Carburator adjustment Holley 4150

Cobra 65
Posts: 15
Joined: Fri Oct 09, 2015 10:52 am

Carburator adjustment Holley 4150

Post by Cobra 65 » Wed Aug 30, 2017 6:16 pm

Hello First Coast Cobras,

I'm not a frequent poster but now I would need some help.
I own a red Superformance Cobra (no stripes) with a Windsor based 427 from Keith Craft Performance engines. Dyno reading HP 616, pound torque 600.
On top sits a Holley 4150 carb. MSD ignition.
A friend of mine (a mechanic) tries to adjust the carb since some time but the engine is not running well.
It"s running rich, surging and misfiring now and then and running after shutting it off.
He rebuild the carb, plugged the vacuum valve, changed jets and air bleeds and of course we changed the spark plugs a couple of times but it still feels like riding an electric bull.

Right now we don't know what to do. I was thinking of doing a dyno run and adjustment but I don't know where to get that done and if that would be the next step or if anything else should be done.

I'm not a mechanic by any means so I don't know what to do next.

Any suggestions and help is appreciated. I hope to hit the road with you guys soon.

Thanks for your help,

Stefan

Tom Wells
Posts: 268
Joined: Fri May 08, 2015 7:34 pm
Contact:

Re: Carburator adjustment Holley 4150

Post by Tom Wells » Wed Aug 30, 2017 6:27 pm

Hi Stefan,

Welcome to the Cobra experience!

We have BlackSnake who is local and very knowledgeable about Holley carbs, and in September which is almost upon us, R^3 the carb Czar is coming to town for a few days to visit. Coincidentally, he plans to work on another Holley in ALtamonte Springs, so perhaps he can find some time to have a look at yours too.

R^3 will be here from September 11-14. My contact information is in the Private Stuff section so if you'd like to call, maybe next week, perhaps we can figure out what may fit your schedule and his.

I love the electric bull analogy, but it makes me wonder whether there are other factors beside the carb - too much cam? for example.

Anyhow, between the two guys above, some progress is inevitable (I hope!)

Tom

Cobra 65
Posts: 15
Joined: Fri Oct 09, 2015 10:52 am

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Wed Aug 30, 2017 8:54 pm

Hi Tom,

Thanks for the fast reply and worm welcome.
I'll surely will give you a call next week.
It looks like there is a lot of knowledge around soon!

I'm glad I took the chance to get in to touch with the club!

I just added my personal information on the members only page.

Take care,

Stefan

mooreken
Posts: 99
Joined: Sat May 09, 2015 12:25 pm

Re: Carburator adjustment Holley 4150

Post by mooreken » Wed Aug 30, 2017 10:42 pm

Welcome. the running when shutting off is not the carb. The old adage is the first thing to do with the carb is make sure the ignition is in order. There are so many things to look at. Are you using vacuum advance or totally manual. Street cars are not race cars so lots of the things to make power that you read about are not really usable on the street. Race cars don't run below 2500 rpm so things are different.

Toms recommendations are good ones. They do know their stuff.
Keep digging at it....it will give up and plan nice one day.

Ken

Cobra 65
Posts: 15
Joined: Fri Oct 09, 2015 10:52 am

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Thu Aug 31, 2017 8:05 am

Good morning Ken,

Thanks for your help. The Cobra got a MSD ignition without vacuum advance.
It seems like my set up is a little tricky...

Looking forward to have her running good.

Take care,

Stefan

Avalanche325
Posts: 35
Joined: Wed Jul 22, 2015 6:06 pm

Re: Carburator adjustment Holley 4150

Post by Avalanche325 » Thu Aug 31, 2017 1:41 pm

I agree that you need to make sure that the timing is correct at idle and at max advance first.

The very first thing on the carb itself is to get the t-slots set correctly. If those are not set, everything will be erratic. After that, each circuit has to be done in the correct order, starting with idle, as they all add onto each other. For instance, when you are wide open, the idle circuit is still in play. When you are at idle, the main jets are doing nothing. I see posts all the time where people are changing main jets to try to fix an idle issue.

How is your mechanic doing the tuning? Is he using a wideband O2 sensor, or going by ear and plug reading?

The only thing that really makes tuning tricky is running a big cam on the street. Ask me how I know.

Here is a good procedure if you are using a wideband - http://www.ffcars.com/forums/17-factory ... 101-a.html
I would use this procedure before spending money on dyno pulls.If everything is really honked up, put the carb back to out of the box settings and start again.

Cobra 65
Posts: 15
Joined: Fri Oct 09, 2015 10:52 am

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Thu Aug 31, 2017 3:15 pm

Thanks for your help.

My mechanic did the timing at idle and around 3000 rpm.
He's not using a wideband O2 sensor, just ear and plug reading.

I'll give Tom a call next week and hopefully we can set up an appointment with R^3 and go from there.
And maybe we have to do the 'back to factory' thing and start all over...

Again thanks,

Stefan

BlackSnake
Posts: 43
Joined: Mon Jul 13, 2015 4:09 am

Re: Carburator adjustment Holley 4150

Post by BlackSnake » Thu Aug 31, 2017 5:36 pm

Where are you located Stefan?

Cobra 65
Posts: 15
Joined: Fri Oct 09, 2015 10:52 am

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Thu Aug 31, 2017 5:51 pm

Hey BlackSnake,

I'm located at the Marsh Creek community on the island.

Take care,
Stefan

BlackSnake
Posts: 43
Joined: Mon Jul 13, 2015 4:09 am

Re: Carburator adjustment Holley 4150

Post by BlackSnake » Thu Aug 31, 2017 9:41 pm

Great, you're local. Let us know when you want to get together to look it over. Btw, what size (cfm) is the 4150?

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