Unburned gas smell

I have a 351W roller block with Aussie Cleveland 2v heads, a B&A Track Boss 351 intake with 750 Holley, with a F303 Ford Motorsport cam, custom shortie headers, DR Gas side exhaust, "Z" box T-5, 8.8 with 3.73 gears in my 92 Mustang. The problem is unburned gas smell is bad from exhaust. True with side exhaust it does compound the problem. Comp Cam told me that a cam for EFI is ground differently to run rich and the O2 sensors will retard the fuel in the injectors to correct this. And if you look at Comps Cams catalog it does point out the hyd. roller Carb cams and EFI cams. Has any ever had this problem? My carb is in good shape, timing is right, plugs look right.

Idle air mix is off or your PV is blown.

Have you rejetted the carb? If it is out of the box from Holley it is going to be rich. Most #4779 750DP's have something close to 70/80 jets. I'd drop to 68 in the front and 76-78 in the rear to start.

As for the cam, I'm not a big fan of the "F". It is meant more for forced induction, it has a wider LSA. I prefer the smaller "B" or "E" for a mild street car. With you engine you could probably benefit from more cam. I like a cam with a tight 108-110 LSA. I've ran a Comp solid lift with a 106 LSA. Makes for a real rough idle and low vacuum, but make the power band more explosive.

I'm assuming this is not a daily driver?

I have had the jets down to 62s in front and 74s in rear, no change. Idle screws from 1/2 turn out to 3 turns out, no change of course did not run right till I re set it. PCV is new and right for size for 351 engine. Also vaccum is low at idle about 15 inches. Have readjusted valves thinking somthing I did was wrong but still same thing. And yes this is my everday work car about 35/40 miles per day. Gas mileage is about 15/16 around town and 20/21 on highway 70 to 75 mph. I am inclined to agree with you about LSA of cams. Thanks Bucketobolts and 1 BAD 88 GT and this is one good sight!!

What is your timing set at for initial and total advance? Maybe more initial advance would clean up the smell?

Originally Posted by BRANDON6

I have had the jets down to 62s in front and 74s in rear, no change. Idle screws from 1/2 turn out to 3 turns out, no change of course did not run right till I re set it. PCV is new and right for size for 351 engine. Also vaccum is low at idle about 15 inches. Have readjusted valves thinking somthing I did was wrong but still same thing. And yes this is my everday work car about 35/40 miles per day. Gas mileage is about 15/16 around town and 20/21 on highway 70 to 75 mph. I am inclined to agree with you about LSA of cams. Thanks Bucketobolts and 1 BAD 88 GT and this is one good sight!!

You may have a more complicated problem. How far is you idle speed screw adjusted? It may be open too far. If you remove the carb and look at he butter flies from the bottom, you should see the idle port and the transfer slot. With the primary butterfly closed the slot should look like a square, just barely showing. If it is open too far it is drawing too much fuel from the transfer circuit not letting the idle circuit do its jobs. Then you may have to open the secondaries a bit to get you idle speed back to were you want. There is a small screw only accessible with the carb off the engine in the bottom of the base plate. Some times it gets corroded then you can tweak the idle stop. In an extreme case you may have to drill a small hole in the primary butterflies to allow enough air to idle correctly. But this is a last resort. Usually not necessary on 4V but common on 2V race engines.

If you cannot resolve with the butterfly adjustment, you may need to bush the Idle Feed Restriction in the metering block. This is a very tedious modification. You can easily kill your metering block if incorrectly done.