running rich

[jjr329]

So the Mach 1 is seems to be running really rich. I was having some problems with it stalling when coming to a stop and on cold starts I would always have to "nurse" the gas a little for several minutes otherwise it would die. Changed the fuel filter but that didn't help.

Found an article to reset the idle mixture screws, so I set them to 1 1/2 out and ended up coming back in 1/4, so they are 1 1/4 out. I also changed the plugs since they hadn't been done in 8 years or so (really no miles in that time).

The car runs fine and feels powerful. I have no stalling issues and it'll lay rubber like no tomorrow. BUT it seems like it's running really rich. The plugs smell strongly of fuel and you can smell the unburnt fuel around the car.

I had been running 93 octane in it but it's low compression so I just started switching to 87 octane. I'd say there's probably 2-3 gallons of 93 left in there and the rest is now 87 (filled up last night).

Here's the specs:

351 Cleveland 2V .030 over with closed chambered Aussie heads, 7.25:1 compression [ previous owner ]

Crane PowerMax 529551

MSD Billet dizzy w/ 6AL

Harland Sharp roller rockers

Holley 750 DP with electric choke

Weiand X-CELerator intake

C6

3.89 locker

B&M Hole Shot 2400

I pulled the sight plugs on the carb and no fuel came out. Some started to come out when gently rocking the engine so I think the float is normal. I will probably check it again to make sure.

So I'm not sure where to go from here. I'm thinking now that the tach started working again (I think it was sitting too long) I need to re-evaluate the idle mixture screws. Anything else I can check? The idle is high, I have not adjusted that yet as I didn't want to change too many things and then not know what I did to fix it. I'd say it's 1000-1050 in P/N and maybe 950-1000 in gear.

 

[Jeff73Mach1]

No amount of idle adjustment is going to fix an improperly jetted carb.

That carburetor is large for your engine at that compression ratio. It will still work, but changing the jets internally is going to be necessary to get the engine to run leaner.

at 1000+ rpm the carburetor is starting to come into the transition circuit adding fuel to the mix. I would bring the rpm's down to about 650-700rpm and readjust the idle screws for both smoothest idle and using a vacuum gauge highest vacuum.

It sounds like the engine was set up for a power adder of some type, perhaps he intended a turbo or supercharger or nitrous. Any idea if the pistons are forged?

 

[jjr329]

I don't have a vacuum gauge. Napa or some other auto stores carry them? Previous owner ran nitrous, I had the heads and top end upgraded.

 

[Jeff73Mach1]

Napa has them and they are generally pretty cheap. They are great diagnostic tools and can disclose not only vacuum levels, but by looking at the needle behavior, you can diagnose born rings, valve seats, timing issues, blown head gaskets and much more. Most gauges will come with a very simple guide. It is also a good idea to buy a section of vacuum line and a t fitting to make hooking it up easy.

 

[Bill73Ragtop]

Craftsman has a decent automotive vacuum set that is not very expensive. Nice BIG gauge face.

 

[Tnfastbk]

Craftsman has a decent automotive vacuum set that is not very expensive. Nice BIG gauge face.

http://www.sears.com/tools-mechanics-auto-tools-diagnostic-tools-testers/s-1021327?keywordSearch=false&previousSort=ORIGINAL_SORT_ORDER&keyword=vacuum+gauge&viewItems=25

 

[TommyK]

I don't see how you can have only a 7.25:1 compression ratio. Aussie heads generally increase compression by about a point and a half over stock US open chamber 2V heads. Be careful running 87 octane.

As far as the rich condition goes, where is it rich? At idle? Cruise? WOT? All of the above?

 

[jjr329]

I don't see how you can have only a 7.25:1 compression ratio. Aussie heads generally increase compression by about a point and a half over stock US open chamber 2V heads. Be careful running 87 octane.

As far as the rich condition goes, where is it rich? At idle? Cruise? WOT? All of the above?

7.25 is what the pistons are rated at, so combined with the heads would be 8.75:1. Is that within range for 87?

 

[marks73]

Definetly

 

[Jeff73Mach1]

needs a turbo

 

[marks73]

needs a turbo

Definetly!

 

[jjr329]

needs a turbo

That's one way to fix it. lol

Jet kit and gauge come in today and I plan on working on it over the weekend. I'll let you guys know how it goes and if I have any questions.

 

[jjr329]

I found a jet size of 71 primaries and 80 secondaries. I had to pull the carb which was a first for me, easier than I thought. I've been doing some reading and there no rules for where to start as there's too many variables. Generally I've been seeing to change the jet sizes 2 sizes at a time. So that would be 69 and 78. Sound good or based on my specs listed should I adjust differently?

 

[Jeff73Mach1]

I'm no expert, but I'd check the power valve and then change the primary jet only as the secondary being lean could burn a piston on an extended high speed drive. In all honesty, you will likely be into it 2-3 times before you get it to your satisfaction. If your compression is as low as you think, you probably can't quite pull the standard 18" of vacuum at idle which may call for a lower numbered power valve. I suspect the secondary has a plug in place of the power valve based upon the other mods. If so, change to a 6.5 and go ahead and drop the secondary jet down 2 sizes and expect to drop it 2-4 more before your done.