mick10
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| posted on 16/6/11 at 04:58 PM |
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Running but very rough
Finally got my crossflow up and running on CBR 1000 bike carbs but it is very lumpy on tick over to the point of misfiring and i quite often get a
backfire through the exhaust although not a very loud one. I have checked for air leaks with acetylene torch and it makes no difference at all so
assume its ok on that side.
The engine is a 1700 x flow with a bcf3 kent cam if i remember rightly, it has powermax flat top lotus pistons and a chambered head with huge valves.
Its probably not done a half a mile since i built it.
The carbs have been completely stripped and cleaned and all the pistons rise together evenly. I have drilled out the main jets to 1.6 mm ( this could
be wrong i know but it improved dramatically after doing this.
The timing is a bit advanced at the moment as i cant remember the setting it should be at but it dosent really improve if retarded or advanced.
I'm running a fiesta electronic dizzy with the vacum disconnected.
The spark plugs are NGKs and are a few years old but have seen no use really but when removed are always very black which points to a overly rich
mixture but dont no why it hasnt been gas tested yet which could shed some light on it. Plug leads are relatively new as well
The valve timing is correct and it has good compression readings of approx 150 psi on each cylinder and pulls away very sharply and accelerates hard
but just want to get to the bottom of this if poss.
Any info and help greatly appreciated, thanks.
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steve m
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| posted on 16/6/11 at 05:13 PM |
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After tickover does it run smoothly ? or its it rough all the way up the revs ?
steve, (also running a xflow)
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David Jenkins
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| posted on 16/6/11 at 05:52 PM |
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My xflow idled horribly until I balanced the carbs - first with a bit of hose, one end in the carb mouth and the other in my ear, then later with a
proper balancer.
It makes a huge difference, as even a slight imbalance will mess up the idle.
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mick10
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| posted on 16/6/11 at 06:24 PM |
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It runs smoothly when accelerating just dodgy on tickover, i have balanced them i think at the rebuild stage but am a bit unsure now i have balance
carbs before using a pipe- when i put a pipe to the carbs nowi just get a kind of noise i would associate with the valves opening and closing it
dosent seem to have the hissing sucking noise it should have I have preliminary set the mixture screws to one turn out at the moment as well
[Edited on 16/6/11 by mick10]
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steve m
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| posted on 16/6/11 at 07:29 PM |
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At about 1500 rpm the "noise" thru the pipe should be exactley the same with all four carbs
if one is quiter that needs opening up
if one is much louder then that need closing
its very easy, but then when you adjust the timing it all goes to pot, and start again(dont know why but my 1700 with twin 40's did!)
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ianclark1275
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| posted on 16/6/11 at 10:15 PM |
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sounds like too rich at idle.
when plugs foul, they tend to go off one cylinder at a time until you change them all.
you need a CO meter at a garage to tell for sure.
IC
measure twice, cut once, scrap it, start again.
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