&*%##@! carbs

[BA80]

I normally don't have a problem with carbs but this set of late (80) carbs has got me pulling my hair.

I've been screwing with them for some time now.

They have all stock Mikuni jets, I was having a flooding issue when parked but replaced the float needles and got that taken care of.

It seems no matter what I do it will load up at stops after the engine is warmed up. Running down the road it's fine unless I let the RPMs get below around 3K and then it stumbles all over itself until it clears out. And I need to rev the engine pretty high to get rolling or it will die.

I've lowered float levels several times, moved them up and down and all that does is screw with cruising and WOT.

Any ideas?

I'm fixin' to put a set of 79 carbs on there and be done with it.

[werdna80]

pilot jet plugs still there?

[motoman]

I normally don't have a problem with carbs but this set of late (80) carbs has got me pulling my hair.

I've been screwing with them for some time now.

They have all stock Mikuni jets, I was having a flooding issue when parked but replaced the float needles and got that taken care of.

It seems no matter what I do it will load up at stops after the engine is warmed up. Running down the road it's fine unless I let the RPMs get below around 3K and then it stumbles all over itself until it clears out. And I need to rev the engine pretty high to get rolling or it will die.

I've lowered float levels several times, moved them up and down and all that does is screw with cruising and WOT.

Any ideas?

I'm fixin' to put a set of 79 carbs on there and be done with it.

fuel levels in bowls possibly a bit high(or way to low WILL cause same snenario).
Idle mixture screws out to far(highest in. vacuum instead of lean-drop method).
Both just a couple ideas, as the later carbs are REALLY finiky concerning above ideas....BTDT more than once.
Realize the 80 carbs are a PITA for checking IDLING fuel levels( not having side-bowl bleeder screws and float bowl drains) as opposed to the 81' and XJ series carbs.
Your second sentence is DEFINITELY to rich for the idle circuit, and either of two suggestions is normally the cause............and yes, to low a running fuel level WILL make it run rich in idle circuit, as I found out after getting home from the Canon City rally two summers ago. Think of it as 'blowing across top of straw in a Full glass of water as opposed to glass being only half full. After riding back home, checked the idling fuel bowl fuel levels.....6-7mm instead of the needed 3-4mm....OMG! In other words, a higher venturi velocity was needed to draw the needed fuel up thru pick-up tube, and when it did come up thru pick-up tube, it is too much fuel at once!.......corrected fuel bowl's IDLING fuel level(re-set idle mixtures and re-synced), and now it runs perfectly thru any and all rpm ranges like it did when I bought bike new back in 81'!

[dbeardslee]

Might check to make sure the slide's are properly assembled and that it has the correct needles at the correct height. IIRC there's a ring on the late model carb slides that can goober up the works if they're not installed correctly. One notch too low on the needles (making the needles one notch too high) will give you a bad stumble in the 3-4k rpm range. JAT

[motoman]

Might check to make sure the slide's are properly assembled and that it has the correct needles at the correct height. IIRC there's a ring on the late model carb slides that can goober up the works if they're not installed correctly. One notch too low on the needles (making the needles one notch too high) will give you a bad stumble in the 3-4k rpm range. JAT

Nope....NA for any metering rod clippy slots on 80-XJ models.

BTW, I also suggest you follow BA80's scenario, and a 'fix' he'll find(early model carbs being swapped in don't count).

[BA80]

pilot jet plugs still there?

These carbs don't have the transfer galley.

fuel levels in bowls possibly a bit high(or way to low WILL cause same snenario).
Idle mixture screws out to far(highest in. vacuum instead of lean-drop method).
Both just a couple ideas, as the later carbs are REALLY finiky concerning above ideas....BTDT more than once.
Realize the 80 carbs are a PITA for checking IDLING fuel levels( not having side-bowl bleeder screws and float bowl drains) as opposed to the 81' and XJ series carbs.
Your second sentence is DEFINITELY to rich for the idle circuit, and either of two suggestions is normally the cause............and yes, to low a running fuel level WILL make it run rich in idle circuit, as I found out after getting home from the Canon City rally two summers ago. Think of it as 'blowing across top of straw in a Full glass of water as opposed to glass being only half full. After riding back home, checked the idling fuel bowl fuel levels.....6-7mm instead of the needed 3-4mm....OMG! In other words, a higher venturi velocity was needed to draw the needed fuel up thru pick-up tube, and when it did come up thru pick-up tube, it is too much fuel at once!.......corrected fuel bowl's IDLING fuel level(re-set idle mixtures and re-synced), and now it runs perfectly thru any and all rpm ranges like it did when I bought bike new back in 81'!

I've played with the float levels as I stated, that only affects performance off idle. That should answer all that except the mix screws and I've adjusted on them also. I've heard your straw blow job story before. I understand the physics of carb operation. That's why I'm confused.

Might check to make sure the slide's are properly assembled and that it has the correct needles at the correct height. IIRC there's a ring on the late model carb slides that can goober up the works if they're not installed correctly. One notch too low on the needles (making the needles one notch too high) will give you a bad stumble in the 3-4k rpm range. JAT

The slides and needles have absolutely nothing to do with idle, but, they are correct.

[dbeardslee]

Nope....NA for any metering rod clippy slots on 80-XJ models.

You don't need clippy slots to booger up late model slides - just get that plastic donut on the wrong side of the clip and I can pretty much guarantee you problems. Which is why I say it's a good idea to make sure the slides are properly assembled.

[kboehringer]

What changes once it's hot?

..... It seems no matter what I do it will load up at stops after the engine is warmed up..

Greg,
This seems to be a key piece of information "AFTER WARMED UP".

What COULD change on a machine once it is hot that would cause "loading up" that did not exist when it was cold?

I supposed to be the stupid new guy here but my Dead Duck was running like poop after warm up at low RPM and the idle was all over the place. We found the battery was bad (thanks Mike). With a good battery it runs fine.

Just a thought from the newish guy.... Let's start thinking WHAT CHANGES ONCE IT'S HOT? Would not seem to be carbs to me.........

Sincerely,
KURT

[BA80]

I was thinking along those lines too but I checked the pick up coils and they OHM out at 730 - 750 on the 2000 setting. That's about right. And, I checked all the connections. Put new resistor caps on and trimmed the wires.

I'm thinking it's carbs because 1-3-4 plugs are sooty black, #3 is a bit rich but the electrode is tan. Not consistent with an electrical problem.

[dbeardslee]

What size jets are installed?

[BA80]

They have all stock Mikuni jets

That'd be 110 mains and 42.5 pilots.

[red bandit]

It's been several years ago but I had a set of carbs I was bringing back to life....or trying to. Had them apart many times. Had all the right jets. Could never get it to run worth a crap. Turns out someone had drilled out the pilot jets and fubared the bodies. Something to look for??? Does the idle mixture hole in the throat look right size? How about the 3 little holes close by?

[dbeardslee]

I had a set of black mikes coils that crapped out on me, and they did a really good impersonation of a carb problem. So good that I went into the carbs four or five times before I finally decided that it had to be something else. Have you checked the primary and secondary resistances on your ignition coils when they're hot?

If you've got another set of known good carbs I think I'd swap 'em out just to see if it made the problem go away. That'll either confirm that the carbs are the problem, or send you in a different direction.

[BA80]

It's been several years ago but I had a set of carbs I was bringing back to life....or trying to. Had them apart many times. Had all the right jets. Could never get it to run worth a crap. Turns out someone had drilled out the pilot jets and fubared the bodies. Something to look for??? Does the idle mixture hole in the throat look right size? How about the 3 little holes close by?

I've been into them several times and the idle mix screws are all fine, those aren't really an issue on the later carbs anyway. The early ones had the tips of the screws that broke off, the later design didn't have that issue.

Yes, the 3 mid range holes are always a cleaning priority for me.

The jets are some I had that were removed from parts carbs and inspected quite well for damage and to make sure they had the square in a square genuine Mikuni markings.

I had a set of black mikes coils that crapped out on me, and they did a really good impersonation of a carb problem. So good that I went into the carbs four or five times before I finally decided that it had to be something else. Have you checked the primary and secondary resistances on your ignition coils when they're hot?

If you've got another set of known good carbs I think I'd swap 'em out just to see if it made the problem go away. That'll either confirm that the carbs are the problem, or send you in a different direction.

I've been thinking about that too. I have a couple other banks of carbs but they are of early design. I may put a set on there anyway. I like the early carbs better. I have several sets of coils too, both 1.5 OHM and 3 OHM.

[motoman]

Greg,
This seems to be a key piece of information "AFTER WARMED UP".

What COULD change on a machine once it is hot that would cause "loading up" that did not exist when it was cold?

I supposed to be the stupid new guy here but my Dead Duck was running like poop after warm up at low RPM and the idle was all over the place. We found the battery was bad (thanks Mike). With a good battery it runs fine.

Just a thought from the newish guy.... Let's start thinking WHAT CHANGES ONCE IT'S HOT? Would not seem to be carbs to me.........

Sincerely,
KURT

fuel/air mixture is TOO rich.........and I believe BA80 realizes that, and is just trying to sort and make eliminations as to why.