Carb Problem

[wildfire]

So today I took my FJ out and was riding at various speeds in all the gears for about 50 minutes when I decided to go to the fun zone in 3 gear. Don't remember exactly but probably 75mph or so

Anyways when I rolled off the throttle the bike was idling at about 1,700 rpms instead of its usually 1,100. I was very close to home and returned to my garage. I turned my bike off and started it again and blipped the throttle to about 3500rpms. It stayed there regardless of releasing the throttle.

So I turned it off and removed both cables from the carbs to rule out the cables. I started the bike and again it stayed idling at around 3500.  With no cables attached and using my hand to fully close  the same result of the high idle speed was present.


What do you think. ? Stuck float, diaphragm,  needle?  All choke levers show in the choke off position .

[Pat Conlon]

Assuming your linkage is correct....It sounds like you may have a stuck carb slide....or it could be a vacuum leak...but I think a gummed up slide sounds more pausable, especially after a high vacuum event (happens in the kookaloo zone when the slides are in the top most position)

If you have UniPods it's easy to check, not so much with the stock air box in place. (See why we like UniPods?)
Take the filters off, or air box out, and look into the throat of the carbs and look at the slides...are they all even? Are they all the way down or is one higher than the others?
Now with your finger, lift up each slide. Do you feel any resistance? You shouldn't. Now let each slide drop. They should all drop at the same rate...if one drops slower than the others, that could be your hanging slide.

To clean the slide bores you just need to take the top of the carb off (4 screws) take out the slide spring and carefully lift up the diaphragm and lift the slide out. Check the rubber diaphragm for any tears or holes, causing a vacuum leak. While that can be a problem, that is not what I think is happening. Your slide(s) are lifted up and hanging in the up position and not closing.

After cleaning, be sure to place the diaphragm back correctly. Match the tab on the diaphragm to the tab notch on the top of the carb to assure the slide is oriented correctly. Keep each slide in the carb it came out of, don't mix them up.

Let us know what you find. Hope this helps.  Pat

[wildfire]

Thanks Pat.

I have the unipods so I will check it and get back. If it is a sticky slide what would you recommend to clean the slide itself and the housing?. After cleaning is there a recommended lube to uset to prevent it from happening again

Tom

[FJ1100mjk]

No lube is required, other than the possible/probable coating of fuel on it when running.

Spritz both the slide (metal part only) and its bore with brake cleaner, wipe with a clean cloth, and check if slide opens and closes freely, by sticking your finger into the carb end and pushing the slide up, then releasing it. The slide should pretty much snap shut, maybe a little slowly at most. If it still sticks, you have something else going on.

[FJ_Hooligan]

To aviod any chance of damaging the diaphragm, I'd suggest using WD-40 to clean the slides.  Probably one of the few things it's actually useful for.  :-)

That said, I don't think a stuck slide will cause this problem.  The slide is mainly there to control the intake air velocity and most importantly the position of the needle.  You can usually reach in and raise the slide when the motor is running and it will cause the cylinder to go slightly lean but not enough to raise the idle speed (since it's running primarly off of the idle circuit).

Sounds more like an air leak to me.  Have you ever replaced the intake manifold O-rings?

Try turning the idle speed down.

[wildfire]

To avoid any chance of damaging the diaphragm, I'd suggest using WD-40 to clean the slides.  Probably one of the few things it's actually useful for.  :-)

That said, I don't think a stuck slide will cause this problem.  The slide is mainly there to control the intake air velocity and most importantly the position of the needle.  You can usually reach in and raise the slide when the motor is running and it will cause the cylinder to go slightly lean but not enough to raise the idle speed (since it's running primarly off of the idle circuit).

Sounds more like an air leak to me.  Have you ever replaced the intake manifold O-rings?

Try turning the idle speed down.

Idle speed is as far as I know supposed to be 1100.  No I have not replaced the O rings . No harm in replace those anyways I suppose.

[wildfire]

Ok so today I did some testing and the slides are moving freely. I went out for a ride and opened it up. I discovered that it only hangs when I go above 3500 or so in gears 2 and 3.   I am thinking  increased suction from the carbs working hard in low gears at fast speed. I expect in the higher gears it would happen too but I dont have anywhere near me to really try this

It does return to idle slowly so as has been suggested I am thinking vacuum leak.

I also remembered that I had somewhat of the same problem on a Goldwing years ago and I replaced all vacuum hoses and problem solved.

Now on a side note today I noticed that when the choke was applied when the bike was fully warmed up the revs increased and the bike did not"stumble" as i expected. From memory am I right in saying that this also points to vacuum leak.?

I tried spraying some starter fluid around each carb seperately to see if the revs would rise but no difference.

Any suggestions as to common locations for vacuum leaks . Typical it had to happen when the weather just got better.

[Pat Conlon]

Ok Tom, cross that off the list. Back to Hooligan's suggestion that you have a vacuum leak. His batting average is quite high, so I've learned to never bet against him.

I had to go back to your first post to see that you have a '92 FJ.
If I can make a suggestion, go to your Profile (button at page top) and add in your signature line that you have a '92. That way you don't have to keep reminding people as to what model FJ you're talking about.
There are differences between FJ's.

For example, if you have a 49 state model** you should have one vacuum hose on your FJ. That hose is connected at the #2 cylinder intake manifold. The purpose of this vacuum hose is to trigger the ignition advance module (located under your fairing on right side) This is done for emissions not performance.
Take the hose off your #2 intake manifold and suck on it....you should not be able to draw any air thru the hose. If you do, you have a vacuum leak, either in the hose or in the module.

** If you have a Calif. model, you will have several other vacuum hoses as part of the charcoal canister system.

I think Hooligans suggestion about replacing the O rings on your intake manifolds is a good one. Perhaps your visit into the kookaloo zone disturbed one of those old seals?

Fret not, keep plugging away. You will find the culprit.  Pat

[wildfire]

Ok Tom, cross that off the list. Back to Hooligan's suggestion that you have a vacuum leak. His batting average is quite high, so I've learned to never bet against him.

I had to go back to your first post to see that you have a '92 FJ.
If I can make a suggestion, go to your Profile (button at page top) and add in your signature line that you have a '92. That way you don't have to keep reminding people as to what model FJ you're talking about.
There are differences between FJ's.

For example, if you have a 49 state model** you should have one vacuum hose on your FJ. That hose is connected at the #2 cylinder intake manifold. The purpose of this vacuum hose is to trigger the ignition advance module (located under your fairing on right side) This is done for emissions not performance.
Take the hose off your #2 intake manifold and suck on it....you should not be able to draw any air thru the hose. If you do, you have a vacuum leak, either in the hose or in the module.

** If you have a Calif. model, you will have several other vacuum hoses as part of the charcoal canister system.

I think Hooligans suggestion about replacing the O rings on your intake manifolds is a good one. Perhaps your visit into the kookaloo zone disturbed one of those old seals?

Fret not, keep plugging away. You will find the culprit.  Pat

Come to think of it last year I replaced the hose from #2 manifold as well as the vacuum plugs on the sync ports as they looked somewhat perished. So hopefully the o rings are the culprits. Could it also be the intake manifold boots?

[theLeopard]

I discovered that it only hangs when I go above 3500 or so in gears 2 and 3.

It does return to idle slowly

mine does this rarely, usually after a long ride (200+) on the california freeway (ie: hot)
Interested to hear your findings.

[FJ_Hooligan]

In addition to Pat's recommendations, if the choke plungers aren't seating well, that could be a source of vacuum leak.

Does the choke cable and mechanism move freely?

[wildfire]

In addition to Pat's recommendations, if the choke plungers aren't seating well, that could be a source of vacuum leak.

Does the choke cable and mechanism move freely?

Well they appear to move in and out fully and freely but i think they have a rubber seal as well. Is that right?

[Pat Conlon]

....Could it also be the intake manifold boots?

Absolutely. Check them out when you remove them. Bend them, look for cracks in the rubber.

I hope you used oem Yamaha rubber caps on your intake vacuum ports. The heavy rubber ones.

Back in the olden days I made a rookie mistake and replaced my vacuum plugs with the regular automotive type thin walled vacuum caps....they cooked off. Lesson learned.

Lots of heat back there. There is a reason those Yamaha vacuum plugs are heavy rubber.

[ribbert]

Back to Hooligan's suggestion ........ His batting average is quite high, so I've learned to never bet against him.

Pat, you would have been well advised to take your own advice in the recent "self adjusting clutch/brake" discussion rather than persist with the "But I felt it" line in the face of overwhelming evidence to the contrary.

Hooli was the only guy that seemed to understand the principles involved, and, strangely enough, with JoBroCo coming in second.

Noel

[ribbert]

Absolutely. Check them out when you remove them. Bend them, look for cracks in the rubber.

Visible external cracks in the rubber do not necessarily mean they are leaking. The manifolds are thick and the cracking appearance on the outside is quite common.
You can always smear some RTV silicone around them to seal them up.

Noel