been years since I did much with vacuum advance. If you dropped timing from 10 to 8, would that not now make your timing total drop from 40 to 38? 2 degrees I`m thinkig if all is working right, should be the same change at all rpms with no other changes,,, I may be wrong and not at home to check this. Only change made was the carb, correct? MSD screwing up? Start retard?
Sea foam the crap out of it and give it another shot. My guesses are vaccum leak lean mixture carbon build up
I haven't made any changes to the MSD. The only thing we changes is put on a new carb (from the edelbrock to the holley). So the lean fuel might be the issue. I've never sea foamed but might be a good idea. Maybe I should mention that another problem I have is a stumble off idle. No matter what gear I'm in the car stumbles when I depress the pedal and then picks up. We changed the power valve from 6.5 to 10.5 but got no real improvement. But anyway, that may not be related. I looked over the carb pretty good, couldn't isolate any vacuum leaks anywhere but very possible. If it's lean we should be able to figure it out next week, we're gonna hook up the AF sensor to it. In the meantime, can I install larger jets?
Yes, aint gonna hurt upping jets. What size cfm carb and jets do you have in now? Is your timing Steady? And have you tried a different timing light and a LIGHT not digital one? What's the MSD box # and do you have a start retard?
MSD is a programmable 6AL2. I don't have a start retard programmed in. I did try my timing light which is not digital and it read the same as the digital one. The carb is a 600cfm with vacuum secondary.
i had a 700 double pumper on a chevy 350 that would stumble just like your describe. it turned out that the idle mixture screws were to far out and it was just too rich for the accelerator pump to have an effect. i adjusted it with the vac gage just like we did on yours mo to fix it. i dont think your idle mix screws are off but try turning each one in half a turn
I'll try that during my lunch break, thanks for the suggestion. If that fails I'll try to go with a little larger jets. I believe bryant had 66 in there before.
the jets were 67, changed them to 70 and drove it around. the hesitation still happens. the detonation sound is a quite a bit better. still there but much more faint. does it make sense for it to be "quieter detonation"? I will be able to test drive it better on the way home.
ya it can lesson. so your on the right path. the car is too lean vs over advancing timeing. when you change jets you will need to readjust the idle mixture screws. best to use a vac. gage to do that. i would go up two more sizes and see how that works. it would be a good idea to get a holley jet kit with all the jet changes you will be doing with the supercharger tuning.
One thing you might want to check is the accelerator pump cam. If it is worn out on the just off idle then it will stumble. see if the cam is touching the linkage at idle. If it is not then it will cause a lean condition and cause a stumble also. Just a thought.
I changed the jets to 72. The car is more responsive and accelerates well. There is no change in the sound of detonation. It starts very faint at 2200 rpm and the sound comes in again at 2800rpm, goes away almost until 3200rpm and then gets louder at the higher rpm. I adjusted the spring that activates the accel pump and it made a big difference but further adjustment didn't make it much better. There is still a hesitation. And out of first gear it will bog the car down to the point of shutting off unless I pump again or slowwwwwly accelerate.
could it be the spring that opens the secondaries? is that maybe why I am feeling that bog when I floor it?
