Fuel Delivery Problem?

[jimlickster]

My New build runs well, but when i get to 3000 RPM it Loses power. I have a 600CFM Carb. Do you think the problem could be an Improper Mixture, or do i need more GAS. I'm running 882 Heads. Perhaps that's just the limitation of the heads. The Carb is an Edelbrock 1405 and the Manifold is also an Edelbrock (Performer).

[strotter]

What is your complete combination? Base motor, approximate C.R., cam, how is your fuel delivery set up? Are there other mechanical problems? What electrics are you using? Need more info, but I must say there must be a serious problem somewhere for the motor to fall down at 3k.

[jimlickster]

It's a 350 that's .060 over

Cam is .218 at @.050 and .458 Duration

Rockers are 1.6:1

Crank is NEW nodular Steel stock Stroke

Rods are NEW Stock Length

882 heads

Performer RPM Intake Manifold

600 CFM Edelbrock Carb

[jimlickster]

The Cam is .218 Duration at .050 and .458 Lift

[A. G. Olphart]

The Cam is .218 Duration at .050 and .458 Lift

 

Although we don't have the lobe separation angle, those specs are close to the old Comp Cams 268, which was/is a great street cam; shouldn't be the problem.

 

Take a look here-

http://www.compcams.com/technical/Catalogs/106-07/122-167_226-227.pdf

 

 

 

Merry Christmas everyone!

 

 

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[jimlickster]

The Lobe separation is 110. It's a Lunati Cam with an advertized Duration of 284. Looks like the Document you posted puts it more at an advertized Duration of 268. So, what do you think? Is it a Fuel Problem? Also i just Got a 2200-2600 Stall Converter that i'm going to install on a TH400 Tranny with a 2.73 Rear. When you change the stall speed, does that mean that you have to change the point at which the Transmission shifts as well?

[bschiltz]

Could it be leaning out? What fuel pump do you have?

[jimlickster]

The fuel pump is stock. I was thinking it MIGHT be too Rich, but i'm a Rookie at this kind of thing.

[Ledphoot]

if the float is set too high in the carb you might be pouring gas down the carb through the vent and this is flooding you out. What does it do during an extended idle? If you pull it in low gear when it bogs and nail it what happens? You might have a bad vaccuum advance as well.. Could also be vapor lock. How is the fuel line routed, do you have a fuel filter and where is it mounted? What distributor are you running?

[Paz8]

Before digging into the carb I would check the vacuum at idle and around 2000 rpm, I'd say anything above 10 in. at idle would be OK, around 18 or 20 above 2000 rpm, you may have a vac leak somewhere. Put a timing light on and check your ign. timing at idle, start at around 10 deg., when you get the engine to rev OK then you can bump up the timing. Also check your throttle linkage to see if it goes WOT with the trans kick down connected.

[jimlickster]

In low it's nice and responsive. Fuel line is how it was routed stock the fuel filter is right next to the carb and is clear. My distributer is a Stock one. It's the kind with the Coil attached to it. as far as the Vacuum Idle, i'll probably have to get a Friend to help me with that. It idles beautifully at around 700 RPM right now even when it's cold. If i go on a decently long road trip, the idle is around 900 RPM at the end. These are some tidbits that i'll definately need help to check, so it might be a while before i can respond to the suggestions. as usual you guys are EXTREMELY helpful.

[A. G. Olphart]

The Lobe separation is 110. It's a Lunati Cam with an advertized Duration of 284. Looks like the Document you posted puts it more at an advertized Duration of 268. So, what do you think? Is it a Fuel Problem? Also i just Got a 2200-2600 Stall Converter that i'm going to install on a TH400 Tranny with a 2.73 Rear. When you change the stall speed, does that mean that you have to change the point at which the Transmission shifts as well?

 

Exactly how does it act when it lays down? Like someone turned off the switch, or does the rate of acceleration just drop off? Does the engine break up (random misfires, often ignition related)? How much initial advance are you running? Detonation isn't kind to pistons.

 

Is there a secondary lock out linkage on the carb keeping them from opening? Paz has a good suggestion that relates to this-- it is easiest to have someone push the foot feed to WOT (engine off) while you watch the butterflies for full opening.

 

A stall converter just lets the engine rev more freely to get into its' power curve. Tranny shift points are hydraulically controled and road speed related-- not affected by choice of converter.

 

Your problem could be fuel flow (insufficent pressure under load), ignition, or even weak valve springs. Are you running Lunati's recommended springs at their correct installed height? The Vacuum advance doesn't enter in at this point, as under full acceleration the vacuum is near zero anyway.

 

Since the engine runs well up to 3000, my guess is that it isn't overly rich. Have you pulled the plugs right after the problem occurs to check coloration? Rich enough to fall down should be dark, maybe even sooty (guessing at this) and lean can go to white.

 

2.73 gears. Is this a Z?

 

Checking your vacuum is a good plan, but if it idles at 700 with a box stock carb (little adjustment needed) odds are good you have no vacuum leaks. They would show up more at idle than WOT, where you have massive mixture flow and not enough vacuum to suck much through a small leak.

 

Truly large cams (although Yours doesn't seem to fall in that category) need 1/2 inch fuel lines and high volume pumps. I don't know where the stock Z fuel line becomes a restriction.

 

Maybe someone familiar with HEI (your coil in distributor setup) can let us know if this is a common problem with one of their failure modes.

 

 

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[A. G. Olphart]

Just reread your last post... if you have been running this car long enough to have done road trips, it could be as simple as tired spark plugs breaking down under load. I had a 1600 roadster that ate Champions. Drove it around town a few days, and the next time I hit a freeway on ramp it would start breaking up. Switched to NGKs and the problem went away.

 

Good plugs of the proper heat range make all the difference.

 

I went Googleing (reading spark plugs) and got over a million hits; here are a couple of links.

 

http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/index.asp?nav=31200&country=US

 

http://www.edelbrock.com/automotive/sparkplugs.html

 

 

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[jimlickster]

I think i got it guys. It's so simple looking back. I changed the Torque Converter today. I went from stock to a 2200-2600. With my engine, it looks like it takes the whole 2600. Had the Engine up to 4000 RPM today and had power all the way through. I broke it's Cherry. I admit that i was worried about the 4000 RPM though. That can't be good for it. I even laid down a little rubber. I think i'm gonna change my Rear to a 3.42 though. Right now i have a 2.73. I want to be able to take long trips with the Thing, but i want responsiveness too. I was cruising down the Road at 75 runnin about 3 grand after i finnished accelerating. I'm still leary of higher RPMs because the engine only has 1000 Miles on it and every single component in the thing is BRAND NEW. I'm worried about blowing an engine that i just spent alot of time and money on.