No 1 cylinder not working VX 8 valve

[Johnh]

would be interested  if anybody has experienced this problem.

 The engine in my caterham is a 1.8 Vauxhall 8 valve 

 The number one cylinder is not working although the plugs are ok.. the leads check out and fuel is getting into the cylinder and the compression is up in line with the rest of the cylinders Also there is a good spark to the number one cylinder. 

Engine runs on 3 nothing from No1  completely dead doesn’t  fire at all 

[Wrightpayne]

How do you know the plug is OK?

[Johnh]

Changed plug with cylinder No 2 that was running but no change and the No 1 worked fine in No 2 cylinder so that  should eliminate the faulty plug test

[rj]

If compression is OK and spark plug is too I'd check the cable and the distributor cap.

 

[Wrightpayne]

John,

Thats exactly what I’d do - can you swap the leads over too to eliminate? Are you pulling the plug leads off to check for change in engine revs?

Ignition systems are fickle - like RJ says inspect the cap too. A faulty part can still produce a spark but not a good one!

Regards

Ian

 

[rj]

And just to add to it: You can have a crack in the cap that's almost invisible.

[Alan.gilford]

I had a similar problem on a crossflow where no 1 cylinder was not firing at idle, turned out to be a leaking needle valve on the 40's flooding it.

Not sure why it didn't seem to affect no 2 but changed and all fine.

Regards

Alan

[Alan.gilford]

Just remembered the only way i found it was to swap carb tops and fault moved to no 3 with no 1 ok :-) 

[Johnh]

Post 7/8 is interesting..just had a carb rebuild..the problem wasn’t there before 

 

[paul_w]

the other thing that can happen on webers is the jet holders (probably not the right term) underneath fall out if the locking tabs haven't been replaced or bent over enough - I've experienced the same symptoms you're describing as a result of this happening on a BDR after the carbs had been rebuilt. if you get a mirror or take pics with your phone look for a missing brass hex head on the underneath of the carb.

[Roger King]

Is this happening under all conditions, i.e. light throttle, full throttle, low revs, high revs?

If it is under all conditions, it is more likely to be an ignition fault and conversely, if it only occurs under some conditions a carb fault is more likely.

Assuming it is a carb problem, it seems unlikely that fuel is failing to get into the float chamber since number 2 is functioning.

Firstly, use a torch and a mirror to look down the ram pipes as you pump the throttle wide open (engine off at this point). You should see fuel squirting out from the pump jets onto the throttle butterflies. If number 2 does and number 1 doesn't, you probably have a blockage in the jet or the feed to it so check everything carefully. If neither barrel works, the mechanism may have stuck; this can usually be freed by removing the top of the carburettor and waggling the pump rod. It is also possible that someone has failed to reinstall something, causing it to stop it working.

If this is OK then it could be a jet blockage. Far and away the most likely is the idle jet which is tiny, so check it. I have rarely seen a main jet block because they're so  big, but check anyway.

I would also suggest taking all jets out and inspecting them to make sure that you have the same ones fitted to all barrels.

Next, have you set up the idle mixture screws? If not, it is possible that the one for number 1 is screwed fully home and won't let any fuel through. This will affect the engine at idle and at light throttle.

Paul W has suggested checking the lock screws underneath the carbs - good idea. These locate the choke and aux vents. If the aux vent one is missing (this is the one nearest to the ram pipe), the aux vent can rotate and block off the fuel supply from the main jet. If this has happened, the engine will probably run OK at idle and light throttle but misfire on large throttle openings.

Finally, was the compression test carried out with wide open throttle? If not, the results will be meaningless and the test should be done again (don't forget to disconnect the ignition first), ideally with a warm engine.

 

[paul_w]

thanks Roger, it was indeed the venturi lock screws I was (dimly) remembering :-D

[john g]

I love these webber/xflow posts