FJ600 Jetting Dilemma

hi, Hollybrook, just a quick question, whilst you are on with this,
do you have a description, or photos of the airbox with the KN filters fitted. i am interested in this ,for my cafe racer, which, KN filter is it?
thanks

 

@bensalf, I have had the K&N filter since I bought the bike and it replaces the stock air filter in the stock airbox. It is an exact replacement other than having a gauze medium instead of paper. I suspect it is no longer made.

 

ok gotcha

 

I just looked at K&N's website and the only filters they show for the FJ600 are the same pods they show for the FJ1100 and FJ1200.

@bensalf, I found the part number (YA-1684) and it looks like these guys might actually have one:

https://2wmparts.com/products/k-n-h...j600-1984-1985-ya-1684?variant=41279848644759

 

@bensalf, if you do not want to buy that K&N air filter, please let me know and I will buy it as a spare.

 

the air filter will not fit ,in the airbox ,cos the back half has been cut off. my filter (honda 50) now sits inside the first chamber.
but thanks for yor help

 

Yes, there is no way to use that filter. After what I have learned about airflow through the stock box and seeing how your filter sits in your box, I am wondering about carb jetting. Are you able to use the stock jetting or have you needed to re-jet for the new airbox configuration?

 

i did about 100 miles on it, before the weather turned. still on standard jets, but it seemed to run ok, but i didnt give it a lot of stick, i really should dig this machine back out and sort it out.

 

Well, I was correct about the sparkplug caps not being the problem, nor was the #1 intake manifold. After fixing both of them, I still could not get the bike to run correctly, though I could get close if I ignored the carb synchronizer and tuned by ear. Also, using a colortune, I was unable to get the mixture rich enough to show yellow.

Being quite frustrated yet again, I decided to take another run at the carbs. Up until now, I have not been able to dip the carbs in a petro based cleaner and only have been using a heated ultrasonic cleaner. Using the petro based cleaner would damage the shaft seals that do not appear to be leaking based on the propane test, though I guess they might be at some times that I am not seeing. Anyway, I got some new shaft seals and also decided to go to the next larger pilot gas jet to see if I could richen up the idle mixture. I noticed that all FJ600s sold outside the USA and Canada used a larger jet size, so with the K &N air cleaner and E10 gas, it makes sense to try the larger jet. I was thinking that I could just turn out the pilot screw a bit further, but the colortune did not show that to be the case.

At this point, the carb bodies have been cleaned in the petro cleaner and the carbs are ready for reassembly. My wife broke her leg and needed surgery to put in a plate and screws, so my garage time is quite limited for the next month or two. I will report back when I have more news on this project. I hope that documenting this will help somebody in the future with a similar problem, though at this point I have fixed so many things on this bike that sat for 10 years, it is hard to say which ones were critical to getting it running like (better) than new.

I have to give a big thanks to @chacal for the excellent parts supply he has helped me with, along with some great advice. It is amazing that with all the parts I have looked for him to provide for this low volume, 37-year old bike, only one circlip has not been in stock! I truly believe that without his help, this would have been an exercise in futility.

 

I have used K&N filters in my cars , HOWEVER my beloved Seca had a K&N the PO had put in , he also claimed carbs were professionally tuned. It had three different spark plugs, it ran kinda soggy is best , bogged when you took off . I put correct spark plugs in was a little better , took carbs to church could not get it to run quite right , took out the K&N filter put stock paper filter ....OMG it was hold on tight bike screamed . So not sure why the difference but this was my experience.

 

@Jetfixer, I appreciate your feedback.

This bike has run well since I bought it in 1986 and it has had the K&N air filter since the first time I needed to change it, probably 1986 or '87. That said, it has always been on the edge of running lean, though performance has been good.

While my brother had it for a bit over 10 years in Florida, it began to not run as well and even though he is an excellent mechanic, he took it to a shop because he was too busy at the time. They cleaned the carbs and drilled out the pilot screw caps to tune it up. He says that it ran OK after that. That was also about the time that the US decided that E10 was a good idea, so there is the good possibility that much of his problems related to the engine already being jetted lean to meet emissions, adding a better flowing air cleaner, and then a fuel change that resulted in even leaner combustion. Each change I have made for richer conditions has resulted in better running for that particular area of throttle/load/RPM, so I think I am on the right track.

When I got it back from him, it had sat too long and was not running. Each time I have rebuilt the carbs without dipping the carb body, it has run OK for a tank or two of gas and then quickly gone downhill. I have been rebuilding carbs on bikes and cars since I was a teenager and rarely had to redo any of them. I also used to successfully tune and race a Datsun 240Z with SU side draft carbs that are quite similar in concept to the CV carbs we all have. I am now hoping that actually dipping the carb body and replacing the throttle shaft seals will resolve any remaining problems that I am having.

This has been a quite frustrating and humbling experience, but as they say. you get stronger when you confront adversity!

 

I believe this explains most of the symptoms you were experiencing. Also note that leaky throttle shaft seals will add additional "leanness" to the engine.

 

If you have not replaced the butterfly seals , Len carries these and are worth the investment. Thanks to xj4ever I have done three sets of carbs , this rules out this as a vacuum leak.

 

Yes, I am replacing the shaft seals with ones from Len. I have never been able to find a vacuum leak at the shafts, but there is no guarantee that I don't have one in some situations. In any case, this did allow me to do a more aggressive cleaning of the carb bodies which never hurts.

The seals I took out were not that bad, but the lips seemed a bit stiff, so new ones should be better.

 

See my post on why you should replace you butterfly seals, one set of carbs I did they litterly were like gum. Another set I did for someone else, the seals were actually packed with RTV .

 

Well, I now have the bike running again, and much better! I can't really say if the new shaft seals made a big difference as the ones I took out were not that bad, but knowing that I have new ones is one less thing to worry about. I also noticed that when I reinstalled the butterflies, they fit better and did not bind on the throttle bodies. Since the screws were peened over from the factory, this was an item that was OK but not perfect, though I cannot see that it made any significant difference.

The bike starts much better, which I attribute to the larger pilot gas jets. I still cannot get a yellow flame on the Color Tune, but do see a nice blue one. I ended up synchronizing and just setting the pilot screw by ear. If anything, the bike seems a touch tamer to me, but I recently got a Tenere 700 and its high torque engine may have spoiled my recollection of how this one accelerated.

I was quite surprised to find out that the FJ will start without the choke -- this never was possible from the day it rolled off the dealer's floor. Again, a huge thanks to @chacal for all his support, parts and advice!

 

I want to document where I ended up in case anyone else is on the same journey to keep one of these bike running on E10 fuel. While the final settings might be slightly different, this should make a good starting point.

My final settings were:



All other settings are the same as stock including float bowl fuel level.

 

Just checking in to say the FJ600 continues to run great as set up in the previous post.

 

And it is still running fine.

 

Excellent thread!

I have two yx600’s, which are very similar to your FJ600. After rebuilding three sets of carbs I’m getting ready to play with needle and jet settings to get these things running.

The yx600 comes with bs30 carbs from the factory - all with 97.5 main jets. Cylinders 1 & 4 use 4CHP2 needles and cylinders 2 & 3 use 4CHP4.

Derick Capito (Yx600 Guru) recommends 100 main jets and 4CHP7 adjustable needles set at the third position from the top.

Like yourself I figured I’d put this information here for future readers.