thermal efficency

[gsxrsam]

heres an interesting problem for you too mull over.. 

xj900s divvy,  starts, sounds  ok,  no 1,2,3 exhaust pipes get hot after 30 secs.

no 4 cold after 2 mins

pull plug lead off no 4, it coughs barks and stops...

put back on all good again but still cold 

carbs cleaned and rebuilt and new plugs etc...

interesting prob huh lol


will be fiddling with it today..

[ByzMax]

My first route would be to swap plugs with a good cylinder just in case you have a dud new un.

Then if you have a redundant spark system (two coils four cyclinders) then swap the plug leads for that  coil.

If the problem is still on the same cylinder then

check compression and then carb..

[trev]

you could try taking the plug  cap off the cold one with a pair of pliers while the engine is running and hold it close to the top of the plug and make it arc across for a few seconds and then put it back on,its worked for me a few times

[gsxrsam]

ok, just to mess with your head a bit,

pull off plug lead it stops engine so its firing..

comp test shows minimal difference between all 4 cyls..

swap leads 3/4 over still  runs but 4 still cold!!

carb now has new emulsion tube and main jet holder in but no difference.

fun huh 

[Manky Monkey]

Sure it's not something really basic, like a blocked fuel line? There's definitely a spark at the plug if you lay it on the cylinder head & spin the engine over? The spark's not getting diverted somewhere else once it's fitted -like a crack in the head?

[gsxrsam]

Sure it's not something really basic, like a blocked fuel line? There's definitely a spark at the plug if you lay it on the cylinder head & spin the engine over? The spark's not getting diverted somewhere else once it's fitted -like a crack in the head?

one fuel line, it is pump fed [cos im posh], it goes to centre of carbs and all float bowls are full..

if head was cracked i would expect comp tester to show up that, plus you really should be able to hear/see if it was arcing off somewere else 

[Manky Monkey]

Yeah, true. Certainly odd.

[Hillbilly Deluxe]

Have you ever had this bike running right ? if so what has been changed ?

[gsxrsam]

ok we have progress,

went up a staggering 44 sizes in main jets and is now on all 4 

still wont pull flat out so might need to go higher 

the joys of motoring huh..