[Fot] Fuel issue

[Mike Harmuth]

Hi Andrew, a couple of things to check.
1st, is this a new problem? if so, what did you touch last?

2d Verify fuel flow, not just pressure i.e Gallons per hour? Disconnect the
fuel line at the carbs, and stick it into a 1 quart or one gallon
clean/clear bottle/jug. Turn the fuel pump on and time how long it takes to
fill (1 Qt/ 1Gal whatever size container you're using).  If you're getting
more than 20 gallons per hour, the flow is OK. Set the bottle aside and let
it settle out, look for particles, rubber, fuel cell foam, dirt. If so, see
where that's coming from. For example, old fuel cell foam will break down
and clog the intake. When the pump turns off, the fuel in the lines drops
back flushing the intake clear until next time. Fuel filter clean? Fuel
pressure reg OK? Not just holding pressure (I run 3.5 on my HS4s) but
actually sending fuel down the line? The gallons per hour test will
indicate if you need to look into any of these areas, if you're gelling
enough fuel, more down the list for now.
link to flow and fuel requirements chart
https://historicracinggroup.com/resources/Reference_Material/Canton/Fuel%20Consumption%20and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf

3. A problem I had with an identical set up, was rubber hose breaking down
and settling into the little box shaped well in the carb bowl where the
line to the jet connects. It's happened to me twice now, last time was in
June with fairly new hose feeding the carbs. It restricted the flow to the
jet, even though the bowl was full. At high load, not enough fuel could get
past the blockage.
[image: IMG_20240630_112925914.jpg]

4. Vacuum leak- Is there a crack or loose bolt on the intake manifold? With
the engine running, spray carb cleaner around the manifold to block, carbs
to manifold. A change in engine RPM means something was drawn in through a
gap.

5. Compression check- Are all the cylinders within 5-10% of each other?

Happy hunting

mike h

On Fri, Aug 9, 2024 at 3:03 PM Andrew Devenish via Fot <fot at autox.team.net>
wrote:

> Guys,
>           My car ( 1300, 12.5:1 comp on Sunoco 110 race gas, dual HS4 ) is
> still giving me grief. I’ve chased all the things I can think of, but still
> same problem. It starts and runs great, but after a few laps of the yard (
> 5-6, only 1000ft  or so per up/down lap, so quick accels then braking to
> turn ) it goes very lean ( I have O2 sensor ) and stops. I’m running it
> without the hood for these test runs. It always stops at the entry to a
> turn.
>          I’ve been working on it a lot, so know it has fuel pressure, and
> the float bowls are full of fuel. All plugs look very similar. The needles
> (AAA) are the spring type, and the slides move freely. I use ATF as fluid,
> but have tried 50 weight too.
>         After a minute or so it will fire back up, but only run enough to
> get back to the shop before going lean again. If I pull out the choke it
> will run, but is unstable.
>        I have wrapped headers and a heat shield around the carbs but they
> do still get hot.
>
>        Any ideas ?  Thinking to try some less volatile fuel as it seems
> heat related and the Sunoco evaporates so fast !
>
>
> Thank you,
>       Andrew Devenish
>
> Sent from my iPad_______________________________________________
> fot at autox.team.net
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