pop, fart, sneeze....

o0norton0o said:

Well,....... the coil wire leads were just barely able to reach the plugs on the opposite sides, so I switched them as a test. The mid range miss didn't change sides, so I am assuming that the missfire can't be ignition related since the miss is clearly on one side and in the mid range RPM's only. The plugs are brand new. The battery measures 12.5 volts with the lights on...

So, here's where I am at:

When I disassemble the carb inner bodies, the side with the misfire slides in and out of the carb body easily. the other side is tight. I am thinking that maybe one carb wore faster than the other and I am experiencing a lean condition at midrange because of excessive carb body wear on one side. Both carbs are sleeved btw.

I don't see myself swapping carbs from one side to the other to check to see if the missfire changes sides with the swap, because the bleeders and adjustment screws would be on the wrong sides. I am going to check for air leaks on the manifold first, and then I am thinking about moving the carb needle up one notch on the missfire side to see if it eliminates the missfire.... If it does eliminate the missfire, could this be a workable solution or is it a temporary bodge?

thoughts and opinions, ??? thanks in advance for all the help...

Click to expand...

I would swap the whole carbs over, just as an experiment. It's a 10 minute job and will prove for sure, one way or another, if this is a carb issue. Further investigation can then be decided upon.

Also check carb slide mechanical sync. Maybe your cable nipple slipped in or out.

Fast Eddie said:

I would swap the whole carbs over, just as an experiment. It's a 10 minute job and will prove for sure, one way or another, if this is a carb issue. Further investigation can then be decided upon.

Click to expand...

Amals can't be swapped. The ticklers get in the way.

maylar said:

Fast Eddie said:

I would swap the whole carbs over, just as an experiment. It's a 10 minute job and will prove for sure, one way or another, if this is a carb issue. Further investigation can then be decided upon.

Click to expand...

Amals can't be swapped. The ticklers get in the way.

Click to expand...

No, but the bowls, floats, needles, slides, needle jets and all like stuff (except the bodies) can be swapped.

maylar said:

Fast Eddie said:

I would swap the whole carbs over, just as an experiment. It's a 10 minute job and will prove for sure, one way or another, if this is a carb issue. Further investigation can then be decided upon.

Click to expand...

Amals can't be swapped. The ticklers get in the way.

Click to expand...

Bugger !

pete.v said:

maylar said:

Fast Eddie said:

I would swap the whole carbs over, just as an experiment. It's a 10 minute job and will prove for sure, one way or another, if this is a carb issue. Further investigation can then be decided upon.

Click to expand...

Amals can't be swapped. The ticklers get in the way.

Click to expand...

No, but the bowls, floats, needles, slides, needle jets and all like stuff (except the bodies) can be swapped.

Click to expand...

...... but if the carbs are sleeved then the wear is on the carb body, so swapping all the guts between carbs still leaves the worn carb body on the same side it was on originally... I thought about swapping the guts to see if I could make the mid range missfire move to the other side, but I then I concluded that it's the body that would wear out, not the sleeved slider... Don't you think?

o0norton0o said:

[...... but if the carbs are sleeved then the wear is on the carb body, so swapping all the guts between carbs still leaves the worn carb body on the same side it was on originally... I thought about swapping the guts to see if I could make the mid range missfire move to the other side, but I then I concluded that it's the body that would wear out, not the sleeved slider... Don't you think?

Click to expand...

I hear ya. I am just saying that if you have to trouble shoot the carb, you can go a long way in this manner.

I sticky slide bore can be remedied with some Semi Chrome. Works a treat. Hit the high spots.

You say one of your carb slides is tight and one is loose. Do you mean that the tight one does slide freely but the other on slops around.
My bike has a hint of that problem. I fitted 2 new anodised slides, knowing the carb bodies were worn a bit. One carb is still not perfect and on inspection you could see the markings on the slide from the occasional back firing. It certainly does put stress that slide. A big problem that causes this is also lazy spark plugs. You could eliminate that by renewing both plugs and trying that.
Let us know what the back of the slides looks like. also does new plugs make a difference. You could fit iridium plugs as well.

Dereck

The tighter slide will stick at the top of it's travel path If I twist the grip that far. It moves nomally everywhere else and the cylinder on that side has no misfire issues.

The other side isn't clunking around by any means in the carb, but it slides out easily. The cylinder on that side is the one that is misfiring occasionally in the 4,000 rpm range...

To me, I see it as maybe the fuel float is sticking and the carb is running out of gas @ 4,000 rpms, or maybe the slightly looser fit of the carb center body on the "misfire side" makes the mixture go lean in the 4,000 rpm range so it misses...

how worn would a carb have to be to cause a lean condtion?? I don't think the looser carb is very loose, but it moves more easily than the side that doesn't misfire...

... As usual the answer is to go backwards and take it all apart again...

I may raise the carb needle on the misfire side to see if richening up the midrange cures the misfire..

How old are the needles and needle jets as they also become worn as well as the slides. Have you tried just swapping those from one side to the other.

If you are becoming tired of all the messing about with old carbs then give some thought to replacing them with a new pair. I put Premiers on mine and so avoid any such issues for a long time hopefully.

o0norton0o said:

how worn would a carb have to be to cause a lean condtion?? I don't think the looser carb is very loose, but it moves more easily than the side that doesn't misfire...

... As usual the answer is to go backwards and take it all apart again...

I may raise the carb needle on the misfire side to see if richening up the midrange cures the misfire..

Click to expand...

If the tight side may hang a little during operation (air flow having a greater effect on a sticky slide during running) it may cause more fuel to enter that side and upon acceleration, or deceleration, cause a small back file out the exhaust.

pete.v said:

o0norton0o said:

how worn would a carb have to be to cause a lean condtion?? I don't think the looser carb is very loose, but it moves more easily than the side that doesn't misfire...

... As usual the answer is to go backwards and take it all apart again...

I may raise the carb needle on the misfire side to see if richening up the midrange cures the misfire..

Click to expand...

If the tight side may hang a little during operation (air flow having a greater effect on a sticky slide during running) it may cause more fuel to enter that side and upon acceleration, or deceleration, cause a small back file out the exhaust.

Click to expand...

It's some kind of misfire. the bike idles fine, since I cleaned the idle circuits out. If I hold the throttle at 4000, it will intermittently misfire then pop out the exhaust pipe on one side only, then start working again for an unspecified number of seconds then happen again...

That's why I think it's something like the float sticking so the fuel hieght is fluctuating...

OR>.... all the crap I read about boyers not being able to cause a miss on one cylinder only is false.. I guess my next move is to swap the boyer plate for my spare, then the magnet rotor, then swap the boyer red box for my old black one.... Then I feel I am back to carbs for sure...

That tightness as the slide rides is usually distortion of the carb body. Not a good thing if it jams up at some time. My 850 did that once so I fitted a hose clip round the carb to put a bit of pressure against the ovality. Worked a treat. Eventually the clip was not needed when the carb found its shape again.[ not the most scientific method but by using a set of multigrips I was able to figure out what was going on ].

Dereck

wow, I've been digging through the whole mess... It's amazing that a bike that ran perfectly for the entire summer has now got a single cylinder occasional misfire... but I perservere...

So far what I have found:
even though I clipped both carb needles in the middle slot, when I pulled the carb bodies the second time I removed the center bodies, both needles were clipped on the bottom slot.. I ordered and changed both needle clips which looked worn.

I swapped the entire red boyer box for the black boyer box.

I fixed a shabby connection on one of the coil terminals.

I pulled the battery and every cell in the battery was low on water... (even though the battery tests 12.4 volts)

I actually pulled off both carbs. I put a new bowl on the misfire carb and cleaned it out and inspected it. I don't see any issues. I took the other carb off too. It has a sticky inner body that is impossible to leave as it is. I initially tryed some fine valve lapping paste, but the fit was to tight to even engage the center body. I washed it off both parts and took some 600 wet/dry paper and lightly removed the glossy sheen inside the carb body. I then put the inner body in and worked it back and forth. Working it back and forth polished the high spots back up so I could see where I needed to remove matterial. It took about 30 minutes of sanding with 600 paper and reinstalling the center body to check the fit as I worked the high spots down. Eventually It moved good enough so I left it alone and brake cleaned the whole carb and reinstalled it...

Right now I am charging the battery.

The amazing thing is that I have one issue that's intermittent so it's torturing me. If it would just outright fail, I would find it in minutes...

Next I am going to go inside the headlight and make sure there aren't any bare wires causing any headaches..

I also have to get new exhaust washers just to make sure that the popping isn't from an exhaust leak. If I get it cured completely, I hope to put the red box back on the bike.

o0norton0o said:

wow, I've been digging through the whole mess... It's amazing that a bike that ran perfectly for the entire summer has now got a single cylinder occasional misfire... but I persevere...

Click to expand...

I don't want to distract you from your quest, but misery loves company...

I did a rebuild on my 74 850 a few years ago. Bearings, cam, pistons, head work. Afterward I had a problem starting hot and with one cylinder wanting to misfire at idle. I've owned this thing since new, 40 years now, and I know it intimately. I have replaced the carbs with new Amals, replaced the ignition and coils with Trispark parts. Valves are adjusted correctly, compression and leakdown tests are perfect. 3 years later, still no joy. I've learned to live with it, though it drives me nuts.

I'm actually contemplating buying a single Mikuni kit, just to eliminate once and for all the possibility of a carb problem. Keep pressing on, eventually it'll be revealed.

maylar said:

o0norton0o said:

wow, I've been digging through the whole mess... It's amazing that a bike that ran perfectly for the entire summer has now got a single cylinder occasional misfire... but I persevere...

Click to expand...

I don't want to distract you from your quest, but misery loves company...

I did a rebuild on my 74 850 a few years ago. Bearings, cam, pistons, head work. Afterward I had a problem starting hot and with one cylinder wanting to misfire at idle. I've owned this thing since new, 40 years now, and I know it intimately. I have replaced the carbs with new Amals, replaced the ignition and coils with Trispark parts. Valves are adjusted correctly, compression and leakdown tests are perfect. 3 years later, still no joy. I've learned to live with it, though it drives me nuts.

I'm actually contemplating buying a single Mikuni kit, just to eliminate once and for all the possibility of a carb problem. Keep pressing on, eventually it'll be revealed.

Click to expand...

thanks for the sympathy...

Since it's confined to one cylinder, I am convinced it's a "timed" issue, but not necessarily timing. The things that are timing related to one cylinder or one cylinder related are:

1)crank and electrical rotor position. maybe I am rubbing the stator slightly at the right cylinder detonation position and getting a weird drop in voltage from it...

2) valve timing. maybe I have a bent valve stem or broken/weak valve spring that holds the right exhaust valve open sometimes so that cylinder misfires, then pops

3) amals. I'm pretty out of ideas here because I have checked and rechecked everything. I'm going to take the right carb off again today and go back over it for a 4th time...

4)coil. I have a dual coil and have swapped the leads terminal side feeds and plugs with no change in the misfire. I can't see how it could be the coil unless it shorts at certain RPM's, but that wouldn't explain why it's always on the right cylinder, so that is not a priority to swap out.

anyway... I am on to check it all, one thing at a time so I can, not just fix it, but figure out which thing was at fault.

Thank you everyone for all your helpful comments. It's great to have so many experienced people adding their experiences and expertise to help me get this figured out....

o0norton0o said:

maylar said:

o0norton0o said:

wow, I've been digging through the whole mess... It's amazing that a bike that ran perfectly for the entire summer has now got a single cylinder occasional misfire... but I persevere...

Click to expand...

I don't want to distract you from your quest, but misery loves company...

I did a rebuild on my 74 850 a few years ago. Bearings, cam, pistons, head work. Afterward I had a problem starting hot and with one cylinder wanting to misfire at idle. I've owned this thing since new, 40 years now, and I know it intimately. I have replaced the carbs with new Amals, replaced the ignition and coils with Trispark parts. Valves are adjusted correctly, compression and leakdown tests are perfect. 3 years later, still no joy. I've learned to live with it, though it drives me nuts.

I'm actually contemplating buying a single Mikuni kit, just to eliminate once and for all the possibility of a carb problem. Keep pressing on, eventually it'll be revealed.

Click to expand...

thanks for the sympathy...

Since it's confined to one cylinder, I am convinced it's a "timed" issue, but not necessarily timing. The things that are timing related to one cylinder or one cylinder related are:

1)crank and electrical rotor position. maybe I am rubbing the stator slightly at the right cylinder detonation position and getting a weird drop in voltage from it...

2) valve timing. maybe I have a bent valve stem or broken/weak valve spring that holds the right exhaust valve open sometimes so that cylinder misfires, then pops

3) amals. I'm pretty out of ideas here because I have checked and rechecked everything. I'm going to take the right carb off again today and go back over it for a 4th time...

4)coil. I have a dual coil and have swapped the leads terminal side feeds and plugs with no change in the misfire. I can't see how it could be the coil unless it shorts at certain RPM's, but that wouldn't explain why it's always on the right cylinder, so that is not a priority to swap out.

anyway... I am on to check it all, one thing at a time so I can, not just fix it, but figure out which thing was at fault.

Thank you everyone for all your helpful comments. It's great to have so many experienced people adding their experiences and expertise to help me get this figured out....

Click to expand...

Since you have switched plug leads and the missfire has not changed then you can pretty much rule out the ignition/electrical system.
You have checked the compression so you know it does not have a burned valve.

You might want to do a visual comparison of the valve lift to rule out a failed cam.

Sticking valves may be possible but are highly unlikely unless you have a recently rebuilt head and are using a fiberglass or lined tank.

I still suspect you have a carb that is running rich at part throttle. If the low speed jet in the carb body is damaged with either corrosion or someone poking a piece of wire through it that is too large then you may have to replace the carb to fix it.

OR it may be that you have a slide cutaway that is too rich and soots up the plugs after you run it for a while.

Plugs that have soot on the insulators will give the exact symptoms you have. The insulators should stay white. Jim

You can't swap carbs, but you can swap intake manifolds. It's a long shot, but desperate men do desperate things...

I did a few things today because I just had to eliminate certain relatively easy things to check before I moved on.

I duct taped my old 6 volt lucas coils to my down tubes and wired them up so I could eliminate the last part of the ignition, since I tested everything else by substitution...

Once I had them on and a cleaned both plugs which were both black soot, I ran the bike and noted the results....

The side with the misfire will run at an idle with the air screw turned nearly all the way in. Once I throttle it up nearer to 2000 RPM it starts to misfire and then normal running kicks back in at around 5,000 RPM...

*Somehow, I think Jim Comstock has a crystal ball, because there's something wrong with the idle circuit because it doesn't adjust properly (I have the turn it almost all the way in for it to idle well. I would guess also the needle and needle jet are out of adjustment because that's the range that the misfire is strongest in. The misfire goes away at 5,000 rpms when I am transitioning to the main jet....

So,.... If the misfire side is from a lean midrange, how much change in mixture will I get if I raise the needle by clipping it in the bottom slot?? (and of course if it's rich lowering it into the top slot?)

Thanks everyone for their help. Obviously I am not there yet, but I have eliminated things and feel like I have a good handle on the issue.

I still have to check my valve lift to make sure it's not a worn cam, but It really runs like a freight train over 80mph, so my intuition tells me the cam is ok...

o0norton0o said:

I did a few things today because I just had to eliminate certain relatively easy things to check before I moved on.

I duct taped my old 6 volt lucas coils to my down tubes and wired them up so I could eliminate the last part of the ignition, since I tested everything else by substitution...

Once I had them on and a cleaned both plugs which were both black soot, I ran the bike and noted the results....

The side with the misfire will run at an idle with the air screw turned nearly all the way in. Once I throttle it up nearer to 2000 RPM it starts to misfire and then normal running kicks back in at around 5,000 RPM...

*Somehow, I think Jim Comstock has a crystal ball, because there's something wrong with the idle circuit because it doesn't adjust properly (I have the turn it almost all the way in for it to idle well. I would guess also the needle and needle jet are out of adjustment because that's the range that the misfire is strongest in. The misfire goes away at 5,000 rpms when I am transitioning to the main jet....

So,.... If the misfire side is from a lean midrange, how much change in mixture will I get if I raise the needle by clipping it in the bottom slot?? (and of course if it's rich lowering it into the top slot?)

Thanks everyone for their help. Obviously I am not there yet, but I have eliminated things and feel like I have a good handle on the issue.

I still have to check my valve lift to make sure it's not a worn cam, but It really runs like a freight train over 80mph, so my intuition tells me the cam is ok...

Click to expand...

Remember 5000 rpm in neutral is cracked throttle, idle circuit. Pulling the bike down the road at 5K is more needle & jet. It's THROTTLE OPENING that tells you what to tune. Good luck :mrgreen: