Good morning all, Hope you all having a good weekend. Temperatures have been warming up so I've been outside messing around more so I thought I would maybe get a list of stuff I would like to do to my new to me '89 FJ1200. I got in November, didn't do much riding over the winter, but ever since I've had it it's always had a backfire/pop from the exhaust. As far as I know it is stock except for the Vance & Hines exhaust. I was planning on going through the carbs at some point this summer, and change the plugs before my 2,000 mile trip in August, decided this morning I would start it up, let it run for a little bit and put an infrared thermometer on the headers at the same spot on each one to check the temps just to see what it would tell me. I believe I found my problem carb.
#1 177 degrees
#2 90 degrees
#3 174 degrees
#4 185 degrees
All are pretty close but #2 seems to not be firing or not getting enough fuel. Any thoughts on what to check or do before pulling the carbs off? I haven't even pulled the tank off on this bike yet so I have no idea how the fuel delivery is routed/hooked up or anything. I know I need to pull the plugs to see what they look like also and make sure #2 is even firing. The exhaust is 4 into 1 but I don't think it would need re-jetting or anything would it? Again, I don't know anything about what's been done to the bike before me. I'm in northern Arkansas if someone has an opinion on jetting.
As for plugs, is there a go to plug that these bikes like? Or is a regular or standard NGK good enough? Thanks in advance for any opinions or comments. Have a great day.
So you see that *at idle* your #2 is sleeping...does the engine rev up? Can you ride it?
The FJ ignition system is robust, by comparison the Mikuni BS36CV carbs are fussy.
I'll go out on a limb and bet a jelly donut that your #2 carb has a gummed up idle circuit.
If you can, take the bike for a ride. Run a can of Seafoam thru the carbs. See it that clears out the carb and wakes up #2.
Report back cheers. Pat
The bike seems to ride fine, revs up fine, just pops and backfires at idle and while riding, doesn't seem like it's struggling for power or anything. I should've thought of trying Seafoam or Techron before posting. I will get some today and dump it in and see if I can go for a ride for a little while today or next weekend.
Dumped the Seafoam in, went for about a 30 mile ride. I will go through the whole tank of gas before doing anything but some observations are:
1.) bogs down a little taking off - been a few years since I've ridden a carb bike, could be normal
2.) Coming up to a stop light it idles at about 2,000 rpm for about 15sec before it drops down to about 1,000
3.) Still pulls hard
4.) still a lot of fun
5.) Temps when got back and checked were
1. 140 degrees
2. 115 degrees
3. 140 degrees
4. 115 degrees
Didn't hear it pop or backfire when I was riding, accelerating or slowing down. Hoping the Seafoam does it's magic.
Quote from: 81Delorean on April 13, 2025, 12:59:39 PM1.) bogs down a little taking off - been a few years since I've ridden a carb bike, could be normal
Definitely not normal, either for a carb bike, or especially for a FJ.
I'd go out on a limb and agree with Pat, but as you mention, I'd also put new plugs in anyway before pulling the carbs apart, just to rule them out as a cause of any potential problem.
Good luck with solving your problems.
Is there a plug brand/type that the bike likes? doesn't like?
Quote from: 81Delorean on April 13, 2025, 12:59:39 PM2.) Coming up to a stop light it idles at about 2,000 rpm for about 15sec before it drops down to about 1,000
That could be because the idle mixture screws aren't set properly. They could be set too rich. 2.5 turns out is about right.
Thank you for that. I was going to look up what the recommended number of turns out was supposed to be and check that after I did the plugs.
81Delorean,
Seafoam is magic stuff, but it is not instant magic. It may take a can (or two) mixed to label specs, to do the deed.
Since the cool temps happened on #2 -AND- #4, I would check that the ground connections for the coils are shiny-clean and secure. Dull metal is corroded metal. You may also have a failing coil. When it gets dark there, pull each spark plug wire, one-by-one, and connect it to a good spark plug. Ground the extra plug (no hands!) and crank the engine. See if each cylinder is getting a solid. healthy spark.
Additionally, there is a coil/relay mod that connects the coils to full battery power, and you can add a dedicated ground wire for each coil. Search here for the process and wiring. Many riders have made this mod on "healthy" FJs, and they will tell you the mod is a good one to do for daily performance.
If your exhaust pipes are double-walled, try taking the temp readings very close to the head, to eliminate the possibility of a bad (rusted) pipe.
Keep us posted.
Cylinders #2 & #3 share a coil and cylinders #1 & #4 share the other coil.
I had a little time tonight to go out and take a look at the bike. Here are my observations:
1.) All idle mix screws were backed waaaaaay out. I should've counted but I bet probably 5-7 turns each. They just looked to far out before I screwed them in and back them out 2 1/2 turns. Was the previous owner compensating for another issue perhaps? or just not know better? I'll find out.
2.) #4 sparkplug insulator cracked/broken from the top down in 2 places. There were pieces laying at the base of the plug/head. I got the shop vac out and got the debris out before I remove the plugs and something drops down in the cylinder. Went ahead and used the vac on all plugs, looks like #4 is the only broken one. I sprayed some penetrating lube in there on all of them also just in case.
3.) I stopped what I was doing since I need new plugs at this point in order to check the carbs properly.
4.) Of all the sockets I have, I do NOT have one that fits these plugs. I can't believe it. Looks like a weekend job since it's going to be raining this weekend.
Quote from: 81Delorean on April 17, 2025, 06:48:50 PM4.) Of all the sockets I have, I do NOT have one that fits these plugs. I can't believe it. Looks like a weekend job since it's going to be raining this weekend.
I use the socket that came in the toolkit.
I forgot if you mentioned, you should balance your carbs.
Quote from: 81Delorean on April 17, 2025, 06:48:50 PMI had a little time tonight to go out and take a look at the bike. Here are my observations:
1.) All idle mix screws were backed waaaaaay out. I should've counted but I bet probably 5-7 turns each. They just looked to far out before I screwed them in and back them out 2 1/2 turns. Was the previous owner compensating for another issue perhaps? or just not know better? I'll find out.
2.) #4 sparkplug insulator cracked/broken from the top down in 2 places. There were pieces laying at the base of the plug/head. I got the shop vac out and got the debris out before I remove the plugs and something drops down in the cylinder. Went ahead and used the vac on all plugs, looks like #4 is the only broken one. I sprayed some penetrating lube in there on all of them also just in case.
3.) I stopped what I was doing since I need new plugs at this point in order to check the carbs properly.
4.) Of all the sockets I have, I do NOT have one that fits these plugs. I can't believe it. Looks like a weekend job since it's going to be raining this weekend.
If your idle mixture screws are turned out that far - there is a very good chance your idle passages and jets are gummed up at least partially. I'm betting a REALLY REALLY REALLY good cleaning is in order - and possibly new pilot jets (which were a bit on the small side to begin with) ...
That might be a good possibility. I'm going to mess with it this weekend. Went to town last night and got a sparkplug socket set from Harbor Freight for $10 and stopped by the parts store to get the new plugs. I'll get those in this weekend, sync the carbs and mess with the mix screws. I'll see how that goes, run a tank or two of seafoam or Techron through it before I move on to puling/cleaning the carbs.
I'm a fan of pulling the carbs and doing it right.
With practice, the carbs can be removed and replaced in an hour, it's pretty simple.
Add another hour to clean and blow the passages, a quick clean, and if that looks good, you're done in 4-6 hours unless you are really good.
Double those times if you want to truly do a deep clean.
NGK Standard plugs, always.
New plugs in, mixture screws set correctly, carbs synched, it is running and idling much better. No more pops/backfires. I have yet to actually go for a ride on it but given what I've encountered so far by the PO's, I will still end up getting 4 rebuild kits, pulling the carbs and giving them a nice ultrasonic bath and then running brushes through the passages, shooting some carb cleaner through them, blowing air through them and then maybe another ultrasonic bath/air before going back together. I wish my ultrasonic cleaner was big enough for all 4 carbs to fit at one time. Thanks for all the help and advice so far. Input is always welcome. Hope you all are having a great weekend.
Carb rebuild kits as well as the screw and O-ring kit ordered from RPM last night. Sounds like I will have a weekend project coming up pretty soon.
Try and use an ultrasound bath for cleaning...
I'm going to. My plan was to separate the carbs, disassemble, soak them for a little while, run brushes through the passages, put it in the ultrasonic cleaner, run brushes again, another ultrasonic, compressed air and reassemble. Maybe overkill but why not?
As long as you are not reaming out passages or jets - there is no such thing as overkill when cleaning carbs gunked up with todays gas!
Quote from: fj1289 on May 01, 2025, 12:34:46 PMAs long as you are not reaming out passages or jets - there is no such thing as overkill when cleaning carbs gunked up with todays gas!
All the holes and passages seem so small. I was going to drill them out bigger so they won't get clogged so easily! :lol:
My carb kits should be here tomorrow, I pulled the carbs off today and dismantled each one. Have the first one soaking right now. I don't know how people are posting pics on here, I don't see the option but I would love to show off how it looked on the #3 carb, no wonder there were problems.
I've got the carbs all cleaned and rebuilt with the exception of one of them. When I disassembled them, one carb was missing the main jet needle plastic retainer, I didn't notice that the rebuild kits didn't come with new ones. Sent an email to RPM and he is going to look tomorrow to see if he has one sitting around. If not, I guess I'm going to have to find a cheap jet needle set just for that one part unless someone on here has an extra they are willing to part with.
Other than that, and being pretty gunked up, everything went pretty smooth. My first time setting float height, I have a float gauge, read a lot on the procedure, didn't seem that complicated. Can't wait to see how it runs now.