Hey,

I went to check the oil in my truck and the dipstick had an gas smell. The guy who rebuilt my engine mentioned the pistons looked like too much gas was being dumped in (all covered with black carbon). It may have contributed to why the engine failed last time due to not enough oil getting contaminated by the gas. I am once again getting that knocking sound on the passenger side up top on the engine.

So here is my question... what can cause this problem?

How can I fix it?

I have a Holley 500 cfm 2bbl carb with only 2700 miles on it.

I am going to post this question in the FE forum as well as see what they say. They tend to not answer as often as we do here.

Thanks,
Karl

 

Might need the float level set. Might be running on the jets and not the idle curcuit.

Does adjusting the air-bleed scres have any effect on the idle?

Also, you need to know if extra fuel is coming in at idle (above will give you a clue) or at cruise...only real reason (assuming the carb is in good shape) it would run with too much fuel at speed would be if you're not burning effeiciently, like maybe the vacuum advance isn't advancing.

Is the tail pipe sooty too?

 

Thanks Mike.

The tail pipes are sooty, but that could be from before this rebuild. I will check the other things.

 

With old Chebbies a failing mechanical fuel pump will let gasoline into the crank case, contaminating the oil. When the diaphram would go, the gas getting around the diaphram would make its way to the cam.
But with Fords, I think they all vent out into the engine compartment/ground from a weep hole.
Still, I thought this might be worth mentioning. You never know, in the early fuel pumps, it may have been the same for both mfgrs back in 1970, I dunno.

Another thought is that maybe your gas cap isn't vented and it might be building up pressure on the fuel system. This would cause gas to dump into the combustion chamber during the heat of the day, where it would seep down around the rings, maybe???

I can't think of any other avenues for gas to get into the oil except through the carburator system or at the fuel pump. Can't think of any other places where they come together. With valve guide seals oil usually gets into the combustion chamber, not the other way... But I'll keep thinking outside the box for ya. Hope this helps.

 

500 CFM? That is a pretty inefficient carb, unless you were racing. Is this the model that lacks any form of a booster(when you look thru the venturi) Is this the carb that came with the truck when you purchased it, or did you have a different one, and put this one on?

 

I had the old one that originally came with it. I got this one carb a few months ago. I can get the model number tomorrow evening.

 

I am pretty sure that is the same carb. Here is a link to the Holley website describing the carb.

http://holley.com/0-4412C.asp

It also has the electric choke kit specified on the webpage.

I appreciate everyone's help on figuring this out.

Thanks,
Karl

 

Hey Karl, here's a thought. What about a bad intake valve, and say, maybe a faulty or backwards PCV valve?
Outside the box I know, but you never know.
Let us know if you figure it out so I wont keep posting strange and improbable theory.

 

I hope to get to work on it tonight. With my limited mechanical knowledge, I hope it is simple.

Here is a link to the owner's manual for the carb
http://holley.com/data/Products/Tech...199R7950-7.pdf

 

Is the Holly 500 prone to draining down like the 2-barrel model? It would be interesting to let it set for a few days and see if there is any fuel left in it or if the fuel drains into the crankcase. One symptom of drain down is long cranking on your initial start in the morning. (It takes a while for the fuel pump to get the bowls filled back up). Good luck, Jag

 

Thanks to everyone who has replied. I am going to work on it a little tonight. I have a few questions though since this is my first time working on a carb.

1. Is the air-bleed screw the same thing as the Idle mixture screws?
There is one on each side of the carb.

2. How do I check the vacuum advance to seeif I am burning fuel efficiently?

3. Would my truck need a PCV vacuum port? How do I plug a port if I don't need it?

4. Could any of these issues be due to the electric choke installed on it?


Here is my plan of attack
1. Eat dinner
2. Check the float level setting.
3. Mess with... I mean adjust the idle mixture screws (How do I use a tachometer to obtain the highest rpms in place of a vacuum gauge? Just adjust the screws until they hit the highest rpm?)
4. Adjust the curb idle speed to around 700 rpm.
5. If this fixes the issue, have beer
6. If this doesn't fix it, have whiskey and consider some of Jag Red's and Oldfordnstone's ideas

My big question is, if it is already making a clacking noise on the top passenger side during warm up, is the damage already done? Should I have it taken apart and looked at before attempting to fix the carb? I really don't want to have to rebuild this engine again.

 

The clacking noise might be a sticking/stuck lifter. As for adjusting the idle until you get the highest rpm, you answered your own question. Just connect a tach, and adjust the screws until the idle tops out. You will have to wait a few seconds after each adjustment to let the idle settle.

 

#1- Yes, same thing

#2- Put your timing light on it, mark the balance at about 45*'s BTDC with chalk or something that'll show up-accerate the engine (in park/neutral) to 3000 or so RPM, you should see the mark you just layed down with the chalk...ar actaull could be strobing past the mark...but should be in the vicinity withn a few degree.

#2a- in the absence of a timing light, pull the line from thevacuum advance and plug the engine side.

Now appply vacuum to the vacuum cannister (will need another vac line, and hand held vacuum pump...or look for an engine vacuum line to use (power brake/etc...somthing that has vacuum all the time).

With vacuum applied to the cannister, engine RPMs should increase 400-500, easily...this let's you know alls working inside.

#3- Yes, slowly back them off till you get the highest idle, then in just a scooch...like a 1/16th of a turn...same with the other side.

Note: If turning the screws all the way in and out don't affect idle speed...we may have found your problem...

#4- Yes, you should have a PCV-should be full intake vacuum tot he PCV to the valve cover...use it.

#5- 700RPMs is a good idle speed.

#6 Good point on the choke...could definetly cause all your issues as well...if the choke is partially closed, you will run rich.

 

fastmover, did you figure out what the problem was?

Or are you still working on it?

I'm curious.

I "think" (it was a long time ago) that I had the same problem on my old '69 Cougar XR-7.

The screws that hold the throttle plate to the main body were ALL loose.

 

I haven't had time to work on it yet. I have family coming in tomorrow, so the weekend is probably shot as well. Maybe early next week.

kgs