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Old 06-17-2010, 08:22 AM
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Edelbrock tuning help

Sorry, it's kind of long.
I'll start by admitting that this is my first foray into carb tuning. All of my experience is on vehicles that are fuel injected 1 way or another.
I reciently put a new cam, intake, and carb on my 79 Chevy pickupwith a 350. I'm running a performer cam kit, performer 2101 intake, and 1405 carb. The rest of the engine is stock except for some cheap LT headers.
Here's the specs for the cam.
http://www.summitracing.com/parts/EDL-2102/


Anyway.... I live at 7000' ASL, and as you can imagine, right out of the box the carb was set slobbering rich. Not so rich that it didn't run well, but rich enough that it will lead to fouled plugs, and bogs a bit while driving.

I went through the owners manual and started with their jet and rod recomendation for 6000'. This ended up being 1427 (.098) jets and 1457 (073 x052) rods. However, I didn't change the secondary jets to the recomended .089 because I didn't have that size, so the secondaries stayed stock (.095).

The test drive went great when just tooling around. All of my mid range bog was gone and responsiveness was great. Then I did a WOT run.... It ran great up until about 4500rpm, and fell on it's face. After the high RPM trouble, I had to nurse it home. Anything more than the slightest bit of throttle and it started surging and hesitating to the point that it almost died.

I'm pretty sure I need to richen it up a bit, but I'm lost when it comes to rod jet combinations. I'm hoping someone with more experience can make some recomendations.

Here's what I have to work with
Jets:
.101
.100
.098
.095
.089 (got these this morning)

Rods:
070 x 047
070 x 037
073 x 042
073 x 047
073 x 052

Springs:
blue
yellow
orange
pink
silver

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Old 06-17-2010, 11:24 AM
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It sounds to me like the carb picked up some trash when you did the wide open throttle blast. When you made the change and it ran fine it should have stayed that way, doing a WOT run don`t change the primaries adjustment. Was the engine up to temp when you did the WOT run? Did you check to make sure the distributor didn`t move afterwards? Check over everything from timing to spark color, check the carb out carefully also. If everything checks out okay go up 2 steps rich on the carb then test.
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Old 06-17-2010, 12:16 PM
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The main downfall of an E-brock carb - dirt!!! I've had several and when they 'die' it's due to dirt. Pull it off, remove the top cover, dump it out, get a spray can of carb cleaner, your compressor and go to work. Put a GOOD fuel filter just before the carb and most likely you will not have that problem again.

That cannister behind the carb is my current fuel filter from Speedway;





These are about $50 and have AN fittings but of course can be adapted to the regular barb fittings.

One more thing with that carb, especially if you are using a banjo inlet fitting - there is a raised area in the carb inlet area that might need to be ground level to allow a flush fit. I went to move my car on Tuesday and had a gas gusher (I had made up a new, shorter line) .
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Old 06-17-2010, 04:36 PM
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Thanks guys.
The thought of dirt or something in the carb had crossed my mind, but I didn't think too seriously about it (read inexperience).

I'll pull the carb and clean it tonight. I think I'll go a couple steps richer just to be sure, then work from there.

I'm not sure what you mean by banjo fitting. I'm using the fitting that came on the carb with a regular hose clamp.
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Old 06-17-2010, 06:06 PM
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Quote:
Originally Posted by Beachernaut
Thanks guys.

I'm not sure what you mean by banjo fitting. I'm using the fitting that came on the carb with a regular hose clamp.
A banjo fitting is a 2 piece inlet fitting that allows the fuel to come in at a 90* angle instead of straight in, allowing for a closer fuel line. This is one from Jegs - a 5/8-20 piece.
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Old 06-17-2010, 06:15 PM
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Ive had this problem before

when i hit it wide open for any more than a couple seconds my carb would run out of fuel! this is after i cranked up the timing and put on some headers and higher ratio rockers...I took the carb apart fitted it with a bigger needle and seat and replaced the fuel filter with a high flow one and that was that
cranking up fuel pressure can cause problems so solve it in the needle and seat or try to enlarge the bowl It could just be dirty too so clean it well and the needle and seat isnt to pricy

Last edited by irippchainsaws; 06-17-2010 at 06:18 PM. Reason: could just be dirty though
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Old 06-18-2010, 07:49 AM
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Ahhhhh..... No, I'm not using a banjo fitting.

Great news. It looks like my fuel pump died. I went out to move the truck to the garage to work on the carb and it wouldn't start. I had my son come out to turn the engine over as I looked for a blockage in the fuel line. I had fuel going into the pump, but none coming out.

I stoped by the parts store on my way to work and picked up a new one.
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Old 06-18-2010, 08:04 AM
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Quote:
Originally Posted by Beachernaut
Ahhhhh..... No, I'm not using a banjo fitting.

Great news. It looks like my fuel pump died. I went out to move the truck to the garage to work on the carb and it wouldn't start. I had my son come out to turn the engine over as I looked for a blockage in the fuel line. I had fuel going into the pump, but none coming out.

I stoped by the parts store on my way to work and picked up a new one.
Check the oil level then - there have been cases of that gas going into the pan

(one plus if it does, nice clean engine innards )

Dave W
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Old 06-18-2010, 09:36 AM
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Remember to pack the new pump cavity with lube such as moly lube also, not doing so will make the pump spring overheat and can ruin the pump.
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Old 06-18-2010, 10:34 AM
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Thanks guys.
I didn't know about possible gas in the oil. It's time to change the oil anyway, so I'll be doing that tonight.
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Old 06-21-2010, 07:51 AM
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Ok, new fuel pump in and it's running much better. I ended up with .098 jets, 73 x 047 rods, and .089 secondaries.
I think I'm still a touch rich at WOT, but I probably won't bother with it much.
My problem is idle. I'm having trouble getting a consistant idle. At approximately 800 RPM, I'm pulling around 12hg. The truck also drops to a very low idle, or tries to die when decelerating and taking a left turn. It doesn't do it when turning right, just left.

I suspect that the vacume hardline from the intake manifold to the trans may have been cracked or broken when taking the engine out, or putting it back in the truck. I'm looking around to find a replacement. Is there a good reason not to replace it with standard soft line?
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Old 06-21-2010, 09:13 AM
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Quote:
Originally Posted by Beachernaut
around to find a replacement. Is there a good reason not to replace it with standard soft line?
Nope - will work just fine. Sounds like you still might need to do a dirt check too
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Old 06-21-2010, 10:14 AM
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Thanks for the quick reply. I'll plan on running soft line unless someone comes up with a reason to use hardline. Much easier to do.

I did pull the carb off Saturday and go through it looking for any kind of debris and didn't find any.
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Old 06-21-2010, 12:12 PM
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The engine die ing on hard left hand turns is a float level/fuel pressure adjustment issue.
The stock recomended float height setting is just a default spec. You can fine tune it from there to find the best. Avoid excessive fuel pressure with this carb.
5 psi is good. More is troublesome. Inlet pressure effects the fuel level height in the bowl and how the floats/needle seats are effected by turns.
The spring loaded "off road" needle/seats will help.

You need enough system fuel flow volume at WOT to keep the fuel bowl full under high power demand but not excessive pressure.
Edelbrock carbs can be retro fitted for dual fuel inlets to help equalize the float height/fuel level on both side of the carb and allows blocking off the fuel transfer passage between the right and left side fuel bowls to stablize fuel level on turns.

These carbs should have been build with two fuel/float level sight plugs like a holley.

Last edited by F-BIRD'88; 06-21-2010 at 12:19 PM.
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Old 06-21-2010, 02:24 PM
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Thanks F-Bird.
It has a new fuel pump on it, but I haven't taken any fuel pressure readings. I can't imagine that it's beeing starved for fuel though. My build is barely 1 step from stock, and with the high altitude that I live at, I had to lean it out quite a lot.

When I had it apart looking for junk, I did check the floats and they are set to what the owners manual recomends.
Please forgive my ignorance. I understand the basic workings of a carb and AF ratios, but I have no idea exactly what the floats do. I'm guessing that they control fuel flow from the pump into the bowl to avoid flooding out in low rpm/power situations, and leaning out under high rpm/power?
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