Topic: 1977 CB550K issue

[Tstarr56]

Hey everybody,

I have spent the last couple years restoring my father-in-law’s bike in my spare time. I finished my project about a year ago but have an issue I can’t seem to figure out and I’m trying not to pull my hair out. The bike has a stumble/ stutter (just sounds muddied) at about 1/8-1/4 throttle. Bike idles fine and pulls great in higher rpm/ throttle range. I have Murray’s Carbs kit on it and he has been trying to help me pinpoint the issue. I tried going up and down a pilot jet size and moving clip position. Not sure if through my adjustments the carbs got out of sync or not but I set them back to base. Following the advice of Murray, I took temperature readings of my headers at idle. 1- 310, 2- 205, 3-155, 4-260. I took a compression test as well: 1- 110, 2-102, 3-118, 4-118. I have changed the plugs, checked valve clearance, and my ignition timing is dead on. Not sure where I should be looking for this issue. Any advice would be greatly appreciated

Bike has Murray’s Carb kit, Dyna S ignition and coils, 4into1 delkevic exhaust

[denward17]

What do your plugs look like after a run, pull them out and give us a picture.

[scottly]

The bike has a stumble/ stutter (just sounds muddied) at about 1/8-1/4 throttle. Bike idles fine and pulls great in higher rpm/ throttle range.

The issue is only at 1/8-1/4 throttle, which is within the range of the needle. Your description of "muddied" sounds like a rich condition, so I would lower the needles.

[seanbarney41]

looking at your header temperature's, they are all over the place, and I would doubt that number 3 is even firing...gonna have to fix that before you can tune.

...and then there are the Murray's, have not actually ever witnessed those actually running anywhere near as good as the stock carbs on several different bikes,

[bryanj]

As a 77K it will have the horrible lean burn PD carbs on it, these are a nightmare to clean effectively especially the press in pilot jets. They also do not like any brassware except the original Honda plus from memory there are no grooves to adjust the needle.
IF you get a set that work properly AND run the bike at least weekly they are fantastic for gas mileage BUT they only like standard setups plus clog up for a passtime if the bike stands for only a few weeks

[Tstarr56]

Thanks for the responses! Here are some pictures of my old plugs and the new ones I just installed after a few spins around the block. I did check to ensure I was getting spark on the low temp cylinders. I’ll try moving the needle clip and report back. Any ideas on the cause for the low temp cylinder could be coming from? Thanks again

[scottly]

Both sets of spark plugs are sooty, indicating a very rich mixture. Once fouled, the plugs may cause that cylinder to quit firing. Save the fancy iridium plugs for after your get the carbs sorted. Sometimes the black can be burned off the spark plugs with a propane torch, making them usable again.
Your main jets are likely too large. Select a proper main jet before fine-tuning the needle.