[DeTomaso] Carb hesitation on level ground at cruise
Forest Goodhart
forestg at att.net
Wed Jul 31 00:07:49 EDT 2024
Sounds like either too much vacuum advance or too lean primary main jets. Try richening the idle mixture screws about 1/2 to 3/4 turn and see if that makes a difference. If so step up two sizes on main jets, if not disconnect vacuum advance and see what that does. If neither of these makes any difference I'm out of ideas.
On Tuesday, July 30, 2024 at 08:54:36 PM PDT, Mike Drew via DeTomaso <detomaso at server.detomasolist.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> 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> 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://www.teampanteraracing.com
>>
>> _______________________________________________
>>
>>
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-------------- next part --------------
Sounds like either too much vacuum advance or too lean primary main
jets. Try richening the idle mixture screws about 1/2 to 3/4 turn and
see if that makes a difference. If so step up two sizes on main jets,
if not disconnect vacuum advance and see what that does. If neither of
these makes any difference I'm out of ideas.
On Tuesday, July 30, 2024 at 08:54:36 PM PDT, Mike Drew via DeTomaso
<detomaso at server.detomasolist.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
<[1]detomaso at server.detomasolist.com> wrote:
>
> i>>?Owner has asked if we could fix all problems with fuel
injection. Iam 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
<[2]detomaso at server.detomasolist.com> wrote:
>>
>> i>>?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
>> ******************************
>> [3]https://w7tsc.org
>> [4]https://www.teampanteraracing.com
>>
>> _______________________________________________
>>
>>
>> Detomaso Email List is not managed by POCA
>> Posted emails must not exceed 1.5 Megabytes
>> DeTomaso mailing list
>> [5]DeTomaso at server.detomasolist.com
>> [6]http://server.detomasolist.com/mailman/listinfo/detomaso
>>
>> To manage your subscription (change email address, unsubscribe,
etc.) use the links above.
>>
>> Members who post to this list grant license to the list to forward
any message posted here to all past, current, or future members of the
list. They also grant the list owner permission to maintain an archive
or approve the archiving of list messages.
>
> _______________________________________________
>
>
> Detomaso Email List is not managed by POCA
> Posted emails must not exceed 1.5 Megabytes
> DeTomaso mailing list
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> [8]http://server.detomasolist.com/mailman/listinfo/detomaso
>
> To manage your subscription (change email address, unsubscribe, etc.)
use the links above.
>
> Members who post to this list grant license to the list to forward
any message posted here to all past, current, or future members of the
list. They also grant the list owner permission to maintain an archive
or approve the archiving of list messages.
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