FJ600 - Trouble starting.

Diaphragms in good order?, sticking float needle on trouble carb? Take a look when its running on three - you may need a mirror - and see if the slider is moving on the throttle opening you should also be able to see the fuel spray (or not)

 

It has new needle and seat, does not seem to stick, diaphragms are good, i am suspecting leaky shaft seals, since they most likely are OEM, and 32 years old.

Carbs are off the bike again again and again.

 

In your very first post here you said you rebuilt them......

 

Throttle shaft seals are a common reason to remove carbs yet again, because people don't think they can or should break the rack initially. Usually if there is leakage it produces a lean condition with possible revving.

 

I did, just not the shaft seals, guess i am paying for that now.

I will order at set, somebody told me Suzuki # 13651-51010 should fit, and they are a lot cheaper than the Yamaha version.

 

Carbs are split, that was super easy and i feared the worst about removing the screws holding the butterfly valves, old seals are pretty sloppy, will order new seals, and new screws.

And while i am waiting for parts i will drop the carbs in my ultrasonic.

 

I'll be interested to learn if that fixes it...
..I'm not sure.

 

Same, i hope it will be a confirmed fix, but i doubt it, because why would it only affect one cylinder, and not the other 3, all the seals are bad.

But i am running out of ideas, so everything goes right now.

 

Try starting it off a car battery.

 

The seller did that when i bought it, was only running on 3 cylinders, also tried with battery and booster, still only running on 3.

 

Have all the ignition components been tested and verified within spec? Coils, wires, caps, plugs

 

Plugs and caps are new, and checked, used 5K caps instead of the 10k oem, but that should make no difference.

Did not check wires or coils, but i did swap wire and plug from cylinder 4 to cylinder 1, and no difference, cylinder 4 is running.

 

If it’s not carburetor/fuel issue, then it’s either electrical or mechanical.

electrical-TCI, wires/connections, coils/leads/caps/plugs, grounds

mechanical - did you do either a compression test or leakdown test, check cam for a bad lobe, etc....

 

I did not do a leak down test, but compression is at 160 psi, and valve clearance are in spec, lobes looked fine.

All ground connections has been removed and cleaned, there is plenty of spark on cylinder 1, a faulty coil should also affect cylinder 4, since its a wastespark system, and plug wire has been moved from 1 to 4 without any change, sparkplug in cylinder 1 is getting some color, so it is running, at least a little bit, its not stone dead.

 

If #1 is not stone dead, maybe it is just super lean?

I just re-read the thread and I didn't see anything about pilot mixture adjustment.

Also, is there any difference when you use the enrichment/choke?

If it is firing occasionally, it kind of reminds me of when you are using a colortune and bottom out the pilot adjustment screw so it is super lean - it will fire occasionally, but not much.

 

Pilot mixture screws are set at 2.5 turns out, it does not seem to do much difference when adjusting it on cylinder 1, when using the choke enrichment bike idles higher as it should, but the exhaust on cylinder 1 is still cold compared to the other 3.

 

How weird.

Since we are grasping at straws, what about some sort of obstruction in the intake or exhaust? Like somebody stuffed a rag in the intake to keep dirt out while working on the carbs and never removed it - seems like something I would do. Or perhaps an obstruction in the exhaust - maybe a family of mice moved in while it was sitting??

I know it may not be inexpensive, but would it be possible to get another rack of carbs? Seems like it would be a small victory to either confirm that the problem in is the carbs or rule them out as the source of the problem.

 

I did actually order a spare carb set, just for testing, still waiting for it to arrive, bike was complete when i bought it, had been standing for around 1 year, was last on the road in november of 2020, intake is clean, did not check exhaust.

Looking on the exhaust headers it looks like its been on 3 cylinders for quite some time, there is a visible difference between 2-3-4 and 1, i dont hope the engine is hurt.

 

Did you try swapping coils 2/3 for 1/4 yet?

 

That is always a good thought on a dead cylinder, particularly at lower speeds. Aside from defective carburetors, the Intake Manifold gaskets as well as the Intake Manifold itself leaking can cause that.

I don't know if just a butterfly shaft seal leaking a bit would make it that extreme.