miss firing

[art]

I need help.My 2002 standard with 100000 mi. is running lousey at cruising speed .At about 45mph an holding it at a steady speed it starts to missfire an run ruff .this gets worse as the engine gets hotter up to running temp.I have checked the plugs an the are a br/grey..the vac. tubes look goodwith no cracks.I have run seafoam an no change.I'm thinking bad coil or bad plug wires.I have cut the piggies an instaled a 6% trigger wheel an get about 36 mpg two up with windshield at highway speeds.Help please an thanks.Art in Or.

[YardBoy]

Thats where I'd start, might be a little easier once  you indentify the bank or specific cylinder/cylinders thats misfiring.

[SCain]

I would start by draining the fuel from the tank and carbs, get some fresh fuel preferably without ethanol and see how it runs before doing anything else.
I had an experience with a tank of bad fuel, ran great cold but when the engine got up to temp the fuel started to gel.
Just my .02

[art]

the fuel is not an issue .I have this problem for several months an a lot of different brands of gas with no change .I went on a 300mi. ride yesterday with two tanks of gas from two diff. areas with no change an got 36mpg. Art

[Chrisj CMA]

You say the vacume lines look good.  How did you "look" at them?  Have they ever been changed?  Also I would be concerned that this could be petcock problems......those OEM valves seem to be worthless by 100,000 miles

[Ricky-D]

If it runs good and you get 36 mpg, then I think you can eliminate any problem with the ignition system. Electrical components are either good or bad w/ very little in between.

I'd look for vacuum leaks, lines and 'o'-rings.

Are the carburetors synchronized properly?