FJ does not want to run right

[chrism40]

This one has me baffled. My 89 FJ1200 Would not idle right and stumbled trying to accelerate.  It kind of ran like the carbs needed cleaning, so I started with that.  I got it back to together and no difference. It will only run at low speeds with the choke pulled out and will run at 4000 to 5000 rpm with the choke in. I had to turn the idle adjustment screw all the way up and it will barely idle. It has an occasional misfire, a backfire, through the carbs and at 4000 to 5000 rpm there is a irregular  misfire through the exhaust.  I pulled the plugs and they were very sooty and looked like they were not getting enough spark to keep the electrodes clean. They were not wet like too rich mixture. I put new plugs in and they were sooty in just a few minutes.  I checked my coils and they ohmed just outside of the good range. So I tried another set of coils. No change. There is very little voltage drop at the coils, but I went ahead and wired in a jumper feed from the battery to the coils. No change. I swapped out the ignitor box. No change. I checked and cleaned the ground for the battery at the engine case and system ground at the coil mount. No change. Is there another ground somewhere? It ran fine the last time i rode it. It has sat for about 2 months. Any body have any ideas? I am going to check the valve gap tomorrow and maybe go through the carbs again, but I am about out of ideas. Have not had this much trouble getting a FJ to run right, even one that sat from 6-8 years.

[red]

Chrism,

What is the idle RPM setting?  If less than 1200, that low RPM may cause a stumble on acceleration, but I expect you knew that.  Are the fuel pump and fuel filter healthy?  Any kinks or pinches in the fuel lines?  Did you change the carb float levels?  Good needles-and-seats in there?  You have checked all of the likely boxes already, so I'm just shooting in the dark here.

How old (and how good) is the gas in the tank?  I'm a believer in fresh non-ethanol gasoline, and the right amount of Seafoam added at the first sign of trouble.

In the USA and Canada, non-ethanol gas will be here:
www.pure-gas.org

Keep us posted.

[Motofun]

Won't idle?  Runs OK once on the main jets?  Typical of plugged idle circuit.  These little buggers are indeed little.  Make sure the "choke" (really enrichener) cable is properly activating the carbs.  If so, redo the carbs and focus on the idle circuits.  I can't tell you how many of us have chased this issue.

[chrism40]

It runs ok at 4000-5000 but it has a misfire, so I can't say it runs good past idle. Still going to go through the carbs again.

[chrism40]

Chrism,

What is the idle RPM setting?  If less than 1200, that low RPM may cause a stumble on acceleration, but I expect you knew that.  Are the fuel pump and fuel filter healthy?  Any kinks or pinches in the fuel lines?  Did you change the carb float levels?  Good needles-and-seats in there?  You have checked all of the likely boxes already, so I'm just shooting in the dark here.

How old (and how good) is the gas in the tank?  I'm a believer in fresh non-ethanol gasoline, and the right amount of Seafoam added at the first sign of trouble.

In the USA and Canada, non-ethanol gas will be here:
www.pure-gas.org

Keep us posted.

I am running fresh gas from an IV bottle with the tank off the bike. With the idle screw all the way in, it will not stay at 1000 rpm or less and trails off and dies. With the screw all the way in it should idling at 3,000 RPM. Checked the float settings and they were all the same and in spec. Good ideas, but I covered those areas once and I am going to do the carbs again just to make sure I did not miss anything.

[Flynt]

It runs ok at 4000-5000 but it has a misfire, so I can't say it runs good past idle. Still going to go through the carbs again.

Make sure you don't have an air leak on the vacuum side...  are the rubber bits and the intake boots in good shape?  Rubber caps on all vacuum nipples in good shape?  Suck test petcock?  Vacuum leaks can cause what your seeing...  the soot could be from too much choke trying to get it running.  Never hurts to do carbs again though...

Frank

[chrism40]

  Well I am still baffled as to why, but the problem is in the carburetors. All four have some kind of problem since the miss firing and occasional flame will come out of all four. This is after I cleaned the carburetors several times.  I put the problem aside for a while. A friend bought the most well preserved 89 blue FJ1200 that I have ever seen. The body work is nearly flawless, It has only 7200 miles and has been sitting since the early 90's. The tires are dated 1991 and show very little wear. It must have been inside and covered up as there was no dirt in the out of the way places that collect sitting dirt. The tank was pretty rusty inside and cleaning it is still in process. The carburetors were extremely clean on the outside and the worse that I have seen on the inside. The brake calipers were frozen and I had to disassemble the calipers while still on the bike so that we could push it. The owner and I spent everyday for 10 days rebuilding the carbs, the calipers, the front forks, new tires, new clutch slave cylinder, new brake lines, new master cylinders and going through every system. It came out really nice and runs great. But after finishing the carbs and before reinstalling them on the bike, I stuck them on my bike and it ran perfectly. Just to prove to my self that it was the carbs, I pulled a rack of carbs off the shelf that came off an 86, pulled the bowls to make sure nothing was too bad and installed them on my 89. It ran perfect. We finished the blue 89 today and it is on its way home. I have carb  kits on the way. I am going to disassemble them and soak them like I did for  the blue 89 and see what happens.

[balky1]

Without ultrasonic cleaner I don't think you'll accomplish anything. Because it sounds, like mentioned before, you have clogged idle circuits and you didn't manage to clean it the old-fashioned way. At least that's what I've concluded from your posts.

[chrism40]

I don't have access to an ultrasonic cleaner. I wish I did. I have 9 Japanese bikes with four carbs each to service from time to time, plus several friends bikes. On the previous couple of cleaning attempts I used my usual technique of using a veterinary syringe filled with Gunk dip soaking cleaner followed by brake cleaner to check the flow in the passages, followed by high air pressure to blow out it all out. I can do that with out taking the carbs off the mounting rails. This time I took the carburetors of the rails and soak each in the Gunk for 4 to 5 hours and then did the syringe and brake cleaner thing. I put them all back together and it runs fine. I did not see any difference in the flow of the fluids while apart the last time than I did on the previous cleanings. There must have been something in the carburetors that only soaking got out.

[aviationfred]

Hi Chris,

Good to see that it has definitely been narrowed down to the carbs.

I have used this Ultrasonic cleaner in the past. It does a great job.

https://www.harborfreight.com/25-liter-ultrasonic-cleaner-63256.html


Fred

I hope you have mentioned and talked your friend with the pristine Blue 89 FJ into attending the Vintage Yamaha Rally??

[gdfj12]

I've got that HF ultrasonic cleaner and it does a good job for it's size. I had their small one an it was good for small things. I am considering a larger one with all stainless steel construction for bigger parts and possibly big enough to fit the bank of carbs together.


George D

[Pat Conlon]

....I am considering a larger one with all stainless steel construction for bigger parts and possibly big enough to fit the bank of carbs together.
George D

Hey George, which one are you considering?
Last time I looked into a ultrasound unit with a tub large enough to hold a rack of FJ carbs, the increased cost was considerable. For as often as I need to use it, it was not practical.
Disassembling the carbs off the rack is no big deal for me. With them disassembled, I can then replace the o rings on the fuel inlet T's

Although now it's even better....I store my FJ's with VP C-9 race fuel.....never a worry about plugged carbs again.

Cheers mate

[RPM - Robert]

It's also a good idea to dis-assemble and change the 30+ year old o-rings, anyways. Ours is large enough to get them in complete but it isn't worth the risk of sending carbs back to a customer without fresh o-rings. We completely dis assemble every set.

Also, T4 smells better than C9 . Step your game up.

[Pat Conlon]

Don't know why the T4 is $12 more for a 5 gallon pail than the higher octane C9.

I like my purple gas.... When I push the starter button on my 1380, that engine explodes into life.

[RPM - Robert]

It's yellow for one, adds to the cost... 

The T4 is oxygenated at close to 6% where the C9 is not. Hank says it makes more power than any other fuel out there, we ran T4 and made close to 152HP with the carbureted Busa in the roadster to the wheel. They changed the rule mid season because those guys were running pump gas and didn't want to spend the money on race gas. We are now running a 93 octane race gas (what is legal now) and only made 141HP to the wheel.

Even the race gas at the pumps at Sonoma, Laguna, Thunderhill, etc. has ethanol in it. We were running track gas 96 octane for a long time. When we started having carburetor problems we talked to the track manager at Sonoma and he said they had to have ethanol in everything but the leaded fuels now. That's when we swapped to the T4 after talking with Hank about some different fuel options.