running poorly - F-head

I installed NGK spark plugs - same # as I took out -
equivalent to a champion J8C. I was hoping to find some arcing inside the cap, but no luck there.
I swapped the plugs, carb, fuel filter, and fuel pump in an attempt to fix the running problem, but so far nothing has changed.

 

Was sitting in the garage for about a week, started it up and it
ran fine, let it idle for 15 minutes or so, then it stalled at the end of the driveway. Would turn over, but not start, leading me to believe there was no spark. Got it back into the garage and let it sit for a week until I had some time to look at it - had good spark and fired right up, then kinda choked out and died. 2-3 days later, I replaced the plugs and swapped on a rebuilt carb and fuel filter- again it fired right up but had no power and was popping thru the exhaust - changed the fuel pump - starts fine but again no power and popping (no backfires yet). Changed the distributor cap last night - no change. no vacuum leaks noticed either.

 

...and new gas

 

I had to clean the tank on mine with a quart of small gravel and a gallon of acetone. Worked like a charm. Just keep an inline filter between the pump and the tank, and it'll settle out with time. At least mine has.

 

You really ought to hook up a vacuum test guage; it's quick, cheap, painless, and can show you a lot.

A plugged exhaust will show as decreasing vacuum, no power. (Squirrels once completey filled my exhaust system with acorns in just a week or two...couldn't get anything more than an idle. And a smell of roasted nuts...)

A vacuum leak is still high in my list of suspicions, too.

Pete

 

17" vacuum at idle, good flow thru the exhaust, slight popping occasionally. Had to play with the throttle to get it to rev up - will not maintain higer rpm - just kinda bogs and dies out.

opened the gas cap - no change.
Checked the coolant - none at the top of the rad - gonna buy some and top off tomorrow but I only had it running for 10 minutes tops, so it shouldn't make a big difference -
no evidence of coolant on the spark plugs either.
Seems to be running rich - VERY stinky. Checked the idle mixture screw - 2 turns from fully seated.
??????

 

I'd vote for carb mixture.

 

Yes, civilian distributor. I have a MSD ignition coil to use with the MSD 6 plus digital box, But I wanted to figure out what is going on before I throw that on - guess I'll try that next.

 

Don't see why it would, but could you have a partial blockage of the line between the pump and the carb? A restriction would allow you to have an idle, but not rev up the engine.

Does your carb line have any kind of filter between the pump and the carb, or in the inlet to the carb?

And could your timing be an issue? forget to tighten down the adjustment screw, maybe? Or am I covering ground all ready covered?

 

new carb, fuel filter, blew out the line - in an attempt to fix this problem - no change. Distributor has not been touched - bolt is secure - I have been thinking maybe an advance weight spring has broken or something, causing the timing to advance too quickly???

 

just noticed the time stamp says 5 pm on the forum, it is 10:am where I am -
have a good night guys!

 

Picked up a Pertronix Flamethrower 3.0 ohm epoxy coil - part #40611 - gonna throw that in and see what happens.....

 

Do you have a skip? my engine ran like crap, turned out to be a leaking exaust valve.

 

Well, I have never set the valves....but wouldn't I notice a gradual decline in performance, rather than the engine dying and not restarting?

 

Did this begin before or after the "new" carb?

Often the last thing you touched is the most likely suspect and as Glenn said, new is not always the same as "good". Just the opposite.

My dad loved old cars and always said 'if it ain't broke don't fix it, you are just asking for trouble.'

All this swapping out, are you sure a vacuum line or wire hasn't been misrouted?

A sinking carb float? Bad float valve? Leaking accelerator pump?

Pretty soon it will be time to consult a psychic (or psychiatrist!). Good Luck!!!

Pete

 

You would think, but... I lost all power in mine a couple of years ago, seemed like it happened over night. I ran compression checks, checked timing, carb, etc etc, till I ran out of things to check. Last thing to check was the valves, and thats what it turned out to be.