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STILL having engine problems HELP!!

Collin

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Still having issues with my 383. Stock HP block, forged crank, diamond pistons on factory rods, comp cam hydraulic roller, ported 906 heads, cast intake, on my 3rd carb. Couldn't get the last dual feed double pumper from pro-systems to run right, so went to a QFT SS-680 dual feed, electric choke. Now running digital point conversion. Running 20 degrees initial timing, and at all in 3,000 RPM at 34 degrees. Running 93 octane fuel.

Trouble shooting so far:

Battery had some bleed down issues as it would never hold past 12.4 volts overnight, however after hooking up the gauge to it and driving it gave a 14.5 v reading the entire time.

Fixed the distributor which seemed to have a little bit too much play as the rotor was making contact with the contacts in the cap.

Dialed in the AFR almost perfect on idle and in the primary circuit.

Had an issue with dropping push rods 2-3 times and put a new set of comp hydraulic lifters in. Re-sealed the intake again.

Heres the issues:

Around town the motor idles and runs the primary circuit beautifully. Put my foot into the gas for a quick launch and no power and pops through the exhaust OR the carb depends on the day. On the highway, again the primary circuit runs great and I can make decent pulls to maintain highway speed. The SECOND I bury my foot into the gas I lose power and pop through the carb and/or exhaust.


So thinking it may have been electrical we seemed to have debunked that, now thinking it could either be a valve sticking or intake leak?? Compression test with cold engine and WOT showed 180 PSI in all banks. Compression seems high which may explain a dieseling problem I have off and on.

Pulling the plugs showed 3&4 were good, the rest are soot covered. The plugs in the back are worse than the ones in the front. Have had the intake off about twice and was careful to reseal the thing up nice. Could I be looking at an intake seal problem? Wondering if it was an intake seal/valve sticking would I have problems just on the secondaries??
 

Russ69Runner

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What type carburetor are you running. Is it a single four barrel or do you have a six pack. Might check for a vacuum leak some where. If plug's show black fluffy soot then too rich a fuel mixture. But still need to know the Carburetor set up.
 

Collin

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Barrels 4
Booster Down Leg
Brand Quick Fuel
CFM 680
Choke Electric
Circuit 2
Fuel System Carbureted
High Speed Air Bleed 28
Idle Air Bleed Size 70
Material Aluminum
Model SS-Series
Primary Main Jet 68
Primary Power Valve 65
Primary Pump Nozzle Size 31
Product Type Carburetor
Secondaries Vacuum
Secondary Main Jet 78
Throttle Bore 1-11/16 inch
Part Number SS-680-VS
 

halftrackman1

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Has the heads been milled to much, this will make the intake leak
 

mac

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questions:
vacuum at idle ?
choke staying open ?
engine at temp when problems occur ?
what plug are you running?
are you using vacuum advance ?
what is your dynamic compression ratio?
 

mac

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usually an intake leak will cause a leaner condition. how did you dial in your primary circuit A/F ?
 

Collin

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Vacuum at idle is 12
Choke is staying open
Yes engine at temp when problems occur
Running Champion RJ12Y plugs
Yes using vacuum advance coming from manifold
Will have to calculate dynamic compression

Primary circuit dialed in using an AFR gauge
 

Collin

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Looks like the valley pan did not seal well and that oil and air were being sucked in. Only about 500 miles on cam so a pic to show the wear. Going to measure the valves

15E84050-9A34-4602-A16A-9F1FD7F8B8D7.jpeg

8F482327-5BA5-4EDE-9B7A-E968E2053FC6.jpeg
 

Collin

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We did that. Think it’s an issue when the intake was milled causing a poor mating surface. Going to take the intake to be milled again. Just in time for spring.... :up:
 

droptop

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Once you get the intake vacuum leak fixed, plan on it running VERY rich on the primaries. If it was running good on primaries with the leak, it had to be dumping raw fuel. That is the reason for the fouled plugs.
 

Roadcuda

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I don't think I've heard the term dynamic compression ratio before. What's the difference between that and the numbers you usually hear about?
 

Russ69Runner

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You had the intake milled before. If you keep milling it will cause more problem's. The wedge will get smaller and the block wont mate up with it or should I say the head's. Ran into this problem building a 440 motor had to get new head's and intake. We tried double gasket's to close the gap but it would only work for a while then start leaking again. Now day's you might get a size match intake or a little larger and cut it to fit what you have now. Good luck hope it work's out for you.
 

mac

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I don't think I've heard the term dynamic compression ratio before. What's the difference between that and the numbers you usually hear about?

takes into account the opening and closing of valves to give a more real world number instead of using only the bore, stroke, and chamber size.
 

Collin

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So just as Russ69Runner stated the engine shop does NOT want to mill the intake. They recommend Indian Head Shellac Sealant by Permatex. They stated that with the metal gasket will be perfect
 

Big John

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Just gonna toss this out there.... On the aluminum manifold for the A12 in 1969, the factory installed a thin gasket on top of the steel intake gasket. I've used them on aluminum manifolds and had good success in sealing them on the first try. They were available from Fel-Pro, but IIRC, I believe the Mopar gasket (if still available) was about half the thickness.

Some guys use them and swear by them. Some don't feel it's necessary. As I say... Just tossing it out there as food for thought.

s-l500.jpg
 

Collin

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I actually tried to use those the last time but due to the work to the heads and intakes the bolts wouldn’t fit
 

BOB KAMMER

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why were you dropping push rods,were they bending? if you milled the heads the pushrods could be to long
 

Collin

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Bob,

Dropped push rods because my hydraulic lifters were bleeding down and getting stuck. Defect from Comp that others have reported as well.
 
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