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#1
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Carb re-jetting?'s
Hi all, I need to richen up the mixture on my holley 750 VS. I plan on ordering the metering block to get rid of the plate on the secondary side, and a jet assortment. My question is, should i change jets on both the primary and secondary circuits or one or the other? Plugs are showing a little too white on my 340 I e-mailed Holley, but have not gotten a response yet. Thanks for your input.
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#2
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Unless you read your plugs immediately after a full power on the return road without idling, they won't tell you what jetting to use on the secondaries. Plug color will give you a decent indication of primary jetting and idle mixture. I would re-jet the primary with reading the plugs, then adjust the secondary by doing little full throttle blats on the highway. Keep the setting that pulls the hardest.
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#3
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The best way to set your mixture is to have the car on a dyno and use an oxygen sensor. Since this isn't an option for most people, the next best way is to use an oxygen sensor while the car is doing a few full-throttle runs down the street or on the track. The next best method is to read your plugs immediately after a full-throttle run with the method Kekoakeakane describes. The advantage of an O2 sensor is that you can read the mixture in real time, so that you can differentiate between the A/F ratio of the primaries and secondaries (by taking readings when the secondaries are not open). You can get an oxygen sensor from the wrecking yard for a few bucks (make sure to get the threaded bung off the donor car's exhaust pipe too).
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#4
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I am thinking about buying and installing one of the A/F meters available from edelbrock, any good?
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#5
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I've never used one, but it looks like a lot simpler than rigging up your own O2 sensor. It costs a lot more however... although for the money it would definitely be worthwhile if you are going to be using it often. I think it's around $125? The versions I've seen don't tell you the actual a/f ratio, just have some LED's labeled "rich" and "lean" and "correct". The question is, what a/f ratios do the LED's represent? Maybe the instructions say, it'd be cool if that was the case.
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#6
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I took a closer look at the edelbrock unit and it has led's from 12-15 with .5 increments. That should make it fairly accurate. I think i will try it.
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#7
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Sounds like a good setup, maybe I'll have to get one myself!
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#8
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I've thought of that too, but don't you need two sensors, 1 for each exhaust pipe? Or can you put it in the crossover?
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#9
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our jingle
" Bowties are for Butlers and babys, Mopars are for Men"
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#10
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Wow...that is really great...ok how about trying again and answer the question that's been posted.
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#11
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Yes, you should use one for each side since some motors like to be lean or rich on just a couple cylinders. You really shouldn't put it in the crossover as the gases will cool off to much by then. O2 sensors work at around 1200F. If the gasses are less than that, it'll read lean. You can sort of get around that by getting a self heating O2 sensor (4 wire), but your readings will still be off if you put it too far in the exhaust system.
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#12
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So where in the exhaust do you install the sensors? A foot from the collectors? Or by the tips?
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#13
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kekoakeakane ; I had read some where that the cross over pipe was the place as so to read each side as close to equal as possible. I can see a problem with a long pipe. How about a pipe about, hmmmm, lets say 5-6 inchs long. Can't be that bad can it?
71383bee; I read from the same article that the sensors should be in the collector. I wonder if I'm forgetting this info? This is a good question. I think to sensors would be the way to go. But, now should I use 2 gauges to read or tie in both sensors to the 1 gauge? Inquireing minds wanna know! |
#14
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Save yourself some money. That plate on the secondary side comes in sizes. You can adjust it just like rejetting.
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#15
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#82
Everything in this thread but the answer. #82 jet size on secondarys. #72 on front, that is your base to work from, on Holley carb 3310-2.
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