hello ,

What is it when you pull the pcv valve ( hose and all) and a misfire ceases?

but, when its normally hooked up it misses ?

valve cover gasket has been replaced

what could this miss be please and thank you

 

How many miles are on this engine? How much oil does it use? How much smoke comes out of the PCV hose when you take it off?

Sometimes a engine will have a lot of blowby. This is from it being worn out. The PCV system has the job of taking all this blowby and letting it go into the intake, but sometimes on a worn engine it's too much for it, and it can cause running problems for the engine.

If this description fits your engine don't worry, if it runs good otherwise you can get a lot of miles out of it still, until it starts fouling the plugs. What I usually do is take the hose that goes to the aircleaner(the intake for the PCV system) and take it off the aircleaner, get a old heater hose or some sort of hose that is longer, hook it to the valve cover and run it down over the side to the frame. You can tie a old coffee can under the hose to catch any water and oil that might come out of the hose. Do that, and leave the PCV valve side hooked up, and try to turn the idle mixture screws on the carb to tune out any miss left. You might not get it out totally, you might have to live with it. But you have to live with some things on a old engine.

 

This is a stretch, but by disconnecting the pcv valve, hose and all, if you did not cap off the port at the intake manifold [you did not say], then you have created a vacuum leak, which would make the mixture go very lean. Perhaps your "baseline" mixture is too rich? Have you checked your air filter to make certain it is not very dirty?

 

sorry here the story franklin 2

1985 ford f150 300i6 np435, Dura spark ii conversion (new non-emissions carter yf)

80*** miles on odometer (previous owner and older paper work confirms this)

had a misfire (thought it was lean so changed the carb. /it had throttle shaft leaks)

turn out the "miss" is still there but, it runs a lot better now (more power, less heat issues )

oil issues none very little oil use and it did have a valve cover gasket leak (squirted it on the exhaust ) and leaks at the oil pan gasket and bolts ,they where/are loose (but not the bearings ) no smoke out of the tail pipe or the pcv

1986f150six ,no I didn't cap it off at the manifold ,

when I'd pull the pcv (valve and hose still connected to the manifold ) it would stop missing


maybe if I just put a older breather type cap for the first intake hose and so it wouldn't get vacuum on both ends makes sense?

 

The PCV valve is a controlled vacuum leak. It's there to suck the bad fumes and water vapor out of the engine to the burned. It does not pull a vacuum on the inside of the engine. Instead as it pulls the bad air out of the engine, good clean air from the other fitting hooked to the aircleaner lets clean air into the engine to replace what's being pulled out. Whether you pull the clean air from the aircleaner and it's little filter thing, or pull it through a cap with the steel wool filter in it, it doesn't matter.

You might try a new PCV valve. If you haven't replaced it. Someone may have put the wrong one in, and there was a debate in another thread where a guy wondered if he should use the original style PCV valve, or use one for a earlier truck since he got rid of the computer stuff and went with a earlier carb. I recommended he go with a PCV valve to match the year of the carb he had. Maybe you should try that if you know what year carb you have now.

 

thank you, Franklin 2

I heard about the "shake test" on pcv valves but I just read about how it can still fail and cause odd problems anyway so I will get a new pcv valve and see if that fixes the this annoying miss

if not who knows what it could be

I will keep you all heads up on this project

 

I did adjustments on the carter yf (1971-74?) and it has a hesitation or bogs

at a curtain rpm ,when I accelerate it bogs down bad should I increase the carter yf's accelerator pump/meter screw in a little more or is it richening too much? and should back it out 1/4-1/2 turn ? or in?

oh and the choke hanges up on its fast cam ( it has brand new parts should it wear in?)



the spark plugs are colored tan/brownish pink make a difference? (sounds perfect too me)

not black and sooty or scorched

 

Turn the adjustment one direction and if it gets worse, turn it the other. Turn it enough to make a difference also.

I do not know what you mean about the fast idle hanging, but if you are expecting it to drop out of fast idle by itself when it's warming up, it probably won't happen. There is too much pressure on the throttle from the throttle spring, and that puts too much pressure on the fast idle cam. The choke mechanism is not strong enough to overcome this, so you usually have to go out and kick the throttle to make it slow down. This takes the pressure off the fast idle came and lets it drop back.

Most people expect these carbs to work like a newer fuel injection system but it's not going to.

 

anyway even when I am driving and either while it is warming up or at operating temp it bumps up on (sticks?) idle or drops down (all from high idle1500- low idle 650 /550

like this warms up , bump throttle drops idle (supposed to do) but, then it while driving and using the throttle it kicks its self up to high idle

Is the steps on the fast idle cam sticking or is the fast idle /choke linkage messed up or bent wrong cause I did adjust that to factory specs.



thank you , TULLY

 

When it's going from fast idle to slow and then back again, get out and look at the choke door. I am assuming the engine should be fully warmed up by then, and if it is, then the choke should be fully open, no flopping around. If it's flopping around, find out why. Mess with the round black adjustment piece and see if that will make the choke door stay open.

 

ok I understand auto choke to an extent but........

is there a measurement on how far it is supposed to be?

all diagrams say either index, or under hood sticker

A- my under hood sticker only says non adjust or not more than 2 tick marks deviant

or B- index? my black choke housing has no tick mark/ reference , only where it screws to the carb

so I just had it closed to 1/4inch open

 

I would not go by the book. It's going to take several cold morning starts to figure this out, chokes are not a easy thing to get right.

When it's cold and the engine has not been started overnight, go out, take the aircleaner off, and push the throttle to wide open(engine is off). The choke door should go completely shut. If it doesn't, loosen the choke adjustment and while holding the throttle wide open(engine still off) turn the black round thing till the door shuts completely. Tighten the screws back up.

Leave the air cleaner off, get in the truck and start it. The choke is already set, and hopefully you haven't pushed the throttle wide open too many times and have squirted too much gas in the engine. If you have, hopefully it will take off.

Once it's running, don't touch the gas pedal. Run out and look at the choke door. It should be cracked open just a little bit. This is from the choke qualifier or "choke pull-off" that you should have already adjusted. If the engine chokes out because the crack is too small or non existent, then you need to work on the choke pull-off.

If everything is ok, let it run for a minute, and then go in and kick the throttle. If the engine runs rough and stalls and the choke door is too far open, you need to turn the black thing to close it just a little bit more, and then try again.

If the choke stays activated with just the little crack, let it run and warm up so more. If after a few minutes it's still not wanting to come off, you need to check the metal line running to the round black piece. It should be warm. If it's not, you need to work on your heat tube that runs to the exhaust manifold.

 

thanks for the heads up

every time I went "by the book" my engines have ran like crap
so jerry rigged and ,odd things go hand in hand some times

anyway, those "books, diagrams, and papers" must be for just broke in engines

and not set in stone,

because each engine (or anything) acts different

 

Franklin2, that choke thing fixed the stumble , thank you for the advice

now to the , misfire

it has power now but the random cylinder mis is still there

can find any vacuum leaks timing correct carb "should"
be correct so.......

 

could abad fuel pump cause a misfire?

or fuel filter

mines mechanical