[artbone]

To make the pilot system leaner do you increase or decrease the size of the pilot air jet (the one in the top of the carb?) Stock is 130 so to lean it out I would go to 135 I think. If anyone knows for sure, please enlighten me.

[Prophet Of Doom]

Not sure why you would want to make an overly lean bike leaner, but bigger numbers on the pilot air jet passes more air and so makes it leaner.
Euro spec for the 11U and 16R models (1982) is F120/R120 and I found that significantly better overall than the 130 and 135 that I've also tried.

[artbone]

As to why I want it leaner, I live at 6500 Ft and regularly ride up to 9500 Ft. The bike pulls strong and doesn’t have a flat spot or the famous Vision Stumble but I still think it feels a little rich. I’m going to try one or two sizes at the time until it feel right to me.

[Prophet Of Doom]

Sorry, I'd forgotten that. Presumably it's hotter in mexico than the rest of the world also - that will have a similar effect to increased altitude.   Hot air is less dense and has less oxygen.
Pilot air will only adjust up to about 1/3 throttle.  The main air jet is hard to swap out, but perhaps think about reducing the main fuel jets as well to get leaner across the board. 

[artbone]

I went down to 122.5 on the main jets and 140 on the pilot air jet. I think the bike runs better than it ever has. I might order a couple sized smaller, maybe 120 and 117.5 but I'll probably leave it alone. I forget to mention that I’ve got MAC pipes on it. It has no hesitation, no Vision Stumble, just pulls like a freight train to 10K.

It does have one other problem that’s just turned up in the last couple of weeks. Sometimes, when the bike has been ridden long enough to get completely warm, then let sit for 30 or 45 minutes, it will crank on one cylinder and act as if one spark plug is disconnected. It will run like that a few minutes then suddenly start running on two cylinders. I can’t determine if it’s fuel related or electrical. It did it today as I was riding out in the country and I putted along until I got to a place I could pull well off the road. I lifted the seat and pulled each of the fuses out. They all looked good so I put them back and tried it again and it fired right up and ran perfect the rest of the way home.

I had replaced the diaphragm in the fuel pump and looked at the diaphragm in the petcock and it looked fine. I replace both the fuel and the return lines. As I said, when it’s running it’s running the best it’s ever ran.

I have intermediate problems.

[cvincer]

Out of interest.......after the bike has been ridden long enough to get completely warm,  let sit for

30 to 45 minutes & then drain each float bowl into a measuring cup & see how much comes out of

 each.

[Walt_M.]

That sounds a lot like a failing rev limiter. Have you disconnected yours?

[artbone]

You are right Walt! That’s exactly what it sounds like. I didn’t know there was a rev limiter on this bike. I take it up to 10K once in a while just to see if it will do it but normally I never shift at over 9K. Where is the rev limiter and how do I disconnect it?

[fiat-doctor]

At the TCI there is a Yellow/Black wire.   This grounds the TCI when the tach senses an over rev and kills one cylinder.  I use a small probe and release the wire from the connector block at the TCI.  This way you can always put it back to stock if you want to.

I have had a couple of TCI's fail where it would quit running on one cylinder when it got warm.
If you have access to a spare it's a 5 minute swap for testing.

Steve

[artbone]

When the problem started in the past was after the bike was warmed up and then shut down. When it started running correctly again it was like a switch was thrown. Yesterday I was riding about 60 mph and it started running on one cylinder again, like a switch was thrown. Because I was messing with the carbs I forgot the old rule of thumb - “Most Carburator Problems Are Electrical.” I was all set to pull the carbs and go through the fuel pump, change all the hoses, etc.

I did a search on “Rev Limiter” and found that the yellow and black wire is the one to cut and tape up to disconnect the offending device. I think for me the easiest place to do that is right at the TCI unit. I can’t face taking that fairing off again. Now I see that fiat-doctor has posted the same info with the suggestion that I release the wire from the connector block so I can put it back to stock if I want to but I don’t know why I would want to do that. As I said, I never turn it over 10K and I didn’t even know it had a rev limiter.

I don’t see how anyone gets or keeps one of these running without being a member of this group. Thanks everyone for the advice.

[artbone]

Okay, I’m back. I let the bike sit for several month, I guess I thought if I left it a little while it would cure itself. Didn’t happen. It will crank and run on the rear cylinder and, once in a while, fire a bit on the front cylinder.
I have disconnected the rev limiter wire, replaced the ignition black box with a known good one, rechecked the carb synchronization, set the front carb at 2 1/2 turns out on the idle screw, and replaced the front coil and plug wire with the one that came off the bike originally. It will crank on the choke and when I idle it down it is running on the rear cylinder but not on the front. When I rev it, it will start firing on the front cylinder but it won’t idle on both cylinders.
As I said before, it was running the best it’s ever ran for several months then we were out riding and stopped for about 15 minutes and when it started back up it started on one cylinder. I rode about 100 yards and it suddenly started running on both. It’s like a loose wire that suddenly makes or loses contact.
I’m running out of ideas.

[jefferson]

First I would check to see if there is spark at idle in the front cyl. and if so then maybe some dirt in the pilot circuit. If a spark issue then check the cap as the front cyl. will be exposed to rain and such and may be corroded as also the wire could be. My mind keeps telling me that there was the rev limiter that cut spark to one cyl. and there was something else that cut spark to the other cyl. For the life of me I can't remember what it is. I would jump out the side stand switch to eliminate that too.

[Rikugun]

If it is intermittent spark problem, (and it seems you've checked most other common problems) have you  considered the pick-up coils under the alternator cover? I don't think they are typically troublesome on these bikes but it's worth checking.

[QBS]

Long shot, easy to do, can't hurt, check for positive\dependable fuel flow to front carb.

[Walt_M.]

Just sounds to me like dirt in the carb.

[artbone]

Thanks for all the above suggestions some of which raise other questions.
1. How can I check that there is spark at idle on the front cylinder? I have new aftermarket coils and new wires and I changed the spark plug and the problem persisted. Also, I cleaned the carbs in an ultrasonic cleaner and the bike was running perfect and this problem started suddenly and sometimes disappears suddenly. I don't think dirt in the pilot jet would act like that.
2. How can I check the fuel flow to the front cylinder?
3. If it is a blocked or partially blocked pilot jet, can I unblock it without taking the carbs off the bike?

Again, thanks for all the advice. I probably won't get to tinker with this for a week. I'm leaving Sunday going to Los Angeles for a week but I'll report back when I'm back to Mexico.

Art

[QBS]

Regarding #2: With engine exhibiting the malfunction, open the front float bowl drain screw and look for fuel flow.  Another possible answer may be dodgy low tension wiring to the spark coil that serves the front cylinder.  With the engine running, move that cylinders' low tension wire around and see if engine operation changes.  Also look for damaged wire insulation that could be going to earth.

[jefferson]

To check the spark you would need to pull the plug and ground the body of the plug and then look for the spark. If all those parts are new then the only thing might be the wire isn't inserted fully into the cap or coil and not making good contact. Don't forget that brand new parts can be defective although the chances of that should be slim.

[Rikugun]

That is a good method to start with but if it's an intermittent problem I'd go a step further. Conditions may exist where the plug will spark outside the cylinder but not (or not reliably) under compression.

You can use an inductive pick-up timing light as a diagnostic tool. Auto Zone loans for free, borrow from a friend or $25-$85 new depending on where purchased. You could use an old school in-line type but the inductive pick-up allows you to go back and forth between the two cylinders while it's still running.

Be sure to check with the engine cold and hot. If you really want to be thorough, run it on the center stand at moderate RPM in second or third gear and load the engine with the brake. An erratic, irregular, or faltering light won't tell you specifically what element of the ignition system is at fault but it will narrow the problem down to ignition or not ignition.

[artbone]

“MOST CARBURATOR PROBLEMS ARE ELECTRICAL!”
I’m going to get a poster made up for my shop. May problem was the pickup coils. I checked them with an ohm meter and they showed open (infinity) when they should show 110 ohms. I kept putting off checking them because I thought you had to pull the cover to check them but all you have to do is disconnect plug from the igniter box. I don’t see how it ran at all with both coils showing open.

Anyway I took the ones out of my other bike and it runs perfect again.