New 383 runs really bad/Please Help

[maddart]

The engine was built by a professional engine builder. Nothing wild .40 over KB 10.1:1 compression -Cam .450/.475 lift 215/225 duration.
They also helped in the engine break in.

ok-set timing 10 degrees btc vac. line disconnected and set carb for max vacuum. Has open headers at this point. Wow this thing runs like crap. at idle it runs like it has a vacuum leak-real rough. I give it gas and it hesitates or spits gas big time.(Has a remanufactured holley 750 vac. secondary). In the 2000-3000 rpm range it sounds pretty strong.

This is my first build and i'm hoping to get some guidence.

 

[Redpolara]

Some of those remanufactured Holleys are an absolute nightmare, they sometimes get to a stage where.......no matter what you do they'll give you grief.
Firstly i'd borrow another carb (quickest and easiest option).....see if that fixes your problem.
Secondly i'd check the valve timing.

 

[68383GTS]

Yep timing or carb.I would put it at 16 initial timing and about 36 total.If you do not have a dial back try 5 before.

 

[68ChargerAG]

I'd say timing too. But I don't have much experience with this either. I have a similar set up on my 383 and have to run with much more timing advance (haven't got it dialed in yet or I would say what it is, work still in progress). It seems to me that the trend on here with anyone running a bigger than stock cam and bigger carb on a 383 has to run lots of advance.

Might also be too much carb. I have a 750 Holley w/ vac secondary as well and am wanting to try a smaller one to see if I can get rid of the dead spot off idle. I am thinking that I might just simply be over carbed and running very lean right off of idle. I had to put bigger jets in just to pass emissions becuase I was failing NOx and CO. I think that helped some with the dead spot, but I still have some dialing in to do. ???

Good luck. Please post if you figure it out so I can see what you did.

BTW... What does your engine builder say?

 

[Deleted member 214]

I had a Holley 750 vacuum secondary on a fairly mild 383 in my 66 Satellite. Stock Magnum cam, Edelbrock DP-4B dual plane intake, 69 HP exhaust manifolds with a 2 1/2 inch dual exhaust system, mild 727 and 3.23 Sure Grip. Ran GREAT right out of the box. Might be a bad rebuild, but I don't think that it is overcarbed.

 

[MprDoc]

Id say timing too, did you install your own distributor?? It could be too that maybe you installed it a little more advanced/retarded than you meant to. Does it start right up or take a few turns??

I strongly dislike my holley. I all ready got rid of it with plans to run something else.

 

[Meep-Meep]

If it runs bad at idle only and you have it at 10 BTC then I doubt it's the timing. That's a pretty normal setting. Vacuum leak is a strong possibility. Is your PCV hose hooked up? On Holley's the port hides under the rear bowl and can easily be missed. Also just for fun recheck firing order. 1-8-4-3-6-5-7-2. What's the ignition system? Points or electronic?

 

[maddart]

I rechecked the firing order 3x and it is correct. the pvc port has a rubber cap on it. When i adjust the idle mixture screws (Both sides) there is a very small amount of variation, not more than 1 or 2 lbs. getting 12-13 pounds of vacuum
The timing is spot on-1-2 pumps of gas and it fires right up.(during break in)
Electronic ignition-orange box

Edit: Tried it this morning and couldn't get it started. I had to pour fuel into the carb to get it running.
When its warm it fires right up.
I will check the timing next for overall timing of 36 degrees at 3000 RPM. This is with vacuum connected correct?

 

[Meep-Meep]

The overall timing should be with the vac advance disconnected.

Do you have the orange box wired correctly? Coil polarity, ballast resistor, etc..

Was there no gas in the carb when you tried to start it? Curious why you had to prime it when a few accel pump squirts wouldn't get it going.

Did you do a compression check just to get more info? Hopefully you have something like 150 PSI or more.

 

[MarPar]

Id say timing too, did you install your own distributor?? It could be too that maybe you installed it a little more advanced/retarded than you meant to. Does it start right up or take a few turns??

I strongly dislike my holley. I all ready got rid of it with plans to run something else.

What are you thinking of runnin' Doc?

:icon_axe: Don't want to hijack, but i would like to pick your brain...think i may have the wrong carb....thanks for the ad space, maddart :icon_salut:

 

[07charger67]

Could you have timed it to the exhaust stroke? I don't want to say thats what you did but I did that and broke the engine in that way by accident. It would run but had no power due to the it being 180 off "idled like crap". Sounded like it had a vacuum leak too.

 

[detmatt1]

Crankcase vented properly??, just trying to leave no stone unturned.

 

[Manifold]

I prefer to set the initial timing by using a vacuum gauge, then adjust the mechanical advance (I run a Mallory Unilite) to give me the total timing I want.

My 383 likes lots of initial advance (likely a low compression motor) and maxes out the vacuum reading at 28 degrees. I do live at about 5600ft, so that adds to the need for more timing.

 

[Gmanzolirae]

Just not right

I'm sorry, but I would have to say that it is a little to much CFM for the motor, being that the engine seems to be of a mild build it is far more carb than needed. A 650cfm vac secondary carb would be your best answer, and if need be you can always rework the jet sizes to accomodate what it may lack if any in the fuel/mix department. Bigger is not alway better.
Timing is always a big issue, but judging from where you live the altitude is not really a factor. But did your cam require center lining? And what is the standard advancement on a stock engine for your area? The more advancement on the timing usually reflects the altitude of your area, or competition location, as well as manufacturers design, and ignition system requirements for the spark advancement, She definately can be firing to early.
Maybe Not?????

 

[maddart]

I checked the timing and the guy that helped me break in the motor set the timing for 10 degrees ATC instead of 10 degrees BTC. I adjusted to 12 degrees BTC and seems alot stronger and running cooler.Maintaining 190-200
Would have liked to set at 36 degrees @ 3000 RPMs but by timing tape has ripped off.
Still not alot of adjustment in the idle mixture but the vacuum is at 15 inches.
When i unplug the vacuum advance there is no decernable difference in the way it runs at idle.
I will see how it starts tomorrow after it has cooled down.

 

[polkat]

Even a 400 ci engine running at 6500 rpm only requires 600 cfm, according to the Holley Manual. A 383 running at 5500 rpm only requires 480 to 490 cfm. Efficiancy changes these numbers a bit, but not that much. A 750 carb, even if running only on the primaries, is way too much. Not unusual as most people way over carb anyway. I'm not saying this is your problem, but your carb is too big.

Frankly this sounds like a vacuum leak to me, maybe around the intake gaskets or carb base. Even with that cam your vacuum numbers seem a bit low to me.

 

[68383GTS]

Yes needs to be between 5-10 BTD.750 cfm will work just fine.I ran a 750 Holley on my stock 383 1970 Road Runner for 5 1/2 years.I now have a 71 Road Runner stock 383 with a Holley 750.

 

[olebrowndodge]

I checked the timing and the guy that helped me break in the motor set the timing for 10 degrees ATC instead of 10 degrees BTC. I adjusted to 12 degrees BTC and seems alot stronger and running cooler.Maintaining 190-200
Would have liked to set at 36 degrees @ 3000 RPMs but by timing tape has ripped off.
Still not alot of adjustment in the idle mixture but the vacuum is at 15 inches.
When i unplug the vacuum advance there is no decernable difference in the way it runs at idle.
I will see how it starts tomorrow after it has cooled down.

i always set mine to 10 BTC then i advance my higher to where it still starts good and does not run hot

 

[69 Runner]

OK....I didn't read the entire thread but.......


OPEN HEADERS? Are you running a cold plug?

 

[maddart]

Rj12yc