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<div dir="ltr">Thanks for all the thoughts. </div>
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<div>It seems we have a common theme that there can be some issues with Pertronix parts. </div>
<div>I think a return to basics might be helpful and so I am going to throw in the points and std coil to see if it fixes it. I’m just running around the yard to test and race conditions are a different case, but if it improves at least I know I am on the right
path. Assuming it does then on to selecting a replacement system. On my GT6 I had great luck with an optical pickup and Crane gold coil, but I think those parts are long gone. </div>
<div>Jason, great point on the O2 reading, and obvious now I think about it ! I was suspecting carb issues and so jumped to lean is not enough fuel !</div>
<div>One day I should write a book about this little adventure as I have had some weird things going on, like chasing timing that would become retarded by 15 degrees after each run.. Luckily I’m retired and no critical goals with the car, and so if it doesn’t
go right I can drop it and come back another day. </div>
<div>I will keep you posted..</div>
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<div dir="ltr">Thank you,
<div> Andrew Devenish</div>
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<div>Sent from my iPad</div>
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<blockquote type="cite">On Aug 15, 2024, at 9:38 AM, JS Performance Motoring, LLC <jason@jsperformancemotoring.com> wrote:<br>
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<div dir="ltr">Andrew,
<div> One further thought: </div>
<div>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.</div>
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<div>Jason Sukey</div>
<div><span></span><span></span>JS Performance Motoring, LLC<br>
</div>
<div>440.984.7720</div>
<div><a href="mailto:jason@jsperformancemotoring.com" target="_blank">jason@jsperformancemotoring.com</a><br>
</div>
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<div dir="ltr" class="gmail_attr">On Wed, Aug 14, 2024 at 4:09 PM Andrew Devenish via Fot <<a href="mailto:fot@autox.team.net">fot@autox.team.net</a>> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="auto">I thought an update might be in order.
<div>Thank you for all the suggestions and ideas. Spoiler - still not fixed.</div>
<div>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.</div>
<div>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.</div>
<div>Could not find any vacuum leak. I’ve had the manifolds off and back on since this issue has been around with no change. </div>
<div><br>
</div>
<div>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.</div>
<div> 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.</div>
<div>As I’m playing with ignition now, what are you guys using for signal and for coil with good success ? </div>
<div>Thank you for the advice and support - it will be sorted.</div>
<div><br id="m_-8551889879533404988lineBreakAtBeginningOfSignature">
<div dir="ltr">Thank you,
<div> Andrew Devenish</div>
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<div>Sent from my iPad</div>
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<blockquote type="cite">On Aug 9, 2024, at 5:10 PM, Andrew Devenish <<a href="mailto:gt6racer@msn.com" target="_blank">gt6racer@msn.com</a>> wrote:<br>
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<div dir="ltr"> Hi Mike,
<div> 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). </div>
<div> 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 😁.</div>
<div> 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”.</div>
<div> 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.</div>
<div>I had checked both the Summit and now the solenoid pump for flow, there is plenty. </div>
<div> As I noted the float bowls are full when it quits running.</div>
<div> 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 ! </div>
<div> 4) always worth a check, but it would have to be something that shows up only when hot. </div>
<div> 5) yes, compression good. Between 220 and 225 for all, measured on crank with throttles open.</div>
<div><br>
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<div> </div>
<div> Thanks also to the other responses that I received, I didn’t cc all on my replies in order to reduce the clutter…</div>
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<div dir="ltr">Thank you,
<div> Andrew Devenish</div>
<div>
<div><br>
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<div>Sent from my iPad</div>
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<blockquote type="cite">On Aug 9, 2024, at 3:51 PM, Mike Harmuth <<a href="mailto:ofracer@gmail.com" target="_blank">ofracer@gmail.com</a>> wrote:<br>
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<div dir="ltr">Hi Andrew, a couple of things to check.
<div>1st, is this a new problem? if so, what did you touch last?</div>
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<div>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.</div>
<div>link to flow and fuel requirements chart <a href="https://historicracinggroup.com/resources/Reference_Material/Canton/Fuel%20Consumption%20and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf" originalsrc="https://historicracinggroup.com/resources/Reference_Material/Canton/Fuel%20Consumption%20and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf" shash="lstQPA6fRu3zdXoF83OwbJ38QlQM9dE1AgtftD/yLJ++QyBo+qGEPtDFl7pDeUNaDvF1p04Q5WFANGJxCAeM3mcYzi5hMR+mFGFya6SfDWbmWVf8Lrfyxbaka6Yasr2yN0N0hRv/lrRb4NfC4FZA9if5B4RpirWV3R4l2iJW0I8=" target="_blank">https://historicracinggroup.com/resources/Reference_Material/Canton/Fuel%20Consumption%20and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf</a></div>
<div><br>
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<div>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.</div>
<div>
<div><IMG_20240630_112925914.jpg></div>
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<div><br>
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<div>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.<br>
</div>
<div><br>
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<div>5. Compression check- Are all the cylinders within 5-10% of each other?</div>
<div><br>
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<div>Happy hunting</div>
<div><br>
</div>
<div>mike h</div>
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<div dir="ltr" class="gmail_attr">On Fri, Aug 9, 2024 at 3:03 PM Andrew Devenish via Fot <<a href="mailto:fot@autox.team.net" target="_blank">fot@autox.team.net</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
Guys, <br>
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.
<br>
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.<br>
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.
<br>
I have wrapped headers and a heat shield around the carbs but they do still get hot.<br>
<br>
Any ideas ? Thinking to try some less volatile fuel as it seems heat related and the Sunoco evaporates so fast !<br>
<br>
<br>
Thank you, <br>
Andrew Devenish<br>
<br>
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