[Fot] Intake manifold vacuum and no high RPM

[Mike Harmuth]

I measured fuel flow at the tee feeding the carbs, and I got 2 quarts in 31
seconds or roughly 60 GPH. The pump is rated for 97 GPH,unregulated, so 60
seems reasonable and able to meet demand.

thanks
mike h

On Mon, Nov 28, 2016 at 10:59 PM, Kas Kastner <kaskastner at gmail.com> wrote:

> Duh!!!  have your measured the flow of the pump to the carbs? Do you get
> 15 gallons per hour? You don't get fuel Mr. you do not get power.
>
> *Never be beaten by equipment.*
>
> On Mon, Nov 28, 2016 at 3:58 PM, Mike Harmuth <ofracer at gmail.com> wrote:
>
>> Thanks for the replies, here are the answers to some of the questions:
>>
>> Valve springs, - Dual springs with alloy retainers. The engine builder
>> tested and shimmed them to a uniform pressure but I don't know the number
>> off the top of my head. I'll ask him tomorrow
>>
>> Silver springs in the carbs, the lightest they make I believe. I have a
>> set of heaver ones (red I believe) that I can try. The pistons are filled ~
>> 3/4 of the way,  up with SU branded oil and the dampers are in place.
>>
>> The fuel pump, Holley red, all the lines, micron filter before the pump
>> and the regulator were changed last winter because I didn't know how old
>> they were. I had the problem then as well, before and after the
>> replacement. I opened the cell up two weeks ago. The foam is in great
>> shape, the pickups and intake line look to be solid as well. The ATL cell
>> is 6 years old.
>>
>> Fuel pressure is measured by a gauge at the regulator 2 feet from the
>> carbs.
>>
>> I'm not sure that the problem isn't electrical but the car runs with a
>> alternator (confirmed working). The distributor was built with a profile to
>> match my engine by Jeff at Advanced Distributors. I've changed the points
>> (using his high speed set), rotor, cap, wires and capacitor over the
>> summer, just in case, but with no affect. Timing is steady, double row
>> timing chain.
>>
>> thanks for all the info.
>>
>> mike h
>>
>> On Mon, Nov 28, 2016 at 5:05 PM, Sam Halkias <atr6racer at hotmail.com>
>> wrote:
>>
>>> What are you running for valve springs? Sounds like valve float to me.
>>>
>>> Sam
>>>
>>> *Sent from my Verizon Wireless 4G LTE DROID*
>>>
>>>
>>> Mike Harmuth <ofracer at gmail.com> wrote:
>>>
>>> I'm tracking down a problem with the Spit race car (1296 Small Journal,
>>> 12;1 compression, APT TR74 cam 295 duration and 0.324 lob lift, head ported
>>> as per Kas's book). Rebuilt European SU HS4 carb setup with AAA needles
>>> (manifold and carbs checked for vacuum leaks), Advanced Distributor for
>>> spark (34 degrees at full, mechanical only, advance @ 3.5K RPM)
>>>
>>> The problem I have has followed me on two different short blocks, I can
>>> easily pull 7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire
>>> case, 4th gear is 1;1,  4:11 locked diff ) gears. In 4th I'm struggling to
>>> get over 6K, no matter how long the straight. Just before the last race of
>>> the season, I installed an air fuel ratio gauge on the header (stahl) and
>>> found out I'm running (progressively)  very lean (19:1) in 4th over 5K. At
>>> 2K I adjusted it rich, to 12;1 and it keeps in the 13.5- 14.5 range until I
>>> get over 5K when it really leans out. If I pull the choke to 1/2  full over
>>> 5K, I get a good ratio again, 13.5- 14%.
>>>
>>> To me that seemed like the carb pistons aren't pulling all the way up so
>>> I drilled and tapped the manifold to get a vacuum reading. It was steady
>>> but low at 6K, ~20 Inches but would jump to ~28 briefly as the revs dropped
>>> if I blipped the throttle. Under 6K, it was in the 15 inch range. Normal
>>> air filters are K&N with stub stacks but I get the same results with open
>>> carbs.
>>>
>>> Am I correct in assuming that the vacuum is too low or is it that due to
>>> overlap with a performance cam? Any ideas on where to look to get the ratio
>>> "normal" at higher revs? Fuel pump is Holley Red, adjusted to 3 PSI at the
>>> engine compartment and steady through all revs.
>>>
>>> I have dyno time scheduled in a few weeks but I'd like to use that time
>>> to tune not debug things.
>>>
>>> thanks
>>> mike h
>>> 63 spitfire
>>>
>>
>>
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