Carb Tuning

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MOPARJ

MOPARJ

What can I upgrade now?
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I noticed that the idle mixture screws on my Edelbrock Performer 600 were turned out about 4 turns. I did not ever remember doing that. So I screwed them all of the way back in, then a full turn and a half back out. How far should these be adjusted out? I readjusted my idle speed to compensate for less fuel at idle and to bring the idle speed back to where I had it. It seems now that the COmp XE268 cams lopeyness in my 318 is more present now, which is ok to me, as it sounds good. It is not misfiring. Is this because it is not as rich of a mixture at idle as there was when the screws were turned out farther?

Cruising, it still runs great, since these have nothing to do with fuel mixture at speed.

Also, is there some kind of phenolic spacer I can use under the carb? It is heat soaking and requires a few more cranks to start when warm. If I take the air cleaner of and listen to the carb when its warm to hot, I can actually faintly hear the perculation of fuel in the bowl.
 
Hook up a vacuum guage toa manifold vacuum source, (on the carb or on a vacuum tee somewhere), and adjust the two idle mix screws for the highest vacuum reading you can get, one at a time. Start by screwing one in until the vacuum drops off then back it out until it doest gain any vacuum, do the same on the other screw and then repeat the process. I find a little reving of the motor occassionally during the process will help clear the intake and give you a more accurate tune. Should be good to go afterwards.

You can get a phenolic spacer for the carb. Transdapt makes a 3/8 inch thick one that comes with longer studs, nuts and washers. Obviously a metal spacer wont help the heat transfer so a phenolic (plastic or composite) material is the way to go.
 
MOPARJ said:
Cruising, it still runs great, since these have nothing to do with fuel mixture at speed.
Click to expand...

Actually your engine will spend most of it's crusing time on the idle & transition circuits and very little on the mains.

FWIW, you need to get the timing right before you mess with the carb. The XE268 cam will want somewhere around 14-16 degrees BTDC for intial timing.
 
dgc333 said:
Actually your engine will spend most of it's crusing time on the idle & transition circuits and very little on the mains.

FWIW, you need to get the timing right before you mess with the carb. The XE268 cam will want somewhere around 14-16 degrees BTDC for intial timing.
Click to expand...

Yeah, right now, if my timing marks are accurate, I am running about 10 degrees with no pinging. Right now, my idle screws are turned out about 2 turns and the cams lopeyness is more noticible now than what it was with the screws out 4 to 4.5 turns. With the screws out that far, the lope wasnt as present and the motors idle was smoother, I guess maybe because of the added fuel to the mix. I dont mind the rough idle, as its the nature of the cam, but I just want the right amount of fuel given to it, not too much but not too little.

I also want the timing set properly. It does feels a little soft right now until you get to about 3,500 rpm, then it pulls like a banschee. Maybe it needs more timing? There is no starter kick back either right now.
 
You will need more intial timing and will likely have to do something to limit the timing on top.

I am running an XE268H in a 360 with 10.6:1 compression and magnum heads. I run 15 degrees initial and 33 total (magnum heads require less than the open chamber LA heads), it is all in at 2500 rpm. I run 89 octane gas in this engine and have no detonation issues.

The throttle response is instant and the engine pulls strong from 1500 rpm. The idle is almost as smooth as a stocker.

The XE268H is more agressive in a 318 than a 360 but you should be able to get a resonably smooth idle even in a 318.
 
Make sure you dont have a small vacuum leak somewhere. This would require the mixture screws to need to be adjusted out. A little trick I do if I suspect an air bleed or mixture restriction from dirt (it doesnt take much to throw off the idle mixture) grab the throttle and choke plate, rev the engine, as the engine speed picks up close the choke plate. This will flood the engine and should keep the engine from overreving due to the lack of air entering the motor. Do this three or four times for SHORT THROTTLE BURSTS. Something in the 4000 to 4500 rpm range should be safe on a healthy motor. Clear the engine out without closing the choke after each time. What this will do is allow manifold vacuum to be really strong all the up to the choke plate. Sometimes this will help clean out the small passages in the carb. Under normal operation high vacuum is only applied to the very bottom of the carb. May sound crazy but it works for me.
 
I hear about that trick years ago. Just recalled it now after reading this. But I recall it a little diff.

Rev the motor up, yeah 4000 rpms and while the throttle is open, throw a clean rag over the carb and open the throttle more. Motor should stall. Repeat a few times.

Now I haven't done that for 20 years, but I do recall it. Does it work ?? Can't hurt..
 
Well I went to adjust the timing last night and I slackened up the distributor just enough to move it if I really pushed on the vaccuum advance. I did not move it at all. Went to fire it, got it running, then I started hearing popping inside the combustion chambers that echoed through the mufflers.It barely wanted to run. I shut it off. It must have jumped the damn timing when I cranked it over, just with the bolt being barely moveable!

Looks like I am going to have to pull #1 plug and pull the cap and see if I am close to tdc. I may have to pull the distributor and check to see if the cam gear is still aligned properly, if not I will have to pull it and readjust it.

I swear, when it rains it pours sometimes.:-k
 
Jumped timing? I doubt it. If you turned the distributor clockwise, it would have retarded the timing, so you might want to put it back where it was. If you loosened the clamp bolt a lot, the distributor may have retarded itself due to internal friction, but the cure is the same, just advance the distributor. If your timing changed substantially, the distributor didn't "jump time" (it cant) something broke like your cam sprocket.

You sure you didn't knock a wire loose?
 
C130 Chief said:
Jumped timing? I doubt it. If you turned the distributor clockwise, it would have retarded the timing, so you might want to put it back where it was. If you loosened the clamp bolt a lot, the distributor may have retarded itself due to internal friction, but the cure is the same, just advance the distributor. If your timing changed substantially, the distributor didn't "jump time" (it cant) something broke like your cam sprocket.

You sure you didn't knock a wire loose?
Click to expand...

Hmmmm, when I first started it, it was running not that bad, a little hesitant but about every 5 seconds under idle, I would hear the pop. It is more of an internal backfire rather than throught the carb. It is a little more apparent when throttle is applied. I tried moving the dist vacuum advance back(retard) a little, but then it wouldnt start, so I moved counterclockwise back(advance) back to where it would start and I limped it back into the garage, popping as that was being done. The funny thing is that it was not misfiring badly from what I could tell. It sure seems like the dist shaft is not perfectly aligned on the shaft, as it seems like it is nearly running ok, but it is skipping enough to cause the backfire. I didnt even try real hard to break it, just slightly slackened the dizzy to move it, fired the motor and it began.

Maybe I should have started it, then loosened it. I dont know. Arrrgggh!!
 
The dist. can only be in time or 180* out and it can't "skip". It's not like a chevy that can jump a tooth. If you only loosened the dist. clamp a little the dist. couldn't have jumped 180 out. You have to remove the clamp completely and pull the dist. up about 1/2" to disengage it from the oil pump drive. If it did jump 180* out it would never start unless you turn the dist. half way around, not just a little bit. If in fact it did jump time it would be the timing chain that jumped on one of the sprockets. No ammount of timing adjustment will cure that. Check your spark plugs carefully. You may just have a bad plug. If their ok check your wires and cap. It could even be that you leaned out the idle circuit so much by turning the idle mixture screws in so far that it's way lean at idle which will cause a misfire.

The reason you hear the cam more now is because you leaned out the idle when you turned in the mixture screws. Also if you run more initial timing like DGC said it will smooth out the idle. It will also have alot better throttle response and get better fuel mileage and probably be faster. I know lopey idles sound cool but isn't more power what were after?

I've worked on 3 Edelbrock carbs that a buddy of mine had on different trucks and I allways had to adjust the mixture screws out 3 to 4 turns to get the most manifold vacuum and best idle.
 
Somehow, and I am lost as t how it happened, number 6 plug wire was on number 2 and number 2 on number 6. Problem solved. That was brilliant. I should have checked firing order first I guess:-k

Anyways, I gave it 4 degrees more initial timing while I was at it. Much more responsive on the low end and I havent really gotten on it yet. I also turned the screws out 3 turns before the timing mishap. Smoother idle, better power.

I will check vaccuum tomorrow, except now on the test drive, I heard a knock knock knock from the rear Got under the car and wiggled the driveshaft. It had play from side to side. Looks like a bad u joint. Hopefully my old 7.25 rear driveshaft u joints will work in replacement of these ones that came on the 8.25 driveshaft.

And the cycle continues............
 
Hey sounds like your on the right track. It's so easy to get wires mixed up like that. I always have to watch myself about wires 5 and 7. Real easy to get them crossed.
 
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