Too much advance. Should be 30-32 total, in by 3000 rpm or so, with vac disconnected. Wrong carb, wrong fuel pressure. Fix all that (buy a proper qjet from one of the gurus here), then see how it runs. Patrick
30 - 32 seems to be a bit low to me but I'm going to give it a try tomorrow. To achieve that my only two options is decrease the initial advance which will cause even less vacuum and more rough idle or limit the mechanicaladvance. Which could be a better option?
You will need to modify your distributor to get about 12* initial, 32* total. The combo needs to work together, but some of your pieces are from a different puzzle, for lack of a better term
It's funny to see the Chevy guys face after they ask what size carb I run on the street and I tell them a 1150 dominator.........it's priceless !
19” at 5600’? That’s outstanding. Yes the carburetor is too small but I still think you need fatter metering rods in it to lean it out.
I have a Mighty Demon 850 on my 462 with a mild cam. I had to jet it up quite a bit to get my AFR readings where they needed to be. Also my fuel pressure is at 7psi. Perhaps these Demons flow a bit less than advertised? Buickrat was spot-on, go bigger with more pressure. Jim/Rott
Not to pour it on, but a 625 is pretty small for a BBB even in stock trim. Heck, mild SBB's often like more carb than that. I've played with 350's that were a little built (cam and some porting, but nothing radical) and 650's were a bottleneck. Impressive gains in not only power but general manners were made going to a bigger carb.
That Holley tech support person is giving you bad info all around. pay attention to what the guys here are telling you. these are the guys that own and drive the very car you are seeking help for. odds are pretty good that Holley tech is using a flow chart to tell you what to do. the Buick engineers installed a 750 cfm carb from the factory. if a 650 cfm would have sufficed or worked better then thats what it would have came with from Buick.
So in conclusion I think it's time to rebuild my Quadrajet. I'm going to search it in the basement and post back the Serial number. I'll need to buy the idle tubes and idle channel restrictors so maybe is a good moment for a complete carb overhaul I had always though that carb CFMs can be a bottleneck at WOT power when the engine CFM needs exceeds the carb capacity but I though that just cruising babying the throttle a small CFM carb will do the work but seems like not Until I have my QJ rebuild I'm going to increase my fuel pressure to 5PSI and also I'm going to lower my initial to 14° and total to 34°. Any recommendation about this?
I like every part of that idea. If you can rebuild the carb confidently yourself, do as you wish. But if you question yourself, send it off to one of our known rebuilders
if your motor is stock, (cam, intake ,exhaust) the the carb you have is just fine, everyone wants to over carb the engine, thinking more is better, if you seldom go over 4800 rpm, you DO NOT NEED A BIGGER CARB, actually the carb you have will give better drivability, as the air speed (velocity) is better, and the carb responds better to faster air speed. a possibility you may check out is restricted exhaust, like a pipe internally collapsed, or muffler collapsed, is the car running hot? ( indication of exhaust restriction,) (also retarded timing) 95% of people drive their car at 1500 to 3500 rpm, and do not need the huge air flow they think they need, race cars are a different story, so I'm not talking about them, here is a good chart to estimate your CFM needs, http://www.wallaceracing.com/intakecfm.php keep in mind most cars are LESS than 90 % efficiency , usually around 80% or less.
Don’t forget that Q-jets are variable cfm carbs, delivering only as much as you need with CFM. That makes overcarbing anything with a 750 qjet essenentialy impossible
I think I've never revved the engine more than 4000 RPM, the lack of power is so notorious that I just avoid doing it, in town I usually shift at 1800RPM or 2500 going uphill I Feel like Both exhaust are flowing free but sometimes also feel like engine is running a bit hot
