GS1000G - Carb Jetting

[KEITH KRAUSE]

It was only 3 of the 4 as I couldn't adjust number 2 however as all the plugs look the same I assume it's seized at 3 turns out.

Would adjusting only 3 of 4 cause the idle problems or is it definitely something in the idle circuit?

So I can do the 1/3rd throttle chop tests with the mixture screws in the current 3 out position?

I think getting another rack off Ebay might be my best option, at least I can then get those up to scratch & then swap them all over in one hit. Think I need a "reserve" bike

Dan

Hard to say where the stuck screw is set.
Just one carb having a pilot circuit problem can cause a rough idle or stall condition.
The mixture screw assists the pilot jet. It's the fine tuning for each cylinders exact needs. Turning it outward (richer) allows more mixture. Factory settings range from about 1/2 turn to maybe 1 1/2 turns out. If it only idles with the screws 3 turns out and the bike has a totally stock intake, then it obviously needs the fuel because it's not getting enough through closer to factory settings. That could mean the pilot circuit is partially blocked or the pilot jet is too small or the wrong length (wrong jet), or a poor carb synch, valve clearances are off, float levels set incorrectly...anything that could cause a lean condition/lack of correct mixture. The screws being so far out is to compensate for something else wrong.
The mixture screws are primarily for the pilot circuit. There can be some small overlap but if you test at a solid 1/3 throttle, then you're on the jet needle with little effect from the pilot circuit. However, it would be optimum to have the pilot circuit mixing correctly (as I planned in my earlier post) and get the most accurate reads you can by road/chop testing. This mixture screw issue creates two problems. One, getting the most accurate jet needle reads, is fairly easy to eliminate. Simply test with the throttle a bit more open to further minimize any pilot circuit overlap. No need to go beyond solid 1/2 throttle, just mark the throttle housing and grip (without allowing for any slack) and you can trust the reads are related to the jet needles. Just don't go beyond because you may start getting some small main jet effect, which you don't want.
The second problem with the mixture screws apparently can't be eliminated though. I previously saw no problem with getting the pilot circuit mixing correctly just by returning the screws to something very close to stock/factory settings. Now it appears one carb could be off and that can cause a poor idle and other performance problems at smaller throttle openings. Things like this can really make jetting difficult. Cleaning/adjusting may help 3 of the carbs, but there's that unknown. I can't say how it would perform overall at throttle openings up to 1/4. Obviously, you want all 4 carbs adjusted correctly, not just 3.
How does the stuck screw look? How does it compare to the other 3? If the head is in good condition, (not shaved off/damaged) does it appear to be recessed nearly the same as the others? The other 3 should appear close to each other.
A word of caution about buying used carbs. I'm sure you can imagine.
I've seen used carbs with different jets, mechanical damage, water corrosion, different floats and parts from other carbs. You really have to ask questions and hope to get straight answers. Even then, the present owner might not be aware of changes made. I used to rebuild/refurbish carbs for side money and you can get screwed even if you think you did your homework. If you get another set, I hope you get an unmolested set and don't open up a can of worms. If you really decide that's best, and there's no other reason you haven't told me, I'd at least try to free the stuck screw by various methods we've talked about at this site.
This is getting deep! We go from simply installing stock mains and returning the mixture screws to normal and tuning your adjustable jet needles, to swapping carbs and talk of pods and other scary stuff!
What did I get myself into?

[salty_monk]

Thanks Keith, well it's been this way for nearly a year (with me) & does not appear to be hurting anything except gas mileage (which isn't that bad), it also seems to run very well down here at sea level unless I open it right up (no roads for that near here!). Very strange.

I'll try to pick up a set of carbs off Ebay & make sure I ask plenty of questions first then fingers crossed & hope....

I have my eyes on another bike too which might make things easier, if that happens I'll take these off the bike & see what's going on before going the Ebay route as I'll have the time to play with it. I can't afford to have it not running for any length of time just yet.


Dan

[KEITH KRAUSE]

OK. Whenever you need help just ask.
By the way, a rich mixture as it appears you have, causes a lot of carbon build up on many parts and that causes problems too. It's not just poor gas mileage.

[J_C]

Be awfully careful if you try to get that screw out. I suggest not using an easy out unless you feel like trying to track down new carb bodies, as I had to. have you tried soaking it with some wd40 or liquid wrench etc?

[kent]

I have never tried this, but a buddy of mine that used to work in a bike shop says he would boil the carbs in water, the expansion rate is different between the different metals, and the heat would cause the aluminum to release the screws and jets. just a thought.

[salty_monk]

Just thought to mention that my carbs have no pipes on the vent T's. Just the vent T's pointing up. I take it this will not really have any large effect unless they are blocked?

Dan

[chef1366]

Someone put a jet kit in there.

[salty_monk]

?? Would they remove the pipes when doing that then?

Dan

[chef1366]

I know the answer but Keith does such a better job in explaining it.

[KEITH KRAUSE]

Just thought to mention that my carbs have no pipes on the vent T's. Just the vent T's pointing up. I take it this will not really have any large effect unless they are blocked?

Dan

Off to work so no time for explanations.
The rule is...if you run pods, or modify the air box with significantly large extra holes, remove the float bowl vent lines to avoid various degrees of fuel starvation (fuel starvation from inadequate venting varies a little from bike to bike apparently).
If you have a totally stock air box, leave the vent lines on. I really don't know if removing the lines on a bike with stock intake has any negative effects. If any doubt, get some lines (about 18") on there and route them under the seat as the factory does.
I don't see how no lines on a stock bike could have anything to do with your richness problem, if that's what you're thinking.

[salty_monk]

Ok, just a thought. Thanks!

Dan

[salty_monk]

Keith,

Here's an interesting one..... I got a K&N from a fellow GS'er today. I warmed up the bike, pulled the side cover & pulled out the old filter.

Started her up, fine. twist of the throttle - same as with the filter in (no load though...) twist further (on the needles now) it goes COMPLETELY flat, doesn't even want to run. Twist again to WOT it takes off like a rocket

Anyway, I stuck the K&N in & rode around the car park, seems fine. I'll get it on the road later today.

I guess though from this I can say:

1. The pilot circuit is rich (but it won't idle if I wind the screws in further than 3 out) so something must be wrong in that circuit somewhere. Any thoughts on the cause? Float levels? Someone messed with the air screws?

2. The needles are likely fine & if they've been adjusted then it's not by much.

3. The Main Jets are rich as we knew.

Anyway, just a little update. I'm working on a circuit bike or car so I can pull these carbs & open them up!!
Kent sent me a set of stock jets to play with too.

If I put a 4:1 on there & raise the needles up a bit more he & I would be on similar jetting (he has K&N in box & a 4:1 V&H) so that could be my next plan

Dan

[salty_monk]

Just a quick update, K&N seems to do as expected. Has lost the hint of bog at pull away & seems to run very strong through the needles. Still bogging down on WOT though.

I think I might run it for a week or two & see what happens, it seems to have found some more power. I think I might try doing the upside down bowl removal & fitting the 115's Kent gave me & see what happens.

Be interested in your thoughts on the pilot circuit.....

By the way, how do I check the float bowl levels?

Dan

[KEITH KRAUSE]

Been away on vacation. Any news?

[salty_monk]

No more news, running strong with the K&N, just ordered a new tool to make the upside down jet removal a bit easier & I'll give that a go asap, drop the 115's in.

Dan