Please help with this mystery.

[hillsy]

How long was the bike sitting not running while you did your cafe conversion? Carb might be gummed up if it was sitting for a long(ish) time.

[Steve]

"Tickover" might have its problems, how about the rest of the rev range? Especially under load.

If, while on the road, it settles in and smoothes out, I would suspect the idle circuit in that one carb.

Just because it "was running fine and smooth, ..." before the conversion is no guarantee that it's still "fine".

It does not matter what part you might want to discuss, it WAS working just before it failed.

.

[mrbill5491]

Clean the spark plug threads in the head on that cylinder and around the plug hole. Could be as simple as the plug not grounding good. Had that happen on a car once. Dead cylinder everything was there for it to fire and it wouldn't. Cleaned the threads etc and went to working again. Just had a slight film of oil preventing the plug from grounding, that was the problem.

[Markyd]

Gutted, compression test all cylinders, 150 psi, 150 psi, 150 psi, 90 psi.

[hampshirehog]

How long has she been sitting?

[BigD_83]

Gutted, compression test all cylinders, 150 psi, 150 psi, 150 psi, 90 psi.

That's interesting...is the cylinder at 90 psi the one causing you some problems with not firing?

[Markyd]

It has not been sitting long, and yep that's the cylinder that's causing the trouble the low compression one. Exhaust valve being the issue, causing the cracking banging as fuel drips into the exhaust. Work under way.

[Anonymous]

I had the same problem with #3 on my 550. Re-shimmed now it idles great. Fingers crossed for ya mate! Did you do a wet test to confirm it's not the rings?

[chuck hahn]

Please expound on your findings leading you to that exhaust valve. Will be good info for the files.

[Anonymous]

It was the intake actually.
I was having trouble getting my non-runner to idle.
Compression test results were: Dry: 130, 130 ,90, 130. Wet: 160, 160, 120, 160
Turns out there was no clearance on my #3 intake valve, dropped in a shim two sizes smaller and the lash was spot on.
Now she idles great and all cylinders are firing nicely, compression 130 all round.
Fried my condensers in the process (forgot to ground my plugs the second time round). Whenever I rush things I always end up making more work for myself.
A lesson learned at a cost of £8, bargain!
My petcock just emptied a 1/4 tank into the sump overnight! While changing the oil I noticed the underside of my 4-1 was like swiss cheese (should have taken some pics, sorry).
Wrapped it today and the difference is unbelievable! Not only does it sound better but my throttle response is greatly improved (I had lag on the increase when I snapped it back before).
Only thing left to do now is shim up my needles. (this is what I had thought the cause of the lag was as it was only evident when I snaped to more than 1/4 throttle)
Any advise on how many mm I should raise it? I've paired k&n's and a 4:1 header. I've raised my pilots from 40 to 42.5 and mains from 97.5 to 105. I was going to start with 2mm up. (no clip positions, I have CV's, BS32's)

Sorry for the hijack Markyd!

[Markyd]

That's cool, I shall give an update hopefully over this weekend, the valve is guna be replaced, the plug was wet.

[Markyd]

Another update, bent crankshaft, more work, more money, more hassle..

[tom203]

That's unfortunate. You know about the welded vs. non-welded crank stuff, right?

[Markyd]

Please enlighten me tom, I won't be doing the repair.

[JTGS850GL]

How did you diagnose the bent crankshaft. Is it just a throw that rotated on it's pin? Cranks car be repaired and used cranks can be found all day long on ebay.

The cranks in our bikes are roller bearing cranks that are pieced together with pressed components. They can be thrown out of alignment and cause what you're seeing. Later years (1983+) the factory put welds on the higher HP larger displacement engines to keep this from happening. You never did say what year/model your bike is?