Too much carb?

yall have been great with all the answers and insight youve given so far, so i figured id throw one more question on you.

i have a 75 cj5, 258, offenhouser, headers, about sea level.

i also have a...1850 600 CFM 4bbl holley that came on the jeep. it does not run good. friend of mine says it is getting too much fuel. says that its way too much carb. mechanic friend says the 258 should handle it. it seems like it is running too much fuel. i have heard that the 600 has the same metering plates as the 450, so i can just put in some new jets, squirters, and something else and it will be a 450 and not a 600 anymore. is this right? i have done some looking and cannot find the information of what part numbers/sizes i need to do this with. any help would be appreciated. and i have rebuilt the carb, and set the timing. put in new filters and new gas before running the jeep.

 

I have had a few different carbs on my Jeep before I went EFI. Had the one barrel, ran like crap. Had a large 4 barrel, ran like crap. Went to a Motorcraft 2100 2 barrel and it did run better. If you want a 4 barrel, the only one I have heard that will work worth a darn is the Holley 390 I believe it is. Motorcraft 2100 came on lots of engines. I went to EFI a few years ago and it has ran great since.

Good luck.

 

i will prob go to efi, but right now money is tight, and im trying to get my jeep running before my car dies so i still have something to drive. im getting pretty close, but its barely running with this gas problem. got to rev it way up to get it to move and not lug out. just trying to work with what i have till i can get the upgrades i want.

 

I'd agree, that a 600 CFM carb is really big for a 258. A passenger car V8 2V carb will be something like 150-250 CFM. Plus, I think the Holley primaries are pretty large - the same size as the secondaries. The problem with a large carb on a small engine is poor mixture control at low speed. The carburetor has to provide enough of a restriction that a useful vacuum is created. Remember that a carburetor is a mechanical device that is powered by vacuum. When the venturi is too big, opening the throttle beyond idle provides too big a hole and vacuum drops. One way to get around this is to radically richen the mixture and provide a huge pump shot so that the loss of vacuum does not stall the motor when the throttle is opened suddenly. Works ok for race cars, not so good for street cars.

Also, a Holley street carb without significant modification is terrible off the pavement - BTDT. I recommend a Motorcraft 21xx, or fuel injection. The smallest Holley Truck Avenger would likely work fine with some tweaking. Quadrajets are supposedly good off-road carbs; they have small primaries and should work ok on a 258.

 

I'm gonna second what tim said.

Get an MC2100 or a Truck avenger 470. Both would be better suited to your 258.

I've got the MC2100 on my 304, its plenty of carb for that motor, and with a few minor tweaks, runs almost as good as EFI off road.

 

ok, i guess if it is not too expensive ill just go with the 2100 motorcraft. you cant argue with the jeepin nerd

where is the best place to find one? i assume its a junkyard item? how much would i expect to pay for one? and while im asking a bunch of questions..how much could i get out of a 600cfm holley?

 

When I look up Holley 8150 I come up with an intake manifold. Got another number for it?
I may be interested depending on what it is. I’ve been looking at Holley DP’s because I’ve put too much cam to my motor for the Carter AFB I’m currently trying to run.

 

I put the wrong number on original post, my apolgies.

number on it is List 1850-2

http://www.holley.com/0-1850C.asp is holleys page about it.

 

Never mind, I think I found it. It’s actually an 1850 isn’t it?

Edit: Ah, see you found it also.
Not quite what I'm looking for, thanks though.

 

if i go with the 2100 it will work with my intake right? will i need to change anything else, or just take the holley off and put the motorcraft on?

corveeper, thanks for the interest. sorry it wont work out. Cest la vie.

 

you will need an adapter. The 2100 is a 2bbl unit. Autoparts stores used to sell them. not sure if they still do.

 

backtracking just a little bit, with the intake i have the holley 390 would not be as good as the 2100 because of the off road capabilities right? only real plus would be that i would not need the adapter...

 

I run holley 8007 390 cfms on my Buicks and have for years. Never had problem one, but then I dont winch it straight up a cliff and expect it to run either. Remember that if your carb is having issues with the angle then what is going on with your oiling? Fuel injection does nothing to keep your bearings from seizing up.

 

The Holley 1850-2 has vacuum secondaries and is 600 cfm, as stated. The beauty of a vacuum secondary 4 barrel carb is that it functions as a 2 barrel until the engine load and rpm needs more carb. Essentially the rear 2 barrels don't even open until air flow through the front 2 barrels calls for it. This means that for idle, off idle, low speed throttle response, and low rpm situations, you wouldn't know the difference between a typical 2 barrel and a vac secondary 4 barrel. Including economy if you keep your foot out of it.

I agree that 600cfm is overkill for a low rpm Jeep 258, but if it is operating properly, the secondaries are probably rarely ever even opening anyway in normal use, so it's basically functioning as a moderately sized 2 barrel. There is no reason that a Holley 1850 shouldn't work OK. And regardless of what size engine you put it on, it is rare to have to vary jet size or the power valve very far from the OEM Holley, out of the box, specs. OEM primary jets on an 1850 are #66, and a 6.5" power valve.

Also keep in mind that 2 barrel carbs and 4 barrel carbs are not cfm rated in the same manner. 2 barrel carbs are rated at 3.0" HG pressure drop, but 4 barrels are rated at 1.5" HG pressure drop. So a 500 cfm 2 barrel is not equivalent to a 500 cfm 4 barrel. Conversion factor is 1.4. 500 cfm 4 barrel = 700 cfm 2 barrel.

You probably have a blown power valve or other problem with the carb if it is overfueling. The 1850-2 did not come with a power valve protection check ball (it was added with the 1850-4), so a backfire can rupture the power valve diaphragm, resulting in very rich operation. Also the metering blocks on Holley's are notorious for clogging air bleeds and other passages due to dirt getting in through the air or fuel.

I am running an 1850-4 on the Ford 302 in my CJ, and it runs excellent.

All this said, the Motorcraft 2100 2 barrel is a GREAT carburetor, and you can't go wrong if you want to take the time to put on an adapter plate and swap one. Look for the smallest size with 1.08" venturi for great results.

 

Thats a lot of information to take in right after class...
As i said i just rebuilt the carb, but there was some backfiring and rucus while setting the timing. im pretty sure that a new power valve came in when i rebuilt it. just the backfiring from setting the timing could blow the power valve?
the jeep idles pretty well right now, and according to the vaccuum gauge is running between 20 and 21 vacuum pressure. it does backfire a little bit while idling, but nothing loud. when i try to move the jeep is when it gets problems.
this is my first time messing with carbs, and as i said earlier i am very tight on cash right now. if i can just fix this one (if it is a problem with something being broken) then thats what i would want to do.

if i get the new power valve, should i go with a smaller one? what size would be good? also, while im in there what size jets would be good since im running a big carb on a small motor? should i replace the squirters? to what?
i know its a lot of questions, but you seem to know holleys really well and im gonna be greedy with your knowledge

 

Yes it is possible with a strong backfire through the intake.

What did you set the initial timing at? It sounds like your timing may be too far advanced. Set it to around 12 deg BTDC. Typical idle vaccuum at sea level is around 17 - 19" HG. If advanced too far, the idle speed goes up, vaccuum goes up, and an intermittent misfire sets in. When set by 'ear', most people typically advance timing too far.

I'd stick with the original jets and power valve size, as I mentioned earlier. Decisions to make changes should be made after everything else is running correct. Think about it, how does a carburetor know what size engine it's sitting on? All it knows is air is flowing through its venturis, and it adds fuel based on that air flow. The air flow transitions points based on engine demand (seen as vacuum) from the carb idle to main circuits and main to power circuits may vary a bit from vehicle to vehicle, but overall all the carb is doing is mixing fuel based on air flow through its venturis. The carburetor is always sensing that air flow through the difference between venturi pressure vs atmospheric pressure in the float bowl.

After you get it running correctly (with the engine at operating temperature I should add), decisions may be made to change jetting based on spark plug reading, and power valve size based on taking vacuum readings while driving around. The power valve should be about 1 - 2" HG below your flat ground cruising vaccuum reading. This will vary with engine size, vehicle weight, and gearing. Altitude (and the corresponding atmospheric pressure change) is the biggest factor in needing to change jet sizes.

 

as i said, i dont know much about this stuff. i had a friend over with a timing light and vaccuum gauge. we set the timing at 8-10 degrees advanced, then with that locked down we adjusted the floats and then set the richness with the vaccuum gauge; adjusting the rich/lean by turning the screws till we got the max vaccuum.

so my next step is to check on the power valve and make sure its not messed up. if that is not the problem what would be the next thing to check?

 

I have had a Holley List 1958 on the 225 for almost 40 years. These are 450 cfm full 4150 Holleys that came stock on the AMC 250 v8's and use all the same spring loaded needles and dodads as the rest. Not sure how one would find one of these now but I paid $40 for the last one. With the spring loaded needles and extended bowl vents, they work great.

 

I have a 600 cfm... four barrel Holley sitting on an Offenhauser four barrel intake.... although I did go back to the smallest Holley jets available due to air/ fuel mix issues, to ensure i was running without any bogging, etc.... LOL although I have machined this ol 258 to beyond the suggested amount... she is still running like a top. I presently have the Transfer case off... to go through and ensure all gears and bearings, seals, etc in top shape... do this every other year to just enjoy the time and ensure no surprises...

Gunner