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11
Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Mudsport96 on May 18, 2026, 09:37:56 AM »
If Mercruiser calls for 8 degrees that is where I would put it. You aren't trying to win races ya know. The problem with trying to get street curved ignition timing on a boat application is that load varies sooo much o. The water vs pavement. That is why the ignition curves are "lazy" from the factory. The odds of losing traction while cruising down the street is exponentially lower than spinning a hub or ventilating the prop. At which point revs go wild obviously.
You could play with weights and springs to get every last bit of timing. But, if you need every last bit of power the 4.3 has... I'd drop in a 305 or 350. As for fuel usage. I have two close friends with almost identical boats. One is a 4.3 16.5 footer and one is a 350 18 footer. And cruising together on the same route, the get within .5 gallon per hour difference.
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Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Cadman-iac on May 18, 2026, 08:35:34 AM »
  I've got a question if you don't mind my asking.  How did you calculate the LPCP for your engine? And since yours is a marine engine, is it any different than one in a vehicle?
 You're not using a vacuum advance if I remember correctly, so maybe the calculations would be different on an engine with vacuum advance?
 Thanks for any help you can offer.

 Rick
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Quadrajet Carb Talk and Tips / I need the stock specs for a 7037213
« Last post by Erick on May 17, 2026, 08:13:39 AM »
Hello,
I just bought a 1967 7037213 quadrajet with 3466 julian date to replace the truck quadrajet I actually have on the car.
I know original measurements should be for main jet (71),  main rod (41), sec rod (AN)
But I don't find  stock specs for:
Main air bleed, air horn and float bowl, idle tube, idle down chanel restriction
upper idle air bleeds, lower idle air bleeds , iddle bypass airholes, iddle needle holes.
the carb seems to be unmolested but I would like to check if those measurements are original or not.
Thanks for your help
Erick
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Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Zyen on May 16, 2026, 05:38:32 PM »
so, i got off the internet, pulled my head outta my ass, and pretended to be the tuner i say i am.   i *thought* previous 70 jets were rich because (as it turns out) some PO had the choke wired half-closed.  i remember removing ties and adding divorced choke linkage.  the 66 jets from merc specs are for the merc carb, which has smaller primaries than qjet.  the change to 70/39 didnt help much so did some math and found that the 67 combo was running an estimated 17 afr and 70s were around 15.7 afr.  the 70/39 and the 'new' 71/41 were both jetted for a 3.8v6.  changed to 73/43 for an estimated 13.2 afr @ 4k, and 8° base using a nib/nos cobra dizzy.  today's run on a 19p ss prop gave me 4600 wot @ 41mph on gps. idle to 3600 was crisp and responsive.  4200-4600 was slow and lazy.  this gives me a good baseline to work on fine-tuning. 
i cant advance timing much more because of the advance 'hump' at 1600 in the timing curve; anything above ~8° base puts my LPCP around a dangerous 10-11° atdc at 1500 - 1800 rpm and not much better till 2500+, but the LPCP at 4800 on 8° base is a lazy 25+ atdc, as seen by the 1.5-2 second climb from 4200 to hitting a wall at 4600.
however, did a good 2-3 minute run at wot with no problems.  hard to see <1.5" hg with the gauge im using, so estimating < ~0.5" hg at wot.
so, unless anyone wants details, i'm gonna say this is closed as fixed.

thanks for the help all.
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Shop News / Website
« Last post by Cliff Ruggles on May 14, 2026, 04:33:28 AM »
We've been having intermittent problems with the website and folks are having trouble checking out.  It appears to be up and working again, but if you experience issues you can order directly by calling us at the shop. 

740-397-2921.

We're here 7am-4pm M-F EST.  Call volume is heavy so if we don't answer leave a good number/message and we'll call you back...tks...Cliff
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Dialing in your rebuilt Quadrajet carburetor / Re: OLDS 4MC Quadrajet 7040251 for a Big Block Olds - Advice Needed
« Last post by novadude on May 05, 2026, 07:34:41 AM »
Fatten up the primary rods a bit.  13:1 is too rich for steady state
, light throttle cruise.  I would target 15:1-16:1 range for max efficiency, longer oil life, less ring wear, etc.
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For Sale / Wanted / Re: A few carbs for sale.
« Last post by 77cruiser on May 02, 2026, 08:49:54 AM »
Must not not want it too bad.
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Dialing in your rebuilt Quadrajet carburetor / Re: OLDS 4MC Quadrajet 7040251 for a Big Block Olds - Advice Needed
« Last post by Kenth on May 01, 2026, 11:25:05 AM »
I would open the sec. POE .054" all the way in.
You may find the 39B pri rods somewhat rich, "tip-in" test will tell.

Other than this i think you´re good to go.

HTH
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Dialing in your rebuilt Quadrajet carburetor / Re: OLDS 4MC Quadrajet 7040251 for a Big Block Olds - Advice Needed
« Last post by DJD OLDS 4MC on May 01, 2026, 09:49:07 AM »
Thanks for getting back to me.

Besides the 2 items you mention, how does the rest of the list of specs look?

Anything stand out as needing adjustment?

Thanks, again.

DJ
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Dialing in your rebuilt Quadrajet carburetor / Re: OLDS 4MC Quadrajet 7040251 for a Big Block Olds - Advice Needed
« Last post by Kenth on May 01, 2026, 12:06:13 AM »
When measuring the primary pump and secondary POE discharge orifices you´ll have to look further into the holes were the restrictions are located.

I have found the primary pump orifices in a 7040251 are .026" and the secondary POE orifices are .029".

HTH
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