Carburator adjustment Holley 4150

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

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Fri Sep 01, 2017 8:02 am

The carb size is 750 cfm.
I'm pretty flexible time wise as I'm retired ;) . Some soccer games and practices....
How about we meet after Labor Day? So we might figure out what needs to be done and maybe what parts needs to be ordered.
Thanks for your help!

Tom Wells
Posts: 270
Joined: Fri May 08, 2015 7:34 pm
Contact:

Re: Carburator adjustment Holley 4150

Post by Tom Wells » Sun Sep 03, 2017 6:41 am

Stefan et al,

R^3's trip is cancelled due to some health issues - we've all been there, done that. I've decided to call it the Irma Flu. I'll post more when we reschedule.

In the meantime, maybe Mike (or someone else) can step in and get some progress on the carb problem?

Tom

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

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Sun Sep 03, 2017 1:57 pm

Hi Tom,
Sorry to hear about R^3 health issues - hope he's doing better soon.
Yes, I would appreciate some help from the club.
Thanks,
Stefan

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

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Thu Sep 21, 2017 1:55 pm

Hi Tom, Blacksnake (I don't know you real name) and all,
I hope everyone stayed safe during the storm.
After cleaning up after Irma I would love to continue to get the carb tuned.
I'll be out of town over the weekend but anytime later would work for me.
Thanks to the group offering help.

Stefan

BlackSnake
Posts: 45
Joined: Mon Jul 13, 2015 4:09 am

Re: Carburator adjustment Holley 4150

Post by BlackSnake » Fri Sep 22, 2017 9:55 am

Hi Stefan,

The other guys have already mentioned some things that you haven't responded to. We need to know certain specifics about your motor before we can offer any reasonable assistance to help resolve your issues. With that said, I have some questions for you. First, since owning this car with that engine combination, has it ever run well? I need to know if this is a new problem or if it's never run correctly.

Next, have you contacted Keith Craft about these issues? If not, why not? If yes, what have they told you? These are important questions, because Keith Craft is a well known and respected engine builder who would definitely provide guidance on the proper setup for that particular engine. That engine is no wimpy SBF, it's clearly tuned near the high end with those HP & TQ numbers. I suspect it has a very aggressive cam and very high compression (at least 11:1, and likely higher), which typically indicates a requirement to run extra high octane race fuel or octane booster additives. Keith Craft would have provided a spec sheet with that motor, do you have that? They would also have provided a recommended setup to include fuel requirements, initial and full timing settings, idle RPM, etc...all of this needs to be known before attempting to troubleshoot.

Also need to know specifics about your fuel delivery system, type of fuel pump and regulator, has pressure been properly set?

Regards, Mike (a.k.a. BlackSnake) ..]

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

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Tue Sep 26, 2017 6:08 pm

Hi Mike,
Thanks for your post.
I tried to answer all questions but I'm not a mechanic and some things I just don't know or never have heard off.

I bought the car used 3 years ago with only 350 miles on it. It was build in 2006.
I emailed Keith Craft about the issues but I never heard of them. But I never tried it again - my fault, I guess.
The carb needed adjustments and I took it to Evans Automotive and they tuned the carb, telling me that it needed to be rebuild. The surging stayed the same as before.
Here 'my' mechanic came into play. He rebuilt the carb.
He checked the timing at idle and 3000 rpm and because of the strong surging he plugged the vacuum. He told me about the aggressive cam as well.
He changed jets and air bleeds trying to solve that surging. All the time the engine is running too rich. I changed the spark plugs several times and whatever we did they where black. At around 2000 rpm I can hear and feel a kind of blubb and is seems like what was holding her back got unleashed (hard to describe). More power but misfiring during acceleration. It's still running too rich - I think. Of course I changed the fuel filter but have no information about the fuel system - sorry.
Carb 4150 with 750 cbm. MSD 6AL ignition system.
I tried running it with octane booster but issues stayed the same.
I've all the engine specs from Keith Craft and can email them to you as I haven't found out how to attach those in this post.
Sorry, I'm not a mechanic but I love my Cobra.

Again thanks for you help.

Regards,
Stefan

BlackSnake
Posts: 45
Joined: Mon Jul 13, 2015 4:09 am

Re: Carburator adjustment Holley 4150

Post by BlackSnake » Tue Sep 26, 2017 9:51 pm

Hmm, interesting, so I presume the car has never run well for you or the original owner. You'd probably have done better to call Keith Craft rather than email, but that's for another day. I posted my contact info in the private member section so you can email the spec sheet to me and then I'll post it for the others to review.

Very curious now to see how the fuel system is configured. I'll try to make time this weekend or next to examine the car.

Mike

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

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Tue Sep 26, 2017 10:01 pm

Hi Mike,
just sent you the specs.
The weekend from Oct. 6th to Oct. 8th I'm at a soccer tournament in Orlando. Otherwise no problem.

Regards,
Stefan

BlackSnake
Posts: 45
Joined: Mon Jul 13, 2015 4:09 am

Re: Carburator adjustment Holley 4150

Post by BlackSnake » Wed Sep 27, 2017 8:55 am

Stefan,

Received the 8 page pdf spec file you sent. File is too large to upload, so I had to break it into individual files to upload.

Some observations:
As expected, cam is pretty aggressive with respect to lift and LSA, lots of overlap. Would not want to run Weber carbs with that cam. No indication what the nominal CR might be, but Mahle pistons are dished, so maybe not as high compression as I suspected. Piston PN SBF245125I26 (not necessarily the same pistons in your engine) specs indicate anywhere from 10.3:1 with 58cc chamber volume vs 9.2:1 with 70cc CV. Should check actual compression in all cylinders to establish baseline and check for variation. We may want to do a leak down check also to verify baseline condition of the motor. I have compression and leak down test equipment to do this.

Dyno sheet indicates timing set at 35 degrees total. A/F ratio appears much more lean in power band than I'd have expected (15 avg). I'd have expected more in the 12 to 13 range in that band. If as you say, the motor is running very rich, something or several things have changed since that motor was dyno'd.

Looks like your motor has an S904 Carter mechanical fuel pump installed, which are not typically regulated for use with Holley carbs. We may need to install a regulator and gauge to verify carb inlet pressure is in the correct range. I have extra regulators and gauges to install.

More to follow. We have work to do...:-)
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Cyl Head Sheet.png
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Basic Specs.png
Basic Specs.png (222.72 KiB) Viewed 105 times

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

Re: Carburator adjustment Holley 4150

Post by Cobra 65 » Wed Sep 27, 2017 10:08 am

Thanks Mike,
I really appreciate your help.
Finally I found people who know what they are talking about.

Take care,
Stefan

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