Barry Grant Carburetor Tuning help needed - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-16-2004, 05:32 AM
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Post Barry Grant Carburetor Tuning help needed

I just purchased a 650 Barry Grant Speed Demon with mechanical secondary. The engine is running extremly well (it's never run this well before) but also runnig rich. When I step on the gas, it's causing black smoke out of the exhaust. I've advanced the initial timing to 13-14 degrees and I've also been adjusting the idle-mixture screws so that I get max vacuum on my vacuum guage. I've also been adjusting the float levels to many different levels and the best level seems to be when the primary float is 1/2 (middle) and the secondary float level is just visable at the bottom. I get the least amount of black smoke when the floats are set this way, but still smokes. I'm getting 16 vacuum on the vacuum gauge. Also, when both float level are set at the same level, either 1/2 way or both float levels at the bottom of the eye level. I can only adjust the idle-mixture screws to get 14 vacuum on the gauge and smokes more when I step on the gas petal.

The next thing I'm thinking of doing is; decreasing the jet size one size at a time, to see if this helps.

- 327 engine
- Munie 4-speed, Manual traning
- Headers
- FlowMaster 40 series, dual exhaust
- I don't know compression or cam size on the engine. :-(
It's not stock but also not something very ratty either.

Do you have any ideas on what float level would help reduce my rich condition or any other ideas to help my rich condition that is causing black smoke when I step on the gas?

Thanks!

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Old 03-16-2004, 09:02 AM
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Delivery nozzles can be to large. Try giong down 2 jets sizes.
http://www.barrygrant.com/
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Old 03-16-2004, 09:15 AM
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Leave the float level at 1/2 to 3/4 in the window. I agree that you need to come down 2 jet sizes in the primaries as well as the secondaries. The idle circuits will have no affect on whether it runs rich or not.
Also, what size are the shooters?

Ron
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Old 03-16-2004, 10:57 AM
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Thanks for the replys guys!
Nothing on the Carb has been changed from what Barry Grant shipped it to me as. The specs on the Carb are at this link.
The Carb I have is the 650 Speed Demon. . .

I'm going to pick up new jets for the primary and secondary, two sizes smaller than was shipped to me and give that I try.

opps, forgot to inclue the link:
http://www.barrygrant.com/demon/default.aspx?page=29
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Old 03-16-2004, 12:49 PM
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I know that individual jets can get pretty expensive. I bought a complete set on e-bay. Just type in "carburetor jets" in the search field. You can use the Holley's of course.

Ron
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Old 03-17-2004, 02:29 AM
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If you are getting the rich smell when you are at idle. If so you need to adjust the butterflys. You are pulling on one idle circuit harder than the other. Do THIS--- Turn your idle set screws on both the primary and secondary until both are completely closed. Now take a dial indicator with enough reach to set on the exact front of the throttle plate. Now screw in to open the plate .020 on the primary and then do the same with the secondary. Now take each of your idle mixture screws and close gently until bottoms out. Now back out 1&1/4 turns on the primary and one turn on the secondary. Your idle circuit is now balanced. If your initial timing is around 16 this set-up should put you around 1000 rpm. Now remember what you do to the front idle screw you need to do the same to the secondary. Say if you want the idle rpm to be 850 you would close the front to drop 75 and the rear to drop 75 rpm. With the engine at operating temp, tune your mixture screws to max vac.
Now for the black smoke while opening the throttle. I think I remember you said this carb. was a double pumper. The accel. pump on the primary has an adjustment bolt that will reduce the amount of gas that is injected into the throats. Tightening this nut and bolt will increase the travel on the pump and loosening will limit the travel. Adjust this until you get a little hesitation when you give it the gas and then back up until it just goes away.

These carbs dump alot of fuel and you will probably not be able to adjust away the smoke when you dump the throttle because the fuel you dump is not atomized very well.

I hope this helps with your problem. Let me hear about it.
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Old 03-19-2004, 03:49 PM
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I would contact BG carbs and talk to tech line. I bet you will find out that the 650 is too big for your engine size. BG calibrates cfm differently than the others. I speak from experience on this. There tech line is very good. Just have all your engine and car specs
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Old 03-19-2004, 05:17 PM
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Could this also not be a shooter problem. On initial wide open throttle, the shooters are firing to much fuel into the carb?

Ron
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Old 03-21-2004, 05:39 PM
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you will have to drop almost everything down a bit. the 650 is a bit big for a 327. my built 355 wouldnt run off a 650 speed demon vs. I had to drop 2 jets in both primarys and secondarys to get away from the smoke. now its a bat outta he**. good luck they are great carbs.
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