89 missing @ higher rpm with wot

[frankd]

About 3 weeks ago after I installed the Progressive fork springs, it was nice and warm here, so Barb and I went out for lunch and a nice ride back by one of the big lakes near here. We were stopped at a stop sign, and when we started again, I cranked it on in first gear. Things were fine until it got to about 5,500 RPM and then it started breaking up (missing). I shifted to 2nd and it pulled good on all 4 cylinders and then started to miss again when the engine got to about 6500 RPM. The strange thing was it seemed like it was missing on all 4 cylinders randomly. I tried it several more times and it still had the problem and I started to think that it had water in the gas. The last time I filled it, I put in non-ethanol gas, but I thought everything was fine and I was pretty sure that I'd run it through the gears after gassing it up a couple of times. When we got home, I drained one of the carburetors into a can, but couldn't see any water in the fuel. I pulled the fuel filter, and there was no water there either. I changed the fuel filter because it'd been in there a while, but afterwards, it still ran the same. I thought about it for a couple of weeks ( the weather wasn't too good) and decided to drain the tank and put in fresh gas. I drained the tank almost completely and put in 2 gallons of fresh 90% gas/ethanol. When I went to start it, I found that the battery had bit the dust. I ordered a new battery and finally got my old one to accept enough charge to go for a ride. The bike still missed at higher rpm at full throttle. Before the new battery arrived, I figured I should check my charging system. Normally my 89 measures about 14.5V, but now it was reading about 13.95V. The bad battery almost acted like it had high resistance, so I reasoned that the voltage regulator was switching too low because of the higher charging spikes, or higher ripple. Seeing that I hadn't found water in the gas or bad gas and it was all 4 cylinders I started wondering if I had a TCI going bad. I'm using the stock TCI, but I also have one of the Dingy specials on the bike also, so I could switch to it. First I decided to try the new battery. Maybe the pulses on the charging system were doing something to it? Not likely but maybe. The battery arrived last week, but the weather wasn't great and I was busy with another project anyway. Today it got up to about 50 degrees, so after church I took it for a ride. When I cranked it on it pulled up to the red line perfectly, so that proved to me that the bad battery was causing the miss. I'm glad it did so I didn't have to get serious to find the problem.

[bongobobny]

Interesting!!

[ChiefCass]

Hmmm, methinks... Looks like I'll have to take a ride with the new battery installed before trying the Shotgun procedure when the weather warms enough. Never thought but cruddy battery -might- have been causing misfires last Fall. Thanks for the idea!

 

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[camos]

Thanks a bunch Frank, you are the man of the minute.

 

My 89 had similar symptoms, seemed to be running on 3...or... 2 cylinders and was missing above 4500 RPM. First ran through a tankful with Seafoam without any appreciable difference. Pulled the plugs after that and they were all exactly the same. Centre insulator was whitish to tan and the rim at the threads was black and damp. This indicated to me there was no obviously misfiring cylinder and no shortage of fuel. Limped along for a week like that with mileage down to 100 miles to the tank.

 

After reading your message, I cleaned and tightened the battery terminals which totally eliminated the high RPM misses and probably 80-90% of the roughness. There is still some there although it is barely noticeable. Had a slight surge of power for a second or two a couple of times so when I get the time I'm going to go through the circuits that feed the ignition system, coils and TCI.

 

I'm pretty sure the battery is in good shape but the symptoms were similar to what you found although it was low voltage to the plugs in my case.

 

Anyway, I was at a loss before reading your message and you made my headach go away.

:clap2: :clap2:

[frankd]

It wasn't the battery after all causing the missing at high rpm. That's the trouble you get into when you do 2 things at once to cure a problem. In addition to the new battery (the old battery was bad), I also drained the gas I had in it, and replaced it with gas from a different station. Then the bike ran normal again, it would rev to the red line (7500 rpm) and beyond. The first gas was non-ethanol gas from a local small gas station. I could see no evidence of water in the gas when I drained it. After a couple of tanks of regular BP gas, I decided to try the non-ethanol again. The miss at higher rpm at full throttle came back again. I ran the tank through the bike, and then switched to regular Shell this time, and when I had a chance to run it through the gears, it pulled good with no missing. It seems like something in the non-ethanol gas is coating the plugs. Any other explanations? I've been thinking of trying non-ethanol gas from a different station, but it all probably comes from the same refinery.