Join Date: Feb 2016
Location: Holland Michigan
Read 'em and weep. Carb tuning issue
Thanks in advance for reading
Recently purchased '65 crew cab malibu. Has 383 stroker with a QF 750 vacuum secondaries. PO told me little about the engine other than it had a Skip White rotating assembly with ProMaxx heads. I do not know the cam in this. The car ran great when I test drove it with the execption of a bad shifting Th350 tranny. Price was right so I took the chance and bought it. 2-weeks later I blew the tranny to pieces at 6500rpm fooling around. Had a local tranny shop build me a new tranny set up for daily driver use. The old trans apparently had a 3400 stall converter and my new trans is 2500 stall.
The issues I am having with the engine is getting it to idle in gear without having to have the curb idle at 1200rpm. the RPM drop is almost 500-600rpm when put into gear. As you can see below, I am also having an issue with plugs fouling like crazy. Plugs are in order with my finger at the 1 and 2 cylinder. Fouling is bad up front and good toward the back.
- I have triple verified that the carb transition slots are little squares in both primary and secondaries.
- I have confirmed the the idle mixture screws have some authority and will stall the engine if turn all the way in.
- Initial advance is 22 degrees, mechanical advance is 10 degrees, 32 degrees total, vacuum advance is not used.
- Carb pulls 11-12 in/hg of vacuum at 1000rpm and when I put it into gear it drops to 5 in/hg at 500-550ish . Idle is quite choppy.
- I currently have a 2.5 power valve installed.
- 6 psi to carb at idle, 5 psi at 3000+rpm on mechanical fuel pump. (converting it now to electric pump)
- Carb has been rebuilt and every orfice chased clear.
- I do not have an AFR gauge.
- For what its worth, jets are 74 in primaries and 82 in secondaries. Even with the above mentioned issues, once the car is driving in part throttle, there is zero bog or lag from part throttle to WOT-- this thing really rips!
- In chasing this problem for a few weeks the issue of drilling the butterflies has surfaced. I will admit to drilling out the primaries and secondary butterflies 1/16" which has improved the fouling problem with the rear cylinders. The drilling also is what helped the idle mixture screws achieve some control over idle vacuum. The drilling has not helped the big drop in rpm when put into gear. I am tempted yet hesitant to continue drilling larger holes.
- I am beginning to suspect that my cam may be too hairy for the converter.
So with that said, I think that I may have multiple issues at once here but I lack any further skill in figuring this out. Your input would be helpful.