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post #1 of (permalink) Old 09-18-2002, 01:41 PM Thread Starter
 
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Holley 2 barrel running rich (long)

I have a 1981 Scrambler with a 1984 I6 258 with stock intake/exhaust manifolds. I am running a Holley 3200 350 cfm manual choke carb. I changed the power valve from a 8.5 to a 5.0 and am using stock 61 jets.

I recently rebuilt the engine and have been running rich ever since (was running rich before rebuil also). The engine was dieseling, but I tuned the carb at idle and reduced the idle RPM's and this solved the dieseling problem.

I replaced the plugs at the same time and they were NASTY! #1 and #2 especially had ash build up (not carbon deposits). I checked the new plugs after 25 miles of stop and go driving and they were covered in carbon.

The jeep pulls 17mmHg vacuum at idle in park and 15 mmHg at idle in gear. I usually cruise around 10 mmHg.

So, why am I running too rich? Also, in stop and go traffic with a light pedal, what circuit do you think the carb spends the most time in: idle, main jets, power valve?

1.) There is no way the carb is too big at only 350 cfm
2.) The idle was tuned with a vacuum gauage (both screws roughtly 1.25 turns out)
3.) I set up the auto tranny to shift late so as to minimize engine from dogging and opening power valve.
4.) Jets are probably too large but I was told the main jet circuit is not encountered until 1500 RPM's (I have size 55 and 58 jets to try as well)
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post #2 of (permalink) Old 09-18-2002, 03:54 PM
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Re: Holley 2 barrel running rich (long)

Hi Jeff, my first question would be...Has the Jeep backfired through the carb at all (even a little one) after rebuilding the motor? If it did, even just a pop, you may have blown the power valve out. Holley PV's are very sensitive to backfires. It's an easy check, just pull the PV out and 'suck' on the 'flat' side (not the fuel side) and see if it has any leaks. If this is the case I would try one of Holleys "blowout proof" PV's. They are more expensive, but if you blow out two of the regular ones, it paid for itself!

The 8.5 you were running before sounds like the right one if your cruise is 10 inches of vacuum. 5.0 sounds like a pretty tight one (does it ever open?). Hope this helps.
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post #3 of (permalink) Old 09-18-2002, 05:17 PM Thread Starter
 
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Re: Holley 2 barrel running rich (long)

I am not sure about the backfiring. It used to backfire all the time but I don't remember if I had changed PV's yet or not.

As for the PV size, I don't have much of a choice. Under load (going up a hill, etc.) or if I stomp on it, my scrambler will stay in in the under 5 mmHg range until I am going 40 MPH. When you are driving it seems like forever until the vacuum gauge needle comes back above 5.
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post #4 of (permalink) Old 09-18-2002, 11:05 PM
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Re: Holley 2 barrel running rich (long)

10" at cruise (loaded) seems a bit low.
Try something - rev it to about 3000 RPM - out of gear (unloaded.) See what the vacuum is there. -- should be at least 16, preferably 18 or more.
Then idle again, now snap it hard, make sure the vacuum goes to near 0, then snap it closed once the R's are up. Vacuum should bounce way up on deceleration, like 19 or 20, then back to whatever's normal at idle.

If it doesn't go up to at least 16 at 3000, and/or bounce up after a fast snap closed, suspect plugged exhaust.

A plugged exhaust can blacken the plugs making it seem rich. It's the incomplete combustion that causes the blackness.

Also timing way retarded can also cause the blackness, again misleading.

Let us know what you find please.
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post #5 of (permalink) Old 09-19-2002, 12:53 PM
 
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Re: Holley 2 barrel running rich (long)

Hey RRich, can you give us a little info on how to select a power valve with the correct rating? Which way would you generally go if you put a carb on a motor that is smaller in displacment than the motor it was originally intended for?

Thanks,
Tim
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post #6 of (permalink) Old 09-19-2002, 02:53 PM Thread Starter
 
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Re: Holley 2 barrel running rich (long)

Rrich, I will check tonight but I am sure sure that my engine responds like you say it should base on previous experiments. As for the exhaust, it is highly unlikey that mine is plugged because it is stainless, less than a year old, there is no CC (abreviated so the eco-nazis don't track me down!), and my muffler consists of an empty glass pack. Timing could definitely be an issue!

As for the power valve selection, I have always read that you should do 1 mmHg below half of your vacuum reading at idle. I am not 100% sure this is the right method, but I know that it is close.
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post #7 of (permalink) Old 09-19-2002, 04:29 PM
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Re: Holley 2 barrel running rich (long)

When tuning performance cars with a Holley, I have always gone 1-1.5 inches below the normal cruise vacuum. This way you get instant richness when you stab the throttle. Probably not the way to tuna a Holley on a Jeep, but thats what I learned.
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post #8 of (permalink) Old 09-20-2002, 09:16 AM
 
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Re: Holley 2 barrel running rich (long)

is there an O2 sensor on the exhaust manifold?

read thru this: http://www.bob2000.com/carb.htm

i have Holley 2300's on 2 of my CJ's. they were left overs from the circle-track days and i decided to throw them on. i think i ended up going to #47 main jets. it idles just a little rich, but crusies in an acceptable range on the DVM.

matt
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post #9 of (permalink) Old 09-20-2002, 04:55 PM Thread Starter
 
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Re: Holley 2 barrel running rich (long)

I have tried the Bob site before without much luck. I don't know if I have the voltmeter hooked up right or whate but I get some wacky irregular readings.

47 Jets!!!!!! That seems way too small but if it works for you maybe I will give it a try.

I am going to check the PV for leaks tonight and jet in down a little and recheck the plugs later. Any other suggestions in the meantime will be greatly appreciated.
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