FJ600 - Trouble starting.

Hi guys.

New member, so i hope this post is allowed since its an FJ600.

Bike is a FJ600 from 1990, US/Canadian import is my guess, but the bike is now in Europe.

It was bought as a running motorcycle, but had been standing since november of 2020 heard it running, but had servere starting issues, and would not idle, or accept any throttle what so ever, and was only running on 3 cylinders.

Since then i did a few things to the bike, carbs has been cleaned, rebuilt and bench sync'ed, float level set with the clear tube method, new spark plugs, new battery, new airfilter, new fusebox it has spark on all 4 cylinders.

Here is the trouble, i had the bike started before swapping out the plug caps, started on the first push of the button, only running on 3 cylinders, found out 3 of the sparkplug caps was bad, so i decided to call it quits and leave it until new plug caps would arrive, a few days passed and now it will not fire, cranks fine, has spark on all 4, but gives no indication what so ever about firing, no popping, nothing, all 4 carbs has fuel in the bowls, and fuel is fresh, feed from an auxiliary tank, so direct feed.

The new plug caps are NGK VD05F 5k, i think the OEM is supposed to be 10k, but i cant imagine that would make a difference since it was running with 3 caps with no connection what so ever.

It has compression, spark, fuel, and air, everything says it should be running, only thing i can think of is a weak spark.

Can anyone shed some light on this bike, season is soon - and it would be nice to enjoy it on two wheels.

Regards
Ronni

 

Does teh spark look weak? Did you try trimming a little off the HT leads (10mm or so) before fitting the new caps. If your caps are resistor AND the plugs also resistor type
maybe that's too much resistor.. Did you try any 'Start ya bastard' or whatever they sell in Denmark ;-)

 

Older XJ's are battery sensitive and don't like to start if the battery voltage drops below 10V when cranking. You mentioned a new battery, but a full charge and load test while cranking would be a good idea.

 

Have you checked the valves? Must want to make sure that has been looked at.

Starting fluid has it firing on all 4?

 

Plugs should be standard to the bike, NGK DR8ES, i did trim around 10mm of the plug wires before fitting new caps, spark is clear blue and strong will jump 1 cm without the plug cap, it fires of on brake clean, and will keep running of the fuel in the bowls.

Battery is new, and fully charged, i do however seem to have a voltage drop when measuring directly on the TCI unit, it drops to around 9 volts during cranking, did clean the grounds, and battery terminals, and fuse box is new, so not sure where the problem is located.

Still need to check the valves, it does seem to run on all 4 on brake cleaner, and on the fuel in the carbs when the RPM's gets high enough.

 

9 volts is nowhere near enough juice. Get a good strong battery

 

Brand new yuasa yb12a-a, fully charged, there is a voltage drop, but not sure where - engine cranks strong, light is bright.

 

Blocked pilot or choke (enrichment) circuit in carbs? These carbs need a deep thorough clean - nothing else really cuts the mustard.
Its a hateful job pulling them on and off but sometime you have to bite the bullet (again). +1 on valve clearances too.

 

Well, if there’s a voltage drop, then you’re STILL not getting near enough juice...
Check your starter or starter brushes......

 

thats the same bike ,and engine as my xj600 , plugs are correct, and yes the Haynes does state 10K plug caps ,but i've been using the same 5K caps as you, for 10 years
without any problems.
clean up the earth wires, theres one on the back of the engine, on the RH side ,on one of the crankcase half, bolts ,
and another underneath the battery tray, on the frame , also the battery terminals

 

Voltage drop is around 1 volt between the TCI and the battery, lets say battery is showing 10v while cranking, then TCI will show 9.

I had them off around 5 times now, just did another clean with brakeclean and compressed air, nothing seems to be plugged, but if they keep acting up i will split them and throw them in the ultrasonic.

 

Ground wires and battery terminals are already cleaned. And yes, it should be the same bike, except the FJ600 is called 3RC in the VIN, not 51j or 3km/3kn.

 

Is the well and jet at the bottom clear and clean? Brakleen and compressed air alone may not do the job.

 

Yes, 100% clear, carbs has been torn apart and cleaned thoroughly.

 

If you only have 10 at the battery when cranking the 9 at the TCI is fairly typical with losses along the way through switches and connectors. 10 would be low for a new fully charged battery.

I know my XJ750 will not fire up cold unless the bowls are near full, it's like the enrichment circuit requires full or near full bowls to function correctly. I have also had issues with auxiliary tanks particularly in conjunction with an on off valve in line - the gas will flow but not completely fill the carb bowls before it stops. So, if you just verified gas in bowls go one step further and use the clear tube method to make sure they are all filling to the correct level.

Yes on the enrichment well being clean, but it would be more convincing if you said yes I used a flashlight down the well to see the pinhole at the bottom of the bowl, or I nearly shot carb cleaner into my eye when I verified they were open and flowing.

Measured?

And yes valves as suggested

 

I must admit i got lazy and only checked compression on the "non" running cylinder, it sits at around 155 psi, so i would call that a good compression, will check the remaining 3.

Guess its time to troubleshot the electrical system a bit more, maybe try and run a constant powerfeed to the TCI bypassing all the switches and connectors.

Float levels has been set using the clear tube method, they are within 1mm of the correct setting, so that should be perfect according to my manual, and no i did not shine a flashlight to check the enrichment, but i did spray carb cleaner through, and verified it came out of the other end.

I will recheck the float level before refitting the carbs.

 

Ahh, the problem here is that the jet may be slightly open. Use a flashlight towards the bottom of the bowl and peer down the well. Make sure you see a nice round hole lit up. If not round it will not be thoroughly cleaned out. You know how wrong sized jets (and clogged jets) perform, I assume.

 

Done and done, just finished another clean of the carbs, enrichment circuit is open, checked with a flashlight.

I am not positive its a carb issue, but i will keep my options open.

 

Back to running, well sort of, it still only runs on 3 cylinders, or 3,5 maybe, since the sparkplug in cylinder 4 is getting some color, i guess next step is to check the valve clearance.

Also swapped sparkplug and plug wire between cylinder 1 and 4, no difference, so it is not a ignition issue.

Compression numbers are:
1: 160 psi
2: 155 psi
3: 153 psi
4: 150 psi

And fuel level on cylinder 1 looks like this:

 

And its not a valve problem.

Back to the carb.