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plug chop screams "lean"

  • Thread starter Thread starter khardrunner14
  • Start date Start date
K

khardrunner14

Guest
Hey guys, I'm still working on getting the bike to run properly. Here is the deal so far....
- pulls pretty well (comparable to my brother's gs400) up to about 5 grand
- after that the bike stops pulling and surges up to about 8-9 grand, then it pulls ok again
- plug chop done at 6g's says I'm lean in all 4 cylinders, and I'm still lean at idle as well
- I've rebuilt the carbs using the old main jets.
- I have a new petcock and new plugs
- I am using the stock airbox/filter and I have new o-rings on the block side
- I did the "spray test" and I didn't find any leaks around the boots

WHAT NEXT??
Thanks!
 
You can't guage these carbs with RPMs. What was your throttle position when you did your chop at 6 k?
Idle to 1/8 throttle=pilot circuit
1/8 throttle to 3/4 throttle=needle circuit
3/4 throttle to wot=main jet circuit
When you understand these carbs and when the lean running is occuring we can help you get them dialed in.
I would check for an airbox leak if your running lean with stock jets.
 
Pretty much 3/4 to WOT is where it lags which would suggest main jets. It's worse at highway speeds (which has nothing to do with which circut it is running on I know).

I'll spray some stuff around the air box to see if there is a leak there. I noticed the foam gasket on the airbox is pretty beat. Maybe it's not sealing well??
 
Sorry about that...I have posted so much lately on the bike that I assumed everyone would know.

81 gs550 with the cv carbs
 
Have you set the carbs to idle using the "highest RPM method"? This should take care of the idle issue as far as running lean (as long as the idle circuits in all the carbs are clean). As for the 3/4 to WOT position, if everything else is clean and working correctly, it sounds like you'll have to raise the jet needles up a notch or two. I'd start by raising them up (move the clips down on the needle one notch) and retest. I had to do this on my bike after everything else was completely ruled out, and the problem went away. Give it a shot.
 
Aftermarket exhaust? If so, you need to up the mains for sure.
 
Everything is stock...original for all I know.

As for raising the clips, I am under the impression that CV carbs have no clips. I would have to rig some sort of shim, in which case I would rather jet up. Maybe I am missing something though.
 
Dave8338 said:
Have you set the carbs to idle using the "highest RPM method"? This should take care of the idle issue as far as running lean (as long as the idle circuits in all the carbs are clean). As for the 3/4 to WOT position, if everything else is clean and working correctly, it sounds like you'll have to raise the jet needles up a notch or two. I'd start by raising them up (move the clips down on the needle one notch) and retest. I had to do this on my bike after everything else was completely ruled out, and the problem went away. Give it a shot.
Click to expand...

Hey, Dave, is all of that in the carb section somewhere here? I've never yet had to mess with my carbs, and my bike is now running on 3 cylinders (#1 is really lean) at 3/4 to wide open from 4k-6k, then evens out. I've been avoiding fixing something that ain't broke, now some problems have surfaced, of course, just before all my scheduled long rides.....:confused:
 
If you've got stock everything then there should be no need to raise the needle or change the jet. You mentioned the airbox/air-filter: That is absolutely critical. If that airbox/filter is letting too much air through it would certainly lead to the symptoms you described.
I was shocked to find out what a huge difference there was after I got a brand-new filter and sealed all the tiny leaks in my airbox (especially between the airbox and the lid). The seal between the airbox to the boots and the boots to the carbs is also absolutely critical.
Another thing that was a surprise to me was how much an exhaust leak (if it's fairly significant) can effect the bike.
See the tons of other posts on this topic.
 
DanTheMan said:
Hey, Dave, is all of that in the carb section somewhere here? I've never yet had to mess with my carbs, and my bike is now running on 3 cylinders (#1 is really lean) at 3/4 to wide open from 4k-6k, then evens out. I've been avoiding fixing something that ain't broke, now some problems have surfaced, of course, just before all my scheduled long rides.....:confused:
Click to expand...

The link below is the best approach I've ever read, for the various stages you need to go through, to get these carbs and all others, to flow seemlessly, throughout the power bands. This technique will work on all carbs with jet needles. Check it out. http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

I'd like to agree, that if everything is correct, raising the needles shouldn't be needed. After correcting all the issues that my bike was plagued with, and having gone through it top to bottom, there was only one thing left to do...raise the needles, and the slight flat spot from 3800RPM to 5500RPM was gone.
 
Thanks, Dave. I assume this also means I've got to pull the carbs off to make the adjustments? I did check my airbox gaskets and they're all well seated, should have no leaks, I just hate to disturb something that was working previously. Y'know, "if it works, don't fix it":-D ....
 
I hear you...the big thing is to rule out all air leaks first, at every connection point, boots, head, airbox and lid, exhaust (though you should hear that), filter properly oiled and sealed with grease, ect. ect. ect.
 
I'm still not sure raising the needles is an option without fabing a shim. Please correct me if I'm wrong. I will work something out for the airbox as I am sure the lid gasket is part of the problem.

I've read the stuff in the link. First I need to figure out if jets are the problem, or if it's something else. THen I need to know where to start with jets....and where to get them.
 
I'm not sure the filter is properly oiled and sealed...how do I do that? I had it out to clean it, and I put some 10w40 on it. That was it. Thanks again!
 
khardrunner14 said:
I'm not sure the filter is properly oiled and sealed...how do I do that? I had it out to clean it, and I put some 10w40 on it. That was it. Thanks again!
Click to expand...
Do you have a stock filter or a K&N? Oiling the filter w/10w40 if it's a K&N is absolutely the wrong thing to do. Does it still have the stock foam outer cover, or is that what you oiled? If so, there should be a paper filter inside the foam one.
 
khardrunner14 said:
I'm still not sure raising the needles is an option without fabing a shim. Please correct me if I'm wrong. I will work something out for the airbox as I am sure the lid gasket is part of the problem.

I've read the stuff in the link. First I need to figure out if jets are the problem, or if it's something else. THen I need to know where to start with jets....and where to get them.
Click to expand...

If you're running the CV carbs, they're there. The are connected to the diaphragm and slide assembly with C-clips. You'll need to get a pair of snap ring pliers with the interchangeable tips on them, as to get down and into the slide, you'll need about two inches of tip to work with.
 
I had the carbs apart and didn't notice anything...smeone else here told me that they weren't there...either way I guess I have to yank the carbs and check again.

As for th air filter it's stock. I have the metal basket inside the airbox with a foam element cliped onto the one side. The other side of the basket has a rubber seal.
 
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