First time re-jetting a carb

[CEORanger]

Have a Ford crate engine 302 with a 4 barrel 650cfm holley carb in my ranger.
it seems to run really rich based on looking at the sparkplugs and all the soot on them.
any tips or suggestions on re-jetting it or should i just take it somewhere.
drive it at various desert spots so it would be nice to re-jet for each area that has a different elevation that would have an impact. would like to learn too.

[amr126]

I went the Innovate Motorsports route with the LM-1 and had good success with tuning myself. It is pretty difficult to do a really good job of rejetting by just looking at the plugs, unless you've got some experience under your belt. Also with LM-1, you can get the rpm converter with lets you have 6 analog channels to record things like throttle position, rpm, water temp, etc. which proves helpful with checking the overall health of whats under the hood.

[Co-Dog]

If you want to learn how to jet a carb yourself. The first requirement is a lot of patience. There is a lot of satisfaction in dialing a carb in without all the fancy equipment, but it takes time. I suggest first getting a book on Holley's. HP Books has some decent one's. That way you can get familiar with your carb. No way to jet it if you don't understand how it works.

Also, a vacuum gauge is a must have tool to do this yourself. Chances are that you won't really need to jet it. The carbon your seeing on the plugs is from idle. It may not be running rich at wide open throttle. Float level may be too high. That's a good start point. There is a brass screw with a wide flat head on the side of each float chamber. Remove the screw, careful not to lose the washer, it sticks to the carb sometimes. If gas pours out, then level is too high in that chamber. If no gas comes out then try to see where it is sitting through the hole. It needs to be at the bottom of the threaded hole. I'll explain how to adjust float level if you need to make an adjustment.

If your serious about learning, I can walk you through some basic checks necessary before touching the jetting.

[sickrick]

If you want to learn how to jet a carb yourself. The first requirement is a lot of patience. There is a lot of satisfaction in dialing a carb in without all the fancy equipment, but it takes time. I suggest first getting a book on Holley's. HP Books has some decent one's. That way you can get familiar with your carb. No way to jet it if you don't understand how it works.

Also, a vacuum gauge is a must have tool to do this yourself. Chances are that you won't really need to jet it. The carbon your seeing on the plugs is from idle. It may not be running rich at wide open throttle. Float level may be too high. That's a good start point. There is a brass screw with a wide flat head on the side of each float chamber. Remove the screw, careful not to lose the washer, it sticks to the carb sometimes. If gas pours out, then level is too high in that chamber. If no gas comes out then try to see where it is sitting through the hole. It needs to be at the bottom of the threaded hole. I'll explain how to adjust float level if you need to make an adjustment.




If your serious about learning, I can walk you through some basic checks necessary before touching the jetting.

I giving you a rep point for taking the time to help him out. This is the first thing every holley owner should learn.

[tltony]

I've been jetting/tuning carb's since the 70's. I thought I was pretty good until I got myself a wide band O2 sensor. With todays gas, you can't really read plugs to get close, they just don't color up like they should. If you want to learn, spend the $ on an Innovate or other O2 sensor and get a good Holly tuning book. So often, the mixture is screwed up by the power valve, or pump squirters, not the jet sizes.
GET THE MACHINE. I learned the hard way by burning up an engine by having it way too lean. And I thought I knew what I was doing. That mistake cost me $3700. to correct, then I still had to buy the wide-band.

Go here: http://www.innovatemotorsports.com/products.php

Good luck,

Tony. I'll help you once you're set up. PM or call me.

[Co-Dog]

That's a hard lesson learned, Tony. Fortunately my learning experiences weren't that costly. I used to have a lot more time than money and could never afford a sensor.

I have gotten cars through smog checks by rejetting after seeing the results of the test. Having some numbers sure does make it easier. I can't count the number of times I've seen people blame the carb, and insist that it needs rejetting, when the problem was a vacuum leak or ignition problem.

Last time I checked, a decent sensor cost about $500. That was many years ago. How much are they now?

[loufish]

If you're really running rich, there could be be many causes, Co-Dog pointed out some great starting places. There are many questions that can help determine the rich issue...Blown power valves are common, and if it's not just at idle, you could have the vent tubes splashing fuel into the venturies, etc...
How much fuel pressure are you running?

I would set the float level(as Co-Dog recommended) first thing, for off-road I set my floats a little lower then street/strip. Then verify fuel pressure, I wouldn't run over around 6-7 lbs.
Turn in (clockwise)the idle mixture screws all the way in(don't force them), then back each one out 2 full turns.

If you did everything above, you're at a good starting point to see how the truck runs.

BTW. When you first fired up the truck, did it back-fire up thru the carb? Back-fires are big time power valve blowers...
If the idle burbles, look down the carb(use safety glass's) and see if you can see fuel coming out of the venturi boosters...Good sign of blown power valve.

[tltony]

An Innovate wide band O2 sensor from the site I linked above $349.

The point of this whole thread is that he dosen't KNOW whether he's rich, lean, or what.

Power valves aren't that fragile, though people want to believe they are. A more common problem is too stiff ( high number) of a power valve for the vacuum signal that the engine generates due to valve overlap. This will make it rich at light load.

To make optimum power and still be able to pull a ten mile sand-wash on a hot day and live, you have to be right on, not guess.

The wide-band gives you real-time, bar graph mixture readings at all throttle positions/load ranges, so that you know EXACTLY whats happening under all conditions.



A buned piston and/or valve or washed out rings are a lot more expensive than $349.

Tony

[Co-Dog]

I couldn't agree with you more, Tony.

I know that Holley, in particular, would like everybody to believe that you just pull it out of the box, bolt it on, and it will run fine. They have done a pretty good job of engineering one size fits all carbs, but don't expect them to let you know the down side of it.
My guess is that they err to the rich side, because the damage comes slower and is less noticeable.

My original point was that the shade tree mechanic can make basic adjustments that will help overall in most cases. Component changes should be the last resort, and you should absolutely know whats going on before doing that.