XJ 650 Runs only on 3 & 4

Hello!

I am new on this forum and also a newly owner of a couple of years restored XJ650 4KO -81. I bougth it for a couple a weeks ago and the plan is to build me an caféracer of it. Now to the trouble, it only runs on no 3 & 4 cylinder.
Spark is good at no 1 but a little bit weaker on no 2 and gas is coming thru correctly, maybe even to rich.
I really want it to run well before i go bananas with the deassembly of the bike. Anyone who have any clue what it could be?

Cheers
Robert

 

Change the spark plugs, maybe do a compression check on all cylinders. Plugs may be good enough to spark in free air but too weak to spark under pressure.

 

Ok, thanks. I read somewhere that the XJ got a weak spark, i will change them and se if i get a better spark after that and doing a compression check too.

 

Inspect your spark plug wires and caps. I pulled my caps off the wires a couple weeks ago and the inside of the wire had a nasty case of the greenies

 

Ok Beekman, i will check that too. i did a compressiontest today and i fell out like this:
no 1) 6
no 2) 8,5
no 3) 9
no 4) 10
Not so good eh?
Also took a look inside no 1 carburettor just because to see if it hungs up somewhere and owerflow, but i didn´t see any obvius problem, checking no2 tomorrow.
(It´s dripping gas from the exhaust between the collector/muffler)

 

Am I correct that you are measuring in bar and not PSI ?

6 bar is not good at all, and the spread across cylinders is also not good. A combination of misadjusted valves and stuck cylinder rings might account for the low compression. Hope for that being the reason.

cylinders 2, 3, and 4 are in spec for compression (though 2 is just barely in spec).

 

Are you sure the spark plug wires are going to the correct plugs?

 

Plug caps should read 5k ohms bad caps kill spark ,easiest thing to check when doing a service on a bike when installing new plugs

 

Yes, bar it is. Poured a teaspone oil in the cylinder at the second attempt but it just raised o,5 bar.

 

yes, they are all in correct order.

 

Ended out to the garage again, did a new compressiontest (the right way this time ) and what a difference:
11,2
10,5
11
10,8
Better isn't it?

 

amazing what happens when you do things the right way....... lol

 

Yes, i don´t know what i was thinking about.... lol
Still have problems with cyl 1+2 thou. Took apart caps and cables, cleaned them and changed plugs (now i got a really good spark on no 1) but still no startreaction.
I begin to think it´s an carb issue too, no 1 drowns in gas but no 2 is dry as the Gobi desert. I think i´m going to take a chat with the pre owner of the bike and se if he had some troubles with the carbs, i think he mentioned something about an carb dissembly but i´m not sure.

 

Time for carb rebuild

 

I assume you did comp test with throttles wide open as imbalanced carbs will give you imbalanced readings same goes for valve clearance
Ps nice Mini

 

I agree that the carbs need to be tended to. A guide for your perusal: In the Church of Clean

 

Thanks for your input guys, seems to be an rebuild time for me then.
That guide could be very useful for me.

 

Hello, it's me again
Took apart the carburettors and cleaned theme up well ( a cloggy mess),
Benchsynced them and put it all back again. I also took a good look at the sparkcaps, cables and contacts one more time and let them meet Mrs Oxideclean. Now it runs on all 4. It was my goal to make it run on all before i start my buildproject.

 

There ya go!!