HELP! XJ900S Diversion experts needed!

Deagol

If anyone thinks themselves an expert on older bikes - I'd really appreciate some help! I have an old but super low mileage XJ900. But it's running badly. I'm convinced cylinder 2 isn't firing most of the time - but I've checked / tested / eliminated just about everything I can think of and I'm really struggling to figure it out. I'm located in west Clare - if there's anyone anywhere nearby who's got serious expertise or loves a challenge - there's a few beer vouchers in it for the person the solves the problem. Issues checked and confirmed:

1) Sparking fine

2) Compression fine

3) Carbs cleaned and checked

4) AIS checked and cleaned

5) Intake rubbers - perhaps dodgy but I've sealed with rubber compound and can't imagine they are leaking enough to cause an issue (but willing to be proven wrong).

Bike has only 12900km's on it so limited number of things it can be? Any suggestions gratefully accepted!!

goblin59

https://www.boards.ie/discussion/2058214391/help-xj900s-diversion-experts-needed

Have you checked the Valve clearances on the cylinder head? I'd work backwards though from the spark plug, measure and check everything.

Sparkplug gap, resistance on the coil cap, coil leads, then the Coil and keep going until you're at the CDI. If you have the Clymer or Haynes Manual it will give you the measurements you should be looking for.

I'd recommend going onto a XJ900 forum on facebook or online and asking there though, being an old bike its most likely something thats come up before for people.

Deagol

https://www.boards.ie/discussion/comment/118065423#Comment_118065423

I didn't check valve clearances as I perhaps wrongly assume (?) - if compression is fine (10+bar) then valve clearances should also be correct? Or am I making a faulty assumption? I also would have thought it's highly unlikely (?) that valves clearances could be far out on a bike with such low mileage? I've avoided taking the head off because it's such a pain but perhaps I'll have to :(

I've checked resistances through caps, checked back to coils (I found a dodgy corroded connection on both secondary coils but fixed that). Used a spark checker and good sparks on all 4 cylinders. Resistance on both primary and secondary sides of the coils are fine. I actually found the official workshop manual online and used that for the values.

The guy I bought it off told me ahead of time that it was acting up, he's a serious car man - he does up rally cars for his son etc, he was convinced it was float heights or something to do with carbs but I can't find anything - unless it's something related to jet sizes but again, can't see why it would be an issue on a low mileage bike.

Anyway, appreciate the response and suggestions. Cheers!

goblin59

https://www.boards.ie/discussion/comment/118065555#Comment_118065555

Some of those older bikes just act up anyway.

My Dad has a few low mileage Carb'd bikes and you still have to do routine maintance,

For the valve clearance does the head have to come off on it? my DR650 is a valve clearance every 6000km or once a year, I've done it three times this year already and will be doing it again soon too with the oil change.

If your floats are fine, see if anyone near you has an ultrasonic cleaner and just put the carbs in that for 30 minutes to give them a clean, it could be related to the Ethanol fuel as it eats through Carb rubber.

I've to rebuild some bing carbs soon to make them ethanol resistant.

galwaytt

I'm assuming plugs are new. I'm assuming leads are checked for resistance & continuity and are serviceable. I don't see valve clearance causing intermittent issues.

So, I'm putting on money on the carbs (still). It's a complete PITA, but carb'd bike just don't like being stood. You need someone with an ultrasonic cleaner really.

Deagol

https://www.boards.ie/discussion/comment/118080536#Comment_118080536

Plugs ping out on multimeter perfectly and they are shiny out and in - but i've ordered 4x new ones just in case. Leads etc all been checked - there was some corrosion on the coil side but I disassembled and cleaned it all and potted it back together and resistance's on both primary and secondary look perfect now.

I've taken the carbs off again and cleaned them out with airline. Don't know anyone with an ultrasonic cleaner (a real one!) but inside of them look good - I can't see any bad residue's etc. I did notice the rubbers on the float valve seats were not very tight to the sides of the carb, I wondered if fuel is leaking past the needle valve that way? - so I've ordered 4x float needle kits from wemoto. Hopefully that eliminates that.

Other thing is the carb inlet rubbers are not in good shape. I covered them with a some gunk called MS11 and I think they are sealed if not pretty! But I think I will now replace the rubbers with some silicone hose instead (found that from a guy online doing a simliar bike). If it still won't run right after that - does anyone want to buy a low mileage XJ900S? Runs beautifully!!! ;)