XJ700 Running on three... Advice needed

Hi all... I'm hoping you can help with a problem I'm having with my 1985 XJ700 based trike. The engine was running rough so I used some seafoam (possibly too much) and had a problem starting it... constant backfiring and wouldn't fire up.... I kept trying, assuming that there was still seafoam in the float bowls, and eventually, after taking out the plugs 3 or 4 times and drying them off, I got the engine running on choke and then settling into a rough idle. The problem is that number 3 cylinder seems to not be working... the exhaust is barely getting warm whereas the other three are too hot to touch. I pulled the plug and it was black and wet (petrol not oil) so i assume petrol's getting in ther... the plug lead is fine... good healthy spark with dynacoils, and swapping plugs still had number three not warming up. Could the mix be so rich that it won't run? What do I need to look at... I assume the jets can't be blocked if fuel is getting in there, so any suggestions welcome!

 

check you pilot mixture screws. Set them backed out from bottom 2 1/2 to 2 3/4 turns out. Then tune with colortune. Sounds like its way too rich. Also check you spark plug gap.

 

Spray something flammable in to the back of carb 3 and see if it burns & heats the pipe... If yes, then it's a carb issue... If no then it's electrical

 

Thanks for the initial advice... is it possible to get such a rich mix that one cylinder won't run? Or could an excess of seafoam still be causing an issue?

 

I would try a fresh set of spark plugs first......I have had plugs that would work outside of the head, but would not fire under compression.

Kenneth

 

I doubt Seafoam is causing your problem... But the Seafoam could have dislodged something in your carbs that is causing your problem

 

Hold on - - we really have to start at the beginning, which is, compression test, valve clearance test, Ohm - out the coils, and basic electrical tests, as well as the other good advise above.

 

And the prize goes to.... Kenneth (Mr Etobicoke)... when I swapped plugs from 3 to 4, No 4 cylinder stopped woking despite seeing a healthy spark at the plug! I bought another set... popped them in and she's running beautifully!

Incidentally... I bought the first set on Ebay... they've only covered around 500 miles... the new set were from a local, and well regarded parts supplier... they look very different... coppery looking washer at top below terminal, as opposed to silver on old ones, similar coppery colour on main body and threads as opp9osed to silver on old ones and completely different crush washer... now either NGK have updated their designs, or I got sold a set of fakes.... at £8.40 for four brand new plugs... why does anyone bother!