[dv657172]

Just finished rebuilding my Holley 750 DP (0-4779-6), 1st time for one of these and only 2nd ever so definitely a rookie.

Put it back on car which fired a few times when started but wouldnt run and fuel puked out of both vent tubes. What did I do wrong? Float bowl settings? Whats a good initial setting for these.

I know you adjust them after the car is running to where they trickle out the hole but need to get it to run first.

[Scott65]

Either float adjustment, or if you had the floats separated from the bowls, the orientation may be incorrect. A good book comes in handy when you're first getting started.

[dv657172]

Thanks for the reply. Guess I will take a look at float bowls again.

I thought I had a good book...guess we arent all experts are 1st time....

[Scott65]

Absolutely. Take your time, you'll get it. Another thing, if you have jet extensions, or vent "whistles" added, extra caution is required. Sometimes it's helpful to fit the bowl to the metering block, and give it a shake to make sure the float is free, then stab the whole thing to the main body.

[dv657172]

Scott

Thanks so much!. It does have the whistles added so I will definitely give that a try as I thought I put it all together correctly.

[Tom Vaught]

Have posted in the past about the white whistles being too long for performance work from Holley.

I trim the whistles the distance of the factory window on top of the whistle and make a new window in that shortened whistle. Works much better for performance work.

Also your #4779-6 should be the first year of the 4 corner idle adjustable metering blocks. Where do you have the screws set for the rear metering block??

Tom V.

[dv657172]

Tom

I turned the idle mixture screws all the way in and then backed them out 1.5 turns for both the primaries and secondaries. Planning on adjusting them once I get float bowls at the correct level.

Will have to go and find some of your past postings on the whistles and take a look.

DV

[Kenth]

For center hung floats Holley recommends setting the floats in center of bowl as an initial setting with bowl bottoms up.

[dv657172]

Thanks Kenth - very helpful

[Tom Vaught]

Originally Posted by dv657172

Tom

I turned the idle mixture screws all the way in and then backed them out 1.5 turns for both the primaries and secondaries. Planning on adjusting them once I get float bowls at the correct level.

Will have to go and find some of your past postings on the whistles and take a look.

DV

The 4 corner idle carbs vs the 2 corner cars you would think would be the same on the idle circuit and mixture screws.
THEY ARE NOT.

Prior to the 4 corner idle carbs, the 2 corner idle carbs used an IDLE FUEL FEED RESTRICTION ORIFICE at the lower part of the metering block. The Idle mixture was drawing from liquid fuel for the calibration.

When Holley came out with the 4 corner stuff, they moved to a high position Idle FUEL Feed Restriction up near the vent whistle on the metering blocks. Now the idle mixture was influenced by the high position in the circuit. The idle speed is erratic at times depending on weather conditions. Most carbs really need the idle circuit changed BACK TO the lower restriction position. Erratic idle depending on the weather is the main issue.

Jeff (Shaker455) could return the carb to the previous IFR location easily.

One of the first Mods Holley did to a carb that was working fine with the previous idle circuit but they HAD to change stuff, (just like Edelbrock with their 4 circuit carbs) today.

Tom V.

[dv657172]

So I set the floats lower with carb off the car and it started right up with no fuel puking out the vent tubes when I put it back on but.......

I have a fuel leak around the secondary needle & seat adjustment nut & screw. I am using new plastic gaskets which came in the kit and the sealing surfaces all look fine. The primary needle & seat does not appear to have a leak around it.

With the car now running my guage at the end of the fuel line is showing a PSI of 8 lbs which I know is high. Is that likely the issue or is it a needle and seat issue which is brand new.

[Scott65]

Check the condition of the o-ring on the needle and seat assembly. I used either Vaseline or Dow Corning o ring grease on them to help them slide without cutting/tearing. That's if the gaskets for the screw/adjustment nut aren't obviously torn.

[dv657172]

I originallly put a little oil on the o-ring but will inspect it again. The gaskets are plastic so they shouldnt be the issue.

Will reverse assemblies tomorrow if they look ok and see if issue moves to primary side or stays on secondary side.

[Tom Vaught]

Good Luck and post up when you get to the 4 corner idle settings.

Tom V.

[Don 79 TA]

before you head out and work on it, get yourself a little information overload lol and search this topic on youtube...
man.... some really great videos on there that can help out, especially explaining how to set things like the float levels
i just had my XP carb apart and when i replaced the needle/seat (since it came in the kit) i set them low on purpose, so when i powered up the fuel pump, it was easier to adjust the float up, then to have it where it starts flooding out already
but as mentioned, if the floats were taken off or moved, that could be an issue as well
i do remember on 4150 i was working on, needed that ole slight hammer tap on the bowl, and wallaha.... level corrected itself
by tap i mean used the rubber handle to tap on the bowl, and never had an issue after that...

boy.... back in my day... the guy at the counter parts store is what youtube is today..... Man... was i lucky back then to have been able to tap resources like that when i was a kid.......
however...... man.... youtube videos really do help out so much too.... as well as forums like this, especially from folks like Tom V. and so many others

[dv657172]

Definitely agree on the you tube videos and the guys here being real helpful especially Tom V and Scott65!

I shook the carb before putting it back on and could here the floats moving up and down so I think they are moving freely.

Have learned a lot already about the 4150 even though I dont have it working just right yet. Making progress...I think.

[dv657172]

Ok so I switched needle and seats around and even went back to the old ones too and I still have leaks at the adjusting nut even with the float level set basically about as low as it will go.

With 8 lbs of fuel pressure at the carb do you think that is the problem? Either it is or has screwed up the floats (which I have not replaced during the rebuild as looked like new basically) possibly or its just pushing out from under the gasket which is plastic??

Any thoughts appreciated...and fuel pressure regulator recommendations

[Scott65]

8# shouldn't cause a leak. Have you verified that all old gasket materials have been removed from both sides of the nut, the top of the needle and seat boss and the bottom of the screw, and that all are flat. A hone works well for verifying flat without removing metal.
ETA: regulator recommendation will depend on how much power you plan to make/how much fuel volume you need to flow through it.

[AG]

Originally Posted by dv657172

Ok so I switched needle and seats around and even went back to the old ones too and I still have leaks at the adjusting nut even with the float level set basically about as low as it will go.

With 8 lbs of fuel pressure at the carb do you think that is the problem? Either it is or has screwed up the floats (which I have not replaced during the rebuild as looked like new basically) possibly or its just pushing out from under the gasket which is plastic??

Any thoughts appreciated...and fuel pressure regulator recommendations

I run my race car at 9 psi at idle and it goes down to 5 psi down the track, never any issues with the floats holding or fuel dripping.

[Tom Vaught]

Originally Posted by dv657172

Ok so I switched needle and seats around and even went back to the old ones too and I still have leaks at the adjusting nut even with the float level set basically about as low as it will go.

With 8 lbs of fuel pressure at the carb do you think that is the problem? Either it is or has screwed up the floats (which I have not replaced during the rebuild as looked like new basically) possibly or its just pushing out from under the gasket which is plastic??

Any thoughts appreciated...and fuel pressure regulator recommendations

Do you have two gaskets on each needle and seat location.

a) One gasket between the N&S assy and the carb float bowl and a second gasket between the the adjusting nut and the top screw driver blade
lock nut?

Tom V.