[Fot] Fuel issue

Thu Aug 15 10:09:03 MDT 2024

 Excellent point Jason, we had that problem with a TR-4 on the dyno a few years ago.
Re distributors in general, I favor optical units strictly for reliability but in reality, conventional points are OK for any of our 4-cylinders up to 8k, it's all about dwell/saturation time.The 45D type Lucas is a good unit to work with, it has an asymmetrical cam for increased dwell, & wide separation between the contacts to prevent x-firing.Of course it has to be setup with whatever curve is needed, & good points & condensers, but all's very reliable & easy to troubleshoot if necessary.
Glen Efinger

    On Thursday, August 15, 2024 at 10:48:28 AM EDT, JS Performance Motoring, LLC via Fot <fot at autox.team.net> wrote:   

 Andrew,           One further thought: If your engine is misfiring when your wideband O2 reads lean, it's quite likely you are seeing a false lean reading due to the unburned oxygen in the exhaust gas stream related to the misfire, and not due to an actual air/fuel mixture issue.

Jason SukeyJS Performance Motoring, LLC
440.984.7720jason at jsperformancemotoring.com
https://www.facebook.com/JSPerformanceMotoring/

On Wed, Aug 14, 2024 at 4:09 PM Andrew Devenish via Fot <fot at autox.team.net> wrote:

I thought an update might be in order.Thank you for all the suggestions and ideas. Spoiler - still not fixed.I have removed and cleaned out the bowl/jet lines, the front had black debris, but I don’t think it was enough to block the line, and it did not fix the problem.Fuel pump. I have checked pressure and delivery from the pump, all is well. I have now changed to a smaller capacity positive displacement design as there was concern over interaction of the internal and external pressure regulators. Still not fixed.Could not find any vacuum leak. I’ve had the manifolds off and back on since this issue has been around with no change. 
A couple of replies were pretty confident that I have an ignition vs fuel issue. As I can’t find any fuel issue, I now suspect they may be right. I run Petronix ignitor 1149 with their coil 40611. This is the correct 3ohm set up per Pertronix. I purchased a new coil from Amazon - but the replacement coil was defective and had a misfire from the start which I could ABA with the old coil. Talking with Pertronix the were concerned my new part was not theirs, and maybe a cheap copy - I returned to Amazon, now waiting on a coil from Pertronix direct.As I’m playing with ignition now, what are you guys using for signal and for coil with good success ? Thank you for the advice and support - it will be sorted.
Thank you,       Andrew Devenish
Sent from my iPad

On Aug 9, 2024, at 5:10 PM, Andrew Devenish <gt6racer at msn.com> 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

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