Carb trouble

[Cowsert_C]

Hey guys, I've been dealing with a fussy set of carbs on my 81 special and can't seem to tame them. I'm a newbie when it comes to this stuff as this is my first bike. I got it on a whim and realized I may be over my head trying to start with a 4 cylinder.

I've cleaned and rebuilt the carbs twice now. The previous owner took the airbox off and put pods on, which I can't stand. I'll be replacing those very soon with a breadbox filter. I know the factory airbox is ideal, but due to budgeting the breadbox was in the right place at the right time.

To compensate for the pods, I put 45 pilots and 125 mains. New fuel mixture screws, seats, needles and gaskets all around. New manifold boots. The problem is this. I have a high idle, 4K-5k with no choke and 1k-2k idle with full choke. The Rpms also stay high when the throttle is released and very slowly come down. I have made sure the throttle cable is not sticking anywhere and that there are no vacuum leaks. I have done a bench sync, but not a vacuum, which I know is what I'm mostly going to be told. I'm still trying to find someone around with the tool to do it that way I don't get charged shop price. My idle mixture screws are set at 1 1/4 turn out.

Also, cylinder 2 isn't firing and there's some fuel blowback through the no. 2 carb.

I would appreciate any and all help. I've combed through the forums looking for answers, but I decided to go ahead and ask directly.

[JeffH]

I'd start with this #2 not firing issue. So your saying the bike is idling at 4,000 rpm and if you spray water on #2 exhaust that its a cold pipe? Or warm? Or eventually gets hot?

Don't waste time on anything else till you get that issue resolved. Bench sync is more than adequate. I rode my XS for 2 years with just a bench sync and when I finally did a proper sync any improvement in cold start or hot start or driving was extremely minor. If its got a problem a vac sync is about worthless. #1 identify the problem.

How long had the bike been sitting before you got it? Did it idle when you got it? Using Genuine Mukuni carb parts? Where did you get the jets and parts?

So is #2 float maybe hung up? Have you carefully checked the float to bowl gasket clearance. It the #2 wire cap corroded or not seated? Some guys have luck whacking the carbs with a leather mallet to loosen stuck carb but DON'T do that till a guru advises about other issues first.

Give us a little more info about this #2. If all 4 ain't rowing to start with then your just chasing your tail and the rest is just distractions.

Jeff

[Cowsert_C]

I'd start with this #2 not firing issue. So your saying the bike is idling at 4,000 rpm and if you spray water on #2 exhaust that its a cold pipe? Or warm? Or eventually gets hot?

Don't waste time on anything else till you get that issue resolved. Bench sync is more than adequate. I rode my XS for 2 years with just a bench sync and when I finally did a proper sync any improvement in cold start or hot start or driving was extremely minor. If its got a problem a vac sync is about worthless. #1 identify the problem.

So is #2 float maybe hung up? Have you carefully checked the float to bowl gasket clearance. It the #2 wire cap corroded or not seated? Some guys have luck whacking the carbs with a leather mallet to loosen stuck carb but DON'T do that till a guru advises about other issues first.

Give us a little more info about this #2. If all 4 ain't rowing to start with then your just chasing your tail and the rest is just distractions.

Jeff

Thanks for the reply. The pipe isn't entirely cold but not as hot as the other 3. I can hold my hand on it, albeit uncomfortable. I just attributed this to the residual heat coming from the other 3. I'm more than certain the float isn't stuck. I had the carbs off, and taken apart on my table for about a week. Everything that needs to move does. #2 was firing when I first got the bike running, around April, but hadn't for about a month prior to this. I haven't checked the float to bowl gasket clearance, are you referring to float height?

The bike wasn't running when I got it, it sat for roughly 4 years. I used genuine mikuni parts from an authorized seller on Amazon.

When I took the float bowl off #2, the press in button over the primary jet was at the bottom of the bowl, I thought that this would be the issue, but since the rebuild it appears not to be.


The spark cap is not corroded and I get good spark from it. As a cautionary measure, I trimmed 1/4 inch off and put the cap back on to no avail. Should I begin to suspect the pickup coil?

I also forgot to mention that I bypassed the octy valve by capping the prime and going straight from reserve to carb with a inline filter and fuel shut off, I don't know if that would make a difference or not though.

[TopCatGr58]

Hey there,

Another thing we need to know is what parts did you put in besides the jets, and are the jets GENUINE MIKUNI, or generic/K&L brand?? The K&L brand are junk, not metered to the same amount as Mikuni, and so the Pilots may be excessively rich?

With the #2 cylinder not firing....and that carb leaking can cause a flooded fouled plug. The 81 has the newer plastic style floats, they are less apt to leak and sink, so as was suggested, ensure that it's not hanging on the new bowl gaskets.

ALSO, did you replace the float needles/seats? Again, generic K&L or Mikuni? Also the float seat requires an O-ring, and if not careful, it can get damaged when reseating, as well as shrink/leak if OLD and not replaced.

Have you verified that you have spark on #2 cylinder??

T.C.

[JeffH]

A few things:

Thanks for the reply. The pipe isn't entirely cold but not as hot as the other 3. I can hold my hand on it, albeit uncomfortable. Get a squirt bottle and fill it with water. Start bike and see who drips and who steams. Keep notes. just attributed this to the residual heat coming from the other 3. I'm more than certain the float isn't stuck. I had the carbs off, and taken apart on my table for about a week. Everything that needs to move does. #2 was firing when I first got the bike running, around April, but hadn't for about a month prior to this. I haven't checked the float to bowl gasket clearance, are you referring to float height? no not the measured height the side clearance. If float is hanging up on the bowl gasket it will do as you are describing.

The bike wasn't running when I got it, it sat for roughly 4 years. I used genuine mikuni parts from an authorized seller on Amazon.

When I took the float bowl off #2, the press in button over the primary jet was at the bottom of the bowl, I thought that this would be the issue, but since the rebuild it appears not to be.


The spark cap is not corroded and I get good spark from it. As a cautionary measure, I trimmed 1/4 inch off and put the cap back on to no avail. Should I begin to suspect the pickup coil? no not likely since that comes in 2's. Unless 2 pipes not hot.

I also forgot to mention that I bypassed the octy valve by capping the prime and going straight from reserve to carb with a inline filter and fuel shut off, I don't know if that would make a difference or not though. File feeds the T so 1&2 get fuel down that same shared T.

Sorry on cell phone so the bold & underline are tough to fix.

BTW: is your idle adjuster screw too high opening the butterflies? Or is that adjuster tab not even touching the carb tab there between 3&4?. Sorry on cell phone so can't see what I'm typing too well.

[TopCatGr58]

Just saw your post after making mine.

Okay, the 81's do NOT use the pilot jet tower rubber caps, take them all OFF! The carbs and pilot circuit needs to feed directly from the float bowl....it does NOT get any from the main jet tower since there isn't a sharing tunnel between the towers....ON 81 carbs. Now if someone put on 80 carbs which were known to SOMETIMES have that sharing tunnel, then that could be a different story.

Did you do a compression test on the bike?? Sitting for 4 years can get the piston rings to stick, hopefully you read about using some MMO in the oil to help remove sludge/varnish and unstick piston rings to allow them to reseat better once the bike is running again. So...once you get it firing properly on #2, then you'll want to try to put a few hundreds miles to help reseat the rings, then you'll be able to perform a better synch.

T.C.

[Cowsert_C]

Just saw your post after making mine.

Okay, the 81's do NOT use the pilot jet tower rubber caps, take them all OFF! The carbs and pilot circuit needs to feed directly from the float bowl....it does NOT get any from the main jet tower since there isn't a sharing tunnel between the towers....ON 81 carbs. Now if someone put on 80 carbs which were known to SOMETIMES have that sharing tunnel, then that could be a different story.

Did you do a compression test on the bike?? Sitting for 4 years can get the piston rings to stick, hopefully you read about using some MMO in the oil to help remove sludge/varnish and unstick piston rings to allow them to reseat better once the bike is running again. So...once you get it firing properly on #2, then you'll want to try to put a few hundreds miles to help reseat the rings, then you'll be able to perform a better synch.

T.C.

The press in buttons in the primary jet tower I was referencing are metal with a pinhole in the middle, not rubber. I've checked that these holes are all clear. I did a compression test and was reading 130+/- 2psi across all 4. Since I got the bike running, I've put 112 miles on it, this is only a recent problem. I went out of town for a month and everything seemed to be wrong again when I got back.

[JeffH]

The press in buttons in the primary jet tower I was referencing are metal with a pinhole in the middle, not rubber. I've checked that these holes are all clear. I did a compression test and was reading 130+/- 2psi across all 4. Since I got the bike running, I've put 112 miles on it, this is only a recent problem. I went out of town for a month and everything seemed to be wrong again when I got back.

So for 112 miles over a few On-Off Cold-Hot-Run cycles it ran adequately. Idle not bad or hanging too high? No popping or bucking? Pretty smooth across the powerband ?

So you parked it a month. On the side stand? Fuel on or off? If you rode in running good and parked it you might have stuck float or some debris junk in the carb. Fuel filter is good but is tank rusty inside? Fuel filter even good ones won't help much in keeping that fine rust powder out of the carbs if you have a badly rusted gas tank inside.

Should be able to deduce the smoking gun from the info. If it was not bad for 112 miles then its like what goes wrong when bike sits a month. Again. Sorry this cell phone makes it tough to type.

Jeff

[Cowsert_C]

So for 112 miles over a few On-Off Cold-Hot-Run cycles it ran adequately. Idle not bad or hanging too high? No popping or bucking? Pretty smooth across the powerband ?

So you parked it a month. On the side stand? Fuel on or off? If you rode in running good and parked it you might have stuck float or some debris junk in the carb. Fuel filter is good but is tank rusty inside? Fuel filter even good ones won't help much in keeping that fine rust powder out of the carbs if you have a badly rusted gas tank inside.

Jeff

The idle was pretty constant around 1100rpms. I had a backfire on deceleration and a bog in the low end. From 1k it stumbled to get to 3k, but from 3k to 8k it was very responsive. I did the whole 3 step lining kit when I first got the bike as a precaution. I left the tank dry and the the carbs blown out. I had it on the side stand with a cover. One day the wind caught in the cover and blew the bike into a nice soft Kia (purchased that day). That's a great surveillance video. I've had the carb apart and cleaned again just this week when I re-jetted to compensate for the pods.

Sorry if I'm repeating myself, I just want to cover all the bases. I'll check the float clearance in the morning and hope that's the issue.

[JeffH]

The idle was pretty constant around 1100rpms. I had a backfire on deceleration and a bog in the low end. From 1k it stumbled to get to 3k, but from 3k to 8k it was very responsive. I did the whole 3 step lining kit when I first got the bike as a precaution. I left the tank dry and the the carbs blown out. I had it on the side stand with a cover. One day the wind caught in the cover and blew the bike into a nice soft Kia (purchased that day). That's a great surveillance video. I've had the carb apart and cleaned again just this week when I re-jetted to compensate for the pods.

Sorry if I'm repeating myself, I just want to cover all the bases. I'll check the float clearance in the morning and hope that's the issue.

I'd wait for a pods guru to chime in. Seems it ran but not well, but ridable then you re-jetted for the pods and now it doesn't run at all and can't ride it like it is. Though it sounds like your original pilot jets or the passage ways were clogged but once you got on the mains it ran pretty OK or at least good enough.

This maybe gets into the what mufflers you got. Seems the pods guys struggle and its a real crap shoot to get things dialed in but the guru guys seem to be able to work it out with time, money, knowledge & patients. I just like to ride and stick with stock parts and stock setup that really rips and is reliable. Dialogue has maybe helped with a few ideas. BTW that is a dead blow hammer. I've seen these carbs with stuck floats get unstuck with a good whack that I'd never dare to do.

So it seems with tank liner any rust issue isn't an impact to this problem. So in that 112 miles was different 1st 20 vs middle 80 vs the 12 miles home? Any clues from that?
Again pods are tempramental beasts. Let see what the POds Carb -Muffler gurus suggest.

I think we now have a better understanding of the chronology of events. That is critical to link timeline to what problems you are having and how you got step by step to this juncture. Knowing you had actually ridden 112 miles not running great but maybe fine on mains but not on pilots really is key info for us.

Good luck
Jeff

[JeffH]

BTW: you sure you got the vac lines in the right places and things capped off properly?

Riding 112 miles albiet poorly on the pilots to re-jetting and now idles at 4,000 with cold #2 could be a compound problem. Unless that bench sync you did got whacked or vac line open.

Just tossing out ideas. Gotta be an answer in all this chronology of events and work and reassembly.

Jeff

[cajun31]

Just tossing ideas

be sure to check the wires inside the left side cover on the engine. from what you are describing you may have a break in one of those wires. especially since you stated that it ran ok for 112 miles and after being parked it is now hit and miss.

[donebysunday]

Pods

What pod brand are those ?
At this point I'd be inclined to work without them.
Certain pods can cause you to be committed, do to irrational behavior they can bring out in your life ! };-)

Hey guys, I've been dealing with a fussy set of carbs on my 81 special and can't seem to tame them. I'm a newbie when it comes to this stuff as this is my first bike. I got it on a whim and realized I may be over my head trying to start with a 4 cylinder.

I've cleaned and rebuilt the carbs twice now. The previous owner took the airbox off and put pods on, which I can't stand. I'll be replacing those very soon with a breadbox filter. I know the factory airbox is ideal, but due to budgeting the breadbox was in the right place at the right time.

To compensate for the pods, I put 45 pilots and 125 mains. New fuel mixture screws, seats, needles and gaskets all around. New manifold boots. The problem is this. I have a high idle, 4K-5k with no choke and 1k-2k idle with full choke. The Rpms also stay high when the throttle is released and very slowly come down. I have made sure the throttle cable is not sticking anywhere and that there are no vacuum leaks. I have done a bench sync, but not a vacuum, which I know is what I'm mostly going to be told. I'm still trying to find someone around with the tool to do it that way I don't get charged shop price. My idle mixture screws are set at 1 1/4 turn out.

Also, cylinder 2 isn't firing and there's some fuel blowback through the no. 2 carb.

I would appreciate any and all help. I've combed through the forums looking for answers, but I decided to go ahead and ask directly.

[Cowsert_C]

What pod brand are those ?
At this point I'd be inclined to work without them.
Certain pods can cause you to be committed, do to irrational behavior they can bring out in your life ! };-)

They are K&N pods, but will be in the trash soon enough. I have a breadbox airbox on the way to replace them. I have been doing all the diagnostic tests without them on.

[mack]

Stumble

I'd be looking into the pilot ccts'. Just from the description of the 1-3K stumbling. Verify that that the main and pilot towers don't have the cross over tunnel on all four carbs. Someone may have bundled together a set from a pile of used carbs. Point is they may not all be the same year carb bodies.