6 Pack Plug Fouling Problem

[Chargered]

I've been having a lot of problems with plug fouling lately and after a lot of trial and error trying to adjust timing and idle mixer, I decided to pull the carbs to inspect them. I pulled the center carb and you can see in the pictures all the carbon in the intake manifold. Also the lower plenum is pretty wet, the upper one seems dry. Any thoughts on what's going on here?

 

[wagonman]

First thing to check is float level. The gasket looks kind of funky, offset and looks like kind of an eyebrow on the bottom pic. Are the gaskets directional? I would not be happy with it.

 

[Chargered]

First thing to check is float level. The gasket looks kind of funky, offset and looks like kind of an eyebrow on the bottom pic. Are the gaskets directional? I would not be happy with it.

Float levels are good. Gaskets are okay, they are just slid over a bit in the pic. I took the carbs apart and they look really good, although I have 64 jets in the center carb and 82 in the outboards. I might change the center to 62 and 81 for the outboard carbs.

 

[R413]

Jets are in use when going down the road, they do nothing at idle.

What are you cam specs?
What is the idle speed hot engine?
What is your idle vacuum?
What power valve do you have?
Has it backfired through the carb?
Is the choke connected and working?
Do the end carbs close all the way at idle?

 

[Chargered]

Jets are in use when going down the road, they do nothing at idle.

What are you cam specs?
What is the idle speed hot engine?
What is your idle vacuum?
What power valve do you have?
Has it backfired through the carb?
Is the choke connected and working?
Do the end carbs close all the way at idle?

Not sure on the cam specs (it was built prior to my ownership), but I was told is a mild purple cam.
I had the idle set at about 800 hot.
Idle vacuum is at about 16 inches.
PV is 6.5
It did backfire through the car a couple of times prior to getting my idle mixer screws set correctly.
Choke is disconnected.
End carbs are closed all the way at idle. I have the mechanical outboards so there is no mixture screws on those.

 

[66Satellite47]

The backfire may have broken the power valve. Normally looks like float level. Try opening the end carbs a tiny bit. But I have no experience with the mechanical end carbs.

 

[Chargered]

The backfire may have broken the power valve. Normally looks like float level. Try opening the end carbs a tiny bit. But I have no experience with the mechanical end carbs.

I have the center carb apart now. I wonder if there is a way to tell if the power valve is bad? I have spare 6.5 and will try putting that in.

Since I've checked just about everything else, I'm now wondering if my fuel pump might be putting out too much pressure, thus causing my plug fouling problems. If I get it back together and still have problems, I'll try a new fuel pump.

 

[Outsider]

Tell if the power valve is bad? A hand vac pump and a holding chamber device, or if you're old school, put it to your lips and suck on the diaphragm side.

 

[Chargered]

Tell if the power valve is bad? A hand vac pump and a holding chamber device, or if you're old school, put it to your lips and suck on the diaphragm side.

Just check the PV using the old school method. It pulled in and seems to be okay.

 

[ckessel]

I've found that PV's can still be bad after a backfire even when they held vacuum.

 

[1968rt]

Clean out your air bleeds. A clogged one will cause dripping out the venturi causing a wet plenum and rich idling

 

[Fran Blacker]

Thought PV's should be 50% of vacuum???

 

[RJRENTON]

Float levels are good. Gaskets are okay, they are just slid over a bit in the pic. I took the carbs apart and they look really good, although I have 64 jets in the center carb and 82 in the outboards. I might change the center to 62 and 81 for the outboard carbs.

The end carbs do not have replaceable jets...they have metering plates UNLESS you've changed to the PROMAX conversion units. Also look for a leaking power valve gasket or bad power valve diaphragm in the center carb. I run my carb float levels "slightly" below the sight port threads.....helps with percolation.
BOB RENTON

 

[wagonman]

I've found that PV's can still be bad after a backfire even when they held vacuum.

Correct, the old school method is just that. I have a Snapon adaptor for PVs. Should hold the rated vac for at least 30 sec. Had one a week ago that the diaphram was going south. Was wet on the chamber side also.

 

[wagonman]

Thought PV's should be 50% of vacuum???

Just a guide not gospel.

 

[RJRENTON]

Thought PV's should be 50% of vacuum???

Power valves are calibrated to respond to a given manifold vacuum expressed in inches of mercury; example: 6.5 = 6.5" of vacuum (opening point). 50% of what number are you referring to?
BOB RENTON

 

[Fran Blacker]

OP's Vacuum gauge read 16" of vacuum.

 

[RJRENTON]

OP's Vacuum gauge read 16" of vacuum.

A Power valve's opening point is determined thru the tuning process....when does the additional fuel need to be added during acceleration: to eliminate a flat spot in the acceleration curve or a lean condition. At 16" of manifold vacuum, the standard 6.5" power valve (or valve of preference) would be closed. If fuel is being added, it is possible that the power valve's diaphragm has ruptured, allowing fuel to be added. 16" of manifold vacuum is typical of idle or part throttle cruise or deceleration vacuum readings....just taking out loud.
BOB RENTON

 

[66Satellite47]

I agree with Bob, you have symptoms of a ruptured power valve. Try another power valve. The 6.5 should be good with a fairly mild cam.

 

[RemCharger]

The end carbs do not have replaceable jets...they have metering plates UNLESS you've changed to the PROMAX conversion units. Also look for a leaking power valve gasket or bad power valve diaphragm in the center carb. I run my carb float levels "slightly" below the sight port threads.....helps with percolation.
BOB RENTON

I thought the end carbs were supposed to run 1/2 way up the sight plugs... or was that just the 340s??