SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: Brad @ SCJB on May 19, 2014, 04:17:06 PM
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I have a standard 454 chevy with a demon 850cfm single with vac secondaries. Timing is at about 34.
Originally I just threw the carb on it and ran it. It would choke itself out as soon as the secondaries opened up. Turned out it had 67's in the front, 75's in the rear.
I bumped it up to 80 front / 81 rear to see if it would fix the issue, which it did, but now its running super fat.... tons of exhaust soot all over the transom. I havent even bothered pulling a plug to read it as im sure they are black as night.
I dropped it back down to 75 front / 75 rear...I havent ran it yet, but im getting sick of messing with it......is this a good baseline to go with on this setup? seems like im all over the place and this might be a good 1/2 way point.
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I have a standard 454 chevy with a demon 850cfm single with vac secondaries. Timing is at about 34.
Originally I just threw the carb on it and ran it. It would choke itself out as soon as the secondaries opened up. Turned out it had 67's in the front, 75's in the rear.
I bumped it up to 80 front / 81 rear to see if it would fix the issue, which it did, but now its running super fat.... tons of exhaust soot all over the transom. I havent even bothered pulling a plug to read it as im sure they are black as night.
I dropped it back down to 75 front / 75 rear...I havent ran it yet, but im getting sick of messing with it......is this a good baseline to go with on this setup? seems like im all over the place and this might be a good 1/2 way point.
Is the timing locked out brad? i would start with the 75's
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Is the timing locked out brad? i would start with the 75's
i believe so...its just a marine mallory unilite....i dont believe those have any advance in them.
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I had the jetting on my demon 4 sizes apart.....
Or you can put the plug in the power valve and square the carb up.
72 & 76 .... I think.
Or 74 & 78
Can't remember.
-beerjet-
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i think im at 72/76, I'll have to look at my jet plate to see which ones are missing. Demon 650 vac 2nd.
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I don't have any specs on the Demon stuff, but Holley had a couple 850 vac that were offered on the 502 crate motor that used either 80/80 or 78/82.
Going off of what info you have posted, I suggest starting off with 75pri/80sec (using jets you already have) and run it to see how it looks.
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Probably not what you want to hear, but I just went through this with my nephews boat. Stock 454 vortec motor with small marine cam from Comp Cams, 850 Holley DP. Boat ran good but would burn your eyes if you idled very much. We did the same thing, bigger jet, smaller jet, PV changes on and on but did seem to make much difference overall. I convinced him to send it to C&J Engineering to have John make it right. John said the 850 was to much carb on a stock 454. I found a used 750 vacuum secondary carb and had John go through it. The boat picked up 800rpm, accelerates hard, plains much quicker, I didn't have a gps, but seat of the pants was probable 5mph faster and it just purrs at idle with no more burning eyes..
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Probably not what you want to hear, but I just went through this with my nephews boat. Stock 454 vortec motor with small marine cam from Comp Cams, 850 Holley DP. Boat ran good but would burn your eyes if you idled very much. We did the same thing, bigger jet, smaller jet, PV changes on and on but did seem to make much difference overall. I convinced him to send it to C&J Engineering to have John make it right. John said the 850 was to much carb on a stock 454. I found a used 750 vacuum secondary carb and had John go through it. The boat picked up 800rpm, accelerates hard, plains much quicker, I didn't have a gps, but seat of the pants was probable 5mph faster and it just purrs at idle with no more burning eyes..
Stoked you guys got that running. Ever figure out what was sticking on the float?
Sent with my Fingers
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Stoked you guys got that running. Ever figure out what was sticking on the float?
Sent with my Fingers
Ya, it had a brass float and needs the nitrophyl float according to John. The brass float kept pinching when installed. We just put a little "tweek" in the float to let it clear the metering plate. Once we got it working, it was impressive what a difference it made. When we got home, it got sent back for a re-check.
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http://www.bgsoflex.com/holley.html (http://www.bgsoflex.com/holley.html)
Brad check this out