3X2 Holley carb?

Do the front and rear carbs on a 3X2 setup have power valves? I know the center one does, just thought I would ask before I went to the parts store. The carbs in question are part of the over-the-counter dealer kit that was sold in the 60's and early 70's.

I've got all the symptoms of a blown power valve. Black, sooty smoke at idle. No smoke at cruise, but has a slight surge. Hard to start after sitting 10-15 minutes like it's flooded. The idle mixture screws have no effect. I can turn them all the way in or out with no change in idle speed or quality. Horrible gas mileage. Getting something like 5 mpg.

Carbs are on my 67 Fairlane w 390. Engine has 3K miles since rebuild and is stock except for 3X2 and small hyd cam. Just a little rumpity idle.

Suggestions on a power valve number? I'm betting the center one has a 6.5 Should I stay there or change #'s

I just worked on a 3x2 setup on a 1967 Corvette with the 427. They were the Holley carburetors and the front and rear did not have any metering blocks (just the jet plate like the vacuum carburetor secondaries) so they didn't have any power valves, nor did they have anything to do with the idle. It does sound like the power valve is bad and I think that I would stick with the 6.5. I would also check the diaphram on each of the other carbs. I had one that had a small tear right next to the steel plunger and the other one had moved and had most of the vacuum hole plugged.

I read up on them and found an easy way to check for the opening of the additional carbs. With the engine off, you can open up the throttle and use a air nozzle and blow air through the middle carb on the passenger side front of the venturi across the port that supplies the vacuum.

Good luck

David Cole wrote:Do the front and rear carbs on a 3X2 setup have power valves? I know the center one does, just thought I would ask before I went to the parts store. The carbs in question are part of the over-the-counter dealer kit that was sold in the 60's and early 70's.

I've got all the symptoms of a blown power valve. Black, sooty smoke at idle. No smoke at cruise, but has a slight surge. Hard to start after sitting 10-15 minutes like it's flooded. The idle mixture screws have no effect. I can turn them all the way in or out with no change in idle speed or quality. Horrible gas mileage. Getting something like 5 mpg.

Carbs are on my 67 Fairlane w 390. Engine has 3K miles since rebuild and is stock except for 3X2 and small hyd cam. Just a little rumpity idle.

Suggestions on a power valve number? I'm betting the center one has a 6.5 Should I stay there or change #'s

Which power valve to use really depends on how many inches of vacuum you have at idle, so you may want to put a vacuum gauge on it and check. Also as was stated above the end carbs should have no idle circuit or power valve.

Ah, but if the end carbs DO have idle screws....it makes it soooo much easier to get a decent idle.

Ah, but if the end carbs DO have idle screws....it makes it soooo much easier to get a decent idle.

Ah, but if the end carbs DO have idle screws....it makes it soooo much easier to get a decent idle.

Thanks for the info guys. I'm scratching my head over this one. Freshened up all 3 carbs yesterday and I'm still having the problems. The center carb is a Holley #2436, 350 cfm w a 6.5 power valve and auto choke, jetted w 58's. The outboard carbs are the correct # 2437's 350 cfm. No power valve, no choke and jetted w 68's. The outbound carbs are mechanical, not vacuum operated. All three carbs have idle mixture screws. The linkage is progressive. All 3 supply a little air at idle w the center carb used for most driving. 2nd carb comes in at about 70% throttle and the 3rd is only open at wot.
Symptoms:
For the past 5-6 weeks I had noticed a rich idle w sooty black smoke whenever I started it on weekends to cruise. Was ok at cruise, but mileage was bad. Smoke got worse the other day. It would leave a black spot on the pavement under the exhaust if it sat idling for 5 min. I double checked the float levels. All good. The idle mixture screws made no diff. It had all the symptoms of a blown power valve. While tuning on it I must have fouled the plugs. It was running ok, just black smoke. Shut it off, came back 2 hours later. Tried to start it and it backfired out the exhaust LOUD. Blew one of the mufflers APART.

The power valve was not blown. Checked it with a hand vac pump and a little adapter. The gaskets looked pretty soggy and there was some trash in the bowls, so I took all three carbs apart, cleaned them well and put them back together with new non stick gaskets, new accel pump diaphragms and a new pv in the center carb

It will start, but is smoking alot. Now it it looks like there is a little oil smoke as well. Same amount of smoke out each exhaust. Each side is on it's own with no H pipe.

What I have done/checked:

All 3 carbs fresh.
New plugs, new wires (already had them), swapped coil just grasping at straws. Rotor looks ok. Ignition is a Pertronix conversion in stock distributor.
Checked timing
Check all vac hoses to make sure it wasn't sucking fluid from the brake booster or trans
Sprayed carb cleaner along head/intake junction to checked for sucked in intake gaskets, but again it's smoking from both sides equally.
Looking down the carbs with the engine running there is no gas pouring anywhere. Everthing looks normal. The float bowls were full when I removed the carbs. They had not leaked down into the engine.
After I shut it off yesterday I checked the oil. It smelled like gas and was 2 qts HIGH.

I'm wondering it the fuel pump is bad and letting gas in the oil to the point it's getting past the rings and the smoke I'm seeing is gas/oil. The fuel pump is 6 months old. Carter muscle car series pump. No gas out the weep hole on the pump. The fuel filter is glass and there is no obvious oil in the gas.

One last item. Since Friday, in about 12 miles of driving and 40 minutes or so of stationary tuning it has used almost 3/4 of a tank of gas!

Going to change the oil today and try to plug/disconnect the two outboard carbs to rule them out.

Ideas or suggestions?

Thanks

David Cole

I'm thinking that I would want the two outboard carbs to "not" be functioning at idle. It sounds like you are dumping fuel in from one (or both) of them. I would completely shut them off and idle off the center only and see where it goes from there.

I have had a fuel pump leak and fill the crank case and not come out of the hole in it.Have you run a compression check to make sure the compression is up to par.I had a old 6 banger that started puffing black with low compression it cranked fine and run fine but flooded alot.We went through the carb put new points and everything but still did the same thing even tried a different carb same thing.Pulled the engine and freshed it up.After we got the compression back up it quite puffing might not have enough compression to burn all the gas.Just something you might want to check.

Jim

Two things stand out - if the oil level was that over serviced and smelled like gas... don't run it like that anymore until you change out the fuel pump & the oil! I'm sure you know gas has no place in the crankcase.

Second, power valves do not affect idle mixture (standing idle in the driveway). They change the mixture in transition from part to full throttle. You could take it out and start the motor and you'd see no change. Same with the main jets - except they tune WOT - but won't affect idle at all.

Hope this helps!

Thanks for the input guys. I found and fixed the problem. It was one of those dohhhhh moments.

The brand new-in-the-kit Holley brand gasket was wrong on one of the carbs. The kit had 3 metering block gaskets. 2 right, 1 wrong and I didn't catch the wrong one. The wrong gasket was for a vac secondary carb and had no gasket area around the accelerator pump hole from the body to metering block. It was sucking fuel straight from the bowl and out one of the drain holes in the base between the throttle blades. Found it when I pulled the carbs off again today and the intake was wet under #3 carb.

Fixed it, changed the oil. Fired up and ran great, smoked for the first few minutes until I drove it and blew the soot out. Also trickled a little water down the center carb while running to blow some of it out. Runs as good now as ever. Good idle, no smoke at idle. I guess it was pouring sow much gas through that it washed past the rings and diluted the oil. Seems to be no harm done though.

As far as the idle adjusment. I found out that with these carbs you start at only 1/4 turn out on the mixture screws since there are 6. I ended up about 3/4 turn out.

These carbs DO have idle circuits on all 3. They are designed to be run that way. Came from optional from the factory on 61-63? model big Fords. It was also available as an over the counter kit from 66-71. That's what mine has. Cost $240 in 66. Complete deal now runs $1800-1900

Link to pics of a setup just like mine. Note the idle mixture adjustment screws on the outboard carbs.

http://www.hptrends.com/4sale.htm

Very cool, David! That's one of the ones that bite you where you can't see

Similar scenario: A while back a buddy of mine had a Harley Sportster that developed a top-end tick after having the right side cover off..

He wasn't Harley-savvy, nor was I, but I love troubleshooting.... I found the 'straight-from-the-dealer' side cover gasket he got was missing an oil transfer hole that fed the cam journal, and subsequently the top end...

A razor blade and re-torque later it was miles down the road forgotten