Engine Troubles

[Oh.go.on.then]

Morning all

Just returned from a 500 mile trip to Cornwall and the engine is lumpy just of idle, hesitates and generally doesn't feel right. It cruised lovely at 55mph and had plenty of power but could still feel it wasn't quite right.. Before I went the engine was driving me round the bend as it wasn't running 100% but I couldn't work out why.

This is the story, rebuilt engine 1500 miles ago, seemed a little lumpy so changed plugs, leads, cap, rotor, changed to accuspark from points.

Has 009 dizzy, twin weber 34 ict and c25 cam.

Timing was running too far advanced so I reset it although it does run better with a bit more advance. About 10deg at idle. Checked TDC on the crank pully and it is correct.

I've had a check this morning and three plugs look like the one below (a little lean maybe) and number four sooty (I did wipe some off with my finger, it was sootier).

Why would I have one black plug?

I've checked the resistance of the leads and they are similar 500ohms, coils fine, valve gap checked and fine, cards reasonably balanced.

The other problem I had when away was a slipping clutch so the engine has to come out to investigate (god knows what that is). I'm contemplating taking the heads off while the engine is out to have a look but would prefer not to if I can help it.

Have I missed anything? I will need to get it set up on a rolling road but need to make sure all is well first.

Three plugs like this:



Number four cylinder like this:

 

[dazza1975]

No wonder if you plugs look like a camper!! :lol: :lol:

 

[Oh.go.on.then]

Blimey, you read that quick, it must have only taken me 30 seconds to change the picture.

Good job it was just a picture of the camper that ended up there.....who knows what else may have found its way on the post!

 

[K@rlos]

You want the carbs spot on rather than reasonable tbh mate. Is it jetted right? Might have an air leak too.

 

[Trikky2]

Also worth checking the carbs are not being over fuelled. Some of the webers can be a bit fussy about pump pressure, particularly if the needle valves are a bit tired. This could also lead to one black plug since the excess fuel could tend to run down to one cylinder rather than both.

 

[Oh.go.on.then]

Cheers for the replies. The carbs were new with the engine and have a pressure regulator set at 2psi. 55 idles 140 mains on a 1776cc

The manifolds don't have a balance tube so I'm going to fit one when I do the clutch.

They seem pretty well balanced but my Gunson carb balancer isn't the best.

I've just checked the compression on cylinder 4 and its 130psi so no issue there.

I think I'm going to try a different plug and maybe even the points back in just to check.

Failing that I can't think of anything else to try so may just have to get it rolling roasted (love the iphone spelling changer) when I've done the clutch.