Gs1000g carb stutter at 2500 to 3000 revs

[DaveWatts]

Hi,

i recently serviced my carbs but the bike still doesn’t run right. It seems to stutter at 2500 to 4000 revs regardless of gears. Do you know which jet this could be, or could it be a sticky diaphragm? Any ideas before I strip them again.

cheers

Dave

[Tom R]

Stock exhaust and airbox? Jet kit?

[DaveWatts]

all stock, the exhaust is a 4 into 1 but legal, I don't think that will effect it, It seems to stutter all the way up to 4000 revs not 3000 as I said before. Looks to me like it could be the needle/needle jet or that pesky diaphragm.

[mmattockx]

Hi,

i recently serviced my carbs but the bike still doesn’t run right. It seems to stutter at 2500 to 4000 revs regardless of gears. Do you know which jet this could be, or could it be a sticky diaphragm? Any ideas before I strip them again.

cheers

Dave

The RPM is irrelevant, it is the throttle opening that controls what circuit you are on in the carbs. To check this put a piece of tape on your throttle housing and mark full throttle and closed, then divide the travel into 1/8 increments. Pilot/idle is 0-1/8, needle is 1/8-1/4+, main is anything over about 3/8. A test to try is to get out on the road and when it is in the area that is giving trouble pull the choke. If it cleans out you are lean, if it bogs horribly and falls on its face you are rich and if it bogs slightly then it is about right.

When you say it 'stutters', what do you mean? Can you describe it more fully? A lean condition will cause it to surge and buck and it will struggle to get past that point. Rich will usually just bog without the surging.


Mark

[DaveWatts]

The RPM is irrelevant, it is the throttle opening that controls what circuit you are on in the carbs. To check this put a piece of tape on your throttle housing and mark full throttle and closed, then divide the travel into 1/8 increments. Pilot/idle is 0-1/8, needle is 1/8-1/4+, main is anything over about 3/8. A test to try is to get out on the road and when it is in the area that is giving trouble pull the choke. If it cleans out you are lean, if it bogs horribly and falls on its face you are rich and if it bogs slightly then it is about right.

When you say it 'stutters', what do you mean? Can you describe it more fully? A lean condition will cause it to surge and buck and it will struggle to get past that point. Rich will usually just bog without the surging.


Mark

It's like the fuel isn't getting through, so I guess it's more like bogging, but in jerks, from 4000 onwards it's fine, plenty of power, I can't believe it would be the diaphragms. It must be the needle jet/needle, I will pull them on the weekend. Last time I pulled the plugs they were black.

[jlyon40]

I'm currently having this same problem with my dad's 850. All stock and it happened mid season. It just bogs at around 4,000. And like what you said after 4000 it's fine. Went through the carbs and they're all good. I'll let you know if I figure it out before you do.

[mmattockx]

It's like the fuel isn't getting through, so I guess it's more like bogging, but in jerks,

That sounds like a lean surge. Has the bike ever ran correctly? Where are your mixture screws set? Are you sure the jetting is all stock?


Mark

[DaveWatts]

The bike has not run correctly from since I got it. Mixture screws are about 2 turns out. I think everything is stock, but I must check again

[Nessism]

Why are the pilot screws at 2 turns? That's typically too lean, especially with an exhaust installed.

[mmattockx]

The bike has not run correctly from since I got it. Mixture screws are about 2 turns out. I think everything is stock, but I must check again

2 turns out is pretty lean. Try opening them up to 2.5 and then to 3.0 turns out and see if you notice an improvement. Definitely pull the float bowls to confirm everything is stock, you never know what a previous owner may have done in the name of 'improving' it.


Mark

[Nessism]

I'd try 3 turns and lift the needles. And if you don't know how to raise the needles check the carb rebuild tutorial linked in my signature. Hint: you don't place washers under the needles to lift them.

[DaveWatts]

I already had the carbs apart, but I am going to do it again, this time more thoroughly (like check the float level with a fuel hose). Do you think this bad running could be due to the rubber airbox gaskets, they are impossible to find in good condition, I tried my best with them but they are still not perfect. The other thing I'm going to do is carefully check the intake hoses, I thought they were alright last time I looked, but I may have missed something.

[Nessism]

The airbox and filter must be completely sealed. There are lots of older threads here discussing replacing deteriorated foam on the box and filter cage using weatherstrip foam from the hardware store. I think basscliff even made a tutorial so the info is out there.

[Nessism]

http://members.dslextreme.com/users/cbsaunders/gs/airbox-sealing.pdf

[DaveWatts]

It is good to read this again, there is interesting information about lining up the carb boots, I didn't know about this!