[Fot] Fuel issue

Fri Aug 9 15:54:45 MDT 2024

Does this happen in both right and left turns,  on such a small run try the
opposite direction, could be float hinge problems if it always quits in a
corner.
Carl Stenquist

On Fri, Aug 9, 2024 at 5:44 PM Andrew Devenish via Fot <fot at autox.team.net>
wrote:

> Hi Mike,
>           The first question is a good one. The car was built for
> autocross by a guy in Indiana who knew his stuff. However, I bought it from
> a guy who had bought it to run PIB, but knew nothing about race engines. He
> had run it lean and holed #4. He told me he had not changed anything, but
> that is turning out not to be the case. (I suspect it holed the piston
> because I found he had fitted gros jets with the float level way too low).
>         I rebuilt it to same mechanical spec. It ran great but a little
> lean on the AAU needles for road course, so I’m now on AAA. It still runs
> great, unless it doesn’t 😁.
>         The car has had this issue since I built it. At first I thought
> the obvious - float heights, needle/seat, regulator pressure etc etc but
> while it always runs great I have this issues after a few “laps”.
>       2)   The car had a Summit racing 3136 pump which has around 90GPH
> and an internal blow off at 7PSI, my regulator is at 4 PSI. Today I had
> taken the pump apart and checked it but all looked OK. I fitted a cheap
> solenoid pump in its place. Issue still there.
> I had checked both the Summit and now the solenoid pump for flow, there is
> plenty.
>       As I noted the float bowls are full when it quits running.
>     3) Great point - could be what I have. I know the fuel level in the
> jets is fine when not running, but a poor flow from bowl to jet would
> change that when running. My O2 is in the collector, so I can’t be sure if
> it’s both carbs or just one. All 4 plugs look very similar, but that is
> possible as this “lean” condition is only for a few cycles before it stops
> - not enough to color the plug. Will check when I can ( unfortunately a
> busy weekend coming up as I race sailboats too ). I’ve been thinking it is
> heat related, but it could just as easily be time. When I tried to run
> autocross it started to play up after 10 or so seconds of full throttle
> (which I can’t do in my yard). On autocross it would pull like crazy, then
> go very flat, and then come back on, repeat. Your idea would do just that !
>     4) always worth a check, but it would have to be something that shows
> up only when hot.
>     5) yes, compression good. Between 220 and 225 for all, measured on
> crank with throttles open.
>
>
>        Thanks also to the other responses that I received, I didn’t cc all
> on my replies in order to reduce the clutter…
>
> Thank you,
>       Andrew Devenish
>
> Sent from my iPad
>
> On Aug 9, 2024, at 3:51 PM, Mike Harmuth <ofracer at gmail.com> wrote:
>
> 
> 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.
> <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
>>
>> http://www.fot-racing.com
>>
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