[4116sst]

Just bought a Holley ultra hp 950. Came with 72/74 jets. Prior to installing, I changed jets to 86/88. b/c my previous carb had 90, but was rich. I now have a stumble as soon as the squirters shoot, (mashing accelerator from idle). The tech line shows soooo many possibilities to remedy this problem. Was wondering if anyone could help, so I dont have to try too many mods, as I hate to start wrenching on a brand new carb. Also, the instructions claim that the jets should not need to be changed more than 4 numbers from what was installed @ the factory. Is this true, did I mess up with too much jet? We are 12' above sea level.

Thanks

 

[Professor Fate]

Personally I would have started with the factory setup and see if any changes needed to be made. New carb, new baseline.

 

[The Big Al]

the HP carbs come with a modified down leg boosters.

"DOWN LEG" boosters require smaller jets, they flow more fuel.

Holley is a smart company, and I bet your carb was correct before you messed with it.

And if your changing carbs sounds like your other had issues.

Sorry to be so blunt. But it's true.

Put the carb back like it came.

IMO
AL

 

[4116sst]

I agree, I shouldn't have messed with it. The reason why I had to change carbs was because the one on it before was borrowed to get me going, my friend wanted his back, and not let me buy it. So... I bought the same thing, but jetted it because this is what jets he said was in it, but come to find out, he didn't know what jets were in it, so I will jet it back to the way in arrived. I'll keep you posted.

Thanks

 

[levisnteeshirt]

close but no cigar

Holley is great , but i've never saw a new carb that didn't need something changed ( squirter, cam, power valve ).

 

[4116sst]

I will put the jets back to get a starting point, but what causes the initial "bog"?, Squirter or jet? It came with 31 squirters.

 

[The Big Al]

I will put the jets back to get a starting point, but what causes the initial "bog"?, Squirter or jet? It came with 31 squirters.

May need to bump the timing up.

Could us more entail timing, a hotter plug maybe.

maybe carb is to big!

Al

 

[6NOVA4]

did it come with power valves? On a track only car I don't run PV's just jet it accordingly. On an 950 I did for a buddy of mine I started at 85/88 with 31 squirters squared. I ran the white cam in front and the small pink cam in the back. No bog or hesitation. This is on a 406 11.5 to 1 comp with a 640 roller cam.

Get the timing figured out, jet the carb back to where it was from the factory. Establish a baseline then start playing with jetting. As far as the bog can you duplicate it in park just revving it? in other words can you snap the throttle and will it bog or only when launching?

You're probably gonna have to play with the accelerator cams or squirters or both the find its happy place. Also be sure the accelerator pump arm has just a tiny bit of play at rest.

 

[bowtie0069]

Put it back the way it was and try it--Then you can start screwing with things.

 

[4116sst]

Just finished putting it back to where it was. "Bog" is still there, doesn't seem as bad. I'll check the timing tomorrow. Oh and it has power valves.

 

[bowtie0069]

Try richening the idle screws before you make any changes and see how it responds--won't cost you a penny and will only take a second.

 

[levisnteeshirt]

plural ??

does it have a power valve in the front and back ?? How much idle vacume do ya have ?? I'd set the dile mixture screws 1/4 to half turn rich ( more open ) past the highest vacume reading

Check the clearence between the arm for the accelerator pump and the arm at the pump . I like them with no clearence but i think Holley says .015. This will need adjusted after you have set the idle. You might get away as easy as changing the position of the screw that holds the accelerator pump cam to the other position if it has 2. I'd get the pump cam kit and a few bigger squirters cuz they're just good to have on hand and cheaper than a whole trick kit.

http://cgi.ebay.com/ebaymotors/Holl...hash=item170271258641&_trksid=p4506.m20.l1116

http://cgi.ebay.com/ebaymotors/35-S...hash=item390039313804&_trksid=p4506.m20.l1116

http://cgi.ebay.com/ebaymotors/37-T...hash=item390041410210&_trksid=p4506.m20.l1116

 

[4116sst]

It has power valves in front and back, the arm for the accelerator pump is touching, will put a feeler gauge on it today, and will try adjusting the idle screws. Thanks

 

[The Big Al]

What is this carb installed on?

Engine? mods?
Converter?
Gear?

 

[4116sst]

355 ci sbc
640 lift solid roller
5300 stall 8" PTC
Powerglide
transbrake
10.5:1 cr
2600 # tube chassis
4.88 gear
33" tire
cross @ 7000
shift @ 6500

I know it seems to be too big of carb, but like I said, I borrowed the same carb from a friend and it worked wonderful. He didn't want to sell it, so I bought the same thing, but knowing not all carbs are the same.

 

[Sooner1]

silly question- would low float level contribute?
i recognize this seems like an accelerator pump/cam type problem.
wouldnt changing the screw position on the cam delay the accel pump?
what about considering cam change.
i am going to assume he has satisfactory accelerator pump function and adequate squirters...

 

[4116sst]

The accel pump is touching the arm @ idle, shouldn't it have some clearance? The squirters are 31's.

 

[Sooner1]

The accel pump is touching the arm @ idle, shouldn't it have some clearance? The squirters are 31's.

i would think 31's would be fine.
i think holley recommends ~.015 clearance. of accel pump arm

steve

 

[levisnteeshirt]

if it wuz me

i'd adjust that arm , where it is just touching the pump lever at idle with minimal pressure. Something is wrong , because you can get a Holley to respond just as sweet as fuel injection IMO. The big misunderstanding is that the engine is experiencing a rich condition off idle if it stumbles when the opposite is true 99 % of the time in that its lean. Its just had the throttle plates slammed open. Now atmospheric pressure above the throttle plates has forced a rush of air into the intake because of the low pressure situation created downstream of the intake manifold. The depression caused by the pistons downward motion creating a vacume also known as a low pressure situation. High atmosperic pressure will rush toward this low pressure causing air flow into the engine quickly but too fast for the main circuit in the carburator to respond. The carburator is equipped to handle this sudden volume of air while the process of main circuit fuel flow is developing via the accelerator pump. It comes from the factory in a generic state of tune though and is going to need to be tailored to its present needs. If you've never installed a " Trick Kit " in a Holley carb, its alot of fun to discover what a Holley can do. A trick kit has great instructions and will fully explain what to do and how to read what the engine is telling you.

I used 31's with the orange cam alot and had good success with most 650 and 700 dp's i've had and on the primary of 750vs's but not a 750dp on my 355's . I would imagine a 950 is going to need more pump shot than those carbs but every situation is different. Get a trick kit and find somewhere you can play with the car and find out what the accelerator pump needs to provide you with stumble free performance.

 

[Sooner1]

ive read the orange cam is about ~19cc at #1 position and ~24.5cc at the #2 position. seems like it is "middle of the road" as far as the cams.