Topic: Bike Doctor's Diagnosis Needed! (Non-lifethreatening symptoms)

[spmc]

Hey all thought I would get the first and second opinions here as I'd love to get some insight into my bike.

77 CB750f2, end of last season started getting sluggish, feeling like it would go, but not have the torque or responsiveness it should. Would feel like I do as I slowly get up to speed running now as opposed to when I was younger with some explosiveness. I'm sure none of you can relate haha.

This spring rebuilt the top end to try to fix that issue and seal an oil leak I'd had enough of, and while I was there decided to replace the ignition coils and ended up swapping the exhaust with a donor bike I got kicking around (both 4 into ones). Once the smoking stopped the bike felt new again, running strong and I thought I fixed the issue... lasted about 3 months and then it bogged down again. Since the only thing I didn't really touch was the carbs I thought it could be something there, and ran a can of seafood with a tank of gas to try to get the last riding out of the season. No change on that tank, and then refilled and am probably about 1/2 through the new tank with no additives.

As I was riding the other night a bunch of smoke started shooting out of the exhaust at a stop light, it was dark so tough to tell the colour but it seemed grey. Lasted about 10s or so and then gone. Suddenly though the bike was way more responsive and peppy, as if it had burned off some deposit or something had been clogged and was suddenly freed up... Anyone have any similar experience or have an idea of what something like that indicates potentially?

Thanks for the help!

[newday777]

Sounds like you have/had plugged emulsion tubes(pressed in the carbs and need to be pulled out carefully with pliers.
Did you inspect the tank for rust deposits?? Rust particles will clog the idle circuits fast. If you have any rust showing then you need to clean the tank with electrolysis cleaning method and or Evaporust to the top of the tank.

[Sw1ssdude]

Could it be that you were running on three cylinders, and suddenly the fourth one came to life, and blowing out cobwebs and soot and oil through the exhaust?

If so, it would be a good moment to clean the carbs, now that the seafoam has softened all the gunk. . Way worse than plugged jets are ALMOST plugged jets, causing the engine to run lean.

[Deltarider]

Could it have been the air intake? Has there been any blockage there?

[spmc]

Sounds like you have/had plugged emulsion tubes(pressed in the carbs and need to be pulled out carefully with pliers.
Did you inspect the tank for rust deposits?? Rust particles will clog the idle circuits fast. If you have any rust showing then you need to clean the tank with electrolysis cleaning method and or Evaporust to the top of the tank.

I know I've cleaned the emulsion tubes on one set of my carbs, but can't remember if it was the ones on the bike. The tank when I bought it had already been coated on the inside, didn't appear to be flaking, but I haven't checked in a while. I do run an inline fuel filter though so I wouldn't think too much gets through that into the carbs, but maybe I'm wrong.

[spmc]

Could it be that you were running on three cylinders, and suddenly the fourth one came to life, and blowing out cobwebs and soot and oil through the exhaust?

If so, it would be a good moment to clean the carbs, now that the seafoam has softened all the gunk. . Way worse than plugged jets are ALMOST plugged jets, causing the engine to run lean.

I definitely have wondered if I was running on three in the past, but I've checked the heat level at the headers after a ride recently and all seemed to be hot, granted it was the summer so maybe they would be regardless. All new plugs and the rings were in great shape, gave the jugs a light resurfacing as well so I'm not sure why a cylinder would be down then come back to life. Will take your advice and give them a once over regardless to make sure there's nothing glaring.

[spmc]

Could it have been the air intake? Has there been any blockage there?

I wouldn't think so as I've always used the stock air box and new filters and boots so that should be sufficient I would guess. No mouse living inside, this bike anyway.

[Don R]

 I've had problems with inline filters gelling up inside, they appear clean. I only use them when I'm unsure of the tank, I was told to keep them big and, on their side, so the filter media doesn't gum up all at once.
 We've had multiple threads on them, so I hesitate to start it up again.