Bad Running XBR500

[guest1650]

Dear Thumpers,

I have a little problem with my XBR500.

• Ehen it didn't run for a day it is difficult to start, 20 seconds on the electric strart is not uncommon.
• It also lacks power when accelerating
• When the machine is warm and you stop at a traffic light the revs go back to 1200 and then slowly starts climbing to 2500-3000 revs/min
• When i drive with the throttle halfway open (so i'm at constant spreed or deaccelerationg slightly) is runs very bad and misses some strokes
• The bougie is white collored

The things I have already tried:

• Sealing up the exhaust, I suspect it still leaks a bit
• Adjusting the valves, i found this a difficult process so i could have done this wrong
• Adjust the spark gap from 0.7mm to the recommended 0.85mm
• Replaced oil filter

Things i have still to do:

• Check for false air being sucked in
• seal up the exhaust a bit better
• try to locate and inspect a second smaller oil filter someone told me about
• inspect air filter
• remove the cilinder head to check for the famous XBR crack from the spark hole to the exhaust valve

Does anybody have any tip or good ideas for me on what the problem can be?
Input is greatly appreciated! Thanks in advance,
Tjeerd

[Steve H]

If it wasn't for the 'white bougie' I would have said you have a leak in the inlet manifold. A stuck choke is another option but doesn't explain the poor starting.

[SteveC#222]

Blocked air filter? Crap in one or more of the carb jets or airways?

Are the exhaust/ airfilter standard? if not it may need bigger jets.

Don't remove the head to check the crack unless you re absolutely sure there is a problem! Most XBR's have the crack and 99.9% of the time it causes no problems - some folks have enthusiastically repair the crack and caused more problems.

[JOOLZ]

Check the carb diaphragm make sure there are no splits in it, check the carb rubber mounting for splits. Sounds like the engine is leaning out.

[johnr]

has it been left standing for any period of time at all? have you considered stripping and ultra-sonic cleaning the carb?

[guest1650]

Thanks for all reactions and input, when I took off the carb I found out that two seal rings were damaged, this could explain my problems.
http://i.imgur.com/bFKNURb.jpg

I got a new pair of seal rings and replaced the two. On the test run it seemed to run fine at first, then I heard a big poof and the problems were back. Upon inspection I found that i had blown my carb insulator to pieces.
http://i.imgur.com/yjYRQnX.jpg
http://i.imgur.com/jqClhJb.jpg

I replaced the seal rings with slightly thicker rings, original rings were 2.5mm and the replacement are 3mm in diameter.

I could just go and replace the insulator and rings but the pressure to wreck the insulator must come from somewhere, could the thicker rings have caused this, or is there some other problem i missed.

[beeman]

Can't see where pressure would come from to blow out unless cracked already. Your symptons sounded like intermittent air leaking into inlet, usually revs rising and falling so O ring may well be the culprit. I would replace insulator and see how it went. After all before the insulator burst you said it ran ok again. When things go wrong or right what did you do, as in my case, my incompetence is the usual cause of many problems.

good luck