750 dp carbs for 8-71 blower

[rat tuned]

hi guys,
with my recent blower purchase i received 2 750 dp carbs. this guy has a small local shop and claims to have built some blower motors although i know nothing about him other than what he claims. i haven't opened the carbs yet but something doesn't seem right. he took 2 750 dp carbs and installed 2 proform main bodies. he also installed 4 corner idling and the throttle plates have small holes drilled in them. he jetted them at 70p and 76s with 6.5 primary power valves. they have NOT been boost referenced. now i thought that blowers required that they need more fuel. the proform bodies have 72p and 84s jets installed. why would he jet down? what would a good jetting baseline be? i was thinking 76p 90s. should i just block the primary pv and jet accordingly? should i have them boost referenced? remember this is for a street car that is only driven about 1500 miles a year. thank you again mike gridley

[VDRIVERACING]

You own 'em, so why not bolt them on and drive around town to see how they work.

[rat tuned]

i'm nervous that if they are lean that engine damage could happen. this is all new to me. thanx mike

[don johnson]

i'm nervous that if they are lean that engine damage could happen. this is all new to me. thanx mike
Weld/ or tap into the exhaust tailpipes and install O2 sensor bungs. Then buy/ borrow a hand held O2 sensor gauge and sensor and jet the carbs appropriately. This is the best way to tune and take the worries/ guess work out! Also you can jet the primaries and secondaries perfectly this way making throttle response awesome!

[ghittner]

I run 78's and 86's on the same type set up.

[TIMINATOR]

Boost reference the power valves! Engine lean out occurs whenever you back off the throttle under boost, as when you "pedal it" to get traction. As the throttle is closed or feathered, the rpm is still up and the blower is still making boost, the blower is pulling a lot of air and the resultant vacuum will suck the power valves shut, now you have leaned out the motor by 8-10 jet sizes and you are still under boost. Immediate detonation occurs as you back out of it! Every time this happens you hurt the bearings a little bit more, until they are junk. This is why a lot of blower guys need to freshen the motor every season. Blocking the power valves and richening the jets makes the car blubbery rich as transition occurs, right where you drive it the most. That also kills the mileage. Done correctly the blown mileage is little worse than unblown, unless you drive it like a nut.There are other issues here, but this is the main problem. Read the article in ***boat (the magazine) last summer. We can set-up your carbs correctly, we ship them all over the country. No problemo!

[rat tuned]

thank you again. is there a link to this article? i would even order a back issue if possible. timinator, about how much would it cost ? i've rebuilt quite a few holley's so i'm not afraid to do some of my own work. mike

[VDRIVERACING]

Boost referencing is defintely worthwhile where it's not a high rpm only application. Can't tell you how many plugs I fouled trying to find a balance for low and high RPM use. I'd still go fatter on the jets, and work your way down. That's not as sophisticated as the O2 sensor/laptop method, but it works. You might also consider a dyno, or chassis dyno. It's $500 for someone else who has the tools to deal with it.