I've just had a nice track day at Silverstone. The engine behaved beautifully throughout. It was driven hard but with some sympathy and gave no
hint of any problem.
Then I packed up to go home. The engine worked smoothly and sweetly as usual when idling, when cruising at a steady speed and when accelerating very
gently. With any increase in throttle the engine was rough and whilst it would rev, I took it very gently home.
At home I looked at the spark plugs. No 1 and No 2 were a little black and crusty but dry. A bit rich perhaps. No 3 was good. No 4 was a bit oily.
Fresh oil, not the black sticky mess in the Haynes manual. It looked OK but my fingers were oily afterwards.
Next I did a compression test. 120 PSI in all cylinders +/- 5 PSI. Nice and even but very low.
The big ends went 18 months ago and I replaced them all. It sounded bad at idle and worse with any revs. This sounds very sweet at tickover, fast
idle and at a 30 MPH cruise. It sounded fine high higher steady speeds through my crash helmet too.
What can the matter be?
[Edited on 26-9-2008 by smart51]
Does it misfire atall? what made you think it was plugs?
Its obviously hard to tell from a description but it really could be anything from fuel starvation to a loose manifold...
Did you have the throttle open when doing the compression test?
That gives consistantly low readings over all cylinders.
quote:
Originally posted by MkIndy7
Did you have the throttle open when doing the compression test?
That gives consistantly low readings over all cylinders.
Has the noise changed? I had something like this and it turned out to be a leaking exhaust gasket......
quote:
Originally posted by BenB
Has the noise changed? I had something like this and it turned out to be a leaking exhaust gasket......
not something simple like a couple off loosw main jets
tony
Change the spark plugs first sounds like you may have a mis fire.
Change the oily spark plug this is a good indication that that is the one not working
Well I was thinking about this today. It ran beautifully at small throttle openings but badly from 1/4 throttle up so perhaps its fuelling, since the
idle circuit feeds low throttle and the main / needle the rest.
The main jets are all OK but I noticed one of the air jets that was blocked up now isn't. I also did a compression test with wide open throttle
but with a cold engine. 175 PSI in 2 cylinders, 170 in no 3 and 160 in no 4. More or less OK.
Baby duties called after that but tomorrow I'll do a test drive. HOPEFULLY, that will be it but I think that the engine symptoms were much worse
than an unblocked air jet on 1 cylinder could make.
Well that seems to have fixed it. It was the blob of silicone blocking up the air jet falling off that was the cause. I have to say, it was terrible. A nice easy fix too.
can you not solder/silver solder up the hole in the jet to cure it once and for all
Tony
quote:
Originally posted by mad-butcher
can you not solder/silver solder up the hole in the jet to cure it once and for all
Tony
