Cylinder 1 is cold. intake air leak is suspected - need advice

[Guest]

I am new to this forum. Have a 1980 GS1000G. Noticed that my #1 & sometimes #2 was running cold, bike lacked power etc. I checked the coils, plugs etc. no problems there. I pulled the carbs, cleaned them out, seem to be fine. Finally, I tried restricting the intake of the #1 carb with my palm and the cylinder began firing so I am assuming that I have an intake air leak but not sure where that could be.

I know there is an o-ring in the receiving boot on the engine side, but I have not pulled the boots off to check them (afraid I may bugger the screws and have to replace all the boots - will do it if I have to but not keen on just trying to get them off). Could a break in the o-ring make that much of a difference between a cold and firing cylinder? Or is it a carb air adjustment issue?

I looked at the throttle plate in the carbs and there is a difference in the opening sequence when the throttle is pulled by a small there is some lag in the 3 and 4 carbs. I am not sure if this is suppose to be this way. At idle (throttle off) they all seem to be open the same amount but was thinking I may have to restrict 1 & 2 a little more. Unfortunately I do not have a mamometer and was hoping not to have to buy one if I can do this without.

I am a complete novice at motorcycle maintenance so any advice would be appreciated.
Thanks,
Steve

[tkent02]

Carbs are easy to remove on a 1000G. Five minutes. Do it right.

[stephenknoble]

Sorry, you misunderstood. I have removed the carbs and took them all apart and cleaned them. The part I am referring to is the metal/rubber boot that is attached to the engine intake that the output of the carb fits into. These have an o-ring between the metal flange and the engine body that I don't believe could result in such an airleak that the cylinder would not even fire.

[tkent02]

Can't say for sure if it is or if it isn't the problem. You may have other things messed up inside. The only way to make sure is replace the orings and you'll know it isn't. They are so easy to replace it's a no brainer, especially when virtually ALL of them are flat, hard, and cracked by now... unless they've been replaced which you can tell by looking at the screws.

[Nessism]

Your carbs need to be vacuum synced AND you need to pull the intake boots and replace the O-rings.

You also need to read the newbie mistakes thread linked in my signature before you make any more.

Take note of the valve adjustment entry on the newbie mistakes thread and how you can not diaganose running problems on a bike until you do all the routine maintenance.

Good luck. Rome wasn't built in a day...

[tom203]

", I tried restricting the intake of the #1 carb with my palm and the cylinder began firing so I am assuming that I have an intake air leak"

More likely by covering the carb's intake , you created more vacuum on that carb's idle passage, sucking up enough fuel to get the cylinder to fire. The passages in these carbs are tiny, easy to plug up- you would not see this - rest of carb might look pristine! Do all the maintenance, including cleaning the carbs properly- otherwise you will have low and midrange problems that will lead to frustration.

[stephenknoble]

That's a good point. I did totally pull the carbs, took out and cleaned all the jets etc. But will do it again in case I missed something. Will replace the o-rings and after doing some more research, I think my butterfly valves are not all synced so will do that and will see what happens. Thanks for all the advice.

Steve

", I tried restricting the intake of the #1 carb with my palm and the cylinder began firing so I am assuming that I have an intake air leak"

More likely by covering the carb's intake , you created more vacuum on that carb's idle passage, sucking up enough fuel to get the cylinder to fire. The passages in these carbs are tiny, easy to plug up- you would not see this - rest of carb might look pristine! Do all the maintenance, including cleaning the carbs properly- otherwise you will have low and midrange problems that will lead to frustration.

[tkent02]

It's not the jets that need cleaning.

[hannibal]

I'll add that I struggled with 2 dead cylinders for months. Finally decided to reclean the carbs by dipping, spraying carb cleaner, and blowing out with air. Problem solved. I just wish I had tried recleaning them months before.

[bobgroger]

Most likely the pilot jet, the one under the rubber plug. In the end there is a VERY small hole that gets plugged up at the slightest whiff of Ethanol and moisture. Find the carb rebuild tutorial and do everything. Then find the 10 Newbie mistakes and do everything. When you are done, the bike will run well and be safe. Don't skip a step. We all came here looking for a quick fix so we can ride. THere isn't one. Follow the steps for success.

[bobgroger]

Oh, and replace the boots. They are 35 years old FFS.