Can't get the idle low enough (GL1000)

[Sidecar Bob]

I have a GL1000 with a Dyna S and GL1500 coils in an '83 nearly everything else. I haven't had a tach for a couple of years but I do have one in the new Danmoto 180 I just installed. It is a digital meter with analogue style readout (blocks on the LCD go dark up to the indicated RPM). Its resolution isn't very fine (500 RPM per block) but I think it is reasonably accurate.

I did some work on the carbs last year and afterward thought it was idling high. "not a big deal" I thought "I'll adjust it after I install the Danmoto when I have a working tach".

The new tach said about 2000 so I unscrewed the idle screw as far out as it will go. The tach still indicates a steady 1500 RPM at idle. I know with that resolution it could actually be as low as 1250 but it should be 900 so it is still quite high and it feels high. I have verified that the idle screw is hitting the stop.

There is slack in both the throttle able and the choke cable. It starts easily & runs well (other than it uses more fuel than I would like).

Any ideas?

[Whiskerfish]

If the cables are not restricting it and you have a good snap when releasing the throttle then a significant air leak or carb imbalance are the most likely.

[Sidecar Bob]

I was thinking along those lines and if I can make myself go and work over a hot engine on a hot day I'll balance them.

But my past experience has been that those problems usually cause the RPM to be lower than it should, not higher...

[jdvorchak]

You might have set the bench sync too high. In other words the overall adj needed to be screwed in a turn or two more. Hook up the gauges and see if you can reduce the idle and keep them in balance.

[robin1731]

You might have set the bench sync too high. In other words the overall adj needed to be screwed in a turn or two more. Hook up the gauges and see if you can reduce the idle and keep them in balance.

I've never done that before.
Easier to do on inline carbs but possible on any of them.

.

[Sidecar Bob]

I just balanced them and the idle went up. So I twiddled with the air screws and discovered that they were all about 3 turns out and when I set them to the FSM recommended 1 3/8 turns the idle went up again. Now I have the air screws at about 3/4 turn and the balanced really close and the idle is back where I started but when I close the throttle the RPM drops slowly.

Robin I'm not sure what you mean. The book says to balance the right side (which basically adjusts where "1's throttle is relative to #3), then balance the left side (which adjusts #2 relative to #4) and then balance the sides to each other (which adjusts left relative to right). From what I can see that means that everything is adjusted relative to #3 and it doesn't have a separate adjustment.

At this point I'm going to put the pilot screws all back to 1 3/8 again and adjust them from there and see what happens but since the normal procedure is to tune for the highest RPM.....

[Old Fogey]

Bob, sounds to me like air leaks. Try tightening the manofold bands with the engine hot. It can make a surprising difference.
By the way the 'air screws' are not, they are fuel adjusting screws. Turning them out increases the fuel flow.

[robin1731]

[quote="Sidecar Bob"]snip.................
Robin I'm not sure what you mean. [quote]

Sorry, my comment had nothing to do with GL carbs. I meant inline 4 cylinder carbs. Like a CB750.

But Old Fogey is right. If it is slow to return to idle but does so it sounds like an air/vacuum leak.

.

[gltriker]

I just balanced them and the idle went up. So I twiddled with the air screws and discovered that they were all about 3 turns out and when I set them to the FSM recommended 1 3/8 turns the idle went up again. Now I have the air screws at about 3/4 turn and the balanced really close and the idle is back where I started but when I close the throttle the RPM drops slowly.

Robin I'm not sure what you mean. The book says to balance the right side (which basically adjusts where "1's throttle is relative to #3), then balance the left side (which adjusts #2 relative to #4) and then balance the sides to each other (which adjusts left relative to right). From what I can see that means that everything is adjusted relative to #3 and it doesn't have a separate adjustment.

At this point I'm going to put the pilot screws all back to 1 3/8 again and adjust them from there and see what happens but since the normal procedure is to tune for the highest RPM.....

Please note Old Fogey may have already presented my concern, too, while I was composing this reply. But, here it is anyway.

Respectfully, Are you getting confused with what the purpose of the adjustable pilot screw is?
That adjustment is metering the volume of air/fuel mixture discharged out of the brass tube just downstream from the throttle butterfly; not just air.

Synchronized Idle speeds, of all 4 carburetors collectively, is adjusted just as you've detailed in the text above.
But, 'The Idle Drop Procedure', individually utilizing their adjustable pilot fuel screw for each independent carburetor, performed after they are collectively synchronized, seems to be where you are struggling.
Revisit that Idle Drop Procedure again and I believe you will be successful.

I feel the FSM preliminary pilot screw setting is too lean for the amount of air/fuel mixture delivered into the pilot circuit, to have the engine idle fairly consistently at 900-1000 rpm, good off idle throttle response, and return to idle consistency.

Suggestion!
Set all 4 pilot fuel screws, with an additional 1 turn out from their seats, set the hot engine idle speed with the main adjuster screw and take a ride.

[Sidecar Bob]

Robin: Ah, OK.

Cliff: Turning the pilot (yes, not air) screws in leans the mixture and turning them out richens it, right? Maybe the oiled foam air filter and the 2x2 into 1 exhaust has something to do with it but mine seems fine with about 1 1/8 - 1 1/4 turns out (see below)

Well, I wouldn't have believed it. I set the pilot screws per FSM and then adjusted them all in a little bit, re-adjusted the left/right balance and as I turned the balance screw the RPM decreased. I think it might still be a little high because it is 2 blocks soild with the 3rd flicking in & out occasionally and it still takes a little longer than I think it should for the RPM to drop after I blip the throttle but it is a lot better than it was so I think I'm going to leave it like that for now.

John: I figured tightening the band clamps couldn't hurt but the most any of the screws moved was 1/4 turn and the only benefit I can see was that it gave me an opportunity to try one of my new Hozan JIS screwdrivers that came yesterday

[jdvorchak]

Just my opinion and not worth much, but I never really liked the procedure in the FSM about matching 1 to 3 and 2 to 4 them matching left to right. I suppose they had a good reason for explaining sync like that. I've synced more than a few 4 carb setups both inline and on GL's and I have come to the conclusion that I should treat them all the same. On the 1200 #4 had the overall idle speed adjustment where I understand it is on #3 on the 1000 and 1100? In any event I look at the sync gauges, disregarding idle speed for the moment if it is under about 1500 and take the highest reading and try to lower it. Then I'll fiddle with the other 3 carbs to get them to either raise up to it at least move in that direction. I've found that usually two or three iterations of lowering the reading on the high one and trying to raise the others up to that works. Only when I see them all about the same reading do I adjust the idle speed. Once I have the rpm close to 1000 I'll touch them all up to get them to match at the idle speed I want. That reading on my gauges is always between 7 and 9 inches on all 4 carbs. I also blip the throttle often and let it settle down. Another thing I do is to move slowly and pay attention to what I just did and how the gauges react. You have to make small adjustments on the screws then wait a second to see what happens. Often just putting the screwdriver on the screw will change the readings so take that into account.

[Sidecar Bob]

They tell you to balance one side, then the other and finally side to side because that's how the adjusters on the linkages are designed. I have been balancing the carbs on 'Wings for over 20 years and when I started I only had 2 adapters so I connected the gauges to the carbs on one side, then the other and finally one carb on each side and it worked nicely.

What is going on this time I have no idea. Maybe the rubber is separating from the manifold on one of them....

[Sidecar Bob]

I did eventually figure out what is going on. I think. After the last adjustment it was OK for a couple of days and then started to idle at 2000 or so. And then went back to a little over 1000 as before. It The idle RPM has gone up & down periodically since then.

One day when it was idling at about 2000 I looked down and decided to push down on the #4 adjuster screw. Oo & behold the idle went down to normal, or maybe even a little lower and stayed at a reasonable RPM over several more periods of idling. It was before yesterday (about 3 weeks ago IIRC) so I don't remember why I decided to push on the screw the first time but every time I do the idle goes way down. I think maybe something is binding in the throttle linkage. I have been too busy with other stuff to take the carbs off and look at it and now I'm tied up with the stuff that has to be done to the winter machine to make it driveable in time for the 'Wing to hibernate before it snows so I have put it on the list for spring.

[Old Fogey]

Bob, what year are the carbs? Early carbs dd not have the return spring on the #3 and #4 spindle that the later one were fitted with. These could be retro-fitted if you can pick up a set of dead late carbs; the springs were never available separately.
Also, check the synch adjusters between the #1 and 3 and the #2 and #4. If each carb spindle is free on it's own but the pair tightens up when you put the adjuster in place, it is sometimes necessary to due some judicious bending of the adjuster tabs.

[Sidecar Bob]

They are '79s and the linkages were OK until this year. I was thinking maybe I didn't put something back quite right when I had them apart last year but it seemed to work then, although as I mentioned I didn't have a working tach and I did feel it was idling too high (which was confirmed when I installed the Danmoto 180). It is also possible that something started to corrode when it sat outside at work for a month after I lost the end of my finger....