carb issues

[Tuneforkfreak]

You knew the previous owner of this bike for 20 years and you've ridden it many times before it went into storage? Then you come along and purchase it. That alone should tell you that the parts in the carbs had functioned properly so it should be safe to say the parts are correct for the model. Looking back through your posts you never once mentioned soaking the carb bodys in carb cleaner which is standard, you didn't mention running them through a sonic bath which is what all the pro carb guys do without fail. You only said you blew air through the ports. That bike had 8 years in storage to harden  shellack into those ports. Your symptoms are that of dirty pilot circuits as mentioned by previous posts. As stupid as this may seem given what you've been through, it sounds like your carbs are simply still dirty. Just my deduction from the given information.

[ergojack]

I didn't mention soaking in carb cleaner, because as a long time mechanic, it is understood that soaking is part of a carb rebuild.  I disassembled all 4 carbs and soaked them individually for 24+ hours each in carb cleaner.  The carbs sat up for 8 years, but they only had a little gas in the float bowls.  They were removed from the engine; flipped upside down and shaken to drain then, but the PO didn't remove the float bowls or loosed the bowl drain screws so a small amount of fuel remained in the bowls. He then stored them in a box.
Once again though, a plugged pilot circuit would cause a lean running condition - not a rich condition.  Go back and look closely at the spark plug photos - black fluffy carbon after 8 or 9 miles of riding is symptom of a rich running condition.

[Tuneforkfreak]

Even though  I was incorrect about the pilot/lean issue, my point still stands, the parts in those carbs worked before and you yourself rode the bike with those parts so they have to be correct. Thus the issue still remains but I seriously doubt it has anything to do with improper emulsion tubes unless the P/O switched those carbs out while in its storage days?  So what would cause a carb to draw more fuel through the pilot circuit? Is the pilot screw the only variable that can alter the amount of fuel being pulled to change rich /lean conditions or do air jets play into that as well?

[a.graham52]

Here's my feel... unless you rode the bike with 1/4 throttle or less 90% of the time, then your plugs are not a good indication of pilot circuit. What u discribe one "paper" is a plugged pilot circuit. If any of the four circuits is plugged, then no where near enough fuel will get through and a massive amount of power in that range will be lost. You will get popping, you will get stumbles. Just Crack that choke open in small increments while riding. This will make up for a lack of fuel if there is one and it will run smooth in that area. However with the choke on you may run worse in other areas and is normal for what your doing. Just a little choke at a time until you notice a different for better or worse.

[Pat Conlon]

The question remains: If you have flat bottom slides (typical on early FJ's) and you have the shrouded type emulsion tubes, you will have rich running problems.
The shrouded tubes look like this:


These above emulsion tubes should be only used with the curved bottom slides.
Using these shrouded emulsion tubes on flat bottom slides, the shroud sticks up and holds the slide up (and thus the needle).
The shrouded tubes are designed for curved bottom slides.

Check this out and let us know.

[oldktmdude]

The question remains: If you have flat bottom slides (typical on early FJ's) and you have the shrouded type emulsion tubes, you will have rich running problems.
The shrouded tubes look like this:


These above emulsion tubes should be only used with the curved bottom slides.
Using these shrouded emulsion tubes on flat bottom slides, the shroud sticks up and holds the slide up (and thus the needle).
The shrouded tubes are designed for curved bottom slides.

Check this out and let us know.

I will apologise in advance for hijacking this thread but my question relates to the above information. The '85 FJ I'm currently working on, has choke issues.
It starts on the choke but after about 20-30 seconds running on it, stalls, it will re-start with a little throttle, choke off but will not idle until fully warmed. Any further use of the choke just stalls it. The carbs are the early model flat bottom slide version but have been fitted with new cut away slides. Who ever did the rebuild left the original flat top emulsion tubes in it. What effect, if any, would this have on tuning the carbs, especially the choke function? I suspect it won't be effecting it but am open to views from others with more experience than me.
   Regards, Pete.

[Tuneforkfreak]

Let me ask you this, when you apply the choke does the bike raise in RPMS relative to the choke position? Full choke for me is about 3K RPM or so, but sometimes it stumbles on that much fuel when cold and needs a blip of throttle to kick it up to high idle. Further more my bike dont really like much more than about 20 or 30 seconds of full choke, I have to reduce it down to about 1/8 to let it warm up. I actually prefer to shut the choke off and just hold the throttle at 2 or 3 K rpm until it warms, I can tell when its ready as it will sit at idle and purr like a kitten. Mine is cold hearted for sure.

[Tuneforkfreak]

After reading Pats post I'm starting to raise eyebrows about my own carbs and rebuild. My bike was completely raped of parts as it was in fact purchased as a parts bike to serve two other FJ's. I know one of those bikes was an older red and white model and I think the original carbs from my 90 went onto that bike. Heck I might need to tear my carbs back down and have a closer look. Shoot depending on the cost I might send them to Randy as well, pretty confusing to say the least when looking at those emulsion tubes, I don't have a clue what you guys are talking about when you say curves and shrouds and so on. But that's why I'm here, to learn how to use a 30 year old bike and be able to have it get me back home.

[Pat Conlon]

Only the very early FJ1100's had the flat bottom slides. I recall Randy mentioning that about 1/2 the way thru the 1985 production run, Yamaha went over to the curved bottom Mikuni's.....so for most folks, this is not an issue, just us early FJ owners.

You can see without removing the carbs. Pull the air filter off....see the slides? The bottoms will be curved, or flat. lf they are curved, you're fine.
If you lift the slides you will see the tip of the shroud poking thru into the throat of the carb, that's why the slides should be curved.
The tip of the shroud of the emulsion tube will hold up the flat bottom slides.

[Pat Conlon]

     The carbs are the early model flat bottom slide version but have been fitted with new cut away slides. ....

Hey Pete, Are you  *absolutely sure* you have the flat bottom carbs with curved bottom slides?

I understand that is a no-no. Putting different slides into the bore of a carb. The slides are closely mated to the bore. That's why when rebuilding you need to track which slides come out of which carb, just so you are sure not to mix them up and put different slides into different carbs...

....let alone putting completely differently designed slides (curved bottom) into a set of carbs that were designed for flat bottom slides.

Who ever did the rebuild left the original flat top emulsion tubes in it.

Well, you could try using the proper shrouded emulsion tubes with your curved bottom slides....see if that helps.

What effect, if any, would this have on tuning the carbs, especially the choke function? I suspect it won't be effecting it but am open to views from others with more experience than me.

If this is the case, you are in uncharted waters. Along with the difference in the design of the slides (curved vs. flat) and the issue of slide vs carb bore mating, how about, what's different internally (in the body of the carbs) between the flat bottom carbs and the curved bottom carbs?
  I don't know the answer to that question.

[ergojack]

My bike has flat bottom slides and un-shrouded emulsion tubes (See attached pic).
I'm just not sure if I have some wear in the tubes that I can't see.   

[FJ_Hooligan]

I thought the flat-bottom slides used a really think jet needle? 

Are your needles adjustable?  If so then they may not be correct (aftermarket?).

Also, if they are too small, it will run really rich.

[oldktmdude]

Hey Pete, Are you  *absolutely sure* you have the flat bottom carbs with curved bottom slides?
If this is the case, you are in uncharted waters. Along with the difference in the design of the slides (curved vs. flat) and the issue of slide vs carb bore mating, how about, what's different internally (in the body of the carbs) between the flat bottom carbs and the curved bottom carbs?
  I don't know the answer to that question.

Pat, I don't know the history of the bike, my conclusion was drawn from the fact that the carb bodies look to be 30+ years old, emulsion tubes are also old looking but the slides and diaphragms look fairly new, no pin holes, rubber still very soft and new looking and the slides are still very shiny. The bike was run on a dyno 3 weeks ago and the air/fuel ratio was fairly good throughout the rev range but he advised to fit 1 size larger mains. The main issue we are having (not my bike) is the choke problem. It will not accept any choke application after the initial 20-30 seconds of full choke and will not idle until fully warmed up.
PS. Pat, please feel free to shift this discussion to a new thread if you want. I have not intended to hijack the original thread but thought the discussion of mismatched slides and emulsion tubes may be of help to others.
   Regards, Pete.

[ergojack]

P.O. put in jet kits very early on. It had run for years on the existing carb setup.  The needles are adjustable - 2nd groove down from the top.

[Pat Conlon]

Ok, so you have the correct emulsion tubes for your slides....cross that off the list 

Hooli has a sharp eye and good point (as usual)
That does not look like the stock Mikuni needle, it's too thin. I think you have a Dyno Jet needle.
Dyno jet kits are well and good but, they use a proprietary needle (thinner) with their proprietary jets.
You can't mix and match Mikuni components with Dyno jet components.

If you are using Mikuni jets (you are) you should use a thicker Mikuni (adjustable) needle.

Also, check the slide springs you have.... Chances are if you have the Dyno Jet needles, you also have the Dyno Jet springs
The Mikuni slide spring is stronger, it takes more vacuum to raise the slides, perfect for the larger Mikuni jets.
The Dyno Jet slide springs are softer, the slides pop up faster, again, it's fine with the Dyno Jet kit components but not so good with Mikuni components.

Don't mix and match Mikuni goodies with Dyno Jet goodies.