xanadu

I think i'm starting to go backwards now.
Have an LS1 with a HP street 750 on a
Edelbrock Vic Jnr inlet running a MSD 6101 module.

Cannot get rid of a mid range flat spot.

Carb specs:
Pri IFR 029" Sec IFR 032"
Pri IAB 072" Sec IAB 075"
Good clean idle @ 21in vac. Plugs reading very good.
037" Pri squirter 031" Sec squirter
4.5 Pri PV Sec plugged / Should be maybe 6.5 or 8.5???
69 Pri main jets 76 Sec main jets
PVCR 062"
Engine made 301HP on the chassis rollers however i have no AFR
readings although the plugs looked very good.

My problem is a minor flat spot about 3/4 into the primary operation
and then another flat spot going into the secondaries.

Holding the primaries open on the transbrake the engine is fine
but when going WOT the engine stutters and cuts out / too rich - black
smoke. Stall is low at 2800Rpm.

Originally the Pri HSAB were 029" and Sec HSAB were 035"
I seemed to have made progress with Squaring the HSAB to 038"
but this is were i think i am going backwards.

Also using pink cams front and rear and did try a 50cc pump on the
front, but really makes no difference.

Any help appreciated... Thanks...

3pedals

iTrader: (3)

the 4.5 PV is causing mid range and part throttle lean spots. put in the 8.5PV at least.
- you state the engine makes 21" of vacuum at idle, thats lots, the 4.5pv doesnt open till the vacuum drops to below 4.5" - it may not get that low untill WOT
Also go back down to a 31 squirter on the primary - you shouldnt need a 37 squirter, this has to be causing the black smoke when going wot on the transbrake

xanadu

Thanks. I'll give that a shot tonight with the 031 squirter
and an 8.5 PV. I think i'll return the HSAB back to what they
were after the chassis dyno.

speedtigger

iTrader: (16)

I don't know about the street hp 750, but the current regular 750 hp comes with much larger jets. If I recall correctly, they are 74 primary, 84 secondary. This makes me suspect that you may be lean.

TXoldskool

iTrader: (1)

did you get any a/f readings you can reference with the dyno?

speedtigger

iTrader: (16)

Here is a page that specifies what comes in the latest standard HP Series 750 from the factory:
http://www.holley.com/data/TechServi...%20Listing.pdf

Carburetor - R80528
Model - 4150
CFM - 750
Primary Main Jet - 122-72
Secondary Main Jet - 122-84
Primary Pump Nozzle - .031
Secondary Pump - .031
Power Valve Primary - 125-65

I don't know if the street HP is calibrated differently. I read in a couple places that the Street HP comes with 75 primary and 82 secondary jets, but I am not certain on that.

What is the elevation where you are?

xanadu

Put an 8.5 PV in and changed the discharge nozzles to 031"
and put the HSAB back to what they were after dyno, responded very well, although still a slight flat spot off idle.

Put the 50cc pump on the pri. side and we've got it about 98% right
for throttle response, either need to go a 028" 0r 033" pri. squirter
but don't have one yet.

Holds fine at WOT on the transbrake. Thanks all...