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 Post Posted: Thu Aug 16, 2012 6:15 am 
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Thanks Donee. I know the jet minimum now and the bleed minimum. As weather changes I'll get more data. The rest is easy. I really didn't realize the effects on 60'.

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 Post Posted: Thu Aug 16, 2012 9:08 am 
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Beretta wrote:
Hummmm I always seemed to start somewhat rich and kept on jetting up till the MPH slowed down then go down about 2 or 3 #'s and run it there...It if jumped around much I would go down another # and watch the MPH.
Now this was before all the O2 and EGT stuff we have now and my 540 on gas runs about 13.1 to 13.4 and the EGT's were 1380 to 1405 with it's best MPH.
The O2 and EGT is just a tool and as we know every body's engine will be somewhat different..
Looking forward to that new post Chuck..



The reason for this post Webber..

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 Post Posted: Thu Aug 16, 2012 9:33 am 
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Yes, anytime you change the main jet the AFR should change in line with the flow change from the jet change you just did. In a Holley one jet size larger makes that barrel half an AFR ratio richer. So going from say a #73 jet at say 13:1 to a #74 jet should make the AFR 12.5. (If you do all barrels that will be the case). If it doesnt change in line with expectations then the engine is producing an incorrect gas balance or its not efficiently burning the fuel you just added (or perhaps the bowl is running out of fuel he he). Any average carby of reasonable setup should deliver the AFR but it depends on what the engine does with it as to how the WB's read.
WB's are definitely overly sensitive to CO percentage, it causes them to read richer than there specified accuracy. WB's are only accurate to about half an AFR ratio when reading in the 12;s anyway so dont expect accurate results from race tuning.

If your main jet size is feeding an emulsion system thats overactive the main jet wont be the controller of the AFR and changing the size of the main jet wont give you the fuel change your looking for.
The emulsion carburetor design work best when the main jet is the controller of the overall flow and the emulsion is used to trim the vacuum generation characteristics of the booster. This trimming is achieved by air bleeding into the emulsion section of the main well and by the size of the main well which controls the flow velocity of the fluid in the well.

Engines that need richer mixture at maximum torque than at maximum horsepower are engines that have too much compression at that point of the RPM range for the fuel used. When that is the case you have to throw out the rules of main jet control and emulsion trimming and use aggressive emulsion and a main jet thats sized too large for it to be the controller of the system. Then the aggressive emulsion becomes a top end lean out design. This is why people on here all have different answers to the same questions. Its not that there are different ways of solving a single problem but rather its a lack of understanding of how to identify the correct issue to be solved. It is a fact that the AFR does not need to be varied at any point in the RPM range for a given load provided the fuel stress is the same across the RPM range of any engine. Its when we design engines with power peaks and then sharp drop offs away from power peak that AFR variation needs to happen. AFR variation is a crutch for a poor choice somewhere in the engine or fuel design in reality.


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 Post Posted: Thu Aug 16, 2012 9:40 am 
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webermaniac wrote:
gearhead1011 wrote:
WR169 wrote:
When we were testing with Chucks car he ran out of jets to get the O2 where they should be. We lowered the jets a bunch and it kept going faster and not changing O2 very much.
It's not that it wasn't changing Steve. The AFR indicated it was getting way leaner than what it should be. The O2 is a good tool to tune with it's just not reading what I expect it to. I planned on starting a thread on this.

If the AFR was reading way leaner than its supposed to it indicates a large percentage of O2 left behind in the pipe. Either an exhaust leak or an inefficient burn can do that. Its not uncommon for race engines to have inefficient burns that leave a lot of O2 unused and power wasted thus.

When the WB's read leaner than what you should run safely and changing a jet doesnt follow the AFR correctly there is a strong possibility of engine damage to come in the future. The engine may go faster the leaner you make it but it will suffer eventually. When I get ones like that I stop testing, try to figure out how to fix it and send the racers on there way back home to do a rethink. A common factor that can do this problem is a lack of ignition energy.


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 Post Posted: Thu Aug 16, 2012 5:45 pm 
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I promise to start a thread on this tonight. I got some stuff to do and I'm trying to decipher some of the stuff I have so I can be as accurate as possible. Just hold the comments for that thread and maybe we could move some of these. Sorry about jackin' your thread Steve :-

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 Post Posted: Thu Aug 16, 2012 9:29 pm 
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No problem Chuck. It did go in a different direction. But change is good. LOL

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