GS1000G - Carb Jetting

[KEITH KRAUSE]

This may seem like a dumb question, but is it possible to get one or two cylinders reading two rich while the others are fine; when all your jets, needle positions and mixture screws are set exactley the same? And if this is the case is it o.k. to run different needle positions or mixture screw turns for individual clyliders to remedy this? I would think that all your plug reads should be the same if all the adjustments are the same...but Im getting different reads for different plugs.

I'll answer your question but it's best to start your own thread about your problems.

There can be several reasons why you would see uneven plug colors, some reasons are worse (more expensive/more work) than others.
Poor compression, worn parts, weak ignition/spark, etc, can cause it.
You can still get uneven plug reads even if there's nothing "serious" wrong.
Most common reason is a poor vacuum synch. If the carbs aren't synched well, different levels of vacuum will draw different amounts of mixture. I always tell others here that the carb synch is a basic part of jetting and you can't get accurate reads or trust the reads if the carbs aren't synched well.
Many owners adjust the various mixture screws/pilot fuel screws/air screws incorrectly too.
Float levels may be a little different.
Worn jetting parts or damaged o-rings will factor in here.
I personally would never set jet needles at different positions or install different jets across to repair a problem. That's what I call compensation jetting and it doesn't really work. Other problems will come up sooner or later. I suppose if you have no choice (money or enough knowledge) and it's a matter of the bike simply running or not, then it's your bike. I've seen it all when it comes to temp fixes to make up for the real problem.
Adjusting the various mixture screws at slightly different points is nothing unusual though. These screws are meant to be the pilot circuit's fine tuning that's needed because there can be small differences in each cylinder. The screws can come straight from the factory set a little different from each other. I doubt they are set beyond 1/2 turn difference though and usually are closer, within 1/4 turn of each other or better.

Dan, If you would like, I still have the factory needles and am pulling the 115 jets and putting the 120 jets back in my carbs this weekend, your more than welcome to have these if you would like to go back to stock, then make adjustments from a baseline. Also at the same time I would replace the carb boot o rings

Fine tuning?

This may seem like a dumb question, but is it possible to get one or two cylinders reading two rich while the others are fine; when all your jets, needle positions and mixture screws are set exactley the same? And if this is the case is it o.k. to run different needle positions or mixture screw turns for individual clyliders to remedy this? I would think that all your plug reads should be the same if all the adjustments are the same...but Im getting different reads for different plugs.

[KEITH KRAUSE]

OK, stock bike. Sounds like you'll be happy with that.
What's obviously wrong is the larger main jet and the excessive mixture screw adjustment. What could be wrong is the size of the jet needles but we can just test and hopefully the needles can be adjusted and everything's fine. It also sounds like the jet needles are positioned too rich.
Here's what I'd do if the bike were here. I'm trying to minimize the work so...
I'd first pull the plugs and clean them off decently and be sure to check gap. Then, pre-adjust those mixture screws to something closer to factory, about 1 1/4 turns out. If the air filter needs cleaning, clean and oil it correctly. Don't over-oil, especially since we'll be checking plug reads. Now warm up the bike completely. Set idle to factory recommended idle, about 1,000/1,100 rpm's. Adjust the mixture screws for highest rpm/best idle. With the bike on the centerstand, start at any carb. Slowly turn a screw in either direction until you hear the rpm's max. Fine tune it. Now re-set the idle to base idle by using the idle adjuster knob. Repeat to the other carbs. If there seems to be no response from adjusting the screws, tell me. That suggests the pilot jet is the wrong one or other pilot circuit problem. If it goes as it should, your mixture screws are now set correctly.
Now you need to take some solid 1/3 throttle position chop tests to see how rich those jet needles are. The larger 122.5 mains still in there will not effect the jet needle reads as long as you keep it at this throttle position. Mark your throttle housing and grip if needed. Don't measure any throttle cable slack. Be careful. I'm lucky to have a great place to high speed test without police or lots of traffic. Take a plug wrench and rag and a piece of snug fitting tubing to help you remove and install the hot plugs those last few threads. Be careful of cross-threading.
As I said above, I can just get into top gear and settle at 1/3 throttle and chop off. You can test at 4th gear and keep the speeds down some without it feeling like you're revving hell out of it if that helps you. After full warm up, on level or uphill road, run it approx' 1/2 mile at 1/3 throttle. This helps to burn off any pilot circuit effect on the plugs while getting to the test site. If it's still safe, continue to run another 1/2 mile to 1 mile. Chop off by shutting off the throttle and quickly pulling in the clutch lever and turning off the ignition. Coast to a safe test spot with the clutch lever in. Read the plugs. Depending on those reads, we can make the necessary adjustments. If as rich as we suspect, you'll have to lower the needles by raising the e-clip position. Let us know the colors and any performance issues you felt while testing.
Since I believe the needles will need to be moved and the carbs taken off the bike, I've saved changing the mains for that time. I see no reason why the stock 115 mains shouldn't be used. Your full throttle problems are obvious so I see no reason to even attempt a full throttle chop test just to see how those larger mains effect the plugs. I'd install the 115 mains.
Just to be complete, there are some that would suggest changing back to the 115 mains BEFORE making the jet needle tests. That's fine and I have no problem with that. As designed, your carbs don't allow any main jet effect at solid 1/3 throttle position. But if you want, change the mains first. I just want to make less work. You can use a short tool and access the bowl fasteners with the carbs still installed on the bike if you don't mind working "upside down". I do all the time. Up to you. Just be careful of tightening things too much or leaving something loose or bumping the float assembly too hard, etc.
With the stock mains in and the mixture screws set, the only thing it appears we need to get right is the jet needles.

[salty_monk]

Dan, you can borrow my carb sticks. Let me know. I'll be picking them up from Burbank next weekend probably


Oh, I also have that colored spark plug thing. That might help a bit

Yes please.... We can have a play one day! We still have to sort out your fork seals.

Dan

[salty_monk]

Keith,

At the moment I'm running stock airbox & pipe. I don't have any immediate plans to change that as I can't afford to have it off the road for any length of time but I will if necessary.

I am going to try running it locally with no filter asap to see what happens & will also try to do some chop tests like that if possible. If it runs ok like that then I will likely simply switch to pods as it would be an easy mod. I think that this could be too lucky though!!

I will also try to open up the carbs & take some pics so we can actually see what's in there.

Dan

[KEITH KRAUSE]

Salty, I took too long with the first reply so I have to be a little brief. I'll try to help more after work tomorrow evening.
It seems like your bike is ready for the re-jet so I'll just assume that. However, Chef said your filter was dirty and that needs to be cleaned and oiled correctly first.
What we need to know is if you're going to run the 4-1 pipe or keep the stock exhaust. You even mentioned pods but you're probably staying with the stock air box? Gotta know what you're going to run first.
I agree 1 and 4 are rich and I would assume 2 and 3 are also. Hopefully, the carbs were vacuum synched well so you get uniform plug reads when needed.
I can't say how good the mechanic is but I question how ANYONE can just make changes that drastic (the jet needle position change) and why he would decide to install 7.5 richer mains on a stock bike? Did he Dyno the bike? Did he actually road test at 1/3 and full throttle, etc?? The 3 turns out on the mixture screws is excessive too. No reason for that.
As for a jet kit, it must be in there based on your info. What I wonder is if the kit is stage 1 or 3? A stage 3 jet needle wouldn't be designed for a stock bike and would make jetting more difficult, if possible at all, even if you set it a leaner positions to compensate. The installed main jet may be a hint though that it's a stage 1 kit because a stage 1 main jet would be right about 122.5 in this case. The drilling of the vacuum ports to the diaghragm chambers was risky though since it's generally only done when running pods or making significant air box changes. It's meant to improve throttle response. I can't really say from actual test experience what drilling the ports would do to a stock intake bike. Never had a reason to try it. Seems like it could be too sensitive to throttle openings but hopefully there's no real problems here. Without more positive ID info, we'll just have to test and hope the needles and port mods work out.
I hope the carbs haven't had any other changes that would throw us a curve. If not, it should be fairly simple to get your bike running well again.
What pipe will you run and what intake?

[KEITH KRAUSE]

OK. Read the thread a little better.
Something I noticed was a general question about higher elevation jetting for the CV's. I don't have as much experience with that as some of you may, but if you understand how the throttle position relates to each jetting circuit, you can easily test and come up with the right jetting. Of course, as I always say, the bike must be tuned and ready for any re-jet.
I've seen some jetting charts that suggest what to do/use depending on the elevation. I admit I haven't looked at one in quite awhile and I'm going by memory and some limited past experience with this type of jetting.
A 5,000 foot gain would generally require 1 full size (5) smaller main jet. A step (2.5) smaller would certainly help but I think 5 is right. Just remember, it won't really matter unless you open the throttle to 3/4 and beyond. The main won't have any significant effect, if any at all, below 3/4 throttle posion.
As for the jet needle, that's more of a problem at least for US bikes because the stock jet needle is non-adjustable. If you really want the mixture to be closer to correct and don't mind the work involved, then you can place a jetting spacer meant for "1/2" position changes, directly on top the e-clip. If the only change is the 5,000 foot elevation, a 1/2 position change may be a tad too much but it should run well enough and a tad rich is better than a tad lean on a longer trip. Personally, I think lowering the jet needle about .015" is even closer to correct but it can be hard to find such a specific spacer so that generally puts you back to using a typical jetting spacer that's approx' .022". If you do have adjustable needles, then just do the same thing.
As for the pilot circuit and any throttle position up to approx' 1/4 throttle, simple leaner mixture screw adjustments should be all that's needed. Using the highest rpm method, the screws can be set once you're at that higher elevation. If you can't reach the screws because of the tank or don't want to play with them on the ride, then you have to make a guess as to how to set them before the ride. Any factory caps have to be off of course.
About 1/4 to 1/2 turn in leaner would work for most bikes.
Setting them correctly without being at that elevation will take some possible trial and error as you can imagine. The CV mixture screws can vary from 1/2 turn to approx' 1 1/2 turns straight from the factory. A 1/2 turn on bikes with their screws at the "leaner" factory setting will stall if you seat them that 1/2 turn in. If your bike has them set further out you obviously have something better to work with. If pre-setting them, best you can do is keep a record of how the bike ran and make any needed adjustments for the next ride. You'll find the sweet spot and be able to set them before any high elevation ride. You can of course modify your air box by adding air flow that can be reliably re-sealed when no longer needed but that's up to you. CV's can be finicky about modifying the air box flow too much.

Yep! I sure do. You can certainly borrow it

[chef1366]

Dan, you can borrow my carb sticks. Let me know. I'll be picking them up from Burbank next weekend probably


Oh, I also have that colored spark plug thing. That might help a bit

You have a color tune? I wan't to borrow that.:-D

Dan, you can borrow my carb sticks. Let me know. I'll be picking them up from Burbank next weekend probably


Oh, I also have that colored spark plug thing. That might help a bit

[salty_monk]

Hi Keith,

Thanks for joining in! The no flash pictures are probably more true to how they are in real life especially #4 no flash. The #1 no flash is a little dark.

As far as the jet kit etc, I honestly don't know. Doesn't make sense to me either! TPO gave it to this guy for a carb clean & synch because he had had an operation & left it sitting for a while.
He was about 70 & owned the bike from new so I don't see it ever having run pods or 4:1 or anything different. Maybe he was trying to rejet it for the Uni filter or maybe he just left it to the mechanic who thought it would run better that way!

I got it about 50 miles after the work was done.

The valves were recently adjusted by me. They are all approx 0.06 now so all well within tolerance.

It has new DYNA green coils, new wires & plugs also fitted by me so spark is good. I don't know about ignition timing, I assume so as it runs well. I don't think you can change it anyway as it's CDI not points??

The mechanic was meant to clean the carbs & there seems to be no problems with them getting fuel so I think they are clean. They also seem to be synched quite well, I don't have the tool to check them but there is no excess vibration etc that would make me think they are off by any huge amount.

Idle is stable at 1,050 (although I did have to tweak it back down as it started to rise after a 1,000 miles or so but after I tweaked the stop it's been stable ever since).

It starts well on choke & doesn't hunt or do anything else horrible.

Hope that helps.

Cheers,

Dan

[KEITH KRAUSE]

Hey guys, just read this thread. On my way out 'til later this evening.
Jeez! Those plug reads with/without flash are SO different I can't figure them out. No help really. One looks rich and the other looks lean. Don't know why but plugs don't photogragh well sometimes.
I'll have to read all the comments first and try to help with any jetting changes. It does sound on the rich side, both main and jet needle position at least. I have to wonder why the mechanic decided to raise the needles two positions? Also, on a stock bike, ???, why the apparent jet kit? If stock, why a 122.5 main if 115 is really the stock size?
Salty, one necessary question, is the bike ready to be re-jetted? Other than jetting, is it tuned well? Valves, good blue spark, ignition timing, clean carbs, synched carbs, etc?

You went at a 1/4 throttle through stop lights and stop signs??? Youre hard core for these plug chops man!


Let's take a field trip to Keith's house \\/

[salty_monk]

Some plug reads of #1 & #4 after my 4 mile toodle home at around 1/4 throttle, through lights, stop signs etc

#4 with flash


#4 no flash


#1 no flash


#1 with flash