MIssing Cylinder

[Captain Spoons]

Have a 1700 XFlow Supersprint with a mysterious problem!!
Missing on Cylinder 3- but getting good spark from NEW plug, much head scratching going on!!!, any ideas in a "idiots guide" sense, gratefully recieved.
Cheers!!

[The Wookie]

You should be able to find it between Cylinders 2 and 4.

HTH

[fergus]

Is it actually missing, or have you got an air leak on the induction side on #3? Does the plug tip look pale or very sooty? The plug tip colour would be my first point of call. Is it missing under idle or only under load?

[Captain Spoons]

Its missing from start up, plugs look ok to be honest

[fergus]

Captain Spoons said:

Its missing from start up, plugs look ok to be honest

Have you tried swapping the plg leads between cylinders to eliminate the basics, such as a duff lead. Are all the plugs the same heat range, with the same gap on them?

[Captain Spoons]

Fraid so, 4 new spark plugs from caterham and leads all ok- have been swapping between them all weekend- always #3 that is the problem.

[davidball]

Have you done a compression test on the cylinders?
What carbs do you have?
I had a similar problem a few months back on #2 cylinder. Turned out to be low compression due to a worn head gasket and badly seating valves.

Edited by davidball on Monday 14th December 13:10

[sam919]

Has it a single coil, or a pack like the Rover k.

[Captain Spoons]

car is on twin 40 DCOE webers, regarding peassure test- my tiny mechanical brain is working against me on this- how do i do that?
the coil is a single one- standard classic SE car with supersprint engine

[Captain Spoons]

car had new head gasket about 500 miles ago and had carbs balanced 50 miles ago approx- if that rules anything out?

[bikemonster]

Captain Spoons said:

car is on twin 40 DCOE webers, regarding peassure test- my tiny mechanical brain is working against me on this- how do i do that?
the coil is a single one- standard classic SE car with supersprint engine

Hook up a compression gauge on each cylinder in turn and spin the motor.

I wouldn't be too worried about the size of the numbers, but ideally all cylinders should produce a similar number.

If one cylinder is markedly down on the other three, you can do a "wet" test by adding some oil to the errant cylinder and re-testing. If the number improves, then the problem is rings/bore. If it doesn't improve then the problem is likely to be valve-related or head gasket related.

James

[StEVEN7]

Does sound like a compression issue, it also maybe worth doing a head gasket test to see if it was done properly...annoying isn't it!!

[mickrick]

Sounds like a valve sticking to me. As has already been said, do a compression check.

[Captain Spoons]

thanks for the wise words, will limp to a garage as dont have a compression test thingy!!