A month or so back I posted a thread regarding a high-speed miss I was having with my '91 FLSTC. I'd changed out literally all the ignition components without remedying it.

I'd get up around 4K RPM and the bike would start to 'stutter', missing until I backed off. Sometimes...when it was a cooler part of the day...the problem was either absent, or very much reduced.

I decided it was the carb. I bought a Premium kit (and a few other things) from CV Performance and when my throttle cable broke, was motivated to attack the carb problem as I replaced the throttle/idle cables.

The emulsion tube had quite a few holes plugged. I suspect this was the primary source of my problem as this comes into play under hard accel/high RPM. I replaced it with the part I got from CVP. Also replaced the pilot (idle) jet, the slide, put a four-sided needle valve in, and replaced the plastic gas inlet fitting with brass (also from CVP).

When I first got it back together, there was some gas out the overflow port on the carb. I didn't change the float setting, just the needle valve. It was a weird leak in that it seemed more like the valve wasn't seating all the way. Sure enough, I tapped on the float bowl with a screwdriver handle, and shortly thereafter the leak stopped and hasn't returned.

The jets in the carb were a 165 main (Cal. bike) and a 40 pilot. I replaced these with a 185 and 46, respectively, per the CVP recommendation for my engine (Stage 1 1340 EVO).

I'm still doing 'fine' adjustments to the mixture and idle, but boy does it run better. The miss is gone, regardless of temp. It's still on the ragged-edge of being too lean (fine during day, but a little bit too lean when it's cool), so like I said I'm still dialing these settings in. I bought an EZ Just for both the mixture and idle screws, so it's real easy to adjust these.

Thanks to all of you who suggested things. In the end, I think I probably did it all! The instructions from CVP were good. They also have videos on YouTube, and there's other stuff out there that pertains. I'm at best an average Joe-Bag-of-Donuts mechanic. I didn't have any problems (well, I had to 'chase' the threads on the carb that bolt the air-cleaner...but everything else was no more than following the instructions).

I think I spent around $170 because I bought new stuff rather than clean some of the old stuff up, and added a few things that weren't strictly required. I expect I could have gotten away for half of what I spent, maybe less, if I was re-using jets, emulsion tube, and the slide (which is like 38 bucks itself).

Alan

 

So we can *** u m e that all is good? Now ride the **** out of it.... no just kiddin. Enjoy and ride safe man...

 

good to hear it's running well for you. I had a hard cold start (when under 55 degrees) an an occasional hi speed miss an lots of popping when cold...I changed the intake seals an it seems to have solved the problem. Plus I was running lean judging by the plugs but the jets weren't that big (45/180)

 

Alas and LOL. The bike continued to miss. Also, the 'transitory' leak I experienced when I first re-installed the carburetor was not a 'glitch' but a small piece of metal hanging around in the needle-valve seat. A result of me removing the original brass insert/plastic-elbow. I blew the circuit out with lung-power, the first time around. I ended up using compressed air the second time.

I didn't trouble-shoot this very effectively. Everything was learned in hindsight. Amazingly enough, very similar to the way I've lived my life. LOL.

I tried to make the miss temperature dependent. I tried to make it a problem with the carb's having sat for significant time. I thought it might have been 'age': ignition (coil, plug-wires, ignition module, cam-chest pickup) related...

In fact, one or more of these might have contributed to the problem. But at the end of the day, the miss was still there. Starting at 4K, the bike would break up (firing) so bad I had to back-off.

The answer was in front of me all the time. The clue: The fact that when I hit about 4K RPM, the cover on the ignition switch would pop open. I finally thought to look at my tach when the problem was occurring (and I'd visited every other issue I could think of). The needle moved wildly. Not just stuttering, and falling off, but jumping literally all over the tach face. Like the power to the tach was being disrupted...

It was the ignition switch. I had been turning it to 'Ignition' to run the bike. I tried turning it to 'Lights' and the problem doesn't occur. I suspect the former position has an issue. The latter has been less used, and so is more reliable. (There were times, once every 30 or 40 starts, when the problem didn't occur in the 'Ignition' position...this is what I tried to correlate to temperature...but in fact I think it was just at these times, the switch found a chance 'sweet spot' for a while, and didn't open up).

So let this be a lesson to you. If I ever open a motorcycle repair shop...you might want to go somewhere's else. LOL.

Alan

 

At least you got it figured out!

 

I had a broken wire on the switch on my 76 shovel once. Was hard to pinpoint at first, but easy once you pulled the dash cover and wiggled it.

Mine would die with the lights on, but switch to "ON" and it was fine. Pretty spooky when merging into traffic at night and the lights and bike go dead suddenly.. LOL..

Griz

 

flchchaz, thanks. In fact it IS fixed. I've gone back to that realm of RPM quite a few times lately, and no repeated mis-fire episodes. The switch was causing a miss when the RPMs got up around 4K, and the vibration was getting 'heavy'...

That said, IBDAGRIZ, your post is pretty coincidental.

So... I've got the bike squared-away as far as the engine goes. ****-eatin' grin on my face I'm riding to work one morning earlier this week at oh-dark-thirty. I'm crossing the dry lakebed, flat and straight road. It happened to be early. There were taillights in the far distance ahead, a mile or two. There were headlights behind me, following me out of town, maybe 2-3 miles back. I'm alone. Running at 70+. (If AF Security forces are reading this I was running 64.5 MPH LOL). And guess what? Yep. I've got the hi-beam up and it friggin' goes DEAD. I'm riding through starlight. My a**hole immediately grips the seat very tightly. Then I realize I can actually see the perimeters of the road. Still. It's dark. I fiddle-futz around and manage to hit the dimmer switch. The passing lamps come on. Ok. A short while later, the low-beam headlight comes on...

...I turn the high-beam back on. It flashes on but quickly goes out. I'm running under starlight again. Switch back to low-beam headlight. Passing lamps on instantly. After a few moments the low-beam headlight comes back...

The ignition switch 'Ignition' position works fine with the high-beam. For some reason the 'Lights' position doesn't. Next project...my first guess is, it's one of the breakers that sit under the console between the tanks. (I sold a '14 SG to buy my '91. I'm an Evo guy, I guess, because it was one of the best moves I've ever made...LOL).

alan

 

I can't tell by your post but did you actually replace the ignition switch or were just running it in the other position?

If you haven't replaced the switch, do so immediately. They are a known problem and can melt your wiring when they go bad.

When mine went, I burned my fingers when I went to turn it off.

 

Prot, thanks for the warning. I have not yet replaced it but I do have its replacement sitting on the bench, going in this weekend.

Alan

 

Today I replaced the ignition switch with the newer style (pc board versus the brass roller and contacts). The original switch didn't look too bad, actually. I think it was just that, in the 'Ignition' position the spring that keeps the roller in touch with the contacts wasn't sufficient to overcome the vibration. I mean, it REALLY SHAKES at 4K and above.

I also replaced the breaker tied directly to the 'Lights' position, as that was the position the switch was in when the hi-beams quit working.

Took it out and tested it. Hi-beams stayed on. No missing up to nearly redline.

Thanks again for the help...

Alan