307 poor high-rpm performance


opensourceguy
10-27-2008, 05:04 PM
I have an 85 estate wagon, with the 307 olds.. electronic primary quad 750 4 barrel and HEI ignition. I rebuilt the carb to fix an external fuel leak, lately I have been having a probelm with the engine revving high. I understand this is no fast car by any means, and revving it high doesn't even make it go faster.. but this is definately a problem. It doesn't have any fuel problems, as far as bad lines or a rusty tank such that it would clog the [700mi on it] fuel filter. But the past few hundred miles after the rebuild have made the car just completely stop making power to the point it can merely idle nothing more. You accidentaly or not hit this 'bad spot' the car won't accelerate but roughly maintain a 25mph speed but could never accelerate to 25 should I not even be going that fast. I don't have a tach so there is no real rpm i know of.. but it happens at 35 just about every time. Motor cold it won't do it, but the car runs rough cold. Like it wants to flood out, but goes away after a few taps of the gas. And every morning the car takes many cranks to get fuel to the bowl. Accel pump is dry, bowl is dry, but one quick shot of carb clean and draining the last spray or two of the accel pump she fires right up, but if you gas it right away to clear it out, it'll die.. like the fuel pump hasn't quite caught up yet. And this condition happens under any throttle position, WOT or just enough gas to let the engine rev that high. It's the oddest thing. Let the car just idle down the road and it'll be fine to get up to speed.. most of the time.

Also it's been having an intermittent miss at idle. No SES, and otherwise car runs great. Have driven cross country in the car with no problem, but can't figure this one out. Anyone have some suggested roads to point me down?

HotZ28
10-27-2008, 06:28 PM
I assume you have checked the choke blade on the primaries to see if they are closed when cold and open after the engine warms up. If so, it sounds like the fuel pump took a dump!

opensourceguy
10-27-2008, 06:37 PM
Yes the choke functions properly.. It gets worse about every few days or so now... should I be concerned about it completely failing soon? I've never had a MFP fail... and i'm sure we all know how the EFPs fail lol.

Have you by chance ever messed with one on a 307? There is this accessory bracket that appears in the way.. looks like a lot of work to get to. And every time I fix something.. i break something in the process on this car. It has original everything.. and it shows! lol.

maxwedge
10-27-2008, 06:49 PM
The bowl plugs on this carb were famous for leaking down leaving the carb empty number one, number 2 the MC solenoid and tps adjustment should be checked also when doing an overhaul and retuning the engine, a dwell meter is used on the mc solenoid for starters, unless you have the tools and know how this is a tough carb to set up. There is also a small filter in the carb inlet fitting that is usually overlooked.

HotZ28
10-27-2008, 08:14 PM
Thanks Max, I forgot about the bowl plugs on the QJ, its been a long time since my carb days! Anyway, IIRC they use to make a epoxy repair kit for the bowl plugs. This could very well be the problem, since the OP mentioned the the fuel bowl is empty.

Add your comment to this topic!