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86 fj bucking/cutting out.

Started by bluesix, September 09, 2011, 01:44:41 PM

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 Hi to all.  I have an 86 1200 that i purchased not too long ago. I believe i have a carburation problem. The problem is most noticable when cruising at highway speeds( 60-70 mph). The bike has a kerker header on it, unknown whats in the carbs as i have not had them off. what happens is a severe cutout/bucking at about 1/4 throttle, i can accelerate out of it. The cutting out also can happen at lower speeds and lower throttle openings. It's not as noticable at the lower speeds but i can tell it's happening. also on cold startup i think it's happening too, at first i just attributed it to a cold engine. My first inclination is pilot's plugged. I've also thought about a fuel line collapsing but that seems like i could rule it out due to the fact I can accelerate out of it on the highway with wider throttle openings. what about a torn diaphram? would that have any affect on  steady cruise fuel delivery? It also seems i can rule out electrical as I can accelerate past the stumble/cutout.  Maybe I should try some seafoam first? Any and all ideas appreciated.  Thanks Mark


Check those diaphrams.
A lot of people overlook the diaphragms.

Mark Olson

clean your carbs . new to you fj so get in there and do it.

check this out

welcome to the group. :hi:
Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"


Thanks Mark and fj for the replies. I have saved the illustrated carb guide and the carb cleaning file for refrerence. I have taken apart and cleaned some mukini vm28 carbs that are on our rd 400's so I'm not a total neophyte. I have not taken apart any diaphram carbs yet. I also was looking at some similar posts and had not thought about an air leak. The bike will sometimes backfire when bucking/cutting out.
                                              Once again thanks all, Mark


Dirty carbs.

easy enough to do but make sure and do the job right the first time or you will be taking them back off again.



VM's are definitely different than the BS's, but the ideas are mostly similar, so you shouldn't have much difficulty.


Well,I'm not so sure it is the carbs. Rode it today and noticed when it's cutting out/bucking the tachometer is erattic.  Doesn't Make sense as I can still accelerate out of it. I'm going to pull the carbs and disassemble and clean tomorrow. Any ideas on the correlation between the cutout and erratic tachometer?  Thanks mark. One. Other thing, it has k&n type pod filters on it.


   I think that the signal for the tacho comes from one coil or pickup not 100% certain but  that would be next place to look if cleaning the carbs doesnt cure the problem


Ok, pulled the carbs today and cleaned. soaked in carb cleaner and washed with water and blew out. the carb has 130 main jets, 138 main air jet, 37.5 pilot jets. the needle jet is what looks like 378/y-2. in between the 378 and y-2 there is a sqare  symbol witha little square at the lower left. the carb slide has the bleed hole? enlarged. the jet needle is on the second notch from the top of the needle. a total of 6 notches. the pilot air screw is 3 turns out.  #4 carb was missing the pilot air screw o-ring.  float level was around 1". i reset to  .88 inch. i don't know what the jet kit manufacturer specifies. i have the carbs off for now, waiting for feedback. here in broken arrow we have about 600 feet of elevation. so far did not see any smoking gun which would cause problems. after removing jets i blew them out with breath pressure. ( feel free to make smart ass comments, i probably would) after the gas cleared with little pressure i did not see any clogs. after soaking in carb cleaner  i blew the jets out with high pressure air.  do the jets sound typical. as far as i know it's just got the header on it with k and n pod filters.


The little square within a square symbol is the mikuni logo (or one of them). 

The air jets seem crazy to me, stock was 155?

The 130 mains are on the big side also, within reason for what factorypro includes with their jetkits though.

Pilots are stock.

I have to  think this thing should be comically rich with that setup, but I'm tired.  Factorypro gets away with a huge main jet, but I thought they used a 155 air jet still.  Can't tell if someone put a jet kit in it and then farted about with their own "custom" tuning or something perhaps? 


dont forget to pull the emulsion tubes and clear out all the little holes in the sides.... you may need something to mechanically clear the varnish.... like a brass wire from a grill cleaning brush for example.



Hey all, thanks for the input on my problem. I finally got a chance to take it out on the highway today.  Ran fine at highway speeds without a problem.  Did about 40 miles. I guess i was wrong about the possibility of it being  electrical. The tach bounced some on my ride today without it cutting out. Maybe the shudder from cutting out exacerbated the problem with the tach. Thanks everyone.


I'm back.  Well i haven't done anything with the bike for the last several months, just been riding my rd400.
Got sick last week and had a bad cough, tried sleeping but coughing every minute put an end to that. I spent the night going over the forum looking for anything that could help. Ran across the power to the coils thread and checked the next morning. 11.8 volts at the battery and 10.3 at the coil power plug. i put a relay in and ran fused power right from the battery through the relay and used the original coil power to energize the relay. Took the fj out and it still cut out. I thought well let me see what happens if i just wire power direct.
               I rode 20 miles and no cutout. I ended up wiring up a toggle switch to the bars with an idiot light on the load side so i won't forget to cut power to the coils. 70 miles so far riding around town with about 10 on the the highway and not one cutout.  Using very little throttle opening 1/8th or less once cruising. I'm going to run it like this for at least a couple of hundred miles then if it doesn't cut out I'll start looking at whats in between power and the coils, ignition/relay's.
                                                thanks to everyone who has posted here helping me out,


 I guess I should clarify, the missing came back. I posted a comment in BigR's thread about his low rpm miss.       Mark