Adjusting Speed Demon

norcalsvt · Jul 13, 2004

Exhaust is very rich smelling. Usually I need to air out the garage for a 1/2 hour when I pull in. Thought I would try to adjust my Speed Demon 650 & I am confused. I figured out the 4 screws on the side of the carb are the idle mixture & when I tried to use a starting point of 2 full turns for each one, the engine idled very poor. AFter I retried at .75 turn it idled higher & alot better. Still smells rich, but not sure if maybe thats how it's supposed to be. A couple of things. Noticed very large puddles at each exhaust. They are turned down under the car, so it puddles pretty large for that short time. It dried up before I could test it. Is that gas running through the exhaust b/c it's rich or just water? Surprised it dried up so quick if water since it's about 56 degrees when I did the adjusting. Also, what are the 2 screws on each side of the carb. I'm assuming some sort of idle speed, but why 2 & how do I adjust those? It seems I have to idle around 1100-1200 & 1000 rpm in drive otherwise it seems to run poor

mdjay · Jul 14, 2004

Have you tried adjusting the floats. There is a sight glass on my Mighty Demon that you can see the fuel level. Should be right in the middle. Not sure if its the same on the Speed Demon. However it sounds like it's dumping fuel. Can be float bowls, or a needle & seat getting stuck. Maybe a small obstruction. The puddles are more than likely just condensation that far back. The screws on the sides are the primary and secondary idle screws. They are adjusted separately on the Demons. There are specific settings for the two. If my memory serves me correctly, the idle transfer fuel slots should be showing only a .020" visible when the butterfly is in the closed position. These would be the adjustments prior to installing the carb. If you have the Idle-Eze base plate, you can adjust the front and rear separately and further adjust the cam plate to fine tune your secondaries.

Great68 · Jul 14, 2004

You did everything right for the most part. Check your float levels, adjust the idle mixture screws for the best vacuum (on my car this was only about 3/4 of a turn, I can see how you had problems with 2 turns), use as little idle speed screw as possible.

rfedd · Jul 14, 2004

I would drop 2 jet sizes in both front and rear and run the car. See how it performs.

Ron

65racecoupe · Jul 14, 2004

I know that out of the box, my 750 speed demon ran 12.5 to 1 Air/fuel ratio at idle. I had to adjust it to 14/1.

I do have one of those wide band A/F ratio guages, so that helped. My car would make me a little dizzy in traffic with that rich running engine. I could have ran nitrous on the engine with how rich it was running.

Just play a little with the screws on the side of the carb (4 of them). You will have to adjust the idle screws too, but no big deal.

BTW, since I LEANED out the carb, my car spits and sputters just a little when I start it for the first time of the day. I let the oil pressure build up and give her a little gas, then I cruise. After the engine is at op. temp. the A/F is where it is supposed to be, and it idles at a nice 900 - 1000 rpm. Any time that day that I have to start it again, it is just fine.

6t6stang · Jul 14, 2004

Demon problems

Both my friend and I have speed demon 625 vacuum carbs on our cars.
66 mustang 302 ( warmed over)
65 mustang 302

The demon is super rich at idle. As soon as I get into it it leans out fine.
I took it to the dyno and thought I was going to be super rich and it didn't need any tuning at all. The carb was rich at idle but leaned out fine .

Excellent curve on tghe dyno with the carb. i love it

Just my .02 cents.

rfedd · Jul 14, 2004

14 to 1 is just a bit to scarry for me. Take a look at what Dynojet recommends.

Qoute: What A/F ratio should I be looking for when I'm tuning?

On a naturally aspirated engine, you'll make best / safe power between 12.8-13.2. Vehicles running "power adders" will need to run a little richer, between 11.5-12.5 for best / safe power.

I installed one of their Wideband Commanders on the car (here). No more trips to the Mustang Dyno EVER: http://www.widebandcommander.com/ Man what a marvelous tool.

If you would like to see a copy of the report the box creates for you I can do a cut & paste.

Ron

norcalsvt · Jul 14, 2004

thanks for the replys everyone. I am going to check the floats when I get home. I started it up this morning & now the engine or maybe the exhausts sounds like a popping sound. It's not backfiring, but I can hear it during idle when I apply gas to the pedel. Not sure if that means it's rich or lean.
I also looked for the gas level but I guess I don't have the glass to see it.

Adjusting Speed Demon

norcalsvt

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mdjay

Great68

rfedd

65racecoupe

6t6stang

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rfedd

norcalsvt

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