SBC Hesitation/stalling at different RPM's....
 

Hey Pelicans,

Don't wanted to get flamed in the 911 forum, so I came here....

I have a brand new carburated Goodwrench crate motor in my 911, which runs smooth as glass at idle. The problem is that it's been stalling on deceleration (occasionally), and cutting out when accelerating (not heavy acceleration because I'm still breaking in the motor). It just loses power for a moment, and you have to rev it to recover. It seems to be most pronounced between 2nd to third gear changes. I'm definitely thinking that it's a fuel delivery problem, but I could use some additional input.

I replaced the 50 PSI pump intended for fuel injection with a more or less generic parts store model at about 5 PSI, because 50PSI is too much for a carburator. Another very irritating issue is at takeoff. This thing jumps all over the place, and it feels like the 915 is going to be ripped out of the car. Sometimes I can feather the clutch enough to minimize it, but it's not 100 percent reliable. I'm thinking that all of these issues are related to fuel delivery

Resolved all the overheating issues which fried my heavily modded 350. Now I just need to resolve this issue, and this car will be awesome. BTW, this problem was also present with that motor too.

Profile:
Goodwrench 350/260 HP 8.5:1 compression
Generic fuel pump (~5psi) mounted where the original unit was
Edelbrock 1406 600CFM
Mallory HEI ignition
Beefed up 915 transaxle (the original unit that came with the car) and Kevlar clutch with ~2000 miles since full rebuild

Any relevant advise is appreciated. Thanks!

Just take it to a local shop, I'm sure many would leap at the chance to work on this type of car and should not set you back a few hundred $$ if they're halfway honest.

It's either fuel or ignition, hard to tell without seeing the car though. Good luck.

hehe. This is an SBC. How tough can it be for the collective intelligence of this forum to troubleshoot? I'll find the issue myself, but it'll take time. All issues are resolved, except this one. I'm hoping someone has experienced this before, so that it will save me time. Remember, we're tinkerers, and we enjoy the challenge of hunting down the issue. The shop is the last resort.....

YellowBird, have you posted any pixs of the installation? If not I'd love to see them.

how full are you running your fuel tank? whats the gph rating of the pump (SBC usually runs around 6.5- 7.5 psi for an electric pump and 60-80gph) how well grounded is your whole setup (engine to chassis should have atleast 3 different grounds) I'm not super familiar with mallory hei but which advance style does it have, and has it been setup?

had the same problem went to a quick fuel 750 race street carb, runs great now! also check your vacuum advance adjustment at dist.

:) New motor but what about the carburetor ? sounds like you might be smart to remove the carb air-horn and look inside. The float bowl could be dirty etc. Ignition wise you could drive into the local shop and toss the car on a scope. Check the patterns for their quality and what kind of distributor do you have meaning, vacuum advance centrifugal advance or all electronic ? As stated the fuel volume is also in question. :)

I 2nd what was written earlier. Im running almost 7psi on my edelbrock electric pump mounted in the stock location that feeds my Holley avenger 670.

I had my 996 LS3/480 HP put on a dyno last week. I've been told that GM Performance does a pretty good job of setting up their ECU so the car runs well right out of the box. Mine did, but the idle was lumpy with the cam, also it was very thirsty. After the dyno tune it runs a 100% better, smoother, the mileage went way up and I got 10 more horsepower. I guess my point is that the money spent on a dyno tune is well worth it. Probably more so for an injected/ECU engine.

I second Mitch's answer. Night and day after my dyno.