Topic: Cylinder 4 Misfire

[Mighty550]

So before I cleaned the carbs, my number 4 cylinder was misfiring, no much so that I could touch the pipes after it had been running for a few minutes.  I cleaned they carbs (that one was a mess) and reinstalled last night.  I didnt have a chance to sync them yet, but its still misfiring on cylinder 4.  So far i've replaced the plugs, adjusted the valves (they sound much better now), cleaned the carbs, and smoothed out the inside of the intake runners.  I still have to change out the points/condensers, and set the timing.  Will this fix my misfire?  This is what the plug looked like after a quick trip around the block last night (i checked, it has good spark)


   

[nayto550]

If cleaning the carbs and the other general "tune-up" stuff didn't fix it, I would look really close at the plug wire on #4.  Especially where the wire and plug boot mate up.  Seems to me that any ignition problems further down the line (points, coil, etc.) would be presenting themselves on the #1 cylinder as well.

[Mighty550]

i did the old pull the plug, plug it in, set it on the head and start it, there seemed to be pretty good spark, ill check the others the same way and compare.  I thought the same thing about the coils, points, ect., there is no issue with cylinder 1

[phil71]

do you know for certain the bowl has fuel in it?

[lucky]

To see if the cylinders are getting a spark, just clip on a inductive timing light onto the spark plug wires ,One at a time and look for even consistent firing.

Spark plug looks ok.

[mrrch]

Try swapping the plug caps on #1 and #4. If it's still acting up on #4 try a different coil.

[Mighty550]

There is fuel in the float bowl.

I switched the 1 and 4 wires, cylinder 1 gets hot, cylinder 4 still stays cold.

SO...the carb is getting gas, the plugs, wires, and coils are fine.

I just replaced the points and condensers.  Tried to set the timing, thought i had it, started it up and it pegged to about 4k rpm without any throttle, so i guess my timing is off.  charging the battery now before I try again.  BUT, for the 5 or so seconds that the engine was running, cylinder 1, 2, and 3 headers got warm, #4 was still cold.

[Mighty550]

as soon as i get the little brass adapters for my pressure gauges, and get the timing set right, i will sync the carbs.

[phil71]

I know you don't wanna hear this, but you missed something when you cleaned the carbs. Do it again. If you can't get it cleaned ultrasonically, get a bunch of guitar strings and really go crazy in the jets and circuits .

[Mighty550]

i know the jets are clear, i ran wire through them and made sure that they were clear, both the pilot and the main.  The only other thing it could be is the "pathways" for the fuel from the bowl up to the intake.  I blew carb cleaner through it when i cleaned it.  When I took it for a quick run, i gave it a good amount of throttle, and it wasnt getting much from either jet.  cant believe, or I dont want to believe, that its still clogged.

[phil71]

look at it this way, the only other possibility is there is very little vacuum present to draw fuel in , which would be a much bigger deal. It's also a hell of a lot more likely you just missed something, especially on what you already described to be a carb that was pretty far gone.

[Mighty550]

ITS ALIVE!!

Took the carb off, made sure that carb 4 was totally clean and clear, put it back on and it fired up, and the header got nice and hot.  WOOHOO!!

[Duanob]

Second or third time is always a charm.