Diagnosis

[pemz0r]

I need some help diagnosing this. If you watch video you can hear that the engine sounds healthy in straight and right before the turn, but after the turn it's gutless. It happens every time the car gets over 200 degress. 2.7E with webers.

What causes this and how can I fix it, because it's getting annoying.

https://www.youtube.com/watch?v=SU4B1SVPLpw

[lvporschepilot]

When did it start doing this? Have you messed with the carbs or ignition timing lately? Any other changes recently made?

[pemz0r]

I haven't changed anything but I have never driven the car this hard for this long before.

The car runs good at 180/200 degrees but once it gets up to 210/220 degrees it experiences loss of power.

I could do 1.5 laps then come into the pits and let car cool and go back out again and do another 1.5 laps.

[pors1968]

Do you have carb insolator.

[pemz0r]

Yes, I do.

[lvporschepilot]

Sounds like a fuel heat issue. Fuel getting so hot in the bowls that it changes the mixture when it goes to emulsify. I do not have any further solution for that issue. I see it on 512 Boxer Ferrari's, the ones that are rarely driven hard that is. Try bumping the main jet size by one or reduce the air corrector size a couple sizes. Not sure if you have hooked up a wide band to it or not but they are very helpful

[pemz0r]

That's what some buddies and I were thinking, sorta like vapor lock? I'll look into a wide band.

in the meantime I posted a full video of the entire session for more data.

https://www.youtube.com/watch?v=xJm_PylH4uE

1:22 min - Squirrel
2:47 min - first sign of issue
3:09 min - yells at car
4:52 min - cooling in the pits
6:15 min - Sings "I dont understand why you do this to me car"
8:47 min - back on the track
11:38 min - car shows sign of issue

[Trackrash]

My car goes lean when hot. HOWEVER when you are driving on the track with all that air going through the carbs, I can't believe the carbs are getting hot. Heat soak of the carbs occurs, at least on my car, after I park.

You may want to play with your float levels. I have found that with mine set at the low end of the spec, mine don't have a problem on the track. If set on the high end of spec my motor will go down on three cylinders in a turn.

Another possibility is one or more floats may be hanging up or are loose on the shaft causing the needle and seat to leak in turns when the floats move around.

[pemz0r]

Thanks Trackrash.

I was experiencing this same issue during some auto x as well, so I decided raised the float level because I thought I was running out of fuel in the bowls.

https://www.youtube.com/watch?v=P6lzGR80Fnc (0:41 seconds the issue starts again)

I will set my float level on the lower side and see if there's any changes. I am still stuck on that it only happens when the car gets hot. That auto x run was my 3rd run and that's when I started experiencing it, the first two runs had no issues at all.

Ill check the floats/needles again.

[Walt Fricke]

I once had 40s on a 2.3 motor, and it stumbled coming out of corners. I cranked the acceleration pump volume down to very little, and that solved it. Otherwise the AFR, per the EGT readings, was pretty much right on.

Might not be your issue at all, but I was amazed at how little a squirt was needed. The 46s on a 2.7 were the same.

But in my case, after the cornering influence was gone in some feet, the engine picked up and ran as usual until the next hard corner.

[ed mayo]

Originally Posted by pemz0r

Thanks Trackrash.

I was experiencing this same issue during some auto x as well, so I decided raised the float level because I thought I was running out of fuel in the bowls.

https://www.youtube.com/watch?v=P6lzGR80Fnc (0:41 seconds the issue starts again)

I will set my float level on the lower side and see if there's any changes. I am still stuck on that it only happens when the car gets hot. That auto x run was my 3rd run and that's when I started experiencing it, the first two runs had no issues at all.

Ill check the floats/needles again.

I assume you're running Solex p-40's? You may need float bowl baffles, if you don't already have them?

[pemz0r]

Originally Posted by ed mayo

I assume you're running Solex p-40's? You may need float bowl baffles, if you don't already have them?

I am running Webers IDA3C with baffles already installed inside the bowls on a six cylinder.

[pemz0r]

Originally Posted by Walt Fricke

I once had 40s on a 2.3 motor, and it stumbled coming out of corners. I cranked the acceleration pump volume down to very little, and that solved it. Otherwise the AFR, per the EGT readings, was pretty much right on.

Might not be your issue at all, but I was amazed at how little a squirt was needed. The 46s on a 2.7 were the same.

But in my case, after the cornering influence was gone in some feet, the engine picked up and ran as usual until the next hard corner.

The issue keeps happening in the straights too.

[Lapkritis]

Fuel pump/base pressure adjustment shouldn't be forgotten. A higher flow rate pump designed for low operating pressure may also help.

Sent from my SM-N960U using Tapatalk

[Trackrash]

Originally Posted by pemz0r

The issue keeps happening in the straights too.

That does sound like a supply issue.

An AF gauge may give you an idea of which direction to look, depending if you are going lean or rich.

[Lapkritis]

Heat related makes me think it could be a tired fuel pump. Output drops as the fuel pump heats up. Mix in a corner or heavy breaking and a bowl that isn't filling fast enough...

Sent from my SM-N960U using Tapatalk

[ed mayo]

My mistake for thinking you had a 912, hence the Solexs. I had and solved a similar problem with my 67S in autocross situations, but it was not heat or time related.It may not be so much heat related as it is time on track related. Your in tank filter may be partially clogged which gets worse the longer its driven hard. Which is why a short rest stop lets the engine work well again for a short time.

[pemz0r]

Can cold or hot plugs make that sort of difference?

I am using DENSO IW22 Spark Plugs and I can't find if they are cold or hot.

[dannobee]

A 22 is the same as an NGK 7 or Bosch 5 WRT heat range. A 24 would be colder.

I'd check fuel flow first. And list the details of the car/build. Electric or mechanical fuel pump? Steel gas tank or fuel cell? When was the fuel filter last changed? And OEM fuel filter or aftermarket? Any kinks in the fuel hoses?

[pemz0r]

Originally Posted by dannobee

A 22 is the same as an NGK 7 or Bosch 5 WRT heat range. A 24 would be colder.

I'd check fuel flow first. And list the details of the car/build. Electric or mechanical fuel pump? Steel gas tank or fuel cell? When was the fuel filter last changed? And OEM fuel filter or aftermarket? Any kinks in the fuel hoses?

65 912 with 74 Mag Case - 2.7 E Cam 9.5:1 Webers.
Electric Pump
Original Steel Gas Tank
I have 3 fuel filters, one big canister one and two solid states right before the PMO fuel bars. It's been around 3 years and 6500 miles since I changed them. No kinks.