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drag racing the short bus
Join Date: May 2002
Location: Location, Location...
Posts: 21,983
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Incidentally, I have CIS on a 9.3:1 3.0 engine, and it does backfire on decel and sometimes between shifts. There are no vacuum leaks in the CIS and no exhaust leaks from the H/Es. What I don't have is a decel valve and all the quasi-computer crap that came with the motor. Not having that decel valve is the cause of the backfiring. SVK: for what it's worth, Tyson set double-gaskets in my heat exchangers when we put on the Triad muffler. If you have the chance, you might want to consider this. I'm not saying it'll solve your problem, but it's peace of mind nonetheless. |
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08-27-2005, 02:17 PM
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drag racing the short bus
Join Date: May 2002
Location: Location, Location...
Posts: 21,983
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 Bob, I'm right there with you. Looking at this photo, I might have found my next 911 project. 
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08-27-2005, 02:23 PM
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Gon fix it with me hammer
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running rich is would usually make it run less hot , something to do with the flame front not traveling as fast if the mixture is rich got the lm1 , and that confirmed, my mfi is running rich...
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Stijn Vandamme EX911STARGA73EX92477EX94484EX944S8890MPHPINBALLMACHINEAKAEX987C2007 BIMDIESELBMW116D2019 |
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08-27-2005, 02:26 PM
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Registered
Join Date: May 2001
Location: Peoples Republic of Long Beach, NY
Posts: 21,140
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gas droplets have to very small for the ignition to create good combustion. For example if we take a gallon of water as one unit the outside surface will have x exposure. If we turn the gallon of water into a mist the exposed surface will have many many times more exposure than as a whole single unit. Same deal with gasoline. The idea of carbs is to turn the liquid into an atomized state. The atomized state can be large or small particles. The larger will not ignite as well as the smaller. For the same volume of gas entering the combustion chamber there can be different amounts of combustion power depending on atomization. The carb design affects this transformation in many ways depending on the carb parts installed. For instance the main venturi creates a negative atmospheric state allowing the droplets to expand. The greater the drop from atmospheric 14.7 the greater the droplets expansion. My 40 carbs will run better at idle and mid rpm with 34venturi that a 36venturi due to this process. Granted the total high rpm intake air volume may be limited if the venturi becomes very small. Anyway the CHT/ Cylinder Head Temp also becomes a factor in atomization. In my last post I suggested a longer warm up to increase atomization for your carb adjustments. And too rich of an idle circuit adjustment creates larger atomization relative to the carb adjustments and parts installed. The idle circuit carries into the mid rpm range so it's a touchy feely situation on setting the idle mix screws. I'd run it as lean as necessary for your idle to main circuit transistion and have all screw adjustment almost equal. A 1/4 turn of the screw is a significant difference in combustion power, assuming you have a good engine and carbs. The idea is that you want 6 independent carbs working in unision creating equal power in each cylinder. btw, what jets, venturi, etc are in your carbs.
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Ronin LB '77 911s 2.7 PMO E 8.5 SSI Monty MSD JPI w x6 |
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08-27-2005, 02:52 PM
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Registered
Join Date: Mar 2005
Location: Florida
Posts: 168
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Depends on what you feed the crabs!!
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'86 Carrera Cab "The Grey White Whale" '98 Kirkham 427 Cobra(in rehab) '94 Dodge Intrepid ES(very Porsche-like) '99 F-250 SD Diesel(Cowboy Cadillac) |
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08-27-2005, 06:41 PM
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BimForce the Third, Esquire
