Old bike gremlin rears it's head

[bmeyer6472]

Some of you may remember a recent thread I started concerning an ignition problem, and its eventual fix. Well, today was nice, so I fired up the Vision to go for a ride, let it warm up while I got my helmet and gloves on, swung my leg over it, and it promptly began to run on one cylinder, and the tach went to zero. I revved it up a bit, and after about 3 or 4 seconds it caught, ran on both, and the tach returned. So away I went. Next thing I know, the speedometer quits working! Well the speedo was easy - the cable had come loose from the speedo head, all I had to do was take off the fairing and screw the cable back on. But the one cylinder running and tach, I don't know. From Lucky's site, it seems that the problem might be the rear pickup or the TCI. Except the TCI is a good one I got from Lucky, and the pickups both test about the same. The battery is up, bike starts immediately, I've checked all the connectors; hell I don't know. Maybe it's just the old bike gremlins. Any ideas? BTW, it ran flawlessly after it finally caught on both cylinders - nary a miss. I'm stumped, as usual. This bike has run almost perfectly for over 20 years until this. I know I'm missing something - again. ???

[Lucky]

I think your looking at a carb problem, or vacuume leak, if your sure it's the rear that's cutting out, then look for a vacuume leak at the rear intake or YICS leak.

 if the carbs are 83's (I lose track of who has what) then strongly suspect the accel pump controll valve built into the rear carb. these have a diaphram in them that gets stiff with age (they do not interact with fuel that would normally help keep diaphrams soft) when they get stiff they do not seal well and cause an INTERNAL vacuume leak

also on the 83's check the vaccume line for the above mentioned valve going to the rear intake.

dirt in the carbs can also cause problems like this as well as mal-adjusted carbs (you do have a fuel filter installed right?)

to help locate a vacuume leak, with the engine idling, take a can of carb cleaner, sich as Gumout, that has the small red straw tube attached, & squirt TINY shots of cleaner at any area that could be a source for a leak. listen to the engine as you do this, noting any change in idle. when you locate a leak, the idle will change ar the vacuume leak now has 'fuel' mixed in with it. procedure is: tiny squirt & listen, tmove to another spot, tiny squirt & listen, etc, etc.

--Lucky

[louthepou]

I didn't read the previous string, so i may be typing this for nothing, but here we go anyways.

It might be as simple as a spark plug cap not making good contact with the plug, or the spark plug wire not making good contact with the cap.

Louis

[Paul_Jungnitsch]

That tach thing is strange. However crappily my ran when starting cold, missing or not, IIRC the tach never zeroed. Some sort of intermittent short in the tach circuit that is killing the ignition to whatever cylinder it reads from?

I know automotive tachs hook to the negative side of the coil, presumably if that wire would short to ground it would cause failure of the spark.

Have you tried disconnecting the tach pickup wire from whatever part of the ignition system it is hooked to, to take it out of the equation?

Another tach related possibility would be a tach overrev kill circuit cutting in when it shouldn't.

[Bob Meyer]

The tach thing is why I suspect the ignition. Unless I'm mistaken, the tach gets its signal from the rear coil primary wire, so if the problem recurs, I'll disconnect the tach and see what happens. You may be right that the tach itself is the problem. I've already cut the rev limit wire, so that's not it. The plugs and caps are new, so that eliminates that too. Fuel filter was installed a long time ago, but vacuum leaks would be a consideration if the tach was normal. I'm also pretty sure that the carbs are OK, cuz the bike has not ever been left sitting for long, and it seems more like ignition anyway. BTW Lucky, it's an 82. Thanks for the input.

Bob

[bmeyer6472]

Bob Meyer is bmeyer6472 - I forgot to log in... :P

[Walt_M.]

I think you are on track with the tach but check the wire from the TCI to the tach. I'd be willing to bet a nickel you will find a bad place in the insulation and it is intermittantly grounding out.

[bmeyer6472]

You still have a nickel, after maintaining Mrs. V?  ;D Good idea to check the wire, I'll do that first. Maybe not today - too much else to do. (honeydo list) :P

[Walt_M.]

V owners should always have a spare nickel or 12.

[Extent]

... but a spare stator is better....

[bmeyer6472]

Rode the V today, and it ran perfectly. If the weather stays nice, I'm gonna take the tank, fairing, and covers off and check for a frayed or pinched wire somewhere in the tach circuit. Even though it ran great today, I'd feel a lot more comfortable if I knew why the tach and one cylinder cut out the other day. If I get it figured out, I'll be sure and post. I wonder if there's a chance that the recent damp weather has affected the tach itself? I don't know if that's even a possibility.  ???

[Coil Coyle]

Re: Tach and one cylinder die.

Heres an earlier thread from archive search,
This is what I've got happening. The Tach and one cylinder die together.
Did Bob or anyone else find a frayed and grounded wire? Where?

coil

[h2olawyer]

Doesn't look like Mr. Meyer found the problem or forgot to post when he figured it out.  I've got no other ideas beyond the rev limiter or a frayed wire.  Maybe if you let it sit & try it later, the problem will vanish.  How clean are the rest of your electrical connectors?

Need to get some sleep.  If something else occurs to me before I become wrapped in the arms of Morpheous, I'll log on & post.  Keep us informed of what you find - if anything.  Sorry to leave you hanging, but I've exhausted by ideas on this one - at least for now.

H2O

[bmeyer6472]

Sorry I somehow did not post when I found the solution to my misfire problem - thought for sure I did - gettin old. ::)

I went through the normal stuff - cut the rev limiter wire, cleaned all the connectors, tried a new tci, and so forth. To my great chagrin, the problem turned out to be a bad spark plug cap. The resistor in the cap had gone bad, and the plug for that cylinder fouled, even though it did not look bad. I solved my problem by installing new plug caps and plugs. Goes to show that sometimes it's the simplest thing, even though with these old bikes we're tempted to think it's a gremlin. In my case, I can't explain why the tach should have been affected, but it was - maybe that was the Vision gremlin at work! I hope you are able to solve your problem - my Vision has been running great ever since I managed to figure it out and fix it. Again, I apologize for not posting earlier.

Bob

[Coil Coyle]

Bluegillspeed,

        Here is a Bumped thread to get you started.

coil

[Coil Coyle]

DaveTN,
            That's why I bumped it also.
;)
coil