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Any Holley Ultra Double Pumper Guru's ?
#1
[Image: 00m0m_7_Rs_Y18_To7s_J_600x450.jpg]

Here is a pic of my car. I just built a 351c 4V factory iron heads with a Torker II manifold and a Holley 76750BL Ultra Double pumper carb. The carb is running too rich at idle to tune it. It is fouling plugs after about an hour of run time. I have ruled out vacuum leaks in the lifter valley and hoses. Tried tuning to increase the air bypass by opening up the secondaries with the screw on the base plate which helped but still not enough. I am pulling 13 inchs of vacuum at idle. This is a brand new carb right out of the box. The idle screws are turned out 3/4 of a turn tuned with a vacuum gauge, anything more than that and the vacuum and idle drops. I verified that the curb idle transfer slots are not open too far. I am at the point of drilling the butterflies but would prefer not to. I built this with a Howards cam and lifter kit part# MC230041-12. I don't think that this is such a radical cam profile that it should require drastic measures to tune it. I have never had a problem tuning Holley's before and I am at a stand still with this until I can get it figured out. Any help would be greatly appreciated. Thanks
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#2
That is a nice mild cam and should not be the source of your problem. I would go to a 6.5 power valve (if it is anything else) on the primary side and jet down 2 sizes. If that helps, but doesn't fix it drop 2 more. Do not be tempted to mover faster than 2 sizes at a time.

What is your idle RPM right now It probably needs to be higher. I run 1000 rpm with a manual, but even an auto can need 700-750 to run smoothly with some cam and carb combinations

Where is your timing set at and when you look at it at 3000 rpm what is the total timing shoot for about 34 degrees total unless those are open chamber heads you can go a bit further- maybe as far as 38 Base timing will probably be best between 12 and 16 degrees-factory timing numbers are meaningless.

One other thing that can be a factor is running without a thermostat or a way too cold thermostat. Iron engines need to be up to temperature to work their best.

and finally, are you dead certain your ignition system is performing up to standards> You would be surprised at just how many carb problems are actually ignition issues.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#3
I have already rejetted the primaries, factory jet 73 now 70. Factory power valve 6.5 now 4.5 because vacuum was at 9 until I started to tune this. Ignition system is all new with an MSD Coil and a MSD ready to run distributor. Initial timing was bumped up to 20, total 32 all in by 3500 RPM (closed chamber heads). Thermistat is brand new made especially for the Cleveland holds at 190 running. Idling at about 1000 RPM (Don't have a tach). Correct me if I am wrong but isn't the idle circuits independent of the main jets?
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#4
If of any help, ran 25 years a similar combo with Holley 650 DP and got same issues. Rich at idle, and would sometimes ran bad after a good wot back to low rpm.
Spend time tuning, checking and replacing ignition parts etc...

What really made a diff were simple often overlooked details.
Ditched the paper air filter by a k&n filter. From the noise I could tell right away it was nicely breathing.
Not part of the tuning, just for the coolness of it, I bought this now classic Summit dual feed line with metal fuel filter and fuel pressure gauge,
Once installed, it was obvious I should have a fuel pressure regulator.
Running an offy dual plane intake, I've added a spacer as well.

Once the reg, the filter and spacer were in place, most issues were gone. (aside almost impossible restart when hot), but no more flooding conditions.
I say most because, even if it ran after that fine, its when I moved to efi that I saw how much better the same combo could run.

edit: forgot to add, that I never got it to run well bellow 850 rpm in park. 750-800 in drive. Probably me sucking at fine tuning carbs tho.

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
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#5
(06-05-2018, 12:50 AM)scacer1 Wrote: I have already rejetted the primaries, factory jet 73 now 70. Factory power valve 6.5 now 4.5 because vacuum was at 9 until I started to tune this. Ignition system is all new with an MSD Coil and a MSD ready to run distributor. Initial timing was bumped up to 20, total 32 all in by 3500 RPM (closed chamber heads). Thermistat is brand new made especially for the Cleveland holds at 190 running. Idling at about 1000 RPM (Don't have a tach). Correct me if I am wrong but isn't the idle circuits independent of the main jets?

You are correct that the main jetting and power valve opening point have no effect on idle mixture.

When you turn the idle mixture screws all the way in does the engine die?

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#6
(06-05-2018, 07:12 AM)TommyK Wrote:
(06-05-2018, 12:50 AM)scacer1 Wrote: I have already rejetted the primaries, factory jet 73 now 70. Factory power valve 6.5 now 4.5 because vacuum was at 9 until I started to tune this. Ignition system is all new with an MSD Coil and a MSD ready to run distributor. Initial timing was bumped up to 20, total 32 all in by 3500 RPM (closed chamber heads). Thermistat is brand new made especially for the Cleveland holds at 190 running. Idling at about 1000 RPM (Don't have a tach). Correct me if I am wrong but isn't the idle circuits independent of the main jets?

You are correct that the main jetting and power valve opening point have no effect on idle mixture.

When you turn the idle mixture screws all the way in does the engine die?
Doesn't die but runs rough. Also the mixture screws aren't consistent when turned in, 3 of them have a definite effect on idle the other 1 has a minimal effect which seems to me to indicate an internal leak but I have replaced all the metering block and fuel bowl gaskets.
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#7
(06-05-2018, 09:24 AM)scacer1 Wrote:
(06-05-2018, 07:12 AM)TommyK Wrote:
(06-05-2018, 12:50 AM)scacer1 Wrote: I have already rejetted the primaries, factory jet 73 now 70. Factory power valve 6.5 now 4.5 because vacuum was at 9 until I started to tune this. Ignition system is all new with an MSD Coil and a MSD ready to run distributor. Initial timing was bumped up to 20, total 32 all in by 3500 RPM (closed chamber heads). Thermistat is brand new made especially for the Cleveland holds at 190 running. Idling at about 1000 RPM (Don't have a tach). Correct me if I am wrong but isn't the idle circuits independent of the main jets?

You are correct that the main jetting and power valve opening point have no effect on idle mixture.

When you turn the idle mixture screws all the way in does the engine die?
Doesn't die but runs rough. Also the mixture screws aren't consistent when turned in, 3 of them have a definite effect on idle the other 1 has a minimal effect which seems to me to indicate an internal leak but I have replaced all the metering block and fuel bowl gaskets.
Remove the carb and check how much of the t slot is exposed on both the primary and secondary.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#8
I'd also check your float height, it may be too high and dripping out the boosters. The engine should die when you close the idle mixture screws. If it doesn't and the float adjustment is correct, you might have an internal leak which would be a warranty issue.

If I have issues setting a four corner idle carb, I close the secondaries and get it sorted on the primaries, then work the secondaries back in.

Don't ever assume the carb is good, Holley's QC has failed me in the past. I recently purchased a replacement baseplate for a friends HP carb. The secondary shaft was bound up internally and nearly impossible to move. summit swapped it right out, but good thing I checked it before doing anything.


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#9
Update: I removed carb and pulled it down, changed power valve back to 6.5 now that I'm getting 13" of vacuum. Jets are now 70 on the primary's and 73 on the secondary's Drilled all 4 butterflies with .130 drill bit. Now idling with 15" of vacuum. Idle screws have a profound effect on the idle. They are adjusted out 1 1/4 turns now. I haven't changed a plug yet to see what it looks like since I changed the setup. I am waiting for it to cool down now. I think this did the trick. I still need to look at the timing again and see if I can back it down some. I set the floats first thing. Thanks guys for taking the time to consider my problem. I hope this helps someone else that might be having the same problem. I will update this thread with any new info. Thanks again.
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#10
Look forward to hearing a positive report!

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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