What a nice set up, inexpensive for the real time information it gives you. Hmm I want one.

 

I don't meen to hijack the thread but am confused. Jrock has a still to be determined cam but most likely hotter than stock , pro comp aluminum heads, weiand manifold, and headers. Im thinking that he should have good flow throughout the system. Other than carb or timing adjustments, isnt his motor equipped to handle a lot of air and fuel once the mixture and timing is correct? I have a Eddelbrock 600 with matching cam and manifold with a good flowing exhaust, and mine runs fine in my 0 to 4500 band which is what I had targeted. In the beginning I made the mistake of hooking up plug wires thinking the distributer ran clockwise. Now that caused power issues. I would like to learn more on this subject as it applies to "jrocks" truck. Ill stay out of the discussion and and hopefully learn as jrock gets his problem sorted out. Sorry for the disruption.

 

IMHO the carb is bigger than necessary but not unusable with proper set up but it will not have good low end response as the air fuel mix will not be great because of low intake velocity

 

The correct way to do a plug reading is after a WOT run, fuel pressure also needs to be checked at WOT, any other time is giving you false data . I also agree reading plugs with todays gasoline's is difficult. Although my F1 does have a Edlebrock carb I don't have much tuning experience with it so I can't help there. I disagree that you have too much carburetor, I have a Holley 750 cfm vacuum secondary carburetor on my 289 and after tuning it, it runs strong - no hesitation ect. to 6000 RPM. Years back I always ran a 600 Holley on the same motor and was told small block Fords like carboration, I upped the size and noticed improvement.

 

Back in the day I had a 75 3/4 ton, 460, long tubes and all that. put a holley 750 on thinking big motor-big carb. Ran like crap. My buddy had a 600 economizer I think,he loaned it to me and it was great. Never had any experience with tuning them though. Maybe tuning down is the way to go.

 

I have comp cams 352383
http://www.cjponyparts.com/comp-cams-camshaft-set-xtreme-energy-xe262h-hydraulic-flat-tappet-1300-5600-rpm-351w/p/352383-V/

All my engine specs here on machine shop bill. From previous owner:



Thanks for all the info guys.

 

Yep, I'd also play with the timing. Make sure the ignition systemis dialed in.

I believe that is too much carb. My 450cfm works great on my 302. But that's with my daily driver style build.

Another thing is you might also be fighting is those heads. I looked them up when I was building my 302. Mixed reviews at best. Chamber and runner size, casting inconsistencies were brought up. Driving style is very important on an engine build.

 

Yeah i'm not a big fan of these heads either, i had an issue with the freeze plugs popping out, leaked coolant everywhere. i know they're just cheap aluminum heads....

 

I have been following this thread for awhile and thought I would add my $.02. While the 750 may be a little large for your engine I think it should run just fine, have worked on many engines where the carb was larger than recommended and had no problem getting them to perform fine. My personal car is a 56 Ford with a 312 Y-block and a mild cam. The first carb I used was a Demon Jr 525, similar to Holley (most carb size selectors recommend a 450CFM) ran fine at most RPMs and returned pretty good mileage to boot. Only problem was a hesitation just off idle, sometimes slight at other times substantial and at others none at all with no discernible reason why. I drove myself nuts trying to eliminate it, timing, jet size, accelerator cam, accel pump nozzle, etc. It would sometimes run great for a couple days and I thought I had it cured then hesitation would return. I contemplated going to EFI but since I have never had problems with carbs before I decided to try a new one.

I spoke to Holley and ordered a new Street Demon 625 on their recommendation, it is a carb similar in operation to yours and definitely larger than many size charts recommend. From the time I installed it the engine ran perfect, no hesitation, great idle and decent power. Two things I noticed were the feeling of slightly less power and less fuel economy.

I felt the engine was running a little rich even though the plugs looked good and the engine was running so well. I had no way to be sure and installed a Innovate air/fuel gauge similar to the one Russ suggested. Now that I have used it for awhile I don't know how I ever tuned with out it. I have changed the jets, metering rods and rod springs. AFR went from 12 to 1 at cruise to 13.5 to 1. Light acceleration from 9.5 to 1 to 12.5 to 1. The throttle is crisper, power improved and mileage similar to what I had with the old carb.

I think most of the problem you are having is a engine that is running too rich. The only way to know for sure and tune properly is to install some type of air/fuel gauge such as the one Ross suggested.

 

I use to run brand x350's with the 625 carb all day and ran great, I stroked it to 383 and still ran great but I wanted a 750. The 750 should be fine and only need to be jetted down some.

 

I installed the Innovate system and was shocked at what I saw on what I thought was a good-running engine. Especially since live at 5300' and have driven up to 9000 and down to under a 1000'. I picked a set of jets that is a compromise, runs a little rich at 5300 but leans out as I drop down. My Rochester carb also has an adjustable power valve, and I was able to fine-tune it.

Right now I'm in Missouri (under 2000') and while at cruise at home I run right at 14.5 - 14.7, I'm solidly in the mid-15's here. No difference in performance, engine is running cool, no pinging. I wouldn't have a clue what jets to use without the Innovate AFM.

 

Thanks guys for your help. I just ordered one of the air/fuel ratio gauge kits today, I'll install and report back. Thanks again

 

Okay, I just got home from a SAR EXPO, for work, deep in the Sierra's with no internet.
First off Pete, we listed almost the exact same engine criteria except I listed 6500 RPM. Knowing about his engine from back when he had oil passage issues and such I knew it was a little hopped up. I also had an idea how he was going to drive it (or how I think he should) so that was why I listed 6500 RPM. Any decent built SBF will spin to that all day long. So based on the info I had a 750 carb should work fine when adjusted properly. (Ironic you mentioned the Rubicon, that is in my patrol jurisdiction )

As to all the others comments, this about thread is about J ROCKS ( you really need to add your name in your sig, I and others don't like using user names, to impersonal) truck.

I do have alot of tuning experience with these carbs, as well as almost all the other performance carbs. The Edelbrock/Carter AFB carb is an excellent carb but they operate slightly different than most. One of the big differences is in the secondaries. An easy way to explain how they work is akin to having your choke butterfly closed and opening the primaries. It don't matter how much you open the primaries it won't flow air and fuel until the choke butterfly is opened. The secondaries on his carb have a counterweighted butterfly at the top of the venturi. As the engine (read vacuum pump) builds vacuum it will pull the counter weighted butterfly open based on secondary opening and vacuum demand. So if your old tired engine had an 1000 CFM carb but could only pull 500 CFM that is all it would get and therefore would need to be adjusted (jets, metering rods, springs, acc. squirter nozzle, etc...) accordingly. This is a short and simple explanation but hopefully it helps some.

Jrock, I got your pm and will respond Monday evening. Between the O2 sensor and going over things with you we will get it running good, as long as the other components on the truck are correct.

 

I ordered one also. Boy that didn't stay on my want list very long.

 

Thanks jimmy! Signature updated