408 breaking up

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I have the same motor it came with a mighty demon 825 mech. It seems huge to me, but works fine. Mine came with an msd ready to run dist.. I had to tune out a slight stumble by changing the acc pump cams.
 
How do you richen up the cruise circuit of a Holley ? I know carters are just a metereing rods swap but have no clue about holleys. Never had a lean Holley before I guess
 
cruise is a mix of jet and air bleed on a holley. On most you can't adjust the air bleed sizes easilly. That's where initial carb sizing can be a big deal. And why I like Edelbrocks more for street cars...lol.
 
I had an edelbrock 600 on my 69 Barracudas 340 and it all ways ran great and pulled hard. I switched to a Holley with a Proform body and blew the motor up. LOL

Dwayne Porter said the metering blocks from the 650 didnt match the Proform body and caused it to go way lean. Oops.

I stuck a T.Q. on the dart with a stock 71 intake. If I switch it will be a RPM intake and Eddy carb.
 
AdamR said:
How do you richen up the cruise circuit of a Holley ? I know carters are just a metereing rods swap but have no clue about holleys. Never had a lean Holley before I guess
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Until you get over 4-5 sizes, just by changing primary jets.

You mention going to a holley and blowing up the motor, meter block issue right?
no big.
 
I appreciate all the advice guys I guess its time to see what is in this carb for jets etc(maybe I do need a bigger one) but I've got a jet kit so I will try that first I'm definetly gonna check out that web site. BUT is it possible that I have an issue with that box(also) I do know of one other person who had an issue with one from summit though I dont think it was the same issue. Oh yeah as far as edelbrock versus holley I've always liked the edelbrocks, the one on my cuda which is basically stock is awsome but I put an edelbrock 750 on the 408 while I changed the holley base plate and I had to open the hood and make sure there wasnt a stock slant 6 in there! so I dont know to think thanks pete
 
If you do a rod/jet change in the Eddy, they can run hard. But just check to see what jets are in your holley carb.
 
Furry, Yes, I'll be there. Not sure if I'll have my car, a friend's car, or my Neon, but I'll be there.
Pete, It's all about patience, perseverance, and tuning. Take your time, change one thing at a time, and note what you did so you can go back if it didn't help.
 
So just an update on whats going on at this point, I now have a small annoying surge or miss at low rpms and speed and it breaks up at 6000 I went and checked all the ideas that everybody's had so far. I've checked the plugs ,changed the coil,turned up the fuel pressure to 7.5 psi, took out the box ,changed distributors, checked for vacuum leaks, checked the alternator, checked for bad wiring and yet Its STILL there I thought I was on to something when I took out the ign box but on a second trip out it came back. SO I found out that the carb is a 9379 race carb with a 6.5 power valve and factory jetting for sure. So my next move is since everything else has checked out I 'm gonna check to make sure I've got no blockages in my fuel line from tank to carb then im gonna pull the valve covers and check that I dont have a loose rocker then I'm gonna jet the carb bigger on both sides and change the power valve to a 3.5 I'm gonna do these things one at a time and see if it changes anything. AH the joys of fresh rebuild gremlins!
 
Check the vacuum the whole way down the 1/4. Really check it at part throttle, and see if vacuum is making the power valve mis-function.
I hate holleys, but deal't with them so long....
 
I would check the vacuum, a 3.5 power valve will lean out the carb more. It will open later, not until your vacuum drops to that level. I recently tuned a 347 in a Mustang with a 650 DP. I had to install a 8.5 power valve because of a lean spot. This car had a roller cam and was making good vacuum though.
 
latest on the engine issue is I pulled the valve covers and checked the springs also reset the valves just to be sure and still ran rough from idle thru 2200 and broke up up high SO I pulled the carb apart and it had 75 jets in the front and 78 in the rear so i stepped up to 78 front and 82 rear still had issues Plus now its blowin black smoke out the tails, went back to 75 in the front thinkin about 80 in the rear cause it did seem better up top. But heres where things are weird. I retimed the motor, when the engine "misses" the timing light stops blinkin for that split second. I didnt have the light on the other dist. I tried but even with the other dist it had the miss????? so i'm gonna start completely over again and run back through everything just in case I missed something.
 
try 73's in front, 78's in rear maybe go to 80's, but what PV's do you have? What is the vacuum rating at idle in gear?
 
Test plug wires!

Test vacuum at idle in gear and select power valve half to 2 lower than your vac reading @ idle

If only running 1 power valve in the primary, you need to stagger your jetting 8-10 sizes apart.
If you have 2 power valves then the jetting needs to be the same primary/secondary. Too small of power valve can cause surging=lean cruise.
Also you need to first start with the primary, not both at the same time.imo

If you are not doing any of this then we can't help you.
 
I completely changed the wires with new ones and still have the issue.As far as the carb i'm a little new to holley tuning and have tried to follow and try the advice I've gotten here I will check out the power valves next, my question is will the power valves cause the timing light to flash irregularly when it "misses"?
 
I,m following your thread closely.I also am having a surging problem,my car ran fine then all of a sudden I,m getting a surge.I,ve swapped carbs(tq to a 750 Holley to no avail.I also swapped ecu from chrome to orange..still surging.Personally I think it,s an electrical problem(with mine).Oh I also swapped harmonic balancer(360).Hope you get yours figured out and post your problem if you do?I will also,if I figure mine out.Good Luck!
 
I've followed everyones advice and done them all one at a time and so far no dice.I was convinced I had an electrical problem too but after changing or replacing every electrical piece and following every wire end to end I confident its not that. The only thing I havent done so far is change the power valves, I put a vacuum gauge on it yesterday and it fluctuated from 5 to 8 continuously so now I'm thinking I ve got a vacuum leak somewhere, (I thought I'd corrected all of them,) or an issue with the carb or both. I cant get it to change rpm when I spray around the intake and carb though. The other thing thats weird is the timing light cutting out at the same time it misses. I'll keep posting what I find as it happens good luck with yours Petty blue dart. Wild and crazy guy before I tear into the carb again does this new info today with the vacuum gauge readings still tell me to go the power valve route? I appreciate all the help and advice and am trying to do it as it comes I assure you I'm trying everything.
 
Take your old dist cap and drill two 1/2" holes carefully in it exactly next to one of the terminals on the top of the cap. It doesnt matter which one so long as you remember what number cylinder it is in the firing order. Then install that cap and wires and use the wire for that cylinder as the one you put the light on. Then fire it up and see what the rotor is doing. While it's running, the timing light should flash every time the rotor points at the cap's terminal. If it fires too early or too late, or when it's not aligned at all, you have a distributor or oil pump drive issue. If you find the rotor is in different positions at each flash then you have issues in the drive. At that point, try unplugging and capping the vacuum advance hose at the carb and try again. If it's smooth but not lined up, it could be a reluctor phasing issue.
 
Cudapete said:
I completely changed the wires with new ones and still have the issue.As far as the carb i'm a little new to holley tuning and have tried to follow and try the advice I've gotten here I will check out the power valves next, my question is will the power valves cause the timing light to flash irregularly when it "misses"?
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certain time lights and or plug wires keep the signal from reading unless you rev it up and get some energy.
at least I've had that experience with my buddys new blue borg warrners and my dial in kragen time light.
 
SO I think I've got the issues resolved though there wasnt just ONE thing that caused it. Any way I talked to blueprints tech department and comp cams the other day and they both told me the xe285hlcam in a stroker is only gonna be good to around 5800ish and after looking at the dyno sheet and going for a ride it does flatten out after 5800 and if I keep pushing it ,it would break up. So I went through and found #4 wire was bad after all. Then turned my attention to the carb when I took the metering blocks out it had 75 front and 78 rear jets and two PV block offs so I did some playing and came up with 74 fronts 82 rears and 5.5 PV then turned the fuel pressure up to 7.5 psi then bumped the timing up to 37 degrees @ 3000 rpm now the car still flattens out after 5800 but will go 6200 with no breaking up. starts hot and shuts off nicely and runs about 185 with this combo. Thanks to all for your help Pete
 
Hey Pete,Ialso have a mild stroked 340(372)with a 3.58 crank pushing 452hp at 5700rpm also flattens out.That,s in my 73 Dart Sport.My surging problem is in my 66 Dart 360/904.What was wrong with you plug wire?What kind?I,m running Taylors and am gonna do a one over to make sure they,re all firing!
 
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