I had my Q-jet rebuilt 8 months ago and it has been a pandoras box ever since. I have not been able to get the thing to run right. It is the original carb so I asume the factory had it set to work for 30 years. It has no low end response and will hesitate and backfire when floored from a stand still. It also bogs in the mid range secondarys. I have adjusted and readjusted . Some days it runs rich others too lean. So the question is I have a brand new 650 edelbrock and was wondering if 650cfm's will be enough for the 455. It's a stock '72 engine with 8.5:1 compresion with 74000 miles and an 800 Q-jet. Any ideas or thoughts let me know.
650 is not enough....you will want to find the problem with the bog.... Check your timing, vac advance (hooked up to FULL manifold vacuum) It sounds like a timing issue to me. But it could be many things. 800cfm is ideal for a stock 455.
I have to advance my timming to 16 degrees to keep it from pinging and the vacuum is 14 pounds at 550 rpm.
Not trying to say anything here, but I have to cover the bases.... Do you disconnect the vacuum advance and plug the port in the carb when you adjust the timing? If not, then your timing is retarded too much. With the engine off, take a look inside the primary side of the carb and give the throttle a hit. You should see 2 clean streams of fuel squirting into the venturis. If not, then you may have an accelerator pump problem.
Yes I do plug the carb vacuum nipple. When you give it a squirt it shoots feul out in 2 streams. I had to place the rod on the outside hole because it was giving it too big of a shot. I have also checked the gasket seals and all is tight. I thought about a vacuum leak at the throttle body but that wasn't the case. The guy that rebuilt my carb is 110% chivy and swears that it is correct. Maybe thats the problem it thinks its's a chivy now.
Is your vacuum advance cannister working at all? Have you checked your timing while it is hooked up? Its should read about 25* with vac advance hooked up. Also, when you said you moved the rod to the outside hole because it was giving too big of a shot - Moving it back to the inside hole will make the shot less hard. Moving it out will increase the power shot. I would move the rod back to the stock position....but I don't think that is your whole problem. There's something big that we're missing.
I'm sorry, I ran out to the car and checked it is on the inside now(damn it's cold). It was on the outside hole and too rich. As far as timing it runs out of numbers on the timing cover so as to what the timing is when advanced I haven't a clue. I did have to bypass my temp switch and went direct to constant vacuum off the carb(it was running hot). The dwell is set a 30. I haven't checked the plugs in a while but they where fouling black before I put platniums and wires in. new cap rotor points. All the idles check in drive within +- 10 rpms. Feul pressure is good, new filter tank and lines are clear. It doesn't act like feul starvation I am just listing every thing I can think of. The airpump has been pulled and the air passage blocked at the intake with a plate. Thats all I can think of. everything else is original.
Have you messedwith your plug wires in a while? You may have a mixup thereo No: Does it run smoothly at idle?
Plug wires are right. It has a miss under power but smooths out. When at idle the RPM 's roam abit but only within 5 to 10. The resitance in the wires checks out. I put them on about 8 months ago and it had a miss in it at idle before but went away after the Q-jet was rebuilt. Now in the last four days it is missing under power. Thats one reason I suspect carb.
Still sounds like an ignition problem to me. A 650 is undersized but the engine will run just fine with it, you just won't have the top end potential that a larger carb will get you. I'm running a 650 holley d.p. spreadbore right now and my 9 to 1 430, small cam engine (absolutely zero porting or cleanup) made 385hp.
