HELP - Cough and Splutter on Full Throttle


When revving hard on the highway with my 2001SY, the bike starts to cough and splutter, slowing me to a crawl, as it's not revving cleanly.

It ticks over ok without any throttle twisted on, but as soon as I twist the throttle back on, it starts to cough and splutter again.

This seems to clear after a few minutes and everything's ok again. This only ever happens on the highway, and never off road.It seems to make no difference if it's in the dry or the wet. Fuel tank can be full or near reserve.

What I've tried / checked so far.

There's no water in the tank.

The fuel screen is clean

I've tried running with the petcock on both Res and On

I've done the kick-stand switch mod.

I've tried running without the fuel cap, just in case it wasn't venting properly

I've not changed anything related to the carb

I reckon it must be a fuel starvation or carb problem

Please HELP!!!!

sounds like the needle retianer has come loose.

Burned, thanks for the suggestion.

Er, what's the Needle Retainer, and how do I fix it?



I might be wrong but i believe its the plastic piece that holds the needle in place. You take the black cover off the top of your carb then gently remove the diaphram there. It will come out with the needle holder part and stuff.

Look like this:

In there is a white plastic piece holding the needle.

Make sure that is seated properly inside there...reach down with a pair of pliers and gently push/twist it to make sure it is seated properly..

IF this isnt the needle retainter, i have no idea..but thats how you get to the needle. and its accociated parts.

Anyone else get this problem and found the solution?

I've not had the carb off yet, so not tried Burned suggestion.

Try it with the petcock in the "PRI" prime position. Your bike may be old enough to have developed a problem with the vacuum controlled petcock diaphragm. Both the ON and RES positions are vacuum dependent for fuel flow.....PRI is not, it just opens the valve.

The chances of Burned being wrong are very can try this fast and without disassembling the carb.

Ray Stedronsky

Davis, CA


I checked the needle retainer and tried the petcock on prime, still having the same problem.

I'd appreciate any other suggestions.



You've got Prime on your UK petcock?


I assumed this was the same as res.....

Guess I was wrong.

Either way I've still got the problem :D

No, Reserve ain't the same as Prime. The US bikes have a vacuum fed fuel system and "Prime" is like our "On" setting - it switches to gravity fed fuel.

So, it's not the petcock.

Didn't you have the carb out the other day, rejetting the bike? I seem to remember you reset your float height at 14mm. Maybe it's a float height issue.

Whadya reckon, Burned?


I had this problem before I took the carb out to do the 3x3 mod.

The carb is still on my bench waiting for tomorrow when the postman should bring my 140mj, so I thought I might try and find the source of this problem at the same time. I've not changed the float height setting - do you need verniers to do this accurately?



I , too have developed this problem, had it once before and thought it was gone. Mine seems to develop when i hammer through the gears to 5th and then try and cruise, it will run great and then a hard pull and sputtering and coughing and then nothing. The only way to get bike started immeditately afterwards is t pull choke all the way out.

It really came back when I installed the full yosh system yesterday. Rode it today and on highway did what described above, then got to some trails, where you are on and off gas, and rode great.

All the mods, 3x3, 134mj, 25 pj, 4th clip. dj kit.

Fuel canister removed, S-model, stock tank and petcock.

just want to :D cheers, brian


Thanks for all your advice.

I didn't find a solution for this so I thought I'd get on with the 3x3 mod.

I bought the dynojet kit so changed the needle, spring and opened up the airbox. I changed the main and pilot jets to 140 and 25, and cleaned everything in sight on the carb. I also made sure that all the hoses were on firmly.

Result cough and splutter gone. I don't actually know what solved the problem. But I'm grinning from ear to ear after my test ride. The bike pulls harder all the way through the rev range.

I've fallen in love with it all over again. :D:D

Thanks to all of you who took the time to offer suggestions.I reckon my next mod will be to go up to 47 on the rear sprocket to make use of all that new power.


Billy the grin.

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