Q-Jet on BBC - not right

[pismorat]

I pulled the 383 stroker out of my truck and put in a 489 stroker. I used the same carburetor, an Edelbrock Q-jet 1902, which can be and is used on both SBC's and BBC's. When I jump on it, WOT, it only pulls for 3-5 seconds and then runs out of gas. What do I need to do to fix this issue? I have a high volume mech. pump with an inline electric for backup.

 

[throttleissues]

Whatever fuel filter you're using may very well be the restriction. The filter in the front of a Q-jet housing is too small for anything useful, so use a large inline filter and take that one out if there is one in there.
Also, what size fuel lines are in your truck. BBCs came with 3/8 and SBCs came with 5/16 in most cases.
Another possibilty is debris in the pickup sock in your fuel tank.

 

[Hogback Fabrication]

Do you have any of the books on Q-jets? I know they talk about dealing with this issue.

 

[4X4HIGH]

I pulled the 383 stroker out of my truck and put in a 489 stroker. I used the same carburetor, an Edelbrock Q-jet 1902, which can be and is used on both SBC's and BBC's. When I jump on it, WOT, it only pulls for 3-5 seconds and then runs out of gas. What do I need to do to fix this issue? I have a high volume mech. pump with an inline electric for backup.

Ditch the electric pump and i'll bet your problem goes away. A mechanical pump is made to push fuel not suck fuel which is exactly what you're making it do with an electric pump before the mechanical pump.

 

[pismorat]

I'll pull that paper filter and check the line size today. When I run it with the elec. pump off, it does it all the time, if I turn the electric pump on to push fuel to the mechanical one, it doesn't do it so bad. I was thinking of ditching both pumps I have and getting a good electric pump with a regulator, but don't know. And also, could the float levels be set wrong? I just had the carb gone through before the swap...BBC float level higher than SBC??

 

[folkenheath]

Ditch the electric pump and i'll bet your problem goes away. A mechanical pump is made to push fuel not suck fuel which is exactly what you're making it do with an electric pump before the mechanical pump.

You got it backwards there, mech are better at pulling, electrics are better at pushing. Which is why electrics are usually in the tank or close to it.

However, he does have a point, if the electric can only flow so much, it may actually be restricting the high flow mechanical, definitely when it's off, and maybe even when it's on.

If I were you I would get a better pump, either a better mechanical or a better electric with a regulator. If the pump is good enough you shouldn't need both. I have a Holley 110 GPH mechanical on my 489, and it works fine so far.
I do have a holley instead of a q-jet though. Can't help you there.

Do you have the stock fuel tank selector for dual tanks? I do, but I split it and used both the supply AND return, as the supply, with a T before and after to split the supply line in two through the valve, then back to one again. Also, you want a large fuel filter like they said.

 

[COCHEV]

Could just be the at your float is out of adj and is not filling the bowl as much as it should and you are sucking it dry with WOT runs.... just a thought