Hi everyone,
As you may have seen, I've recently acquired a Pontiac with a quite potent 400 motor in it. It's only just been run in, reputedly.
The problem I have is that I'm not really sure where to start with regards to getting it running at its best. Now that I'm back from work, and on a break, I've finally had the time to have a proper look at it (which is why there's been no real thread about it in Reader's rides).
At the moment it will start, idle at about 1000rpm, and drive. It's not fantastically happy, however. It's very rich (or at least smells it) and it doesn't seem to take much to prompt it to cut out.
Because everything's new, I'm essentially going around in circles trying to get some kind of baseline set.
Here's what I know:
- Initial timing is around 15 degrees BTDC, with vacuum, when running at 800rpm. OEM spec is 6 degrees.
- The plugs seem to be getting quite sooty and there's a fair amount of soot from the exhaust as well at idle. Besides being too rich, I think they're too cold a heat range, personally (I will update this when I check them later).
- Running temperature seems fine - it gets up to around 160-180 degrees fahrenheit and sits there.
- Fuel consumption seems very, very heavy. I don't expect it to be brilliant but it guzzles the stuff, even at idle.
- It starts from cold with two pumps on the pedal and catches quite quickly. It settles into an unhappy idle at about 750rpm until it warms up. There is an electric choke fitted but I've only played with it briefly. I turned it on, once, and it instantly fouled all the plugs. Hehehe....
- From hot, it cranks over a few times and will catch of its own accord, with no throttle input. Usually. It takes a while to pick up though and occasionally needs a prod to get to the correct idle speed. I'll occasionally get the odd backfire at idle too when hot.
.....and that's about my lot.
I suspect I have an issue primarily with fuelling (need to get a vacuum gauge, too) and maybe with timing as well.
Specs wise, it's as follows:
- 400ci block
- Edelbrock alloy heads
- Performer intake manifold
- Doug's headers
- Comp Cams XE276HR cam (quite lumpy), hence the 1000rpm idle
- Barry Grant 750cfm Speed Demon carb with corner metering
- HEI dizzy, vacuum plumbed into the ported vacuum port on the carb, not manifold vacuum.
- KB pistons, H-beam rods, etc....
I'm considering taking it to Marlin Motors to get it dyno'd and setup (initially) by them but I'm not sure if it'd be a bit outside their remit.
Any help appreciated - I'm just not sure whether I should be looking at the timing, then the fuel, or vice versa, or if there's anything else I need to consider. There also seems to be a lot of endless (and unclear) debate over ported and manifold vacuum.
I also don't want to damage it, so I'm a little hesitant to randomly fiddling like I usually do. Plus, first time working with a four barrel!
I understand that this has an infinite number of 'what ifs' and 'hows' to it but any guidance appreciated.
Cheers,
Lewis
As you may have seen, I've recently acquired a Pontiac with a quite potent 400 motor in it. It's only just been run in, reputedly.
The problem I have is that I'm not really sure where to start with regards to getting it running at its best. Now that I'm back from work, and on a break, I've finally had the time to have a proper look at it (which is why there's been no real thread about it in Reader's rides).
At the moment it will start, idle at about 1000rpm, and drive. It's not fantastically happy, however. It's very rich (or at least smells it) and it doesn't seem to take much to prompt it to cut out.
Because everything's new, I'm essentially going around in circles trying to get some kind of baseline set.
Here's what I know:
- Initial timing is around 15 degrees BTDC, with vacuum, when running at 800rpm. OEM spec is 6 degrees.
- The plugs seem to be getting quite sooty and there's a fair amount of soot from the exhaust as well at idle. Besides being too rich, I think they're too cold a heat range, personally (I will update this when I check them later).
- Running temperature seems fine - it gets up to around 160-180 degrees fahrenheit and sits there.
- Fuel consumption seems very, very heavy. I don't expect it to be brilliant but it guzzles the stuff, even at idle.
- It starts from cold with two pumps on the pedal and catches quite quickly. It settles into an unhappy idle at about 750rpm until it warms up. There is an electric choke fitted but I've only played with it briefly. I turned it on, once, and it instantly fouled all the plugs. Hehehe....
- From hot, it cranks over a few times and will catch of its own accord, with no throttle input. Usually. It takes a while to pick up though and occasionally needs a prod to get to the correct idle speed. I'll occasionally get the odd backfire at idle too when hot.
.....and that's about my lot.
I suspect I have an issue primarily with fuelling (need to get a vacuum gauge, too) and maybe with timing as well.
Specs wise, it's as follows:
- 400ci block
- Edelbrock alloy heads
- Performer intake manifold
- Doug's headers
- Comp Cams XE276HR cam (quite lumpy), hence the 1000rpm idle
- Barry Grant 750cfm Speed Demon carb with corner metering
- HEI dizzy, vacuum plumbed into the ported vacuum port on the carb, not manifold vacuum.
- KB pistons, H-beam rods, etc....
I'm considering taking it to Marlin Motors to get it dyno'd and setup (initially) by them but I'm not sure if it'd be a bit outside their remit.
Any help appreciated - I'm just not sure whether I should be looking at the timing, then the fuel, or vice versa, or if there's anything else I need to consider. There also seems to be a lot of endless (and unclear) debate over ported and manifold vacuum.
I also don't want to damage it, so I'm a little hesitant to randomly fiddling like I usually do. Plus, first time working with a four barrel!
I understand that this has an infinite number of 'what ifs' and 'hows' to it but any guidance appreciated.
Cheers,
Lewis
I think mechanically the engine and valvetrain is spot on - once it's over 1200RPM (and the cam starts coming 'on'), it revs fantastically. 
