General Category > Quadrajet Carb Talk and Tips
Question about converting a divorced choke to electric....
LouC:
Well now I've got to tell you the rest of my story with this engine and carb(s)...and you will probably get a good laugh out of it. The engine had the Q-Jet on it from new (original un-molested, good shape carb). Ran fine till a bad overheat in 2013. Seemed OK after that but blew both head gaskets during the end of the '16 season. I took it apart had the heads checked, heads were cracked and cooling ports were getting eroded. Machinist thought re-man heads would be a better plan. So, I installed a pair of marine reman heads, Fel Pro gaskets, and a new exhaust system. Did not rebuild the Q-Jet because I 'thought' they were too hard for a beginner like me to take apart. It ran ok for a while then started stumbling, running rough and leaking fuel near the throttle plate.
So....I knew that OMC and Volvo had switched from the QJet, to the Holley 4160 in '90 or so since QJet production was ending. They used a specially calibrated version with no power valve on the primary side and bigger jets to compensate. I 'thoght' converting to a new carb, supposedly calibrated to this engine, that was used by OMC and Volvo for years, was the best plan. Well let me tell you it was a miserable failure! The only thing that worked well was the electric choke. No matter what I did that thing ran so rich it turned 2 sets of plugs black. I had to set the mixture screws 1/2 turn out just to get it to run tolerably well. I pulled the bowls off to check the floats and they were set level. Called Holley tech support a number of times, made sure the idle transfer slot was not over exposed, etc. Still ran super rich.
In frustration, I pulled out the old, trusty Q-Jet. Had your book and an OE kit from Bombardier/OMC. Carefully took it apart, and found....the inside was very clean....so....soaked it well, really blew out the idle emulsion tubes with my compressor, checkd the float setting....put it back together....
And it ran 150% better! Smooth idle....picks up rpm fine....and no black plugs.....
So I am a Q-Jet advocate now for sure and have a brand new Holley 4160 that I will probably never use....
As far as the electric choke, I could see that one of the models on that website will work with my intake manifold. However, if I swith to a Vortec engine in the future, the intake does not have a pad to mount the choke stove and this is where these electric conversions mount their bracket to hold the choke assembly. So in my mind I have a few ideas about how to fab up a bracket....so I can continue to use the Q-Jet....instead of that infernal Holley!
Cliff Ruggles:
"The only thing that worked well was the electric choke. No matter what I did that thing ran so rich it turned 2 sets of plugs black. I had to set the mixture screws 1/2 turn out just to get it to run tolerably well. I pulled the bowls off to check the floats and they were set level. Called Holley tech support a number of times, made sure the idle transfer slot was not over exposed, etc. Still ran super rich."j
The Holley Street Avenger new in the box from Summit we worked on here was just as bad and the E-choke didn't work for chit!
Story goes that my friend (owns a tree removal service) blew the 350 2bbl in his 1 ton Chevy dump truck. He got tangled up with a local Chevy "guru" and they traded some work back and forth, otherwise I would have rebuilt his 350 and retained the 2bbl set-up and points distributor.
My friend actually recommended me to the "guru" for carb work, and the guy called up here telling me about the new engine, Comp XE cam (big enough for a full race engine), "double hump" heads, new single plane Edebrock T-II intake, and that he required at least a 750cfm double pumper.
I told him I only did Q-jets, and he very quickly told me that he wouldn't have a "Quadrajunk" on anything he owned, problem solved and I quickly exited stage left!
So when this gas sucking never wanting to work right POS Street Avenger finally pissed everyone involved off enough and left my friend walking for the last time I had it flat bedded here and we installed a Q-jet for a Motorhome application that was never claimed by the owner. It ran FLAWLESSLY, fuel economy jumped from 2-3 to 8-10mpg, instant cold starts and fast idle, smooth during warm up, excellent throttle response and TONS more power than the Holley even thought about making.
We did have to go into the brand new Summit HEI and make some changes as it was also messed up and adding timing at idle speed, but was an easy fix.
So long story short, just because you open up a catalog or go on a website and buy all sorts of new "high performance" parts, they may not be worth two squirts of duck poop no matter what folks tell you or how much you pay for them.
I am NOT a Holley "hater", matter of fact have extensive experience with them, but this new stuff is CRAP, at least from what I've seen here.......Cliff
LouC:
Well now I feel that at least I'm not the only one! I have been studying the Holley idle circuit diagrams I can find on the 'net to see where the problem might have been with this 4160. The way I understand it the actual idle mixture is determined by the size of the idle bleeds and the mixture screws determine the actual volume or amount of gas being discharged in the throttle bores. So if the mixture appears far too rich based on the black center insulators on the plugs, then if the floats are set right (yes) needle valves not leaking (yes) then if it still runs rich my guess is not enough air is being bled into the flow of fuel for it to have the right idle mixture, correct? I don't think the air bleeds on a standard Holley are replaceable but maybe that's not true. Could there be a restriction in the air bleed circuit? The only other unknown is fuel pump pressure but the Q-Jet never had a problem with either the OE Carter mechanical pump or the Sierra Marine pump I replaced it with. However, I probably should have checked the fuel pump pressure to rule it out....any thoughts?
PS unlike many I have had experience with Quadrajets back when they were in current use. We had a 1975 Olds Delta 88 full size with a 350-4bbl Q-jet. Never had problems with that carb and we owned it from about 1978 to about 1989 or so. It always ran strong, I don't think we ever had to have it rebuilt (straight gas then) in all those years. I cleaned the choke linkage a few times that was it! So I never had a bias against them, just heard that they were all getting old, hard to rebuild right etc. However, they are really not harder to take apart than a Holley as I learned.
Last Question....
these marine intakes (cast iron OE style) are all (even the Vortec) a spread bore style manifold. To use a Holley you need to use an adapter plate (the Holley spreadbore 4175 carb would not fit on the shorter V6 intake manifold due to the thermostat housing, it will fit the V8s though). Can the use of an adapter plate cause the problems I had? I used an aftermarket one at first then changed to the OE one used by OMC and Volvo Penta but same result.
Cliff Ruggles:
Adapter plates all by themselves seldom cause running rich issues, but they can cause air flow restrictions, distribution issues, and some open designs can induce stumble/hesitation/bog when used on spread bore intakes that have a divider in them.
The air bleeds in the Holley units aren't the only thing determining fuel to the mixture screws at any basic setting, the metering block are a little more complicated than that. When we set up Holley's for anything we look at the IFR's and airbleeds, plus which metering blocks it is using. That made changes to the metering blocks in later years (not for the good), and we try to stick with and prefer early Holley units instead of any of this newer crap they are dumping on the market these days.
Holley's also come in many flavors, with a variety of boosters used thru the years of production. I prefer the "down-leg" variety vs annular or they flat ones with the fuel slot in the center of them.
With a Holley you also have to factor in that a high percentage of fuel at low throttle openings comes from the idle system and transfer slots, not from the boosters. The bores are pretty big in the non-spread bore variety and sensitivity at the boosters is poor. This requires a LOT of fuel form the idle and off idle system via the transfer slots.
Next time you mess with a Holley climb up over it and increase the throttle opening and look for fuel flow from the boosters. Most if not all of the fuel will be coming from the transfer slots/idle ports and it takes considerable "tip-in" to see any flow from the main boosters.
So improvements for any particular application most often come from metering block and airbleed modifications vs changing jets and PV's........Cliff
LouC:
Interesting, there is a lot to learn about this....the odd thing about this Holley 4160 (supposedly specially calibrated for the 4.3 V6 for OMC and Volvo) is that unlike the other marine carbs that Holley sells, this one does not have a power valve in the primary metering block, instead the main jets are larger to compensate for not having it. Why they set it up that way is a mystery to me. However, it does not seem that this has anything to do with my very rich idle issue with this carb. OMC and Volvo used this carb on this engine from the end of the Q-jet era to the beginning of the throttle body fuel injection era and I can't imagine they all ran as bad as mind did!
https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80492
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