Well I think it's carb/fuel/exhaust related...

[JimmyR]

I know you fellas like to know what you are dealing with but I'm lost on this one. As you may know, I have rebuilt an '82 GS1100G and have used new pipes (fairly stock style) RS36 carbs and K+N pods. I had a bit of an issue with running rich and I think that was because of an exhaust leak at the headers.

So now I think I have finally fixed the exhaust leaks. It's complicated because the pipes had different flanges from the stock ones, but anyway that is sorted, I hope. So I have been able to reduce the size of the pilot jets now to lean it out a little at idle. I tested today - now the leaks have gone it was indeed running a bit rich - hesitated/bogged under acceleration. So I went down a size, had a ride and it ran beautifully. I think that's got it!

But just when I was celebrating something else raised its head. All of a sudden the engine started vibrating strangely. It still runs, and idle is ok, but under any sort of acceleration it sounds and feels weird. REALLY hard to explain. It feels like I'm riding over very close corrugations in the road - that sort thrumming vibration. What could that be??

I have one suspicion - could it be that a gap in the pipes where they join just before the mufflers (under the bike) would have that effect? I'm not sure that there IS a gap there but there used to be. But then why would it be running perfectly one minute and then not the next?

[hjfisk]

Exhaust isn't going to make it vibrate. Is it a vibration or a rattle ? Is it dropping a cylinder and skipping under acceleration? Is it vibrating all the time or only when in motion? We need a few more details .

[JimmyR]

It's vibrating a little at idle - but it's most noticeable under acceleration. It's not so much a rattle. I also suspected it was not firing on a cylinder. When I checked the spark plug leads cylinder 3's plug connector felt a bit loose, and it was difficult to press it down any harder without burning my fingers! Once I got home and the engine had cooled a bit I could press it down firmly but the engine is still vibrating.

It's really difficult to put in words what it is like. If it's not raining tomorrow I may ride it to my trusted Suzuki place.

[Badooka]

Carb Synch way outta whack? Did you do one after all the changes????

[JimmyR]

No not yet. Actually I've been meaning to but the bike has been running so well I have been doing other things. But why would that make it go weird all of a sudden? The first half of my last test ride was perfect - I mean absolutely wonderful - and then all of a sudden this vibration started and hasn't gone away.

Man this is annoying! I was really enjoying it being perfect.

[MisterCinders]

Carb Synch way outta whack? Did you do one after all the changes????

This could be it. If you synched it before fixing the exhaust leaks, perhaps the restored back pressure has affected the vacuum such that you are now out of synch.

[JimmyR]

Ok I'll check the synch tomorrow. Thanks guys!

[FiftyGS1100G]

It's mystical

Hold on I think your Suzuki may be channelling the Fatboy!

[hjfisk]

Hold on I think your Suzuki may be channelling the Fatboy!

Now that there's funny

[JimmyR]

Dammit I knew I shouldn't park them so close together. It's a contagion, isn't it? I should have seen the signs.

[Steve]

Did the Fatboy all of a sudden get smoooother?

.

[JimmyR]

I don't know - I haven't ridden it for a while! It does amaze me how smooth the Suzuki is. I can be riding at over 100kph on the freeway and the mirrors are perfectly clear. Um, it's not like that on the Harley...

Anyway I think I worked out the vibration issue - other than the Harley factor obviously - (1) I have separated them in the garage, and (2) I found a loose pilot jet in #1 carb on the Suzuki. So the vibration has gone.

The best thing is that it proves that I posted this question in the right forum subcategory. Phew! :-)

Oh, and I did resynch the carbs. It wasn't to bad but now they are spot on. I have worked out the technique of synching flat slide carbs I think.