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I give up on the V12 Lincoln engine! Help please.

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Just recently installed a rebuilt engine (2nd time). Starts awesome, idles ok & seems to run ok in the shop. But out on the road it SUCKS big time! It seems to pull pretty good under acceleration but at a steady speed it misses & seems to have severe dead spots. If I push down on the throttle it seems ok.

 I have an Edelbrock dual manifold, & put on 2 rebuilt Holley 97 carbs from Carbmeister out of FL off eBay, they seem ok but who knows. 

 I'm pulling only about 17 in of vacuum & the guage says "late ignition timing" I would like to see 20 in of vacuum. Can't see how it would be my distributor (it is old) if it is not missing under heavy acceleration. 

 The front carb has a thick fiber spacer under the carb (with all new gaskets of course everywhere) where as the rear carb only has the 1/4" aluminum spacer with the vacuum port & hose going to the oil filler area for sucking out the fumes. Have plugged this off & still ran like crap. 

 Sorry for the long post, I just have given up on ideas. Do you guys think it's carburetion versus electric? 

 One last thing I didn't use any gasket compound on the intake or carb gaskets as I had a hell of a time removing the intake manifold when I did the 1st time when I had to pull the engine the 2nd time ( for an unrelated issue). If I had a spare set of carbs I would try swapping .

Thanks for any help at all, I'm at my wit's end with this car!


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Some of the Holley AA-1 carbs are marked 94.


Some of the Stromberg EE-1 carbs are marked 97.


Have not seen a Holley marked 97.


Are you running progressive linkage (hope not) or straight linkage?


If straight linkage, have you synchronized the two carburetors?



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HA! Welcome to the club! It sounds like you have the same issue I do. I am still Stumped on why it does it. This spring I am going to see If I have a spark plug wire crossed and put into the wrong place in the "Side" cap of the distributor. Find this thread I created last year as we talk about somethings I have done to remedy the issue to no luck..About the 4th post down I explain some thing I have done..  Mechanical Fuel Pump 

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Here is a link to Chris's post



I hope that you do have gaskets on both sides of the aluminum spacer.

Did you check for vacuum leaks at the carburetors by spraying starting fluid around the base of the carburetor?

Do you have a modified grind cam along with your dual carburetors?


If you do not have a vacuum leak, I suggest that you do the fuel delivery test that I told Chris to do. If the fuel pump passes that test, check you float level in both carbs.

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Yes running straight linkage. I checked the firing order at the caps several times with a DOL (continuity tester).

I have not synchronized the carbs other than adjust the linkage the best I can. Thought about swapping the carbs, although can't see what good this would do.

 Does anybody re-use there base gaskets? If I remove a carb I replace my gaskets but am running out of them. 

 It sounds like it's carburetion issues to me.

 I wish I had 2 other carbs to try, if it duplicated it would be something else.

 I'm just done now for throwing more money at this time.

 I think your right carblink they must be Holley 94's. (I was going from memory). 

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Sorry thought my last post went thru, so I just resent it.

Yes I have gaskets on both sides of both spacers. Good quality thick gaskets, but haven't tried spraying around the bases. Did fix 1 small vacuum leak on the intake threads where the 3/16" metal line goes to the distributor.

Talked to the carb guy earlier he said most guys synchronize there carbs in the wide open pos which I did. But now it won't idle down, (one carb doesn't close off enough. So as I can tell there's no way around this. 

As there is some mechanical slop on the throttle shaft.

 He's going to send me 2 different carbs to try.

 I'm about to the point to pull off the dual manifold and go back to the original, might make things a heck of a lot easier!

There maybe a highly polished Edelbrock manifold come up for sale!

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I would suggest synchronize at idle, especially with vacuum power system carburetors.


If the carbs are sync'ed at idle, they will stay sync'ed throughout the entire RPM range.


If you disconnect the linkage from carb to carb, both carbs should completely close. Linkage should be adjustable for length.


I guess I must be an old fogie, but started playing with multiple carb set-ups in 1959, and this is the first I have ever heard of sych other than idle for anything except a dedicated race engine. And I have done hundreds of them.


If you put the single carb manifold back on, do not be to hasty in selling the dual manifold. If you had not wanted it, you would never have bought it in the first place. Do some reading, enjoy the car for awhile, then think about the dual set-up again. If it goes that way, you might think about Strombergs rather than the Holleys (no, I don't have any, not sharpening my own ax), as Strombergs have mechanical power systems, which are easier to tune in a multiple set-up than the vacuum system of the Holley.


If you wish to discuss the issue, 573-392-7378 (9-12, 1-4 Mon-Tues central time).


This article was written for dual single barrel carbs, but the same principals apply to your installation:


Aftermarket dual carbs



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Thanks Carbking, I'll re-synch my carbs in the closed mode. Do you believe there's that much of an advantage of the Stromberg's over the Holley's? I'm feel like I'm kinda tapped out now, can't justify spending a grand on Stromberg's at this point.

 I did talk to H&H Flatheads in CA on another matter a while back & he did recommend Stromberg's & wouldn't even rebuild Holley's. So maybe this may be my only way out.

I've had the car over 30 years & it did run ok years ago with the Holley's, but replaced the carbs I had with these new rebuilt ones because I couldn't stop them from bleeding down after I shut off the engine. 

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A miss at steady speeds is seldom fuel delivery related. The most common causes of fuel related miss at a steady speed are debris in the float bowl plugging the main jets,  float level too low or a vacuum leak. On a single carb system an easy check is to pull out the choke, but that doesn't work very well on a dual carb setup.


An ignition problem is more likely to cause a steady speed miss.


I would start by doing a cylinder balance test at idle and then again at 1,000 rpm.

Connect your tach dwell meter to one of the terminals where the condenser mounts. This will give you a reading ( I am not sure but I think that it will be 50% of the rpm) of the RPM. Short out 1 plug at a time and watch and listen for an rpm drop. Each cylinder should decrease the rpm about the same amount. If any cylinder does not decrease the rpm as much as the other cylinders, examine the wiring to the plug and the plug to determine the cause. If all cylinders create the same drop at idle, repeat the test at a higher rpm.


If the miss was not confined to certain cylinders and you still have a miss at a steady speed, try this tip. Remove the distributor from the car, remove the rotor and fit shrink tubing over the distributor shaft. You should also check for rotational play (none) and end play of the rotor (about 0.005" - 0.010") use shims to reduce the play. Reinstall the distributor and test drive.


Let us know how you make out.

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Thanks Tom, it's acts more like carburetion as it has tends to lope & has dead spots if I modulate the throttle. I moved the accelerator pump linkage to the Winter position seemed to be better. I probably didn't describe the symtoms accurately. It wasn't exactly like ignition miss. But I will what you said when I get a chance

As I recall I do have some rotational play on my rotor (actually quite abit).

Will this mess up my timing? This distributor hasn't been worked on for a long time.

 I think I'm going to pull it & send 2 back Jerry Richman to get reworked.

Thanks again

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A question for any of you dual carb guys:

With direct linkage on my Edelbrock do you run the same jetting in both carbs? Currently #52 jets or run different jets on the back carb?

One guy told me to run #57 on the front carb & #54's on the rear. ( This is older fellow who claims he has set up a lot of these, so he should know what he's talking about). But the carb guy says maybe this other guy thinks I'm running progressive linkage because he did say the front one is doing the most work. Haven't been able to confirm this with him yet.

 It would seem to me that with direct linkage both carbs would be doing equal work and therefore should be jetted the same or I would some cylinders running a different mixture.

 I can't remember the difference between an Edelbrock versus say an Offenhouser (sorry for the spelling). Most people say the Edelbrock is a better setup but can't remember if one carb feeds a certain set of cylinders or everything is combined.

 If one carb feeds 6 cylinders then I would think you would them jetted the same???

Thanks again for any help.

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I guess that I still do not know your symptoms

On 3/22/2022 at 9:15 PM, lincolnmatthews said:

Starts awesome, idles ok & seems to run ok in the shop. But out on the road it SUCKS big time! It seems to pull pretty good under acceleration but at a steady speed it misses & seems to have severe dead spots. If I push down on the throttle it seems ok.

I think what you are trying to say is that it acts like engine is starving for fuel. At cruising speeds the power valve adds fuel to the fuel delivered through the main jets. I would start with putting stock LZ main jets in both carbs. If the mixture is too rich, you can reduce the size of the jets.


Check your spark plugs for correct fuel mixture. Start with clean plugs, drive the car at speeds higher than 35 mph to 55mph (without OD) to make sure you are using the power circuit for about 50 miles and then drive it into your garage without letting the engine idle for more than 1 minute. Check your plugs for correct color.


If the plugs show a lean mixture, change the power valve in both carbs. I would start by having 6.5 power valves installed in both carbs and go to stock LZ main jets in both carbs. If you still have the problem change out the power valves to 5.5 valves. Some people have started out with the 5.5 and not had a problem with a rich mixture.


The 17" of vacuum is probably alright with the dual carbs, Charlie Schwendler can supply you with the correct power valves and will install them for you so that they do not leak fuel and there will not be a vacuum leak between the base and the body. IMHO he is the best in the business for the Holley 94. he can be contacted at  cas5845@yahoo.com


Balancing your carbs for idle mixture is important for idle and speeds up to 25mph.


There should be very little rotational play in the rotor. any play will change the timing from starting all the way to full throttle. If you have play, it can cause starting problems, overheating problems and poor mileage. I use small pieces of shim stock to remove it in used rotors. I return new rotors that have rotational play.


I know it seems like I emphasize testing more than giving you a part to replace, but I do this to make sure that only parts that are not working are the ones replaced. I have seen too many projects go down the tubes and sold dirt cheap because the cars cannot perform properly. It pays to take the time to only fix what is broken and not just throw a part at it because some said it fixed his problem.

Edited by 19tom40 (see edit history)
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I fall into the Holley power valve trap every time that I suggest changing it. I keep thinking that the power valve rating is where it will open, but it is where it will close. A 5.5 valve will close when vacuum is above 5.5" of vacuum at the valve and a 6.5 valve will close when the vacuum is above 6.5" at the valve. When it is open, it will feed more fuel into the venturi.


When you accelerate the throttle plates are wide open and the vacuum is lower, so the power valve will open. At a steady speed above 25 mph, the vacuum will vary with the load and the vacuum at the power valve will remain in a range of about 5" -15.5" depending on engine load. The 1940 Lincoln carburetor had an 8.5" valve from the factory, and that is what I would start with.  What I am trying to say is to get a richer mixture, you need a higher number power valve.


You need identical carbs in a 2 carb system on most dual carb manifolds. This will balance the air and fuel mixture to the engine. Most dual carb manifolds have the carburetors feed a plenum, where the mixture is shared to same extent between all cylinders.


The plan of action should be: Check spark plug color for mixture. If rich, go to lower tension power valve. If all plugs are the same light brown color, you can try a larger size main jets. If that does not fix your problem check your plugs again.


The next step would be to make sure that the power valves open at the the same vacuum and that there are no obstructions to the power valve vacuum port in the base of the carburetor. Make sure that the nozzles are clean and mounted with the correct gaskets and the clamps are secure and not over tightened. Make sure that the throttle plates and venturi are cleaned of any debris or carbon build up. Make sure tat the correct gasket was used between the manifold and the carburetor, and between the base of the carburetor and the body of the carburetor.

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I don't believe that he is. He has his own shop and rebuilds carburetors to a very high standard. He usually installs new throttle shafts and refaces warped and pitted surfaces so that the carburetor performs like it did when new. He uses the Daytona kits with the addition of parts that he has found work better, like the float needle and seat, and power valve. He does not replace parts that are working properly and he can engine test your carburetor before sending it back.

Edited by 19tom40 (see edit history)
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A couple of things:


(1) Would be nice to know EXACTLY WHICH Holley AA-1 carbs are being used.


(2) Tom - with no absolutely no offense meant "At cruising speeds the power valve adds fuel to the fuel delivered through the main jets. I would start with putting stock LZ main jets in both carbs." is not exactly true. The power valve should NOT come into play except under wide-open-throttle conditions, not at cruise (unless you are cruising at about 90 MPH ;) ). The main metering jets should provide all fuel necessary for normal cruise. This next may sound "picky" but I do not mean it to be. On the Holley, the power valve does not add to the fuel delivered through the main jets (Stromberg does), rather the power valve, when open, delivers fuel directly into the intake manifold. This is a MAJOR and significant difference from Holley to Stromberg. The extra fuel in the Stromberg is delivered into the venturii where the increased air velocity does a much better job of atomizing the fuel, than just dumping it into the intake manifold.


And I totally agree with Tom on the jetting. Anytime you are changing carburetors, adding carburetors, etc. ALWAYS calibrate the carburetor to stock calibration for the carburetor; then you have a repeatable baseline from which to tune.



Edited by carbking (see edit history)
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Well thanks again both you guys! Your a wealth of experience! I was going to you Carbking but looked like I could only call you on Monday or Tues. 

 At this point I'm going to have to deal with the guy I originally bought the Holley's from. He admits he hasn't much experience with a dual setup. Some guy Grant out of FL very nice & accommodating on the phone. I've already paid for these carbs and he's willing to send out 2 more free of chg. I will of course send the other 2 back.

 I've talking to John Richman from Mass. Who supplied my water pumps & going to do my distributor. He says he's done a lot of dual carb setups. He said to go with the 6.5 power valve & 57 jets (std on the AA-1 at least what I can tell) & 54's on the rear. So this is what I'm going to tell the guy in FL to do to the replacement.

  I know a lot more now than I did a month ago! Thanks again I will let you know how it turns out down the road.

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Jon, I don't mean any disrespect to you and your knowledge about carburetors is much greater than mine, but here is a diagram that shows the power valve flow being added to the main jet flow. I still believe that the power valve will open and close under load at highway speed. If it did not, you would have unwanted speed changes while cruising. A slight load change due to wind or terrain would lead to starving the engine and a slow down.


Matt, Before I put my foot in my mouth again, I would like to know which carburetors you are using. The 94 on the back of the carburetor just give the size of the venturi. The bowl should have an identification number also and that is what is needed to decide on the jet size and power valve rating. The main jets should be sized to give you a fuel mixture that can be properly vaporized and burnt. The power valve should be rated for the model carburetor that you are using.


I strongly disagree with using different size jets in the 2 carbs on a 2 carb manifold. Unless one set is oversized for the application, you will not achieve the correct cylinder balance. I don't know how the runners on the Edelbrock manifold are configured, but if they are configured similar to the LZ manifold you would be starving some cylinders or flooding some cylinders. Think of it this way, would you put a 54 jet in one side of the carburetor and a 57 jet in the other. The 6.5 power valves will only enrich the fuel under heavier loads or higher speeds.


main supply.jpg

power description.jpg

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Tom - you are correct about the power valve fuel going through the main jets; been a couple of decades since I did one of these. Sometimes I should look before I trust my memory.


Note on your listing the power valve is closed on level roads to about 3800 RPM.



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Well an update: my jet kit came in so I decided to mess around and re-jet the carbs. So the forward carb had 51's in it so I put the 57's in. Took it for a drive wow what a difference! Drove 90@ better smoother with only a slight hesitant on acceleration. But totally acceptable after what I'd delt with. 

 So decided to pull the rear carb off and it had 51 jets! So I put the 54's in it. I couldn't really tell much difference although I think it was better. So obviously I had to small of jets in my carbs. The carb guy is sending me two newly reblt carbs jetted 57 and 54's. So I will keep the two best ones. 

 As it was explained to me the Eldelbrock ports are all tied together (unlike an Edmunds manifold) so in my simple mind I really can't see what difference it makes having one carb richer and one leaner as there all tied together. Although the leaner rear carb might possibly be more apt to feed the rear cyls more because it's closer.

 At this point anyway I would have to say the 83 year old guy seems to know what he's talking about.

 I am going to continue to mess around with the jets in the rear carb. Going with 57 jets all the way around probably would be to rich.

Only doing a plug check (several) will tell the story.

Thanks for all your help and ideas! 

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  • 4 months later...

On going saga! I realized I had an old actual Zephyr carburetor it was  jetted with # 55 jets! So I again rejetted to 55 no difference. So today I re-torqued the intake to 28#'s & re- jetted to 57@ the front & 54 on the rear carb. Not bad but still not where it should be! I think I've got carb issues, you can tell by the sound there just not smooth! 

 I swapped out the coil & distributor & that made no diff! On one carb screwing the mix screw in made no diff but when I screwed the other one in, it killed the engine! So something is going on with these carbs! I guess a crappy rebuild?

If it wasn't a grand for strombergs & all the Hassel fuel & linkage's this might be the way to go?

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  • 1 month later...

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