Hot Rod Forum banner
1 - 20 of 25 Posts

·
Registered
Joined
·
116 Posts
Discussion Starter · #1 ·
Hey guys,
I have a 72 Chevelle with a 383 Stroker. I just put on a new Holly Double Pumper, 650 CFM with a Air gap dual plane edelbrock intake manifold.
Runs great, but when I punch the throttle, it sputters and then kicks in, if Im at a stop, I punch the gas and sputters and nearly dies. But then catches and takes off. Any Ideas? Did I not tune it properly?
Timing is set at 12 degrees advance.

Next issue is that the motor under heats. Before the swap, it ran at around 190 degrees. Now it runs at 100-120. If I stop, it heats up to around 190, but then when I get going again, the temp rapidly drops back to 100-120...

Bad thermostat?

Any suggestions/troubleshooting is helpful.

Thanks,
Mike
 

·
Registered
Joined
·
12,338 Posts
post the stats of before and after. What was the carb and intake before,how did it run,why did you change it? The 650 is way too small but should work great for idle to 5k
 

·
Registered
Joined
·
116 Posts
Discussion Starter · #3 ·
Carb before was a 600 CFM edelbrock. 1405 manual choke.
Intake manifold was holly street dominator, single plane, post 82 with EGR valve spot.
And how is the 650 way to small?
 

·
Registered
Joined
·
12,338 Posts
I would use a 750 on a moderate 350 cube engine.Most 383s are higher out put and you did indicate it was in a chevelle,I was guessing it made some power.
If you used a street master before then you must have been looking for gas mileage?
 

·
Registered
Joined
·
12,338 Posts
correction street dominator,low rpm intake too,not as low as street master. I had a street dominator on my corvette when I bought it. The car mad 205 horse power with that intake,measured on a dyno-jet dyno
 

·
Registered
Joined
·
116 Posts
Discussion Starter · #6 ·
I primarily changed it out because I didnt like the way that the carb was running. Wasnt happy with the product, and it was borrowed. (had to give it back)
As for the manifold, It had two spots for a EGR valve, so it needed two blocker plates. I could also tell that it was restricting the hell out of the motor.
And I did specify that it was in a chevelle. (i double checked)

Once I put everything on, it ran great. I reused the thermostat, prolly a bad idea, but it didnt give me any issues prior to the swap.....
 

·
Registered
Joined
·
12,338 Posts
What is your total timing(@3,000),cam specs/CR,exhaust, even a meek 383 should be at least fun to drive.
The biggest issue is matching the parts,,,combination,combination

then tuning
you need to provide more information please
 

·
Registered
Joined
·
116 Posts
Discussion Starter · #8 · (Edited)
Ok Ill start from the top just so I dont forget anything:

-1972 Chevelle Malibu
-350 block, bored .80 over with a stroker kit.
-Stock heads
-Long tube headers
-Flow master exhaust
-Cam is a mild RV cam. Im not sure of the duration. Very mild though, just above stock.
-Air Gap Edelbrock Intake Manifold
-Holly 650 DP Carb
-Turbo 400
-Stock Differential
-Floor Shifter
-HEI Ignition

If I remember correctly, the total advance is between 32-36. Ill have to double check tomorrow.

I think thats it as far as performance mods are concerned.

Let me know if you need any additional info.

Mike
 

·
Registered
Joined
·
1,684 Posts
I would change thermostat first to eliminate that as a problem. I have read a lot of post with the same problem of hesitation when using the Edelbrock RPM AIR GAP. It is not a good intake to use in cold weather so with the temperature running so cold that is probably the problem. If you can get the temperature up to 190-195 it will probably run better. Experiment with the timing try setting the initial at 16-18 degrees. You will have to limit the mechanical advance to 18-20 degees. What are your camshaft specs? What distributor are you using? Read this Wiki article on setting your HEI and timing. Also there is a section in the article on adjusting the transfer slot on Holley carburetors. Increase the initial timing and close the front throttle plates. http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor. BTW you will need a timing light with advance.
 

·
Registered
Joined
·
116 Posts
Discussion Starter · #10 ·
As far as the cam specs, Im not sure....I dont remember.
Total advance is betweem 32-36, Ill have to double check.
Ill change out the themostat tomorrow and see if that helps..

Thanks for the help guys.

Mike
 

·
TAKE A KID TO A CAR SHOW
Joined
·
2,865 Posts
I would change thermostat first to eliminate that as a problem. I have read a lot of post with the same problem of hesitation when using the Edelbrock RPM AIR GAP. It is not a good intake to use in cold weather so with the temperature running so cold that is probably the problem. If you can get the temperature up to 190-195 it will probably run better. Experiment with the timing try setting the initial at 16-18 degrees. You will have to limit the mechanical advance to 18-20 degees. What are your camshaft specs? What distributor are you using? Read this Wiki article on setting your HEI and timing. Also there is a section in the article on adjusting the transfer slot on Holley carburetors. Increase the initial timing and close the front throttle plates. http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor. BTW you will need a timing light with advance.
Your right the air gaps start to frost in the plenum and carb venturies about 40 degrees! In Michigan it even freezes the throttle shafts on cold days stuck at speed !!!! Not a good thing :pain: Its a warm weather intake there should be a warning on the box when a person goes to buy one LOL
:eek:

Jester
 

·
Banned
Joined
·
9,993 Posts
Ok Ill start from the top just so I dont forget anything:

-1972 Chevelle Malibu
-350 block, bored .80 over with a stroker kit.
-Stock heads
-Long tube headers
-Flow master exhaust
-Cam is a mild RV cam. Im not sure of the duration. Very mild though, just above stock.
-Air Gap Edelbrock Intake Manifold
-Holly 650 DP Carb
-Turbo 400
-Stock Differential
-Floor Shifter
-HEI Ignition

If I remember correctly, the total advance is between 32-36. Ill have to double check tomorrow.

I think thats it as far as performance mods are concerned.

Let me know if you need any additional info.

Mike

".080" over"?! are you sure? That's going to lead to a LOT of problems.

The timing has already been mentioned.

And for that mild combo that 600 edelbrock is a MUCH better match, though it may have needed tuning and/or cleaning.
 

·
Registered
Joined
·
12,338 Posts
RE:
(The stock gears and stock low stall torque converter is not going to be very friendly to getting crisp throttle response with a double pumper carb. Just too much throttle, too fast.
Recurving the distributor advance curve will help. More initial at idle always helps throttle responce.)

please explain this? a 650 DP is extremely responsive,even on a 283 with 3.08 gears?
 

·
Banned
Joined
·
9,993 Posts
RE:
(The stock gears and stock low stall torque converter is not going to be very friendly to getting crisp throttle response with a double pumper carb. Just too much throttle, too fast.
Recurving the distributor advance curve will help. More initial at idle always helps throttle responce.)

please explain this? a 650 DP is extremely responsive,even on a 283 with 3.08 gears?
That depends on how it is tuned. He may have way too much coming in from the accelerator pumps, or too early, or not enough, or too late, or too long/short duration. The joys of running that much pump on a heavy car with stock stall and mild gears...
 

·
TAKE A KID TO A CAR SHOW
Joined
·
2,865 Posts
Is the carb new out of the box or used? If out of the box no tuning except basic. it should work very well and be pretty snappy on your combo! If its used it may have been tampered with! to match a different engines demands!!!

Jester
 

·
Registered
Joined
·
22 Posts
I would say since you just changed the intake and carb the problem lies there not the thermo stat. I bet you need to check your accelerator pump linkage and make sure that gas starts squirting the instant the throttle blades open. sounds like its getting air from the blades opening and then following an instant late with fuel. make sure both promary and secondary blades are set equally and keep them that way. only ajusting both equaly if need be. the transistion slots should only just barely show under the carb below the throttle blades. your pump linkage should have a small amount left in it at full throttle so you dont prematurely wear out the plunger or pump. but it should also be set like .020 from actually squirting gas out. lol like the linkage should be just barely touching the pump arm and you can look down the carb when you apply throttle by hand and make sure that gas and air comes on together. also start with the fuel air screws 1-11/2 turns out and adjust from there with a vacuum guage getting the highest vacuum reading you can and the fuell mixture screws equally turned. what power valve do you have compared to vacuum reading? hang in there bud you got this. also are you running a fuel pressure regulator? and your floats are set right?:welcome: Ive read double pumpers prefer single planes but ive seen all kinds of combos work and work good so that shouldnt be the problem. Have you tried a spacer? I just swapped from a open spacer to a 4 hole and I can definitely feel the better low end response. Although I have a single plane so maybe an open would give you more plenum area? idk oh you can also buy a set of colored pump cams and that will change the amount of pump shot sent to the squirters. maybe larger squirters would get fuel there faster too. you have plenty of room to grow before needing a bigger 50 cc pump shot too. Even new out of the box tho the carb should be checked thoroughly and set to spec.
 

·
Registered
Joined
·
116 Posts
Discussion Starter · #18 ·
Ok, well.....Feel kind of dumb. But have no problem admitting my faults...
I put the thermostat in backwards....Yup....sure did. I was on such a hurry because I was on limited time. So, that problem is fixed. That's my karma for not putting a new one while I was doing the swap.
As far as the sputtering, I adjusted the ratio screws. The process i used was basically set them all the way lean, then turning them 1-1/2 turns to rich. I test drove it and it much better. However I need to see what the total timing is and adjust more from there.
Ill update the page when I am able tomorrow.
Oh yea and by the way I still feel dumb about the thermostat. But whatever.


Thanks for all the replies.

Mike
 
1 - 20 of 25 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top