CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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357 c.i.,750DP
bought motor from another car and ran fine.
Problem is if I open the secondary's quickly it dies or stumbles bad.Otherwise it starts right up great throttle response unless I hit the secondary's quickly.
I did replace the accelerator pump on the secondary's because it was leaking.Original was black,new one is green.Are they different and if so what pump do I need?
Don't say the black one please.
Thanks Mike
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bluegrazz I'm not sure about the jets,but it ran fine before I installed it in my car.It is running a little rich cause the plugs are black.The original diaphram is gone so I don't know what size it was.Got new one from A.Z.so who knows,it was in a kit that only had one where as my carb obviously has 2.So that may be it.
fleet,I do see the stream with the engine off.
You might have to play with the accelerator pump cams, pump stroke length, squirter sizes etc. to get this one put to bed. you might also have to go a 50cc pump on the secondary.
bluegrazz I'm not sure about the jets,but it ran fine before I installed it in my car.It is running a little rich cause the plugs are black.The original diaphram is gone so I don't know what size it was.Got new one from A.Z.so who knows,it was in a kit that only had one where as my carb obviously has 2.So that may be it.
fleet,I do see the stream with the engine off.
thanks guys keep the info coming
trying to make the Sep.7 t&t at M.I.R
So was the carb on 357 you bought, or did you have the carb already?
Check the jet size and the squirters. Then adjust the accelerator pump so it dosent have any slack, but is not compressing the diaphram. Check your float levels also.
The carb came on the motor.
Checked diaphram today and it had a 30cc and I installed a 30.
Gonna check squirter size tomorrow.But motor ran fine in other car.
I have the stock electric pump from a Buick G.N.,3/8 supply and return.
7p.s.i.at the carb.
The motor had a Holley manual pump when I got it,so maybe that change could be affecting it.
Will check floats today, but my sights are hard to see through.
Last edited by raptor80dad; 08-22-2009 at 07:03 AM.
I have the stock electric pump from a Buick G.N.,3/8 supply and return.
7p.s.i.at the carb.
The motor had a Holley manual pump when I got it,so maybe that change could be affecting it.
Will check floats today, but my sights are hard to see through.
So you do have a fpr on it?
See through sight plugs are ok, but they fog up over time. Get the car level and just pull them out. What few seconds it takes to remove the stock style isnt a big deal. I had the clear on my old carb, but left the original on my new 750 Street Hp.
The rear float might have stuck while doing the swap. You would be fine at idle and crusing, soon as the back opens then you would go rich.
I have the Mallory return style FPR.
rear squirter is a 28.
Did not get a chance to check float level,but I am leaning toward that since the motor sat for about a year waiting to be installed.
And I will be installing original plugs on carb,the faded clears look bad and have to be removed anyway.
I will post results of float check as soon as I finish installing the wife's washer and dryer.
Thanks again
Mike
Last edited by raptor80dad; 08-23-2009 at 05:13 AM.
Ok.I checked float levels and the back was a little low so I raised it to the bottom of sight(bought new ones).This got rid of the dying out but it still has a stumble for about a second.
It has a red pump cam on the rear and 28 squirters,which are very touchy.Should I go with a bigger squirter since it seems better since I added fuel?
I am going to play with the pump lever adjustments also and see if this helps.
I know this is trial and error but it is so much easier with someone pointing in the right direction and the help is much appreciated.
OK
Just checked jets.
70+71 pri
77+78sec ????
Changed to 69+69pri.
73+73sec
Just the slightest hesitation now,almost non-existent.
Gonna try a bigger squirter and lower the float a little bit.
Squirters are now 25 primary and 28 sec.
Guy at speed shop told me pri. should be larger,he had a similar combo and ran a 35pri. and 31 sec.
Sound right?
update:adjusted timing from approx. 30 initial,40 total to 25 initial ,35total
Idles better,feels stronger,almost there,still gonna play with the squirters
Last edited by raptor80dad; 08-24-2009 at 08:24 PM.
Got a set of 31 and 35's I'm gonna try .
There is no slack in pump arm.
Yea they were mismatched from side to side and was burn your eyes rich .Smells better now runs better now just need to play with squirters and hook up the wideband.
Got a set of 31 and 35's I'm gonna try .
There is no slack in pump arm.
Yea they were mismatched from side to side and was burn your eyes rich .Smells better now runs better now just need to play with squirters and hook up the wideband.
Sounds like someone tried to cheap out on jets. You never stagger from side to side.
35 squirter up front 31 in rear
69 jets up front 73 in rear
timing 25int-app 38 all in
no hesitation,but doesnt leave very hard.
t+t'd yesterday and best 60' was a 1.83,footbraking at 1,500 anythig higher 60' went up.
Did get a best of 13.23 @ 103.19
You shouldn't need a 35 squirter up front. Assuming this is a 4779, stock was .028/.031 (http://www.holley.com/data/TechServi...%20Listing.pdf - if it doesn't take you directly to the numerical listing, click on "Tech Services", "Technical Library", and "Carb Numerical Listing").
38 degrees total is usually too much for a SBC (I assume you had the vacuum advance disconnected when checking timing). Back it off to 34-36. This is assuming that your timing mark is accurate - only way to know is to use a piston stop and verify it. Or, if you compare runs with known timing variation and your current timing setting is verified to be the one that makes the most power (as measured by MPH, not ET, on the track; or on a dyno).
The floats should be set so gas just barely dribbles out of the sight plug (or barely visible with clear sight plugs). If changing the float level from there makes it run better, you've got something else wrong (like jetting). By the way, those clear sight plugs are for tuning only, not for running. If you're leaving them in there, they are going to deteriorate and fail on you.
The power valve restrictors are equivalent to ~8 jet sizes. So, if 69's are the right size in the front, you should have at least 77's in back. Stock jetting for a 4779 was 70-71 in the primaries and 80 in the secondaries.
Of course, if you're traction limited, you might be better off the way it is.
Yeah I had a 31 up front and changed to a 35 trying to get it to leave harder,but change.
Timing marker is probably off,I gained almost 4MPH going from 20int to 25int by the marker.It has about 12-15 degrees of advance,which I will lock once I get it dialed in.
Had 70&71 up front and was burn your eye's rich.The 69's helped.
I agree the secondary jets may be small because it just feels sluggish and it did have 77&78 to begin with.
This carb was on the motor when I bought it and I'm trying to dial it in.
Traction is not an issue,I'm trying to leave as hard as I can.
It was real bad at idle.I know 2 sizes isn't much but it did make a noticeable difference,at idle anyway.
P.V. only in primary and not sure what size,almost gaurantee has not been change from original.
I have read the sticky but car is not tagged so I don't have the luxury of street tuning.
I bought a wideband but it does not work properly so I'm in the process of returning that now.
I know the heads are killing me from making max power but I am so close to 12.99 .
The intake manifold is a "Professional Products" copy of the Edelbrock air-gap.
Thanks again
Last edited by raptor80dad; 09-09-2009 at 11:43 AM.
Reason: brain fart
It was real bad at idle.I know 2 sizes isn't much but it did make a noticeable difference,at idle anyway.
The main jets don't affect the idle mixture unless the throttle blades are open too far at idle and fuel is being drawn through the booster venturi. The Holley tuning sticky details how to set the throttle blades for proper idle (have to have the carb off to do this). Having the float level too high can enrichen the idle.
Do you mean "Professional Products" intake? Edelbrock makes more than one style of air gap manifold, having both the stock replacement type Performer and the higher powerband Performer RPM in the air gap style. Is yours the Crosswind or Cyclone model? I'm guessing Crosswind.
If you are footbraking to 1500 RPMs and have a 3000 stall converter, you are "flashing" it. When you foot brake to full stall RPMs, the car can be a little sluggish off the line. Braking well below the stall RPMs tends to allow the converter to "flash" to a slightly higher RPMs when you let go of the brake and mash the throttle.
Five7 you are correct it is a "Professional Products" manifold.
Not sure which one,as with the rest of my set up,it was here when I bought it.
The primary float was a little high at first,which I set at same time as changing the jets,so that is where I probably threw off my train of thought on that.
I will still check the throttle blades per the sticky to be sure.
And yes the higher rpm I left at the higher my 60' was.
