Too Lean...help

[justcrusin']

396 sbc 11-1 compression
powerglide-9"rear-5500 stall

850 quickfuel -

performance mechanical pump supplying carb @ 6-7psi
(fuel tank up front)

Holley blue w/reg supplying 100 shot nos. @ 6-7 psi

still very lean, white plugs and flames out headers.

Where to start??? anyone????

 

[Chuck Leeper]

First, I'd take a look at the plugs, [New and clean break], with the N2O turned off....

 

[justcrusin']

First, I'd take a look at the plugs, [New and clean break], with the N2O turned off....

Working on that now. (plugs still chaulky white)
Looks as if the mechanical fuel pump (main carb pump) is not putting enough VOLUME. Pressure is fine, but I am thinking volume is low. Or fuel line needs to be #10 instead of #8.???

I would think getting rid of the mechanical pump would be a good start.


.

 

[Chuck Leeper]

U using a GOOD gauge at the carb?[We just changed a liq filled onmy bud's 500" 409..Was giving good set readings, then as it ran on, it would go to zip...] New unfilled ga, NP.
Are you able to see the actual psi at hi load? [I'd look REAL close here!]
FWIW: I've checked ALOT of the small, dollar sized gauges against the ga on the inj bench... Most not even CLOSE!
Are the needle/seats big enuf?
Have U bumped the main jets up?
What does Quikfuel say?
Floats OK?
Tank well vented?
# 8 will support more than the engine needs, N/A, IMO.

 

[justcrusin']

U using a GOOD gauge at the carb?[We just changed a liq filled onmy bud's 500" 409..Was giving good set readings, then as it ran on, it would go to zip...] New unfilled ga, NP.
Are you able to see the actual psi at hi load? [I'd look REAL close here!]
FWIW: I've checked ALOT of the small, dollar sized gauges against the ga on the inj bench... Most not even CLOSE!
Are the needle/seats big enuf?
Have U bumped the main jets up?
What does Quikfuel say?
Floats OK?
Tank well vented?
# 8 will support more than the engine needs, N/A, IMO.

I thought the oil filed gauges were the good ones? I will check this out.

Tank is well vented.
Floats ok. needle seats ok.

Have not bumped main jets on carb.(should I?)
Have 48's on fuel and nos solinoids.
Have 78's in back and 70's in front on 850.

Have not spoke with quickfuel yet.
You may be right about the gauge.

 

[Chuck Leeper]

A quik way to check the jets, [which sound too small to me], is to throw some 78's in the ft and run it w/ "square jetting", and see what that tells you on the plugs.

 

[justcrusin']

A quik way to check the jets, [which sound too small to me], is to throw some 78's in the ft and run it w/ "square jetting", and see what that tells you on the plugs.

These jets were put in at dyno time and got the best HP results.

I will try what you advise and square the jets.

Typically, do you up the carb jets when using nos?

(This is a friend's chevy S-10 ---I am a Buick Man..lol)

Just trying to help.

 

[Chuck Leeper]

But..

These jets were put in at dyno time and got the best HP results.

I will try what you advise and square the jets.

Typically, do you up the carb jets when using nos?

(This is a friend's chevy S-10 ---I am a Buick Man..lol)

Just trying to help.

The engine was not being subjected to gear changes, accel eration, varying weather, yadda, yadda. Dyno's are for baselining...

A wet shot should be tuned w/ the fuel supplied thru the solenoid. Timing is another factor to consider.

Want to really fatten it up, and do it quickly?? Disconnect the NOS solenoid, and allow the gas solenoid to work..That'll tell you if it's fuel related, fast!
Also, VERIFY the fuel psi at the carb! Remember, the engine was tuned on a dyno with a dyno fuel system, that could likely be totally different.

Oh ya, a wideband should be in the mix, too....

 

[justcrusin']

The engine was not being subjected to gear changes, accel eration, varying weather, yadda, yadda. Dyno's are for baselining...

A wet shot should be tuned w/ the fuel supplied thru the solenoid. Timing is another factor to consider.

Want to really fatten it up, and do it quickly?? Disconnect the NOS solenoid, and allow the gas solenoid to work..That'll tell you if it's fuel related, fast!
Also, VERIFY the fuel psi at the carb! Remember, the engine was tuned on a dyno with a dyno fuel system, that could likely be totally different.

Oh ya, a wideband should be in the mix, too....

We tune the nos fuel at WOT @ 6-7psi
Timing is set back 2 degrees every 50hp
A colder plug should be considered.

We were using 116 fuel on the trial runs just in case.
This might be slowing us down and I think we need to go back to 112

We have decided to move the fuel tank to the back, #10 to large areomotive pump, # 8 to regulator, #8 to nos fuel, #8 to carb

10 micron filter between fuel and pump
8 micron after regulator

I believe that mechanical pump is the main culprit.

My buddy is also considering a stronger engine and getting off the bottle all together. ( a turbo here would be my choice.. lol)

Thank you for all the help

 

[Chuck Leeper]

I don't think I'd put a 10M between the pump and tank.. More like a 40-100 is a good size.
If you are going to go to the trouble to replace the system, how about making it a return style??? MUCH easier to work with.

 

[WarWagon]

Is this a blowthru setup your having lean issues with?