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771 Posts
Discussion Starter · #1 ·
Yesterday, I bought a 1986 F250 with a 300 inline 6-cylinder. When I started it up, after sitting for years, it misfired alot. The more I fucked with the ignition system, the worse it got until it would not fire anymore.

This morning, I replaced the following:
1) distributor cap
2) rotor button
3) plugs
4) wires
5) coil
6) stator
7) TFI module (hall effect device)

We set the timing to 10 degress advanced. It then ran, very rough, and fired on all cylinder. The bitch is that it misfires like mad and seems wayyyy rich on the fuel mixture.

I then pulled the top of the carb, cleaned it out checked the float level and the float valve. They seems to be correct. The accelerator pump works well.

At this point, I am stumped. She runs but sputters and misfires. The exhaust could burn your eyes out. (I smell like I have been on a snowmobile all day. :grinpimp: )

There is a needle valve attached to the actuator for the accelerator pump. It has an adjustment. What is this?

Also, is there a ignition control outside of what I have replaced that could be effecting this?

Help please! I have to drive this pig from GA to WI tomorrow... :eek:

· Registered
771 Posts
Discussion Starter · #5 · (Edited)
throttleboy said:
you said it sat for years? did you get all the old gas out? bad gas will cause the problems you stated. if the gas smells like paint thiner or something other than fresh gas its bad.
It was near empty. I put 16gals of fresh fuel in it.

I found the problem but not the fix. The main jet is dumping fuel into the barrel on idle. I pulled the card open again and replaced the float valve and the float based on the rebuild kit specs. It called for a .780" dry height. I also set the metering valve based on the kits procedure. I re-installed it and have the same problem... main jet fuel on idle.

What else can induce the fuel to the main jet on idle other than the float valve?

This thing is really starting to piss me off!

· Registered
771 Posts
Discussion Starter · #8 ·
glfredrick said:
The interior passages in the carb - idle circut, etc. - are likely plugged with varnish from the old gas. The cure is to soak the carb in carb cleaner, then insure that all the passages are clean. If the idle circut cannot flow correctly it will siphon fuel through the main circut.

Also, is there a free source of air into the engine - to provide venting for the PCV? It is possible that you are drawing too much vacuum and that is siphoning fuel out of the carb.

That is about the limit of my knowledge - anyone else out there have any ideas?
After 3 carb tear-downs, 20-sum beers and 2 cans of carb cleaner, I figured I would spare my liver. I ended up throwing a rebuilt on it. It took care of the flooding/richness problem. It sputtered and misifired though and was a total dog. I spent another 4 hours reinstalling parts I had changed out and diagnosing whether the ECM was screwing up.

I learned a couple of interesting was to diagnose the problem from a local tech. If you disconnect the SPOUT plug and have the same problem, it is not related to the ECM as that is it's only control on the ignition system. I also learned that you must place the coil of the timing gun as close to the spark plug end of the cable as possible. Otherwise, you may get too close to anothee cable and induce a false signal. I proved this one today
:flipoff2: !

Finally, keep your eyes open to the little things. After total frustration set in, I decided to check the plugs that I put in yesterday. It turns out that all of the flloding and carb cleaner fouled the 4th cylinder's plug. I cleaned it and she runs like a champ now. :zzz: It's time for bed now. Only 1,000+ mile to drive tomorrow.

I hope this is educational to learn from my mistakes. Otherwise, this post would be useless :flipoff2: :flipoff2: :flipoff2: :grinpimp:

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