951 misfire

[CYPRESS]

Seeking a guru here:
951 with carburetors that runs great for around 15 minutes, then bogs out / sputters & misfires barely holding 4000 rpm -- I can limp it back.

• Roars through fuel
• Bogged out heavy sound to engine
• Intermittently sputters to speed up
• Sometimes sputters back up to speed, then bogs down again

It wants to go but something is holding it back from wanting to scream.
I'm assuming something ignition / electrical as I've done lots with the fuel side and RAVE valves, with no change to these symptoms.
Anyone with the same experience here?

 

[amcreativ]

Seeking a guru here:
951 with carburetors that runs great for around 15 minutes, then bogs out / sputters & misfires barely holding 4000 rpm -- I can limp it back.

• Roars through fuel
• Bogged out heavy sound to engine
• Intermittently sputters to speed up
• Sometimes sputters back up to speed, then bogs down again

It wants to go but something is holding it back from wanting to scream.
I'm assuming something ignition / electrical as I've done lots with the fuel side and RAVE valves, with no change to these symptoms.
Anyone with the same experience here?

The common theme with these 951 carbs is the carbs. Do you have the old grey fuel lines? When was the last time you did a carb rebuild with genuine OEM parts? Fuel selector switch? Fuel filter gasket?

 

[CYPRESS]

The common theme with these 951 carbs is the carbs. Do you have the old grey fuel lines? When was the last time you did a carb rebuild with genuine OEM parts? Fuel selector switch? Fuel filter gasket?

Carbs are clean, fuel lines are rubber, fuel selector switch looks recent, fuel filter gasket looks fine.
When it bogs down it feels like the timing got pulled. It idles smooth and during bogged it still runs smooth, but sputters when it wants to make a jump for power. First run of the day it screams with power till about 15 minutes later...

 

[Mraw]

Check your reed valves. If they check out I would highly recommend rebuilding your carbs with genuine mikuni kits, including new needles and seats, be sure to check pop off aswell.

 

[Boyd12]

check the plugs when it is running well and when it isnt and see if there is a difference. PS I used aftermarket carb kits on a 951 years ago and they were BAD. I doubt that is the issue, just saying

 

[CYPRESS]

Well, I checked the new spark plugs it came with, and behold the plugs were for the the next year model with DI -- NGK's ZFR-4F11 instead of good old BR8-ES.
Changed those plus ran a ground wire back from the ignition coil box to the battery, and it runs like a champ now!

 

[Boyd12]

Yay! That is great news!