1981 XJ 650 unable to set idle

Hi Guys, I have had the above bike for about five years, but have never been able to get it to idle smoothly. I have had the carbs ultrasonically cleaned and have fitted new parts, including new throttle shaft seals, diaphragms and gaskets. I have also set the float levels and have fitted new rubber intake manifolds, new coils and HT leads and plugs.

The engine starts easily hot or cold, but will not idle smoothly which makes the engine noisy and hard to ride. I can get the vacuum setting on all the cylinders almost right, but when the engine is revved up it goes all over the place and does not go back to the same vacuum readings.

Recently another problem has developed with number two cylinder not running at all, the exhaust pipe is cold and number four plug is black and sooty. I have checked that I have a spark on both cylinders and that was ok, and have done a compression test on all cylinders. The pressure were 155 psi on all cylinders, which apparently is good, So what the hell is going on, I have nearly pulled all my hair out, so your help would be most appreciated. Yours hopefully Mal.

 

No pin holes in the diaphragms ? have you fitted new caps to the vac' spigots ?

 

Have you color tuned your mixture settings?

 

Mal,
Welcome, your issues should get sorted out here in no time.

The things mentioned in your first paragraph; were they all done at once?

Was there something wrong with the old coils, leads and plugs?

 

did you try replacing the spark plug just because it fires outside the cylinder does not mean it is firing under compression.
How "new" are the coil packs and carb cleaning ?
are you running pods or stock airbox and filter

what does the #2 plug look like?

you say set the float levels do you mean you wet set fuel level or dry set float height?

 

Are the valves in spec?

Gary H.

 

I'd put a new plug in ......

 

Thanks for your reply, even with the vacuum gauge pipes on it is the same and the diaphragms are new. Or should I check them even they are new.

 

No I haven't, but I have set the mixture screws all the same at two and half turns out. Is the color tune good?

 

Thanks for trying to help, no I haven't fitted a new plug, but a spark tester showed this HT lead to be firing.

 

Thanks for helping Gary, I have checked the valve clearances are they are ok. But can you explain why this would matter, is it only a tight valve that would cause a problem?

 

Hi. yes the new parts were fitted all at the same time in an attempt to fix the problem. Don't know if the old coils and leads were faulty, just changed them to be sure.

 

Thanks for trying to help. I tested the plug by using a spark tester, which I think tests the plug and current to the plug. The Dynatek coils are new new, and I have cleaned the carbs many times, the last being this week.
I am running K&N pods. Number 2 plug looks slightly wet and black, but no soot.

 

This is a HUGE detail that you left out earlier.
Are you still running the stock jets?

 

Yes the jets are still stock, don't know where to get any others as this bike is quite rare and unloved in Western Australia. The dealers are only interested in the new stuff. As I said earlier I have K&N pods on the intake and a four in one exhaust with a 2006 R6 muffler. Any idea what size jets I need or can they be drilled out? Or will adjusting the mixture screws help. Thanks heaps Mal.

 

Do you have any of the original parts (airbox, muffler/ exhaust, coils, etc.)?

These bikes are a well thought out balanced system that is pert near perfection in a stock condition.
Doesn't mean that mods won't work but it does mean that we (the XJ community) can't tell you an exact jet size to use to fine tune your pod/ exhaust combination.

You may have a lot of experimentation ahead of you.

 

I am running K&N pods.

+1. This is a issue even with the valves in spec.

Gary H.

 

So what...... Is may SAY its firing, but if you have a cold pipe, it's either NOT FIRING, or you're not getting fuel..... Or both-----
Putting in a NEW plug helps narrow it down. Happen to notice if the plug is wet vs. dry? That's an indicator either way, too.

If you haven't:
-adjusted the valves
-thoroughly, totally cleaned carbs
-wet-set
-bench-synced
-new plugs
-correct jets
-correct airbox/clean filter
-colortuned
-running balanced

You're gonna have issues.

But, assuming that's done, we're looking at:
#2-pipe is cold. Therefore no fire. So, either it needs a plug or fuel. If plug is wet, there's fuel. If a new plug fires it.... Problem solved there. If it doesn't, then it's electrical. If there's no fuel, that needs to be addressed at the carb.

#4-black sooty.... It's running rich, you gotta adjust the mixture. Possibly make sure jets are not mixed up.

Still, after correcting those you'll need to do a running sync.

 

Aaaaagh-- I didn't even see the pods comment.....
I'm thinking i might make it a personal goal to not reply to anyone who has running issues unless they can prove that they are running an original airbox and filter with correct jets!!!

 

Ok, I guess I did cover that, though, in my list of things: airbox/filter/jets