351C problem. Help!

Contrary to what you think, you are getting too much air....... this is THE major cause of after-run.

Start by making sure that the choke opens fully when warm... from the sound of it, you'll also need to adjust either the choke idle speed screw, the choke pull off or both. With the motor warm, place the fast idle screw on the second step of the fast idle cam (it's on the choke side of the carb) and adjust the idle speed to about 1600 rpm - using the fast idle screw, natch. With the motor cold, the choke pull-off should open the choke by about 3/16ths of an inch (give or take depending on your climate).

If you are still having problems with after-run, after getting this stuff right you may have to remove the carb and look from the bottom side of the throttle plates. With the choke fully OPEN, look to see if the bottom of the transfer slot is visible (this is a rectangular slot just above the small, round idle hole). Another clue is how much control you have over the idle quality with the mixture screws.... Your 270 cam shouldn't be lopey enough to require drilling the throttle plate but I will say that, after 35 years of doing this stuff, I still haven't seen everything there is to see. If (and ONLY if) everything else is right, you can start with a 1/64th drill bit and drill a hole about 1/8th back from the very front edge of each throttle plate. Again, with that 270 grind, I can't see you going much more than 1/64th, but if you feel the need to increase the size of the hole to regain idle quality or bring the idle speed down (this set up should idle comfortably around 750 in gear), work your way up in 1/64th increments. If you botch it, the holes can be soldered shut....

This modification is not for the faint of heart, those that possess ten thumbs nor is it recommended for those that have said "that's good enough" at any stage in base engine prep.

HTH

Jim Warman snipped-for-privacy@telusplanet.net

"E. Mike Durbin" wrote in news:c2ctrf$ snipped-for-privacy@dispatch.concentric.net:

With the bad gas mileage, coupled with the run on and idling problem, it's gotta be the carb. Do you have the old carb (hoping it was a 4V)? If so, put it back on and see what happens.

Run on (dieseling) occurs because too much gas (and air) is being dumped into the carb throat at shutdown. Ford carbs have an electric anti- dieseling dashpot that you use to set the idle speed. When you cut off the key, the dashpot closes and the butterfly valves close completely. Does your carb have this device? If not, try slowing the idle down, and see if the run on continues.

However, that would have nothing to do with getting bad gas mileage. Carb way too rich, timing problems, a large vacuum leak, just a few things that could cause it.

"Jim Warman" wrote in news:GDo2c.81582$A12.21236@edtnps84:

If there is too much air, how in the world does drilling a hole in the throttle plate help anything? That only deliveres MORE air (and mixture.)

The condition Jim was describing and the modification to correct it (drilling the holes) occurs when the base throttle opening is so great that too much of the idle transfer slot is exposed below the throttle plates. Drilling the air bleed holes allows that the throttle plates be adjusted further closed restoring the proper relationship at idle position of the throttle plates to the transfer slots. The maximum that the idle transfer slot that should be exposed below the throttle plate is .045 inches. This is all well documented by Holley.

Check your timing and make sure it's not advanced too far ahead of what it should be. Also, does it run hotter than normal? The run on is usually caused by excessive combustion chamber temps, which can either be caused by problems with the cooling system, or the timing advanced too far ahead. When you replaced the heads, did you install the head gaskets properly? If you don't get them in the right way, it will block one of the cooling ports and cause the higher temps.

Pintobro

He just finished telling us that he swapped the old 2V carb, intake, and heads for 4V stuff you dimwit!

Merc Thundersnake#16

"Merc" wrote in news:3cw2c.87862$A12.6028@edtnps84:

And this is all you have to add? Asshole.

Neil Nelson wrote in news:nonelson- snipped-for-privacy@newssvr26.news.prodigy.com:

Ok, I get it now. I'm no Holley man. Yes, the run on is always caused by too much air/fuel mixture in the manifold at shut down. Sounds like this could cause it.

Before you drill the throttle plates be sure that they are closing evenly and completely. With the carb off hold it up to a light and look through the throttle bores with the throttle fully closed. You'll probably see a bit of light. The main thing is that it be the same amount on both primary bores, and the same amount on both secondary bores. This isn't normally a problem, but it has been known to happen, especially with a rebuilt carb. Also be sure the secondaries aren't too far open to begin with. They need to be open slightly, but too much initial opening will give you too much air.

Why thankyou for your kind words!

Merc Thundersnake#16