverse switch acting up. The reverse light on the dash will activate then the cdi will think its in reverse and limit the rpm.
 
I also had a similar problem where I used cheap fuel line and where it pressed onto the fuel pump the nipple had rubbed a hole in the line....started sucking air and had those type of symptoms
 
hmmm.....well I tried another CDI and it did the same thing.....the reverse light does not come on? I only have one of the fuel lines left on there that was origional? Maybe I will change it out. It is the delivery line to the pump. Everything else is new.

thanks for the ideas Jim....more are welcome!
 
Its not a fuel problem. It does not backfire it just cuts out. It acts like its dropping the spark. He ran the car about 12 to 15 miles and it ran perfect. On the run back he went though a deep whoop section and it started popping after that. You can hold the throttle at about 30% in neutral and it will still do it. We tryed an early Procraft CDI and still did the same thing. There is a way to test the stator by checking the resitance. I will find the info...

Go to Harbor Frieght and pick up a spark checker.

Inline Ignition Spark Checker

Troubleshoot dirty spark plug connections, defective points, bad cables or connections

ITEM 4424-0VGA

$5.99
 
check the ground cable on the motor.

next check the spark plug wire to see if it actually sitting in the hole properly and connected.
 
Have you checked the two wires that go to the coil? I had an issue on my rhino where one of them came loose and it would cut out. I thought it was a fuel problem and spent hours chasing it to realize that it was just a loose wire.
 
As rog stated make sure the plug wire is not rattling out....I have had alot of issues with that. Also there is a flat tip screw in the end of the plug wire...make sure that is tight. There is some kind of resistor or something under that screw
 
you need to ground out the rev sensor sometimes light doesnt come on. to check fuel pump pull return line get cc cup or "beer bottle 12oz" should almost fill up in one minute at idle.If doesnt you no you got a fuel delivery problem if does fuel pump ok.
 
100% its not fuel pump, I have already verified its getting fuel and plenty of it...I will be trying to diagnose it tommorow and saturday with hopefully a fix..I hope its not a stator issue...
 
Mike L said:
Have you checked the two wires that go to the coil? I had an issue on my rhino where one of them came loose and it would cut out. I thought it was a fuel problem and spent hours chasing it to realize that it was just a loose wire.
Click to expand...

I checked that but will do it again

BiggJim said:
As rog stated make sure the plug wire is not rattling out....I have had alot of issues with that. Also there is a flat tip screw in the end of the plug wire...make sure that is tight. There is some kind of resistor or something under that screw
Click to expand...

What end of the plug wire? The end that connects to the spark plug?
 
JoeyD23 said:
hmmm.....well I tried another CDI and it did the same thing.....the reverse light does not come on? I only have one of the fuel lines left on there that was origional? Maybe I will change it out. It is the delivery line to the pump. Everything else is new.

thanks for the ideas Jim....more are welcome!
Click to expand...
try a electric fuel pump with a regelator
 
BiggJim said:
Yes where it connects to the spark plug...there is a little flat tip screw in there.
Click to expand...

Inside the boot is a resistor & a spring. Mine messed up so bad it wouldn't start. Stock boot with resistor is $35 through Yamaha. I tried to buy an NGK for a lot cheaper but the boot wasn't deep enough.
 
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