Blow thru carb question

4028 Views 23 Replies 9 Participants Last post by Outlaw, Jul 14, 2009

Outlaw

Discussion Starter · Jul 1, 2009

Kind of a vague question.. but on a blow thru carb
what would cause the WOT to lean out?

on my nephews boat he can get the air fuel ratio
almost perfect from idle thru cruise but when he
opens it up to WOT it starts leaning out.

fuel pressure is 7 psi at idle, 12 psi under full throttle
5 psi boost.

I know its a Holley by lance patton, (yes he is going to call him) but I'm curious what can cause this.
if he jets up it still leans out under full throttle.

from the dock it sounds like its missing slightly
when it leans out.

here is his target #'s
Idle 13.5 to 13.8
Accelerate 12.2 - 12.5
Cruise no load no boost 13.0 - 13.3
Cruise with small amount of boost and load 12.5 - 12.7
WOT 5 + lbs boost 11.8 - 12.0

everything is on target but his WOT it starts climbing above 12.5.

1 - 20 of 24 Posts

Hass828

· #2 · Jul 1, 2009

Outlaw said:
Kind of a vague question.. but on a blow thru carb
what would cause the WOT to lean out?

on my nephews boat he can get the air fuel ratio
almost perfect from idle thru cruise but when he
opens it up to WOT it starts leaning out.

fuel pressure is 7 psi at idle, 12 psi under full throttle
5 psi boost.

I know its a Holley by lance patton, (yes he is going to call him) but I'm curious what can cause this.
if he jets up it still leans out under full throttle.

from the dock it sounds like its missing slightly
when it leans out.

here is his target #'s
Idle 13.5 to 13.8
Accelerate 12.2 - 12.5
Cruise no load no boost 13.0 - 13.3
Cruise with small amount of boost and load 12.5 - 12.7
WOT 5 + lbs boost 11.8 - 12.0

everything is on target but his WOT it starts climbing above 12.5.

probably going to need to open up the power valve restriction holes a little, but I would certainly talk to the carb builder before breaking out the drill bits.

Outlaw

Discussion Starter · #3 · Jul 1, 2009

Thanks Hass828, I found a great article about that modification.

http://www.hangar18fabrication.com/blowthru.html

MACHINEHEAD1

· #4 · Jul 1, 2009

Try re-clocking the bonnet 45 degrees or less or more

IMPATIENT 1

· #5 · Jul 1, 2009

is he boost reference'n the regulator off the carb hat or intake? it has to come offa the hat , not the intake.also try the reclocking deal, i hear alot of guys jack with their hats and get a better a/f ratio. i'd be shooting for around 11.5 at all rpms under boost if i were you guys.

Outlaw

Discussion Starter · #6 · Jul 1, 2009

yes boost referencing off the hat,fuel pressure is right where
it needs to be, 7 base and 1 to 1 with boost.
interesting about the hat, we will have to move it around to see what effects that has.

71hallett

· #7 · Jul 1, 2009

PV not referencing or fuel pressure not holding....

Outlaw

Discussion Starter · #8 · Jul 1, 2009

is there any reason both front and back PV would be blocked off??

cfm

· #9 · Jul 1, 2009

Outlaw said:
Kind of a vague question.. but on a blow thru carb
what would cause the WOT to lean out?

on my nephews boat he can get the air fuel ratio
almost perfect from idle thru cruise but when he
opens it up to WOT it starts leaning out.

I know its a Holley by lance patton, (yes he is going to call him) but I'm curious what can cause this.
if he jets up it still leans out under full throttle.

from the dock it sounds like its missing slightly
when it leans out.

here is his target #'s
Idle 13.5 to 13.8
Accelerate 12.2 - 12.5
Cruise no load no boost 13.0 - 13.3
Cruise with small amount of boost and load 12.5 - 12.7
WOT 5 + lbs boost 11.8 - 12.0

everything is on target but his WOT it starts climbing above 12.5.

Outlaw said:
is there any reason both front and back PV would be blocked off??

Looks like you found your answer. Call to make sure and see why the PV's where blocked off.

scott foxwell

· #10 · Jul 2, 2009

It's possible there's some turbulance going on inside the bonnet @ WOT killing the signal across the venturis. If you don't get to the bottom of it with the carb, you might try like machinehead said and either re-clock the bonnet, or try a different one.

Sleeper CP

· #11 · Jul 2, 2009

I read an article along time ago where they used a flame arrestor inside a bonnet as a de-fuser to straighten out the air. The de-fusser ended up being worth 25 hp (something like that) and it smoothed out the A/F cylinder to cylinder.

S CP

Outlaw

Discussion Starter · #12 · Jul 2, 2009

he's going to pull the carb down tonight and see exactly what he has,
and also measure the PV channel restrictors, he tried calling Lance yesterday but as of last night hasn't talked to him. I'm not sure
what bonnet he's running, definitely something to look at.

IMPATIENT 1

· #13 · Jul 2, 2009

Sleeper CP said:
I read an article along time ago where they used a flame arrestor inside a bonnet as a de-fuser to straighten out the air. The de-fusser ended up being worth 25 hp (something like that) and it smoothed out the A/F cylinder to cylinder.

S CP

most guys are just welding on a 2 inch spacer to their hat so it allow more time for the flow to straighten out.

Outlaw

Discussion Starter · #14 · Jul 2, 2009

2

I noticed the new extreme velocity one had a divider built into
it which split it into 4 sections, I haven't purchased mine yet
but thats the one I'm leaning toward

See less See more

Outlaw

Discussion Starter · #15 · Jul 3, 2009

Still no call back from Lance.....
power valves are plugged primary and secondary

thinking about putting a PV in the primary
any recommendations on what size to start with?

71hallett

· #16 · Jul 3, 2009 (Edited)

Outlaw said:
Still no call back from Lance.....
power valves are plugged primary and secondary

thinking about putting a PV in the primary
any recommendations on what size to start with?

prob a 6.5

Outlaw

Discussion Starter · #17 · Jul 3, 2009

the only #'s on the body are 6R3767
I measured the Primary channel restrictors @ .063
with the PV"s blocked off his best tune except
WOT was with 80 primary jets and 86 in the secondarys.
he's going to try a PV today and see what happends.

71hallett

· #18 · Jul 9, 2009

Sooo...what happened?

Outlaw

Discussion Starter · #19 · Jul 9, 2009

I dont think he's had a chance to try anything yet.

IMPATIENT 1

· #20 · Jul 9, 2009

Outlaw said:
I noticed the new extreme velocity one had a divider built into
it which split it into 4 sections, I haven't purchased mine yet
but thats the one I'm leaning toward

go with the pro hat and be done buyin hats

that divider just straightens air out alil, the prohat will do the same and its already a 1in taller.

fyi, there's a group purchase sale on ev hats on turboforums, you can get that hat 100bucks off, i'll dig up the link for ya

1 - 20 of 24 Posts

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