ok my question is half throttle performs just as good if not better in almost all situations on my car, when i give it full throttle it goes the same just gets louder, what could cause this?
carb or efi?
was it running right before, and this just started?
is so is it an auto?
Timing??
old school sbc like 36* @ 3000 rpm (which includes base & Mechanical advance)
its carbed, i was thinking mabe it was a carb issue, i have base timing at 11 i dont remember what it was fully advanced it was near 37 if i remember
yes its a auto its been like that since i had it ive been working all the bugs out and this is next
11 is way low dude. Barry Grant has a good guide on what initial timing should be based on cam duration. You will need to figure out how much mech advance your distrib has, then adjust your base from there. Example- if your mech advance is 20* in order to get 36* you would set youir initial at 16* etc… Are you hooked to ported or manifold for the vac advance?
if you want to learn something i’d be happy to help ya some evening
ill try looking the barry grant thing up, i have a vacuum advance hei setup i have one step lighter springs and the weights to match. i have it hooked up on the ported vacuum port on the carb
according to this cams with less than 220 duration at .50 lift require 10-12 base whic is where mine is and my cams duration is 2.18
http://www.gnetworks.com/v4files/barrygrant/Ign%20timingwithimages.pdf
Could be a bunch of things-
37* timing at 3000RPM should work just fine. A little more probably wouldn’t hurt as long as it doesn’t detonate. I ran my race engine with the timing locked out at 41*.
Is the accelerator pump working? Look down the carb and work the throttle - do you see gas squirting down the carb throat?
Pull a spark plug. What does it look like? Black=rich White=lean
Readjust the carb jetting in accordance with what you find the plugs to look like.
It could be a power valve issue as well. Replacing it with a new one with a slightly higher vacuum rating will allow the carb to richen the mixture earlier when you go to WOT.
Check the carb float level, fuel pressure and fuel filter. It might be running out of gas at WOT.
What size carb do you have on it? It could be either too big or too small for the application.
If the car is an auto, does it downshift when you floor it? If not, the kickdown linkage is probably broken/disconnected/misadjusted.
What cam are you running?
What tranny, gears, tire size are you running?
cars a auto, kickdown isnt hooked up i shift manually it has a built th350, 3000 stall, 3.73s small 26 inch tire, carb is a holley 650 vacuum secondary, i have a lighter secondary spring in it to open the secondarys sooner. the plugs are gray with a slight white tint i know this is lean a lil bit.
the carbs float level is dead on.
the accelerater pump is working it shoots fuel as soon as the throttle gets moved
well i ordered up some jets from summit i ordered some 74,s and 76,s according to holley.com my carb should have either 70,s or 72,s and its a lil lean so 74 or 76,s should help without making it rich and hopefully give me that topend power im looking for
Sounds like the secondaries aren’t opening. What fuel are you running? Sometimes the color on the plugs isn’t always a good measuring stick. I say go to the racetrack, make some passes, then jet up 2 sizes all the way around, make more passes, go up another 2 sizes until the car slows down MPH, not E.T. I remember jetting up and going slower, but the plugs looked the same.
im pretty sure there opening ill test it tommorow but its liek when they open it gives more air and not enough fuel, the choke is completely removed as well so it gets more air then stock
Sounds like the secondaries are lean. Jetting up won’t hurt anything.
Did you check the powervalve?
It sounds like the secondaries aren’t opening or are lean. Possibly timing, but I bet it’s the secondaries, I had the same problem with my 350 s10 and it was the secondaries, I took the carb apart and rebuilt it and then it was fine. Only sad thing about this was that it was after I raced alot of people I should’ve beat, haha
Def doesn’t sound like its getting enough fuel. Do what everyone else says and check the secondaries. Hell I’d check the fuel pump while your at it.
the carb is only a few months old, how do i richen the secondarys? i know i can make them open sooner with even lighter springs but does that richen them? it has a steady 7-8psi fuel pressure i know i need to check wot under load. i would think the pump could feed it enough il change it out to a holley one i have and see if that helps
jets in the rear metering block
74&76 sounds too close together. there is usually a larger spread between the primary’s and sec’s. normally 8-10 steps as i recall. i’m running a 750 Hp and have 72 in the primary’s and 81’s in the rear and thinking about leaning the primary’s even more to lean it out at cruise
i was only going to use one set of the jets either the 74 or 76,s to replace the 72,s that are in it now, its only slightly lean it cruises great plents of pickup with barely touching the gas its just full throttle that should be performing better
ok i just looked up my holley part number it has 67 primary jets and 73 jets for the secondarys, so i should be able to swap the 73 secondarys out for the 76s i ordered and see an improvement
also i swapped in the holley fuel pump i had it has a steady 7psi at idle idk at full throttle but it supported my cousins 400hp nova fine so it should be good
Yes.
Also, when the secondaries open, if it still seems boggy, you might not have enough cam to use all that air/fuel at that given RPM. This is when you change the secondary springs to open them later when the engine has gained more RPM and can use the fuel/air.