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[81Delorean]

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.

[Pat Conlon]

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

[81Delorean]

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.

[81Delorean]

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.

[Millietant]

1.) 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.

[81Delorean]

Is there a plug brand/type that the bike likes? doesn't like?

[Billy Bananahead]

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

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.

[81Delorean]

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.

[red]

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.

[Pat Conlon]

Cylinders #2 & #3 share a coil and cylinders #1 & #4 share the other coil.

[81Delorean]

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.

[Waiex191]

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.

I use the socket that came in the toolkit.

[Pat Conlon]

I forgot if you mentioned, you should balance your carbs.

[fj1289]

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.

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) ...

[81Delorean]

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.