New carb still not running right

[lonnie]

Haven't posted in a long while. My Unique was built about 1995 with a 351W by Bill Keller he was a Ohio builder. It had a 750 Holley on it when I got it. It would fall on it's face with WOT so I have replaced the 750 with a 650 Proform racing with vacuum secondary. I put the carb on adjusted to 1.5 turns replaced plugs and took it out for a drive. Runs fine at partial throttle but when I climb in it it miss then picks back up. Just pulled the plugs on the drivers side and the front 2 are white the rear 2 are brown The old plugs were all fowled.
Do you guys think this is a carb problem or ignition? Car has Ford distributor with mag pickup and a Stinger 2 ignition box the carb is sitting on a Torquer manifold.
Thanks Lonnie

[Jerry Cowing]

From your description, I would guess it's not the type or size of carb you're using. I believe it's a carb adjustment problem.

First, make sure your float level is adjusted correctly. Too high and it will flood or run too rich, too low and it will starve for gas at high RPMs.

Then adjust your idle and air mixture screws to get maximum vacuum at idle to get your highest idle setting (not 1.5 turns, that's just a starting point). If the RPMs increase when you adjust the air mixture screw in or out, keep adjusting your idle screw to lower the idle RPM back to the correct idle for your cam/engine design (500-900 RPM) each time you get maximum vacuum by adjusting the air mixture screw in or out.

Drive the car at 3000 RPM, shut off the engine, and then check the spark plugs. If you let the car idle below 3000 RPM while pulling into your driveway, you won't get a good spark plug reading. Turn off the engine at 3000 RPM and "then" push in the clutch immediately so your engine doesn't diesel. Don't push in the clutch and then turn off the engine at 3000 RPM or your engine may diesel and don't let the car come to a stop with the engine off and the clutch engaged as this will flood the engine. You need to time this procedure properly.

If the plugs aren't tan, then try reducing the size of your jets, but don't get too small (white plugs) or you will burn holes in your pistons. Plugs should be a light tan color. Black & thick/clumpy is oil leakage (bad rings or valve seals), white is too small of jets, tan is good, dark brown/black is too rich.

If it still stalls after getting the jets correct (correct plug color), change the spring in your vacuum secondary. This adjusts how quickly the secondary opens during hard acceleration.

If it's still hesitating when you stomp on it, check the accelerator pump gap. This is an often overlooked adjustment but is critical to responsive acceleration. If it's too large or small a gap, your accelerator pump won't give your engine that little squirt of gas it needs for the initial acceleration.

Or, just take it to a good mechanic and let him adjust it.

[lonnie]

Jerry
Thanks for your thoughts. I'm sure the carb still needs to be adjusted but I was hoping it would run a little better out of the box. The mechanic I hired to adjust the carb when I first got it wants me to replace the distributor and ignition box before continuing to tune it up. At this point I am not at all sure about what to do spend $800 or so for MSD box distributor and coil.
When I first got the car it had the 750 on it with the single plane manifold. The guy I bought it from who is a professional mechanic still tells me he never had any problems with the combination. At first I had no problems but before I had 200 miles on the car the HTO started to leak so I was down while I fixed it. After that it started falling on it's face when I nailed it. Took it to a mechanic who work on it about 4 hours with no change in throttle response. I drove the car the way it was for about 2000 miles and then the 750 started leaking so I bought the 650 and a RPM dual plane manifold. I have not installed the manifold yet. I have gotten a vacuum and plan to use it to try and fine tune the carb.
Just got back from a little longer ride and I got a backfire out the exhaust when getting into it a little. I plan on driving it some more today do you think this will cause any problems?
Thanks Lonnie

[Jerry Cowing]

Yup, back firing is not a good thing. Maybe your mechanic is on to something. Back firing is caused by an ignition problem, usually timing and distributor advance adjustments. Maybe yours are out of spec.

Back firing also normally damages a carburetor by blowing out the Holley power valve which will also cause the carb to run to rich. Usually doesn't affect high rpm hesitation though, just affects idling and running rich.

[lonnie]

Jer
I am thinking the same thing about ignition. It only back fired once on my drive home this morning. Just got back from another drive no back firing but still has a miss when I give it full throttle.
This is the first time the car has been driven this year and it does seem to be running better the more I drive it. Will be driving it again tomorrow if we don't have rain. Next week I'm going to use my new vacuum gage compression gage and timing light don't think I can do any harm and may learn something.
I'll keep you informed here on my results If it's still the same I'll take it to my street cars mechanic who I bought the car from. If he says ignition then I'm MSD bound. If not will try the dual plane manifold.
Lonnie

[pbrown]

All Holley carbs built since 1992 have power valve protection built in. All Holley clones that I've seen also have this protection. It's nothing more than a ball bearing in the vacuum path that acts as a check valve when the engine backfires. These are great when you need them but can cause their own tuning issues.

Certainly your carb needs some fine tuning but you should not discount the ignition system. You can't go wrong with an MSD Pro Billet unit and a 6AL ignition box.

Check out the Innovative LM1 wideband AF meter. It's a great tool for tuning your carb.

[spd4me]

lonnie
I've got a 396 stroker windsor with a holly 750 and single plane manifold. I installed a Proform main body 9 to 10 months ago. I checked my plugs 2 months ago and the back four where white like new and the front 4 were brown. The tech at Proform said it was a problem with the intake manifold not distributing the gas evenly in the single plane at lower rpm. I also read in a Engine Masters magazine where they tested a stroker with a single plane Victor Jr and a RPM Air Gap. The air gap generated more horsepower. The single plane is made to make horsepower in the 5,000 to 9,000 rpm. I very seldom go over 5,500, so the efficency of a single plane isn't good. I just bought a Air Gap rpm and plan to install in about 3 weeks. I also plan to change my jets from 72's to 74's and leave the meter plate alone.
Bob

[Master]

Lonnie, If you can't figure out your issue soon let me know. I have a friend in the Cleves area who helped me dial mine in.

[lonnie]

Thanks for the info guys as you can tell I'm slow working on the car. Rained here all week but today is going to be nice so my son and I will be using my new tools.
PBrown
Read up on the LM1 do you just clamp the wide band into one side of the exhaust?
Spd4me
A dual plane manifold is my next try also. I knew the single plane was not working with the 750 and I was going to try a dual plane with it but it started leaking so I got the Proform 650 to try before replacing the manifold.
Master
Thanks for the offer if I have no luck today I'll let you know. Good to here from someone in the area.
Lonnie

[pbrown]

Read up on the LM1 do you just clamp the wide band into one side of the exhaust?

You can use the optional sensor clamp or weld a bung into your side pipe. The clamp would be the better way to go with the sidepipes.

I just noticed that you are in Cinci. I'm there now and would have brought my LM1 had I noticed earlier.

[lonnie]

Quick question on the proform there are 2 vacuum ports does it matter which one you use to check vacuum and adjust carb

[pbrown]

Quick question on the proform there are 2 vacuum ports does it matter which one you use to check vacuum and adjust carb

One of the vacuum ports is a switched port while the other is full vacuum. The switched port is designed for your vacuum advance on the distributor. It will have little to no vacuum at idle and kicks in at part throttle. What maked it switched is that it pulls vacuum from above the throtthe plates. Connect a vacuum gauge to each port at idle and you'll see the difference. The full vacuum port is used for a vacuum/boost gauge or automatic transmission vacuum modulator.

[lonnie]

Patrick are you at GE today?
Just asking because you are from Seattle and worked for GE for 36 years.
Lonnie

[pbrown]

I do not work for GE. I'm just visiting family. I make it to Cinci every six to eight weeks.

[lonnie]

Should have been I worked for GE

[lonnie]

We checked vacuum at both ports just cranking the motor over coil wire off. On the distributor port we got no vacuum but on the other we got about 1 pound. At idle we only saw 5 pounds would go up to 20 when you goose it on the full port.Total advance with out vacuum was 36 degrees and 54 degrees with vacuum advance at about 3000 RPM.

[Master]

Patrick, If you are here in town and have free time give me a call. I live in the West Chester area. 513-265-5737

[lonnie]

Went for a ride with the vacuum advance off. The car was strong off the line and pulled well the little I was able to get on it in second. No hard 3rd at all to much traffic. It pulled hard as I accelerated quickly
(not floored) until about 4000 fell off and then picked right up.
The total advance with vacuum of 54 seems high I think it can be adjusted from what I have read it should be 46-48 degrees.
Manifold vacuum has me confused. I only see 2 ports on the Proform carb both are side by side on the right side of the carb base. Had the distributor on the smaller front port. With the carb closed and just cranking the engine both ports were reading zero. From what I have been reading maybe both of the carb base ports may be ported if so I need to find a manifold vacuum port.
Haven't really changed the tuning much from the way it was in my first post but it is running better now then it ever did with the 750 CFM that was on it.
Not done yet. Tomorrow we'll be making some small adjustments to the carb new plugs and see if the vacuum advance on the distributor is adjustable.
Thanks for the help will post the results.

[pbrown]

Don't connect the vacuum advance to manifold vacuum. It's designed to work with the switched port of the carb. I'm curious to know what vacuum level you are at when you hit the flat spot. Maybe you can route a vacuum gauge into the cockpit and go for a drive.

Many vacuum canisters are adjustable. If you have a factory ford unit, and it has an octagon shape near where the hose connects, then it is adjustable. If it is aftermarket, refer the the documentation.

Do you have a vacuum secondary or mechanical carb? What power valve are you running? What is the manifold vacuum reading at idle?

[pbrown]

Patrick, If you are here in town and have free time give me a call. I live in the West Chester area. 513-265-5737

I'm here until Tuesday morning. I'd love to see your car if you have time. I'm near the Kenwood country club. In fact the back yard is the country club. I think Sunday would be best for me.

[pbrown]

Lonnie,

I just reread your post. You state you have a vacuum secondary carb. The better choice on a light car with a manual tranny is mecanical secondary. I think your secondaries are not coming in soon enough. Do you have a set of springs? Try going with a lighter spring in the secondaries.

[lonnie]

Patrick
Vacuum at idle is 5 psi goes up to 20 psi when you open it up some.
The power valve is #45 pri. jet #70 sec. jet #80 pri nozzle #31 idle air bleeds are .073 high speed bleeds .033

[pbrown]

Patrick
Vacuum at idle is 5 psi goes up to 20 psi when you open it up some.
The power valve is #45 pri. jet #70 sec. jet #80 pri nozzle #31 idle air bleeds are .073 high speed bleeds .033

5 seems really low for idle vacuum. Engines with stock sissy cams usually run in the 20s. Street performance cams are typically in the teens. I have a Magnum roller cam that is about 8.

[eliminator]

"I just reread your post. You state you have a vacuum secondary carb. The better choice on a light car with a manual tranny is mecanical secondary."

Patrick,

I will have to disagree with you on that statment, vacuum secondaries set up correctly on a light car with a manual transmission are great. It's all about personal preference, you could not run fast enough to give me mechanical secondaries on my car.

[Naumoff]

"I just reread your post. You state you have a vacuum secondary carb. The better choice on a light car with a manual tranny is mecanical secondary."

Patrick,

I will have to disagree with you on that statment, vacuum secondaries set up correctly on a light car with a manual transmission are great. It's all about personal preference, you could not run fast enough to give me mechanical secondaries on my car.

I have driving Cobras with both and prefer mechanical secondaries.
Throttle response on a performance engine is way better with mechanical secondaries. Seat of the pants preference.

[lonnie]

The 750 that was on the car had vacuum secondary and I had read on forum probably eliminator that vacuum was better for street. Thats a side issue though is 5 inches vacuum to low? Guess I could have a intake leak. Is spraying starter fluid around the carb base and manifold the best way to check?

[ralphscott]

Yes

Ralph