[DeTomaso] Carb hesitation on level ground at cruise

Asa Jay Laughton asajay at asajay.com
Wed Jul 31 21:44:20 EDT 2024 

Thank you Larry, that answers a question wasn’t sure how to ask regarding centrifugal only advance.

Asa  Jay

Sent via radio waves

> On Jul 31, 2024, at 18:27, Larry Stock <larrys at panteraparts.com> wrote:
> 
> I time at 36 degrees total advance without vacuum at 3000 RPM, then typically back to 16 degrees at idle, again no vacuum.
> Should have 20 degrees centrifugal distributor advance if working properly, but you can see it working with your timing light.
> I make a strong scribe mark at 36 degrees on the balancer.
> Larry
> 
> 
> On 7/31/24, 6:10 PM, "Asa Jay Laughton" <asajay at asajay.com <mailto:asajay at asajay.com>> wrote:
> 
> 
> The distributor is an aftermarket, presume MSD since it has an MSD6AL and Tach adapter. The dizzy is mechanical advance only; no provision for vacuum advance. It appears to have the typical magnetic reluctor setup. Yes, the mechanical advance moves freely.
> 
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> Sent via radio waves
> 
> 
>> On Jul 31, 2024, at 14:37, Asa Jay Laughton <asajay at asajay.com <mailto:asajay at asajay.com>> wrote:
>> 
>> Thanks Jeff, I’m going after the lean stumble theory first. I’ll let you all know what I find though it may be a few days. Wrenching on other folks Panteras is more of a hobby after I get off my day job. 😐
>> 
>> I’d get a lot more hobby done if I didn’t have to work for a living.
>> 
>> Asa Jay
>> 
>> Sent via radio waves
>> 
>>>> On Jul 31, 2024, at 14:33, Jeff Kimball <jgkrenton at comcast.net <mailto:jgkrenton at comcast.net>> wrote:
>>> 
>>> AJ:
>>> 
>>> RE: "Trouble is there is no AF gauge on it, and my portable can only be stuffed in one of four exhaust tips."
>>> 
>>> Your portable AF sensor should work fine. There is only one carb and the exhaust in all four pipes should be identical. What it reads in one should be the same in all. Check several if you want, but I don't think you'll find much difference.
>>> 
>>> Sounds like a lean stumble at cruise/high vacuum conditions to me and when the power-valve opens under load/low vacuum it provides enough fuel to get rid of the stumble.
>>> 
>>> And.. FYI, I was just digging around in the programing for my Pro-M EFI and noted there are something like 1500 variables that can be messed with.
>>> 
>>> Good luck.
>>> 
>>> Jeff/2467 with twin turbos and EFI.
>>> 
>>> 
>>>>> On 07/31/2024 2:17 PM PDT Larry Stock <larrys at panteraparts.com <mailto:larrys at panteraparts.com>> wrote:
>>>> 
>>>> 
>>>> Take the on off Madd Dawg's Pantera, but don't tell him I told you to.
>>>> Larry
>>>> 
>>>> On 7/31/24, 1:53 PM, "DeTomaso on behalf of Asa Jay Laughton via DeTomaso" <detomaso-bounces at server.detomasolist.com <mailto:detomaso-bounces at server.detomasolist.com> <mailto:detomaso-bounces at server.detomasolist.com <mailto:detomaso-bounces at server.detomasolist.com>> on behalf of detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>>> wrote:
>>>> 
>>>> 
>>>> I wish I did have a spare carb ready to bolt on. Best I’ve got is a Holley 850 collecting dust on a shelf awaiting a rebuild (someday).
>>>> 
>>>> 
>>>> I don’t recall a vacuum advance on this distributor. But now I’m going to investigate more because it should if it’s got a carb, unless there is a crank trigger wheel for something else.
>>>> 
>>>> 
>>>> Plenty of ideas to get me checking things again.
>>>> 
>>>> 
>>>> Thank you.
>>>> Asa Jay
>>>> 
>>>> 
>>>> 
>>>> 
>>>> Sent via radio waves
>>>> 
>>>> 
>>>>>> On Jul 31, 2024, at 07:55, Will Kooiman <will.kooiman at gmail.com <mailto:will.kooiman at gmail.com> <mailto:will.kooiman at gmail.com <mailto:will.kooiman at gmail.com>>> wrote:
>>>>> 
>>>>> It actually sounds like the timing is off. Does it have vacuum advance?
>>>>> 
>>>>> 1) If it has vacuum advance, try unplugging it to see if it improves.
>>>>> 2) Can you try a known good carburetor?
>>>>> 
>>>>> 
>>>>> On 7/31/24, 1:09 AM, "DeTomaso on behalf of Asa Jay Laughton via DeTomaso" <detomaso-bounces at server.detomasolist.com <mailto:detomaso-bounces at server.detomasolist.com> <mailto:detomaso-bounces at server.detomasolist.com <mailto:detomaso-bounces at server.detomasolist.com>> <mailto:detomaso-bounces at server.detomasolist.com <mailto:detomaso-bounces at server.detomasolist.com> <mailto:detomaso-bounces at server.detomasolist.com <mailto:detomaso-bounces at server.detomasolist.com>>> on behalf of detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>>>> wrote:
>>>>> 
>>>>> 
>>>>> I have successfully (for the most part) tuned an Electromotive system. Still some things to learn there but it sure ran a lot better after I tuned it.
>>>>> 
>>>>> 
>>>>> I agree, carbs are fairly simple but there are some complexities. I’m not so much lost as I may be leading you to believe.
>>>>> 
>>>>> 
>>>>> Asa Jay
>>>>> 
>>>>> 
>>>>> Sent via radio waves
>>>>> 
>>>>> 
>>>>>> On Jul 30, 2024, at 20:55, Mike Drew <mikeldrew at aol.com <mailto:mikeldrew at aol.com> <mailto:mikeldrew at aol.com <mailto:mikeldrew at aol.com>> <mailto:mikeldrew at aol.com <mailto:mikeldrew at aol.com> <mailto:mikeldrew at aol.com <mailto:mikeldrew at aol.com>>>> wrote:
>>>>>> 
>>>>>> AJ,
>>>>>> 
>>>>>> If you are a bit lost with a carb I think you will be completely in the woods with injection. A carb is an extremely simple device by comparison.
>>>>>> 
>>>>>> Smart people, chime in!
>>>>>> 
>>>>>> Mike
>>>>>> 
>>>>>> 
>>>>>> Sent from my iPad
>>>>>> 
>>>>>>>> On Jul 30, 2024, at 20:45, Asa Jay Laughton via DeTomaso <detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>>>> wrote:
>>>>>>> 
>>>>>>> Owner has asked if we could fix all problems with fuel injection. I’m not a fan of saying that because I know a well tuned carb can be just as good as well tuned EFI.
>>>>>>> 
>>>>>>> If the owner persists, what is the collectives opinions on various EFI systems out there today?
>>>>>>> 
>>>>>>> Thank you,
>>>>>>> Asa Jay
>>>>>>> 
>>>>>>> Sent via radio waves
>>>>>>> 
>>>>>>>>> On Jul 30, 2024, at 20:37, Asa Jay Laughton via DeTomaso <detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com> <mailto:detomaso at server.detomasolist.com <mailto:detomaso at server.detomasolist.com>>>> wrote:
>>>>>>>> 
>>>>>>>> Hi all,
>>>>>>>> I'm working with a PIM 427 Hammer (stroked Windsor) in a Pantera. This has a Demon carb on it. I don't know what it has for jets. I know it runs a little rich.
>>>>>>>> 
>>>>>>>> Here is my situation and in a bit of humility, am stumped at the moment. Sam and I just took it out for a long test drive and it has problems on leverlk ground, no load, cruising mode.
>>>>>>>> 
>>>>>>>> It idles at about 800 rpm, a bit lumpy but starts right up cold, doesn't die, no choke (no choke on the Demon carb).
>>>>>>>> It revs easily and pulls away from a stop sign beautifully.
>>>>>>>> Under load, moderate throttle or foot to the floor, it runs great.
>>>>>>>> Off throttle, engine braking, it runs fine, though it doesn't burbble like I would expect
>>>>>>>> Uphill great, downhill not so much (that cruise position of the foot on the go-pedal)
>>>>>>>> On level ground, 5th gear, holding cruise at 60 MPH at around 2,000 rpm, it hesitates, jerks, feels like it's misfiring.
>>>>>>>> Same when in say 4th, holding cruise at a higher rpm but no load either with go-pedal down, or engine braking
>>>>>>>> It does this hesitation at nearly any rpm from 1,500 to 3,500 only when holding cruise speed, not when accelerating (even mildly)
>>>>>>>> 
>>>>>>>> I'm thinking the problem is the idle mixture and speed settings. I'm thinking the throttle plates might be closed wee bit too much and idle mixture is compensating. When the throttle is at off-idle, at cruise, the transfer ports aren't giving enough gas, or maybe it's air. Trouble is there is no AF gauge on it, and my portable can only be stuffed in one of four exhaust tips.
>>>>>>>> 
>>>>>>>> <sigh> so I'm asking for the collectives opinions, I know there are some good ones out there. I figure I need to re-check timing, advance, and carb tune again.
>>>>>>>> 
>>>>>>>> Thoughts?
>>>>>>>> Thank you,
>>>>>>>> Asa Jay
>>>>>>>> 
>>>>>>>> --
>>>>>>>> Asa Jay Laughton - W7TSC, MSgt, USAFR, Retired
>>>>>>>> Spokane County ARES-RACES-ACS EC/RO
>>>>>>>> ******************************
>>>>>>>> https://w7tsc.org <https://w7tsc.org> <https://w7tsc.org> <https://w7tsc.org>> <https://w7tsc.org> <https://w7tsc.org>> <https://w7tsc.org>> <https://w7tsc.org&gt;>>
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>>>>>>>> 
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