Stuttering 1980 750 Custom

[Silver Rider]

New member here, so apologies if this ground has been covered before!  I bought this bike last spring for $800 and it ran well.  I changed oil, plugs, adjusted chain, put an inline fuel filter in, etc.  I've since put close to 500 miles on it- easy miles- but in the last 50 miles it has suddenly started to have some loss of power and stuttering.  I hear cylinders on both sides of the engine misfiring (not backfiring) and at constant rpm it bucks and hitches somewhat noticeably. Starting out it sometimes bogs down to the point I wonder if it is going to go!  I've wondered if the fuel filter is clogging up as there is some rust and probably some sediment in the tank, or if the problem might be electrical?  Any thoughts, advice etc on how to get my baby flying again will be much appreciated.

[Re-run]

It does sound like things may be dirty or clogged. Check out the filter you installed, can you see crud in there?
Does adding a little choke help at all? Did you get gas at a questionable place? If it is not terrible yet, maybe dump in a bottle of seafoam and take it on the highway for a while and see if it clears up. Milds build ups and questionable gas can be cleared up by seaoam. So maybe give that a try before tearing into things.

[Silver Rider]

The filter is metal so no can see inside.

I'll pick up a plastic one and switch it out-  does seem to starve for gas.

Wouldn't that be an easy fix!

[Silver Rider]

Nope... new filter did not help.  Going to charge the battery up as the lights are low at idle. Running rough! Might need to pull carbs and clean them.

[eric moon]

Lights will be low at idle as the charging system doesnt put out enough volts at idle and the ignition system takes it out of the battery. If the battery is low it can cause poor performance at higher revs. Use the factory manual to see how to test out the charging system.
Battery may be on its last legs.

[slownugly007]

Kinda sounds like were in the same boat, ive got an 81F and it just starting running bad out of nowhere. Yours doesnt hapen to die on you when youre in 5th gear does it?

[sgtslag]

Cheapest, easiest thing to try, is SeaFoam in the gas tank (follow directions for amount).  If the jets have minor clogging, it will help; if the jets are completely clogged, it won't help, and you will need to pull them off, and apart.  Wal-Mart sells it for around $8-$9 per can.  Give it a shot.  Cheers!

[Silver Rider]

As it turns out, the coil was bad. #1 and 4 cylinders were misfiring and yes, it did sometimes partially shut down in 5th. I bought a set of used coils from my local salvage yard and it now runs evenly on all 4 cylinders. I figured out the coil was dead by starting the bike and touching the exhaust pipes. #1 stayed completely cold, #4 warmed a little. #2 and 3 heated right up. I took seat and tank off, and discovered # 1 and 4 were fired by the same coil.

I did put a can of seafoam into the system as well, and this really smoothed out my ride. Thanks for suggesting that- great stuff!  I have a friend who is resurrecting his old Kawasaki after 15 years in the basement and I passed on the suggestion to him.

I purchased a new seat cover on eBay and installed it today.  It fit beautifully, though was a somewhat difficult and time consuming job to install. In the end, it looks like a brand new seat.  

Very happy with my ride now.

[Silver Rider]

PS: Pair of coils were $80.  At Honda, a single coil was $153!  Ouch!

[robs750]

It would be a good idea to check the valve adjustment.