carb issues

[Pat Conlon]

Yes, I can tell by your correct terminology and diagnostic steps you know your stuff.

I had a problem with the oil rings on the 82mm Wiseco pistons on my bike. Under high vacuum, (closed throttle high rpm) the oil rings would not seal. Vacuum would pull the oil up past the rings. The plugs would foul, and for some reason especially #3.
The carbon buildup was excessive.

Only since I switched to the 83mm Ross pistons, did the problem go away.

[ergojack]

The fouling is clearly rich fuel mixture.  It is very black and fluffy.
There is no hint of any oil at all.  Also, on the 2nd test, #1,2 & 3
completely carbon fouled after only 9 miles of riding.
I wasn't sure I would make it home. 
These engine mods were made at 18,000 miles and it has run great
for 18,000+ more. There is no blue smoke from the exhaust that I can see.

[a.graham52]

I'm surprised you can run with your choke off at 10 miles. My 86 needs at least that before it runs 100% right. Without choke and cold it will run like arse at 1/4 or less.

[ergojack]

I'm in South Carolina, so even when it's cold, it's not really cold. You're in Maine. Isn't that about 20 miles from the artic circle?
Were freezing our butts off when it gets down to 30.  I spend some time in Maine one summer and nearly froze to death at night.

With the #40 pilots, this bike will crank right up. It pops, spits, farts and backfires for 3 or 4 minutes then it will idle on the 2nd
step of the choke. 3 or 4 more minutes and it will pull away OK But, it still runs poorly below 1/4 throttle.

[FJ_Hooligan]

I know you're running rich, but that "pops, spits, farts and backfires" description is a classic indication of clogged idle circuit(s).

I've got a DJ carb kit with 40 idle jets and 140 (may be 144, I forget) air pilots.  It cranks right up and I can turn the choke off at about 1 minute and drive away.

In the winter, I drive away with 1/2 choke for about a mile then it's off.

[Pat Conlon]

Take a look at the discussion by Factory Pro on worn needle jet orifices.
They say,  "if lowering your fuel level 1mm does not fix your rich condition, check your needle jets for wear. It's not that uncommon..."

Scroll down: http://www.factorypro.com/jets,needles,emulsion_tubes,pilot_jets.htm

[balky1]

Hey, while reading these few last posts, your probs reminded me of mine from last year. I had a great running bike also which leaked fuel in the crankcase. To shorten the story, I removed the carbs to change seats and needles and after that it never ran good with sputtering, backfires etc. I tried tons of things I've read here on the forum, nothing helped. It also had the lover RPM range problem. So I even changed the pilots with new ones since one of mine was stripped so I thought that could be it, but didn't help. I got to a point where I drove the bike to a more experienced mechanic who, of course, found the prob immediately.
One of the rubber manifolds was hard and didn't seal well anymore after I initially removed the carbs. I even did the start spray test which showed me no evidence of non-sealing manifolds, but the guy knew it was it, changed it and I was good to go.
My point is, even if the manifolds look good to you without cracks, they could still be the thing to blame.

Ivan

[jscgdunn]

I'm surprised you can run with your choke off at 10 miles. My 86 needs at least that before it runs 100% right. Without choke and cold it will run like arse at 1/4 or less.

Usually choke to start up when cold....10-15 seconds choke off...and runs fine.   That being said I never push it hard or go past 3500 RPM for the first 5 minutes or so anyway.

Jeff

[ergojack]

I don't feel that my choke issues have anything to do with this running rich problem.  I don't ride the bike in 90 degree summer with the choke on.  It can't be a plugged jet, that would cause a lean running problem (unless it was an air pilot jet) However, all jets, passages, etc. are clear.  There is no pitting in the bore for the needle seats.  I have removed the emulsion tubes again and re-checked.  (see tube pics) I can't see any oval shaped wear, or any other wear at all but I am old & don't see as well anymore.  I didn't get very good straight in photos, so some look oval shaped due to the angle of the camera.  They all look consistent with each other.  These tubes do make the most sense as a cause of the problem. I would just replace them all, but at $30 each, I need to be sure. I don't mind spending the money if I could have a high degree of confidence that it would solve the problem.    Randy, could I send these tubes to you for an opinion?

[racerrad8]

Randy, could I send these tubes to you for an opinion?

Yes, but make sure they are attached to the carbs.

The reason I say that is, it looks like them are probably the wrong emulsion tubes. It is hard to tell from the photos but the tubes appear to be the shrouded version. If those are installed into the flat bottom slide carbs it will never run right. Then if someone put the wrong needle that is a problem as well.

The bike sat up in a garage, partially disassembled for 8 years.  Some gas was inadvertently left in the removed carbs, but the gas tank was drained dry. I thoroughly cleaned the carbs and installed all new O-rings and float needles a few months ago when I bought it.  It has had this low speed running issue since I got the bike running.  


This bike was running great when the P.O. stored it.

I think it is time for a set of skilled eyes to go through them and see what is going on.

Randy - RPM

[ergojack]

Randy,
Please put the ship to address in here and I will re-assemble and send the carbs to you. 
Should I leave them ganged, or separate them? 

[racerrad8]

RPM
410 South 5th Av
Oakdale, Ca 95361

Leave the all together please.

Randy - RPM

[Tuneforkfreak]

I hate to say it but I have seen times when people have been lees than accurate in their description when selling something. Heck the P/O could have been fighting the same demons due to wrong parts installed and just didnt say anything thinking you'd stumble right onto the problem and fix it. My carbs where Frankensteined  when i got my bike, I had to get several things to complete these carbs back to stock.

[Pat Conlon]

The problem is *nobody* knows about the difference between the needle jets (aka emulsion tubes, jet nozzles, etc) for the early FJ flat bottom slide CV36 Mikuni's and the later curved bottom slide Mikuni's.

Nobody but Randy at RPM that is...... 

Order a set of new emulsion tubes from the experts at Factory Pro or from you local Yamaha dealer, you will get the shrouded version. Then you will wonder why your flat bottom carbs run like shit.

[ergojack]

Randy,
I'll get these back together and headed your way. It might be the weekend before I get them boxed up. 

I do have a long history with the P.O. of about 20 years.  I had actually ridden this bike many times prior 
to its being stored.  Since it has been sitting up for so long, he doesn't remember much. It may have had
some issues that he just doesn't recall.  The P.O. didn't even have the bike up for sell. I offered to buy it.
I just hated to see a classic old bike sitting in a garage unused. What's the old saying about no good deed
goes unpunished...