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Discussion Starter #1
My 1989 GL1500 had the hesitation off idle issue. I pulled the carbs and installed the #60 slow jets. Hesitation off idle issue solved. However, now I have the idle surge issue???? Idle surges about 100-200 RPM +/-.
I have changed the slow jets (#60), spark plugs (stock NGK gapped at .035) synched the carbs and lubed the idle adjuster by the gas cap. Air filter is clean but it doesn't matter if the air cleaner is in or out, it still surges. I did adjust the pilot screw to 2 turns out rather than 1 1/2 turns per instructions by member agnogel (see attached image, he has been a huge help).
I did check vacuum lines and replaced a couple that were suspect. Maybe I missed one? The 2 under the carbs with the 90 degree bend I replaced just because they seem to give everyone problems.
I am leaning to the pilot screws but not sure where to start adjusting, in or out? Or maybe I need to look in another area? I am now in search mode for answers.
I also have read that the coolant sensor has been an issue for some that has fixed issues.
I just don't know why I didn't have a surge and now I do. Did the new jets cause this?
Any help/feedback is appreciated.
 

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The Rubber Isolators (between carbs and intake manifold) are a common source of air leaks, especially on a bike as old as yours. The leaks sometimes come and go depending, which causes erratic idle.

If you're not going to replace the Isolators, then try re-installing them with a light coat of grease (ex: K&N Air Filter Grease) on the mating surfaces, to seal.
 

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Discussion Starter #3
I will give that a shot. I was careful to make sure those were very tight but I didn't put anything on them.
 

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I will give that a shot. I was careful to make sure those were very tight but I didn't put anything on them.

You can make them as tight as you want, but unless you remove, replace with smaller ones, or make the spacers in them smaller, you will not get them to clamp any harder. I normally either replace the spacers with nuts or grind down the spacers, but only a small amount. IF they need more I just replace the isolators.

If you can still move the clamps around when they are 'tight', you need to do the above.


Bill
 

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Whatever else you do, if you're going to be in there that deep please replace the rubber insulators and all 4 vacuum hoses coming off the carbs! And, remove what you can of that idiotic thin rubber mat that traps the heat that cooks all of them. That mat in the single stupidest thing I've ever seen on a motorcycle!
 

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What is the purpose of that rubber mat? I could never figure it out.
My thoughts for the rubber mat usage are echoed the same to keep heat from rising. As we know the cooling system is borderline when challenged on hot days, any interference between radiator and fan operation above engine for removal of heat however small would compound the problem. The less the fans run the better everything is battery included with OEM alternator.

Second item would be for fuel line vapor lock which is a real problem of carb equipped engines, the low 2 psi pump of the 15 more so. This can be evidenced with fuel line choice, thin walled from pump to filter then it goes to a very thick walled hose after filter the rest of the way to the carbs. This area happens to be right over the mat. Further evidence is that the carb heated coolant riser is thermostatically controlled shutting off carb spacer heat before engine reaches operating temperature. The engineers here are clearly heading off a vapor lock scenario. With the enclosed design there is zero natural air movement under the shelter when standing still which can be correlated to underhood temps of automobiles.

Keeping heat in close would also aid in quickening engine warm up times equaling better MPG, lower emissions and better cold driveability as a side note.
 

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I am leaning to the pilot screws but not sure where to start adjusting, in or out? Or maybe I need to look in another area? I am now in search mode for answers. I just don't know why I didn't have a surge and now I do. Did the new jets cause this?
Any help/feedback is appreciated.
What RPM is the engine currently idling at?

Assuming everything was done correctly one thing that I am sure of would be the engine is now running super rich. Close the mixture screws down to 1 turn open, if surging gets worse then it has other issues.
 

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I have worked with the Japanese for many years in agribusiness. Love the Japanese people and respect their culture. But, they have a tendency to over-manage minutia and over-engineer things. In my humble opinion, that mat is a perfect example of over-engineering. Preventing vapor lock by cooking critical vacuum components? Sorry, it's simply stupid. There IS air movement through the enclosure. It is far from air tight.
 

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In regards to adjusting the pilot screws. Let it warm up. Then turn IN the screws until the engine starts to die down/skip/run rough(which ever you want to call it).
THEN back them out until the engine runs the smoothest. EVERY ENGINE IS DIFFERENT ON PILOT SCREW SETTINGS.
 

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Discussion Starter #14
Idle is around 800-900 RPM's. I still have the rubber mat in since I am not an engineer and figured out had some sort of purpose.
 

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Way out of sync carbs could also compound problems and would need a gauge check.
 

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Discussion Starter #17
Update.....
I adjusted the pilot screws to 1 turn out and re-synched the carbs. This pretty much took out the surge at idle issue. However, it does surge ever so slightly every once in awhile but only like 100 RPM. Not sure why but I can almost live with it... once in awhile.
I do like things to be 100% correct but man was that a pita.
Thanks DriverRider and bones200 for the Pilot screw suggestion. I also, want to thank everyone who replied.
 
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