Adjusting my carb to my new heads

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Marcelo Dart BR

Marcelo Dart BR

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Hi,

Recently I swapped the heads of my 318. The old ones were stock 318 small chamber heads with some cleaning and light porting. The new ones are also 318 small chambers but fully ported with 1.94 and 1.60 valves.

The specs on my car are:

-Mopar solid .528 cam
-Flat top pistons (about 9.8/1 with milled heads)
-Eddy RPM intake
-Headers
-Holley 650 double pumper
-3.91 rear end
-MSD distributor with 2 silver light springs (18 initial / 36 total or so..)


Well, with the old heads I was running 69 jets on the primaries and 75 on the secondaries, with 32 nozzles and 6.5 power valve. When I changed the heads I felt the carb was pretty lean.

I tried some different jets and nozzles. By my vacuum readings I chose the 4.5 power valve.

Right now I'm running 73 jets on the primaries and 79 on the secondaries. The nozzles are 35 on the primaries and 37 on the secondaries.

What I feel is some stumble when I try to maintain light throttle, at about 3000 rpm. I was feeling some big stumble when I stepped on the gas to WOT, but I increased the nozzles and it got better, but it still stumbles lightly.

I am a bit confuse because sometimes I really don't know if it's lean or fat. I was thinking the primary was lean but when I incresed the jets it got worse.

One detail is the gas has 25% of ethanol here in Brazil.


Marcelo
 
On a 340/.060 over and a stock bleeds 650 DP Holley, I used to run 70-71 front jets, with the PVCR's drilled out to .060. The secondary was #80-81 . Holley #82 was too rich as was #72. So as I see it you are too rich on the primary's and too lean on the sec.. The acc. pump used the pink cam set on the #2 hole for primary. Or try the black cam. The sec. pump used the #466 orange cam or the #218 no color on 2 hole. The squirter's were .028-.030 front and .031-.033 back. any more will cause flooding. the power valve was 3.5 since the vacuum was 9-8hg. @ idle. That's the ball park and your using a smaller engine so it will need no more than I used. I had years of drag racing to test this out. It eventually ran 12.50-12.80 et's with 4.30 gear and 28" tall slicks. Cam was .484 Purple cam 108 lobe separation. Stock 998 auto.T. 11" High stall conv. @ 2400 rpm flash.
 
Nice, thanks for the info.

I was trying to keep the primary and secondary jets in the same proportion as they came stock, 67/73 I think. Maybe that's not right.

I don't know if it matters but I removed the choke plate.
 
I have used two Proform center body's, (780 vac. and 800cfm double p.) and both came with #72 F. and # 84 rear jets, so the jets are 10 to 12 sizes apart. You can also look up on the Holley site, the jet and bleed # for every carb. then you can try their tuning.
Choke plate doesn't mater. I even sawed off the choke horn on the 650 DP. Then I used the parts on the Proform 800DP for my 440.
The 340 got the Proform Vac. secondary it uses #71 front, since it has the drilled out PVCR. The back is too rich (sooty exhaust pipes) / #86, so the #84 are going back in. The vac. spring is purple, after many tries. It now runs 12.94 et on 275/60 Kelly street tires, and 3.90 sure grip, see my video from Sonoma Ca. I tried colder N9y and it lost one second. Back to the n12y plugs.
 
Tanks, I'll try 71-81. Actually I don't know if I have an #81, maybe I'll have to drill a smaller one.. No one sells these parts here, I have to import everything from the USA.

I've never tried different pump cams. Do you think it's necessary? The car is driven strictly on the street.
 
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