help troubleshooting my 86 R

[dovesprings250R]

One of my Rs needs help. I have had it bored 2 over, decked the head, and had it match ported. It is running the stock carb, pipe, and silencer. It starts up fine and runs well but it just craps out and sputters on top. It won't pull to the higher rpms. It has new boyesen power reeds and A br8es plug. I run yamalube with 91 octane at 32:1. I have replaced all the electronoics.....cdi, rectifier, coil....from my other R and that didn't help. I was running a 142 main...I upped to a 148 but it didn't help much. Not sure what needle position or pilot I'm running....Would that matter on top? Runs fine on the bottom to low mid (rpm) Do you all think this is most likely a carbueration problem? Piston, rings, whole top end is fresh. Could it be timing or my stator? I live at 1000 feet...ride dunes and desert. I think it may be the carb still but just am getting tired of it. I guess I can always pull the carb off my other one which runs awesome to determine carb trouble. My other carb was bored and it really seemed to help. Thanks for any direction guys......Dove.

[MyMistress86R]

Derrick Adams had a similar problem with his former '83 R. He found that running a bigger carb all together helped immensly.

The stocker on that should be 34mm if I'm not mistaken, so you might consider a 36 or even a 38. I've got a 38 on my 86 with no more than a pipe and silencer and it revs to the moon.

[Bryan Raffa]

38 or 39 flatslide carb is the way too go

[dunerash]

Sounds like your to fat on the top end, it will make it sputter on the top like that.. If you Have a place you can do a plugchop, give it a try:wondering

[Dammit!]

Sounds like your to fat on the top end, it will make it sputter on the top like that.. If you Have a place you can do a plugchop, give it a try:wondering

Yep. Sounds like it's too rich. Quick experiment is to just pop the airbox lid off and see if it improves any but you definitely need to do some proper plug chops.

How did it run with the stock jet?

[ChrisD]

I agree also...sounds too fat. One thing that still puzzles me is that when you increase ths displacement of your motor, you will actually drop jet sizes. I went from a 190 main on my 250 motor to a 175 main on my 330 motor.

I would go back to you stock jet and see if it runs better. If the top end spudder decreases, then you're heading in the right direction. Lean it out another size and see how it runs again.

[Derrick Adams]

I agree also...sounds too fat. One thing that still puzzles me is that when you increase ths displacement of your motor, you will actually drop jet sizes. I went from a 190 main on my 250 motor to a 175 main on my 330 motor.

I would go back to you stock jet and see if it runs better. If the top end spudder decreases, then you're heading in the right direction. Lean it out another size and see how it runs again.



I'm curious if this has something to do with velocity. I'm under the impression that the larger the displacement, the slower it draws in air/fuel. This would also hold true with the engine revving up slower (more rotating mass). So , if this theory is correct, you would actually have more time per stroke to draw in air/fuel. So the use of a smaller jet would be neccessary.

[ChrisD]

exactly....the velocity is slower so you use a smaller jet.

On my motor, to counteract the larger mass problem, I have gone to the PVL ignition with the small flywheel weight and have shaved off 60 grams from the counterbalance......all on a 330.....I know it's technically a timebomb, but it hasn't blown yet and it screams.

[dovesprings250R]

It ran about the same with the 142 jet. I thought it may be to rich. I went to the 148. Smaller jet is richer right? I don't really have a good place to really get on it. I think I am going to have the carb modded like my other bike. Bench flowed and re jetted. I think it's rich too. Thanks guys.....Dove

[DeePa]

larger jets draw more fuel, so larget hets are richer, smaller jets are leaner...

[dovesprings250R]

OK, sounds like I need to lean it out on top. It ran poor with the 142 so maybe a 140? DSo a high rpm plug chop and check it? smaller is leaner, cool. I'll try it. Thanks.