My engine is acting up- why?!

[Wes51st]

I'm having real problems with my bike, can any one please help?

It's a GS550e 1979, was working pretty roughly yesterday and bogged out when stuck in traffic for a while. But today its worse and....

I could get it running with the choke on full and in prime on the petcock. But there seemed to be a high pitched piston whoosh sound every 5 seconds. I tried running with the fuel cap on, then cap off. Nothing changed.

At the end of hours adjusting the idle and doing all the fault checking I can with spark plugs etc, the whoosh sound had gone and I was left with the bike being able to idle with the choke fully on. However when I slide the choke gradually down to off the engine would rise to 4-5k revs, before coming to a slow then spluttering stop as I closed the choke.

Please any advice is welcome, I'm can't spend anymore time in the cold!

Extra info on the carbs: recently cleaned. I've set the fuel screw to 3/4 turns out and air screw 2 turns out.

[chuck hahn]

Swooshing sounds are either air being sucked in or pushed out rather quickly. I would check the plugs are tight and start the bike and give each in take manifold a shot of ether right where the carbs and rubber met up. If the RPMS go up or it instantly dies with the ether youve found the air leak.

Broken clamps, stretched clamps, cracked intake rubber or delaminating rubber from the flanges. or the intake manifold orings are all suspects that will cause vac leaks at the manifolds.

When were the valves adjusted???

[chuck hahn]

Have you checked the oil level to see that the petcock didnt seep some fuel into the crankcase?? take off the filler cap and take a ood sniff to see if it even remotely smells gassy. If in doubt drain it and err to the side of caution.

[Big T]

Are all 4 cylinders running?
Do you still have points?
Is your vacuum line to the fuel tap leaking?

[dem3500]

it sounds like its running lean to me. its probably an air leak

[RICHIE]

To me from what you are describing is plugged up pilot jets, which you are by passing by using the choke circuits. When you bring the choke back to normal closed the mixture is leaning out and rev's start going up. If it was an air leak ,it would be there all the time, usually do not come and go. Most likely dirt or rust broke lose from some where in the fuel system to clog some of the jets. It takes 3 things to run a motor, spark, fuel, compression, you just need to make sure its all there at the right time.

[Wes51st]

Are all 4 cylinders running?
Do you still have points?
Is your vacuum line to the fuel tap leaking?

Yes all 4 are running.
I have an electric system on this bike.
Lastly, no there doesn't seem to be a leak in the vacuum line to the fuel tap.

Does that narrow anything down?

[Wes51st]

To me from what you are describing is plugged up pilot jets, which you are by passing by using the choke circuits. When you bring the choke back to normal closed the mixture is leaning out and rev's start going up. If it was an air leak ,it would be there all the time, usually do not come and go. Most likely dirt or rust broke lose from some where in the fuel system to clog some of the jets. It takes 3 things to run a motor, spark, fuel, compression, you just need to make sure its all there at the right time.

I do think it's running lean, but also wonder about plugged pilot jets. I have really carefully cleaned each one and look at every hole to be sure. But it does run better on the coke system.

Also I experience back firing sometimes when trying to start it.

[dem3500]

Back firing sounds like timing. Check the timing

[Big T]

Yes all 4 are running.
I have an electric system on this bike.
Lastly, no there doesn't seem to be a leak in the vacuum line to the fuel tap.
Does that narrow anything down?

Wes, not so much. It just eliminates those items. There's so much to eliminate on a 39 year old bike

[Wes51st]

Sadly you're right, there are so many things it could be. I've really been diligent and worked my way carefully through each step of the process, but something isn't right. I think it might be time I took it to a garage and bow down to their experience.

But before I do, I'm going to look at the timing, I've not adjusted that yet, but will work out how.

Thanks

[850 Combat]

There is more to having clean pilot circuits than having clean jets. There are a number of tiny passages in the carburetor that must be clean. You can't see through any of them. There are also emulsion tubes. Also, if it was running fine and then changed, I would check the petcock and carburetors for foreign material such as rust or dirt from the tank.

[DumbGenius49]

How would you clean those small passages?

[cowboyup3371]

How would you clean those small passages?

You have to dip the carbs for at least 8 hours but up to 24. Follow the procedures here - http://zeus.mtsac.edu/~cliff/storage...d_Tutorial.pdf