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efi conversion

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kunbarrie

Contributing Member
whats the thoughts of fitting a closed loop throttle body injection system to a 5ltr ,getting sick of quadrajet carby problems.watched video of the affordable TBI system for marine fitting, is designed for the 5ltr v8 with thunderbolt 4 ignition . is closed loop system so no o2 sensor needed. thanks
 
2X on Cost!!!

FWIW, one or more O2 sensors are needed to enable 'closed loop'...you can't have one without the other.
 
"Closed loop" infers the presence of oxygen sensors. You can run in "open loop". The purpose of the oxygen sensor is to determine lean or rich condition. Since the boat is (we hope) not coasting downhill or otherwise entering an unloaded situation, the downstream sniffer isn't really much of a thing. Yes, if you can afford the swap it is better than a carb.
 
This is an EFI system, It works on VE tables, no O2 sensors needed. Better off with the Q-jet

Find someone who actually knows how to rebuild a Q-jet. Start with finding one that was set up for a 5.0 and have it built by a knowledgeable person.
 
Docksidemarineservices said:
This is an EFI system, It works on VE tables, no O2 sensors needed. Better off with the Q-jet

Find someone who actually knows how to rebuild a Q-jet. Start with finding one that was set up for a 5.0 and have it built by a knowledgeable person.
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i have previously bought 2 carbys from national carbys in USA one runs to rich can screw both mixture screws right in, engine still runs ok.but when running in the lake,after 1/2 hour it gradually loses revs and have to idle back to shore,lift air filter,and can see fuel dumping from both discharge nozzles at 750 rpm.same happened some years ago and a new fuel pump fixed it. 2nd carby is a MC 4BARRELL for this particular eng,but has electric choke conversion,bolt this one on and will not idle below 1200rpm and constantly backfires through both exhaust manifolds,has new fuel tank,fuel filter,and extra water seperator fitted..
 
When properly rebuilt the Quadrajet is an excellent carb; I’ve gone thru mine a few times the main thing is to start with a good core and clean it very well (especially the idle air tubes) and to use high quality parts. The problem now is finding good cores because new marine units have not been made since about 1990. I can recommend the Cliff’s High Performance Quadrajets and Quadrajetparts.com. Cliffs site also has a nice forum to ask questions. I installed a better quality accelerator pump from Cliff's and immediately noticed a difference.
I’m one who’s old enough to have had Quadrajets on our current cars 45 years ago! Yes the high performance applications used Holley but all the garden variety GM V8s came with Quadrajets 1966-1986 or so.
BTW, if you are looking for new carbs to replace the Q-jet you can't even get Edelbrock 1409s not new at least, your only option for new right now is Holley. Holley sells a spread bore version of their 4bbl as a Qjet replacement that does not require a spread bore to square bore adapter like the other Holleys and Edelbrocks do if you are putting a square bore 4bbl on an original spread bore intake manifold....
As for EFI yes we love EFI in our vehicles, take it for granted that they run great cold or hot, and don't need much maintenance at all, but cost & complexity would make me stay with a carb for boats. I'm so old fashioned I actually prefer the old style mechanical pumps to the electric pumps, they just seem more reliable, just like divorced chokes are sometimes more reliable than electric. If you have a Vortec engine though you have to go electric for both....
Q-Jet rebuild small.jpg
 
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kghost said:
I you can afford to buy again, But one from this guy, You may be able to send him one of yours to be professionally rebuilt.

https://www.carburetor-parts.com/

This guy knows what he is doing
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x2 on Mike bought several kits from him over the years.

To -op it sounds like I would stop buying carbs from National Carb... verify your fuel pressure is correct as to high fuel pressure will overcome needle and seat and dump gas down carb like you saw.

You certainly can convert to EFI, but as outlined really just need someone to properly rebuild and set up your carb.
 
am in final stages of conversion,need a 180deg thermostate one in engine now is a 160deg looks like a sierra s18 43015,mappimg in ecu requires 180deg,any body know of a similla part,boat part shops on google dont seem to add the degrees in the ads.thanks
 
Since you are in this deep, you may want to see if there is a custom tuner in your area...he should have several 'tunes' as well as the equipment to program the ECU...don't know about 'down under' but up here, the market is still growing....just makes sure they understand 'marine' use...
 
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