Bizzare running FJ

[rhubarbray]

My `88 has no lines leading from any of the carbs. All have a nipple cap from Yamaha. And there`s nowhere on the ignition to put a line as my advance is controlled digitally. `88 was the only year the FJ wasn`t imported into the US but it`s the same as the `89-`90.

Ray

[racerrad8]

The vacuum portion of the FJ ignition system is for emissions. It is designed as illustrated by the spark curve in the manual to spike the ignition timing to to upwards of 50* upon deceleration. This is done to help burn the extra fuel drawn by the carbs when the throttle plate is closed creating the high vacuum on the back side of the carb butterfly.

The ignition system has a built in advance curve within the box which will take it to 36-38* range. We slot all of our ignition plates to 6-8* which will make the total timing in the 42-46* range overall and consistant.

The vacuum portion of the box, unless shorted, should not affect the basic performance of the bike as the ignition curve inside the box is the source of engine timing and performance.

Randy - RPM

[rhubarbray]

OK, update! I borrowed a used stock air filter from FJRPierre the other day thinking it was that,...........nope,same.

I then went out to buy new stock plugs thinking the plugs were misfiring or shorting to ground under load,..........nope, same.

I ran wire from the coil inlets to a meter I had taped to the fairing mount thinking the power is being cut,......nope. Anytime revs are up, I`m well over 13V.

When I was running, I decided to try full choke,.......pulled like a bastard but was revving so high it wouldn`t slow down for the corner! Half choke still ran ok but bogged unless you fed the throttle in slowly.

I tried holding the throttle at a steady 1/16- 1/8 throttle with no choke and the revs would drop and the engine would actually stop.

Oh, and kick me in the nuts while I`m down,........while I was at the local Yamaha dealer inquiring about bringing the bike in for a "expert" opinion,... I was politely told that they are no longer accepting bikes older than 1990!!!!!!!!!!!!!!!!
So now, I can`t even bring it to the dealer!!!

Looks like it`s you and me
Anything else I can try?
Ray

[racerrad8]

When I was running, I decided to try full choke,.......pulled like a bastard but was revving so high it wouldn`t slow down for the corner! Half choke still ran ok but bogged unless you fed the throttle in slowly.

Ray

Ray,
      By your latest writing, you have pretty much diagnosed the problem. It is definitely a fuel related issue since the engine will run good with the choke on with the exclusion of the high idle.

I just pulled the pilots, looked through them, they looked clear and just to be sure I ran a bristle from a brush down the hole to make sure there wasn't a tiny piece of glass there. I then blew contact cleaner into the
pilot jet access hole,...it came out the air jet at the carb inlet.

In this earlier message you said you have removed and check the pilot at the carb throat. That is the jet used for the air mixture portion of the pilot circuit. The fuel pilot jet is located in the fuel bowl in the well directly behind the main jet. The orifice in that jet is microscopic and plugs with the slightest debris or dried fuel sediment. If you can not locate a ultrasonic cleaner and those jets are plugged, you should replace them.

Since FJRPierre is recently versed in the rebuilding of the FJ carb, it might worth seeing if he will assist you in rebuilding and cleaning them.

Randy - RPM

[Mark Olson]

I read all the posts and I did not see mentioned the base set up for the carbs.

so set your mix screws to 3 turns out.

use a 1/16 drill bit as a feeler gauge for the butterflys as a starting point for base idle/carb sync.

you should be able to see light through them when off the bike.

cause it sure sounds like you have a lean problem in the low range.

anyway thats all I  got.

[simi_ed]

Sure sounds like you've got a plugged pilot jet circuit.
When mine starts this kind of s*&t, I typically pull the mixture screws (noting how many turns from open, so I can reset) then spray carb cleaner into the mixture screw ports. 
When I do this, I jam the spray tube into the hole & try for a real tight fit, Watch for the back-spray when doing this!!! 

Do it a few times, then BLAST with compressed air. Fit the air nozzle as described above.  I try to make sure my pressure reg is set wide open, and over 100 psi for this.  This will (may?) blast carb cleaner & air out the air bleed port on the carb mouth, through the passage into the post-throttle port and the pilot jet.  It MAY clean out the blockage.  Good luck!

[rhubarbray]

When I was running, I decided to try full choke,.......pulled like a bastard but was revving so high it wouldn`t slow down for the corner! Half choke still ran ok but bogged unless you fed the throttle in slowly.

Ray

Ray,
      By your latest writing, you have pretty much diagnosed the problem. It is definitely a fuel related issue since the engine will run good with the choke on with the exclusion of the high idle.

I just pulled the pilots, looked through them, they looked clear and just to be sure I ran a bristle from a brush down the hole to make sure there wasn't a tiny piece of glass there. I then blew contact cleaner into the
pilot jet access hole,...it came out the air jet at the carb inlet.

In this earlier message you said you have removed and check the pilot at the carb throat. That is the jet used for the air mixture portion of the pilot circuit. The fuel pilot jet is located in the fuel bowl in the well directly behind the main jet. The orifice in that jet is microscopic and plugs with the slightest debris or dried fuel sediment. If you can not locate a ultrasonic cleaner and those jets are plugged, you should replace them.

Since FJRPierre is recently versed in the rebuilding of the FJ carb, it might worth seeing if he will assist you in rebuilding and cleaning them.

Randy - RPM

I may have been misunderstood. I didn`t say I pulled the pilots at the carb inlets. With the carbs upside down,(diaphragms out just in case- compressed air involved), float bowls off, and pilot jets out of their mounting hole, I then sprayed cleaner into the hole where the pilot jet would have been mounted. Once fluid comes out the jet (path of least resistance) at the inlet I plugged the inlet jet to force the fluid out the mixture screw hole and the three holes at the butterfly. All 4 carbs are clean,clean,clean.
I realize that I`m describing a plugged pilot jet scenario and under normal circumstances, I`d agree with you.

I have another theory, hear me out. What if it`s a weak spark which can`t ignite a normal fuel/air mixture but which CAN ignite a rich mixture such as when the choke is pulled??? I`m wondering if I have a failing pickup coil, TCI, or? Whatever is happening is doing so to all 4 cyls at the same time,....no stumbling,...no rough running. That`s why I`m thinking it`s something which is affecting all 4. Pickup coil, TCI, air filter, fuel line, see what I mean?

slowly going mad!
Ray

Oh yeah, yes my mixture screws are already set to 3 turns out and the float heights are at the lean end of the range but within spec. And my idle is nice and smooth, no out of sync.

[andyb]

What if it`s a weak spark which can`t ignite a normal fuel/air mixture but which CAN ignite a rich mixture such as when the choke is pulled???

Unlikely.  The correct mixture should actually be easier to light off than a rich one, if you've got things warmed a bit.

I hate to say it, but I'm guessing that you're missing something surprisingly simple someplace, a passageway that's plugged solid, a fuel filter that's nearly full, etc.  Start from scratch like you've never touched anything on it, and look very closely at what you're doing.

If you have a 6 year old kid to come help you, that may be best--if you have someone to explain what each portion of the carb circuits are/do, it gives you a chance to work slower through them, and fresh eyes will sometimes catch fallacies or missed stuff between carbs.

Don't give up!  Ran into a simple @!#%!@# moment today, my zx9 wouldn't idle down under 2500 revs.  Turns out the cables were getting pinched when the gas tank came down, and wasn't letting the throttle close fully.  Some swearing, and then relief that it was a fairly easy fix after!

[racerman_27410]

I hate to say it but yours will not be the first set of "clean" carbs that had to come back off for another (more thorough) cleaning.  Dont overthink the problem.

ultrasonic cleaning is preferred.


get some Uni pod filters (2 x Uni p/n 3229) and quit messing with the airbox.... it will make your life much easier.


Kookaloo! 

Frank

[SlowOldGuy]

In your first post, you said it ran okay earlier in the year.  If all it did was sit from then to now and it suddenly has this problem, then it must be something related to the storage.

Bad fuel?
Clogged fuel pump?
Kinked fuel line?

Have you tried running it with an auxiliary tank?
Are the plugs black, brown, or white?

Still sounds like a fuel problem to me.  When I let mine sit for a few weeks, it will idle fine and rev fine with gentle throttle, but when I put a load on it or grab a bunch of throttle, it will blubber and die.  If I can get it off the idle circuit by reving, I can get it going down the road.  If I let it idle and barely turn the throttle, the revs will pick up slightly then it's like it hits a huge flat spot.  If I continue to slightly turn the throttle, the revs will peak at about 1800 then the engine will nose over, start blubbering and eventually die if I hold the throttle at that position.

A dose of Techron and about 30 miles and everything is fine.

I know you've gone through the carbs several times, what about the rest of the fuel delivery system?  Could something have clogged during the down time?

DavidR.

[WS]

Hello Ray, about the fact that it was running fine earlier this year you should check corrosion between the spark plug wire and the caps. It can be also a spark plug cab. Check the resistance. Another thought good luck Werner

[TRoy]

Since FJRPierre is recently versed in the rebuilding of the FJ carb, it might worth seeing if he will assist you in rebuilding and cleaning them.

Leave Pierre alone! He has Rally to prep for!!

[fjrpierre]

>>>If you have a 6 year old kid to come help you, that may be best--if you have someone to explain what each portion of the carb circuits are/do, it gives you a chance to work slower through them, and fresh eyes will sometimes catch fallacies or missed stuff between carbs.

Actually I'm the ideal candidate for the 6 yr old position! 

[fjrpierre]

Here's a thought Ray Why don't you take the carb off mine, put them on your bike and give her a good run. That should eliminate a bunch of "maybe's"   (says Pierre thinking like a 6 yr old)

[rhubarbray]

Here's a thought Ray Why don't you take the carb off mine, put them on your bike and give her a good run. That should eliminate a bunch of "maybe's"   (says Pierre thinking like a 6 yr old)

!!! I just might take you up on your offer! I`ll call you later. That would certainly eliminate or confirm a BIG variable.

Ray