[TerryT]

Hi guys, My car has always run rich(black exhaust on ground when revved up, pipes black, stinks a little) Anyways I just rebuilt the carb at original specs. after I make sure thats set right, I want to time it. I never actually timed anything, but do know how to operate the gun, and to line up the mark on the crank to the timing plate. Its just that I m not sure of what the lines on the plate represent. I see about 8 increment lines and what looks like a "0" at center. Is that tdc? Can someone tell me what my timing should be set at, and where that corresponds to the timing plate? Also what is the normal range that vacuum should be at? And can that reading be taken from a baseplate port? Im hoping this timing needs adj to help ease the richness. The carb idles screws are now 1 turn out and the car idles fine, but with a punch of the gas theres an initial bog and then catches up. The jets are 66.Again Im hoping the timing might correct this. My engine is a 283, Auto.,600 Holley, Edelbrock Performer intake, Mallory elect. dist, and headers.It also has Bosch platinum plugs, if that makes a difference. I bought this way and I dont think anything was done internally. So please give me some numbers to where some of the adjs should be at or near. I did some searching, but everyones engine is set differently, so I thought Id post what I have.Thanks !!

 

[Pro19Nova67]

While using the timing light if you line up the mark with "0" then the spark is being fired at the exact moment the piston reaches top dead center. Each mark above and below the 0 should represent 2 degrees of timing. The marks above the 0 represent Before Top Dead Center (btdc) and the marks below represent After Top Dead Center (atdc). I believe at idle most cars like the 8-12 degrees btdc of timing but its better to check your timing at full advance. Be sure you have no vacuum advance hooked up and rev the engine until the timing stops advancing, this number should be in the 36-38 degree btdc range. To find that number you'll either need a balancer with timing marks all around it, a timing tape, or an adjustable timing light.

Unfortunately I doubt the timing will fix your richness issue. If its rich you simply need smaller jets. If it bogs upon acceleration then catches up you most likely need to focus on the accelerator pump area of your carb. There are several different adjustment which can be made. You can try adjusting the, cant' remember what its called but it has a spring on an arm which pushes down the accelerator pump arm. You might try loosening that a bit. There is also a little accelerator pump cam held in by a screw, that cam will usually have two screw holes, you may try the other hole or you may need to invest in an assortment of them. The squirters themselves may be too small, a number is stamped on them and you may need to go bigger. That's just a few things I can think of, perhaps someone else will post more.

As far as vacuum I can't really answer that, engines are just so different depending on what's inside them. Hopefully someone else more knowledgeable can help you out. However engine vacuum does have a direct effect on the power valve size you should use in the carb.

 

[TerryT]

Thanks ProNova. The accel. pump is new. Power valve is new,6.5 As for the jets,66's are what came origionally. Any idea to what a different size should be? Theres so many different sizes, and I dont want to buy more than I really need to. Also,I was thinking the 0 on the timing tab was tdc.I just wasnt sure what each increment represented. I got to get the timing checked since it never was, since I owned it.

 

[Pro19Nova67]

You're right there are a ton of jet sizes available. It's hard to say just how rich you actually without being there and even then its only an educated guess until you try it out and see what happens. Reading spark plugs is probably a better way to determine how rich you are than reading the exhaust. If they are black, not oily black but soot black, you are definitely rich, you are after a tan color. If its really rich I'd say maybe 4 sizes smaller (or more). If its just a little rich then maybe only a couple sizes. Weather has a lot to do with it too, I'd hate to see you go lean when the weather cools down. You might want to keep an eye on eBay, sometimes you can pick up an entire set of jets for a decent price. Then of course you'll never use 95% of them. In my opinion, if possible the best thing to do is find a buddy with some jets and go to the dragstrip. Check your plugs between rounds and make adjustments as necessary. Test and tune at my track is $25 plus you get an entire day of fun! Not to mention you'll be surrounded by jetting experts.

The accelerator pump can be in perfect working condition and still be out of adjustment. A bog off acceleration almost always points in this direction. Of course too much fuel being discharged from an accelerator pump can make it fall on its face too, different feeling but very similar. It's mostly a trial and error job, at least it is when I do it. When looking down the carb, (engine can be off obviously) does the accelerator pump start to squirt gas just as soon as you move the throttle or is there a delay? My guess is you need more gas sooner. I'd start with loosening that spring I can't remember the name of first, this will start the accelerator pump moving sooner. That adjustment is free, everything else costs money. One turn can sometimes make a world of difference.

My opinion is start with the timing and get that nailed down, then move on to the carb. You never know, the timing may just fix your bog problem but I wouldn't bet on it.

 

[dougy68nova]

get this set from summit. you will have jets leftover for the next time.


http://www.summitracing.com/parts/SUM-210230/