425 Performance and Carburetor questions/ HELP!

Discussion in ''Da Nailhead' started by johntdaddy, Jan 28, 2014.

  1. johntdaddy

    johntdaddy Active Member

    I need some assistance with my 64 Riviera. It has the 425 with a mild cam and stiffer valve springs, I believe it is similar to a TA20 and stage 1 valve springs from TAPerformance. I installed a TAP roller timing chain and degreed the cam as best I could. I added the MSD ready to run distributor and wires so no more points (and the resister wire is out of the circuit) It is still running the stock ignition coil because two different MSDs crapped out on me. I bought the car with an Edelbrock 750 carb with an adapter plate. To me the car does not have the low end power that it should and from what I read on here last year on this site, I believe it may be related to the carburetor. I did change some internal components in the Edelbrock to try to tune it but it does not seem to have helped much. I also recently noticed smoke coming out of the secondary shaft bushing when I was starting it the other day. It runs better than when I bought it but I just think it could be better. I am thinking of changing the carburetor this summer and was wondering what you all recommend? The trans is a 400 w/o switchpitch and it has a stock rear end as far as I know and I am assuming a stock lower end on the engine or maybe 1 rebuild. I am not sure about the valves/seats. I run 93 octane with standard Autolite spark plugs. (I have run two other types of plugs besides what I bought it with and the Autolites are the best) I honestly do not recall where I left the timing but I know the advance is disconnected and I believe I have the timing advanced so I get around 35? Degrees at high rpm with light to moderate advance springs. It has a very rough idle and not much power off the line. I read on the Holley website that the higher cfm carbs are for power on higher rpm applications and lower cfm carbs are for more power on the lower revving engines like the nailhead? Is the carburetor too much for it? Any advice would be appreciated.<o:p></o:p>
  2. CameoInvicta

    CameoInvicta Well-Known Member

    Hey Jim,

    There are a few things I would try. Although your engine might be better suited with an 850cfm carb, I don't think that is what's holding you back. The MSD distributor has infinite adjustability. Shoot for 32-34* of total timing, all in by about 2200rpms. With this, initial timing should end up around 14-16*, depending on the bushing used in the distributor. If the timing isn't right, it could certainly act like a dog. Are you sure there are no vacuum leaks, perhaps from having the vacuum advance disconnected? Also, if the cam was degreed improperly, that could also be an explanation.

    How rough of an idle are you experiencing? Something similar to the TA 20 shouldn't be that radical.
  3. GS Jim

    GS Jim Platinum Level Contributor

    I put a '66 Ported intake with a 750 QJ on my 401. Man what a difference. I'm not a fan of adapter plates. Too much restriction. I have a stock '66 QJ Intake for $350 if you're interested.

  4. CameoInvicta

    CameoInvicta Well-Known Member

    Good point Ponch. I glazed over the part about an adapter plate. If you haven't done the doc dual plane mod on the intake and adapter, it is a very worth while improvement.
  5. Nothingface5384

    Nothingface5384 Detail To Oil - Car Care

    Edelbrocks afb is a mediocure carb...avs version yoi csn tune better
    Id either go with a 750 street demon or a qjet rebuilt and modded through specialist..john osborne used tk.be that guy
    We have our vendor everyday performance thatll be up to that task.
  6. Bigpig455

    Bigpig455 Fastest of the slow....

    My 2 cents - Q-Jet all the way, and Everyday Performance can help you out, to perhaps do a hybrid build..later APT Q-jet with a 64 style throttle arm set up.

    I personally like Bosch 4036 platinum plugs. Don't foul, spark well with a Pertronix III

    All that said, I'd start with the distributor - if you have no vacuum advance, your part throttle performance is going to suffer. Consult guys like Tom T or Carmen Faso for a good curve....
  7. telriv

    telriv Founders Club Member

    Have you blocked off the heat under the carb??? Or used the stainless plate that is supposed to be under the carb??? Would cause a BIG vacuum leak, along with a rough idle, no power low end because your sucking exhaust into the intake fuel/air stream.
    The 750 is not TOO BIG. The dual quads were 625CFM each which equals 1250 CFM's from the factory.

    Tom T.
  8. 487nailhead

    487nailhead Active Member

    I don't know what the gas is like in your state but California is 10% ethanol. Every engine I test run I typically have to go up 3 to 4 sizes on the jets (even on new out of the box carburetors) to get the air /fuel ratio in the 13.5-14.00 range. What your describing is the engine sounds like lean to me, power starts to come on about when the metering rods pick up and the engine richens up. See if you can find somebody with an exhaust analyzer to see what its doing. You can't smell rich because what you smell at the tailpipe is hydrocarbons, a lean misfire increases them too. So rich will smell just like lean.
  9. johntdaddy

    johntdaddy Active Member

    Thanks for all the info and the ideas. I hadn't even looked at doc's dual plane mod sticky, shame on me! The timing is set to about 34-35 and it comes in early but I will double check what the curve says. I am 99.99999% sure there is no vacuum leaks, I have been up and down that intake many times and the plug underneath has a hack weld on it but it seems to be holding. All the times I have been into it, I dont think I took the spacer/adapter off and never realized the exhaust channel. I also dont remember what the intake gasket looked like when I had it off. MORE FACE PALMING!! I will have to check that, I have actually seen that on a Chevy before.... I have jetted the carb to be richer and upsized the rods because I thought it might be too lean but it did not make a noticable difference at the time. But I have tweaked so many things that I cant recall exactly what has helped and what hasnt. By the way, the only reason I did the cam was because I could not identify which cam was in it, now at least I know what I have :)

    Again, thanks for the help, I will dig into it when it gets above zero here in detroit (no heat in the ol garage) and I will let you all know what happens.

    Still not a fan of Edelbrock though! I have always loved the Q-jets but I heard the Holleys work the best on this application? Decisions, decisions....
  10. CameoInvicta

    CameoInvicta Well-Known Member

    I've got nothing but good things to say about my 850cfm Holley DP. It has an incredible amount of adjustability, and in my opinion performs better than the Edelbrock I used previously.
  11. gsgtx

    gsgtx Silver Level contributor

    the factory settings are rich to start with on these carbs, you said you went even richer. check your plugs they might be fouled. go back to stock rods and 107 primary jets. vacuum advance is a good thing to have hooked up and working. make sure you are getting full throttle and secondarys are wide open.
  12. johntdaddy

    johntdaddy Active Member


    Thanks for the opinion on the Holley, I would love to try one out if money allows.


    I have checked the plugs repeatedly and they are not fouling. The vacuum advance was disconnected on someone elses advice from here, I was kinda against it but am trying it anyway. I may try to hook it up again if I can find the real problem. And Yep, I have double checked the pedal linkage to make sure I am getting WOT and the secondaries are opening all the way.

    Thanks for the suggestions, I might get out there this weekend to rip the carb off...again!
  13. John Codman

    John Codman Platinum Level Contributor

    I am surprised that Doc hasn't jumped in here. In fact, I haven't heard from him lately. Does anyone know if he's OK?
  14. bhambulldog

    bhambulldog 1955 76-RoadmasterRiviera

  15. johntdaddy

    johntdaddy Active Member

    telriv, you win the prize, the prize being my gratitude! Well I froze my fingers off but I couldn't wait....All the times I took the carb off and I never pulled the adapter plate,:Dou: the not so mechanically inclined guy that owned the car before me installed the insert for the adapter plate upside down so there was no pressure on the exhaust ports, the result is a blown out gasket...

    So, after I do doc's update and buy a new gasket, I am going to put the pedal to the metal! I can't wait to feel the real power this engine holds. Unfortunately, it will likely be a couple months before I can experience the power. Now I have something to look forward to! I am guessing the Edelbrock will stay for some time yet :( I need to save all the money I can for the Riviera national meet in Colorado, if I can afford it :)

    Thanks for the help guys!

    Attached Files:

  16. johntdaddy

    johntdaddy Active Member

    Follow up,

    After several hours in the cold garage with my air grinders freezing / icing up, I completed Doc's dual plane mod to the best my patience and numbness would allow. :TU::TU: I know I could spend several more hours porting the deep one but it should function ok on the street for now. I also plugged off the exhaust ports like Tom suggested! I put it all back together and she sounds good and has excellent vacuum. After some fair weather tuning, she should run like a top. Hot restarts are a bit rough but I am sure some retuning will help that. Can't wait for this Michigan weather to break so I can get her on the road.

    thanks for the help guys!


    Attached Files:

    Last edited: Feb 25, 2014
  17. CameoInvicta

    CameoInvicta Well-Known Member

    Glad you got it figured out John!
  18. doc

    doc Well-Known Member

    I am still here guys,,, been dealing with my moms death.... getting my feet on the ground again....

    John, glad you found the dual plane mod.... now you need to refine it,,, you need to smooth up the edges on the intake and you need to get or make a 4 hole square bore adapter and make it and the gasket match the intake opening.... the car will perform much better after that is done.... I always keep the heat in the manifold and under the carb.... you need it to make the cat pee gas vaporize , so it will burn.... also make sure the exhaust butterfly is open.... and working,,, lube it with graphite.....
    I make an adapter from 1/4 or 3/8 steel plate, using carb gaskets as a pattern.. and put champher headed bolts holding it down to the manifold and drill and tap holes in the plate to hold the carb to the plate.... then the adapter is also a heat shield for the carb....

    driving on the street you do need the vacume advance and you need to work right... stick the vac hose in your mouth and suck it down and plug the hole with your tongue to see if it holds vacume,,, if it leaks down , replace it ....

    Dont forget to open your air cleaner up to get more air into the engine.... you cant make a 400 + cube engine breathe thru a 1 1/2 '' hole..... free flow in,, free flow out.... :Brow:
  19. johntdaddy

    johntdaddy Active Member

    Doc, sorry to hear about your mom! My condolences!

    yep, I want to refine it, and I will , eventually, the weather was quite the hinderence, freezing my grinders and my hands! As far as the adapter, I realized as I was bolting the carb on is that it has holes that look like it would bolt right to the intake?!? I will be checking into that! While I plugged off the exhaust right under the carb, I kept it to the manifold so I hope that is acceptable?

    The advance will work now that I have achieved vacuum in the intake and I will hook it back up and retime the engine. I have verified it with a vacuum pump plus it is a new MSD distributor.

    Oh yeah, the heat riser was missing when I got the car, so not much I can do with that.

    As for the air cleaner, I am missing the stock lid so I am running an inch and a half open element.

    i know I still have some work to do but it's much better than when I bought it 2 1/2 years ago! Baby steps, lol!

    thanks Doc!
  20. Riviman

    Riviman Well-Known Member

    My condolences. ..

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