When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Swapping the QJet for a Holley 4175. Not getting any help out of the Holley guys, so maybe you guys who have done this swap can help.
There is a large port on the forward bowl, it came unplugged out of the box. What does it do, does it stay unplugged? Maybe its a bowl vent? Some other places think it might be a port for the fuel evap canister, but its a large port, PCV sized. I currently have the cannister plugged into the "Purge" port, #4 on the diagram. Is that right?
Ah, yes I did, thank you. Gonna try it that way and see how it likes it. Strange place for the evap to be, and the port being 3/8 threw me. I've also never run advance off of manifold pressure, but I'll see how it likes it.
And yes, the pull off bracket was bent. Definitely would have caused problems. Got it bent back straight. It amazes me what you guys will see!
Strangely enough, Port #3 on that picture in the post is Ported Vacuum. Lars says use it for Vac advance, but im pretty sure he recommends Manifold Vacuum for advance. Port #4 is manifold Vacuum, so i hooked it up there, like the Holley diagram. Currently its set at 12* without the can, and 26* when the can is hooked up. The evap can is hooked to #1 and #3 is plugged.
Now it idles good, 15hg on the vacuum gauge, nice and steady, but i have to run the idle mixture screws all the way out to get 15 on the AFR gauge. Part throttle is ok, but when i give it anything over part throttle to WOT it goes rich, breaks up, and spits and backfires through the exhaust. Get out of it, and it goes back to idling fine. Ugh.
Strangely enough, Port #3 on that picture in the post is Ported Vacuum. Lars says use it for Vac advance, but im pretty sure he recommends Manifold Vacuum for advance. Port #4 is manifold Vacuum, so i hooked it up there, like the Holley diagram. Currently its set at 12* without the can, and 26* when the can is hooked up. The evap can is hooked to #1 and #3 is plugged.
Now it idles good, 15hg on the vacuum gauge, nice and steady, but i have to run the idle mixture screws all the way out to get 15 on the AFR gauge. Part throttle is ok, but when i give it anything over part throttle to WOT it goes rich, breaks up, and spits and backfires through the exhaust. Get out of it, and it goes back to idling fine. Ugh.
I think there is some confusion about which diagram. The other poster has his own numbering sequence plus Holley's. Lars says not to use the ported vacuum on the metering body for advance other than emissions purposes.
Can you lean it out to 14.7?
Are you doing this WOT in neutral or while driving?
How about some details on your ignition system, what plugs (manufacturer and number), which distributor, have you checked plug wires with an ohmmeter, etc.
Yeah, i can see how these different diagrams and numbers can get jumbled.
Im just using the guys picture with his numbers for reference.
#1 is the big 3/8th at the top of the bowl, thats currently got my evap can hooked to it
#2 is my EGR
#3 is actually ported vacuum, currently plugged.
#4 is manifold, goes to the pulloff, and my Vacuum Advance is T'd into the line, as per Holley.
#5 is PCV of course.
Its actually running lean at idle, i can get it to 14.7-15 if I run the idle mixture screws all the way rich. At this point its idling great, 900RPM (4spd) 15inhg on the vacuum gauge and steady. Doesnt seem to be any miss or smoke or anything.
The breakup and popping is while driving. Idling at a light and easing into cruise is normal, getting on the throttle much at all, it loses all power, runs to about 10-12 on the AFR, pops and sputters. Get off the throttle, and its normal again.
Plugs are Autolite 685 gapped at .045, pretty new, as are the wires. Distributor is stock 1975 HEI, i did replace the ignition module with a Standard model from the local oreilys.
Its funny, this Holley has the little plastic idle mixture screw caps, and they give you like one turn max. So when i say the idle screws are all the way out, its like one turn. Never seen these caps before, and it really limits what you can do.
Have you opened the carburetor and checked float level?
Have you tested fuel pressure?
Just did a quick fuel pressure test, sitting at 5-6 steady even when I blip the throttle.
Pulled the floats, front one was pretty close according to Holley specs, i gave it a slight adjustment. Jets are 58 and 58 just FYI while i was there.
Rear one was maybe a touch low. adjusted it a touch a well.
Ran it again, just idle in the garage. sitting at about 14.7 AFR, again with the those limiting caps all the way rich.
Never seen those before, my other Holley let you adjust as much as you wanted. Can they/should they be removed?
Any chance this carburetor is a reverse idle screws? Anything in the instructions?
Like the idle mixture screws? they are labeled lean with an arrow like in the picture above, so im pretty sure im going the right way. Even i cant screw that up.
Like the idle mixture screws? they are labeled lean with an arrow like in the picture above, so im pretty sure im going the right way. Even i cant screw that up.
Sorry missed the picture, remove them. Certain Holleys had mixture screws that adjusted air not fuel like regular carburetors. Turning the screw counterclockwise leaned the mixture.
What is the list number on air horn?
Sorry missed the picture, remove them. Certain Holleys had mixture screws that adjusted air not fuel like regular carburetors. Turning the screw counterclockwise leaned the mixture.
What is the list number on air horn?
Think i got this one figured out.
I was pretty sure the fuel system was working correctly, so I switched to ignition. Checked plugs and wires, all good. I had a nagging suspicion about that ignition module, so i put in another one that i had, an older one but GM, and it cleared up. That new Standard ignition module was idling fine, but breaking up under load at 2000 RPM or so. What a POS.
Anyway, thanks for everyones input, chalk this one up to another bad from stock new ignition module.
Think i got this one figured out.
I was pretty sure the fuel system was working correctly, so I switched to ignition. Checked plugs and wires, all good. I had a nagging suspicion about that ignition module, so i put in another one that i had, an older one but GM, and it cleared up. That new Standard ignition module was idling fine, but breaking up under load at 2000 RPM or so. What a POS.
Anyway, thanks for everyones input, chalk this one up to another bad from stock new ignition module.
Are you saying you switched from the Quadrajet to the Holley and the actual problem was the ignition module?
Are you saying you switched from the Quadrajet to the Holley and the actual problem was the ignition module?
No the swap to the Holley was planned. 75 wasn't a good QJet year and this one was a later one, the auxiliary power piston was gone, and the jet was factory plugged, plus the choke horn was broken. It ran, but I wanted to upgrade. This problem was new.
Holley 4175 swap
