32/36 tuning guide?

[18Fiatsandcounting]

Engine compression testing today yielded the following:

PSI No throttle. WOT
1. 155. 160
2. 154. 160
3. 140. 148
4. 154. 157

Not sure what's going on with cylinder 3, but they all seem good and not too high based off what I've read.

I agree that these numbers don't see too high. In fact, they seemed a little low to me, but then I seem to recall you're at 6000 feet elevation, right? If that's correct, your air pressure is around 80% of sea level, so would that make a difference or is it all relative?

At sea level, here's what I would expect for compression for the Fiat twin cam:
Below 110 psi: something's wrong
Below 130: weak
130 to 150: OK, but a tired engine
150 to 180: Good
Above 180: Getting pretty high, could be issues with detonation depending on the rest of the engine.

-Bryan

[Nut124]

If Bryan is correct, your sea level corrected cranking compression would be about 200 psig. I did see a chart that showed a 0.915 correction factor for 3000 ft elevation. The chart did not go any higher.

[18Fiatsandcounting]

I did see a chart that showed a 0.915 correction factor for 3000 ft elevation.

Sea level is 14.7 psia, and it's 11.8 psia at 6000 feet. So, if I'm thinking about this correctly, the listed compressions would be 190 to 200 psi on a similar test done at sea level. Definitely on the high side but should be workable.

My dad did a compression test when my '69 spider was fairly new and wrote the numbers on the inside back cover of the owner's manual (which I still have). 185 to 190 psi, and this was a stock 1438cc engine with 8.9 CR, and we lived about 1000 feet above sea level. I vaguely remember that he always added oil when doing a compression test, so that could explain why the numbers are higher than the 170 or so that I would have expected.

-Bryan

[Nut124]

Cranking compression is affected by static CR and cam timing. Your 1438 likely had a short duration, stock cam. These have early IVC and crank higher than performance cams.

I seem to recall that Jon8Christine has a performance cam, the 40/80 or the 42/82. A cranking compression that high with a performance cam would point to either a very high static CR or the IN cam timing being off, advanced.

[jon8christine]

I'm still struggling to get my 1800 running well after building the engine. This is what I've done so far:

- Got the timing set to about 36-37 deg btdc @ 4,000 rpm (need to recheck this after 'running' the car for a couple months now)
- Adjusted the choke screw and spring so it would keep the choke closed longer and let it warm up. Still need to play with this. The car starts right up cold after one tap of the gas to initially set the choke, but then tries to die if you don't keep your foot on a little gas for roughly 3 minutes while it's warming up. After it's warm it idles nicely at 900-1,000 rpm. Idle screw is about 1-1/4 turns in.
- Left the stock jetting 60 pri idle, 50 sec idle, 137 pri fuel, 140 sec fuel, 165 pri air, 160 sec air in
- Once it had warmed up a little it happily revved to 4,000 and was pretty responsive in the driveway so I took it out. While driving it I was disappointed in the engine power and throttle response. It felt like the same old worn out engine it felt like before I had thrown $4,000 into it and still had to downshift up small hills. Made it halfway around our small town and it died and would not restart. Engine temps were normal (170-180ish). It must have cooled down enough while I was checking everything as it later restarted and drive home just fine. Over the course of driving it a few times over the next few weeks this repeated, dying when it got hot, but I was sometimes able to restart it by flooring the gas pedal. Having double checked everything, the one thing hanging out there was the Redline Weber manual says you can't have over 3 psi fuel pressure for these 32/36 carbs.
- I was at 4.5 psi fuel pressure engine off and roughly 4.1 at idle, so I bought a Jegs 1-4 regulator and set it to 2.7 at idle. Drove the car around town and what do you know I made two laps just fine and that seemed to fix the issue, but the car still didn't have the power I expected after building the engine, so after some reading and research I figured I need to start jetting the carb.
- To get that right I needed an air fuel mixture gauge, so I installed an AEM afr just after the 4-2-1 collects all together. With the stock jetting I was running rich (10-11) when cold and warming up, and then it leaned up to 13 +/- for the first few minutes driving around town, but once the engine was hot it went very lean (16+) so I took it home.
- After some reading on high altitude jetting someone on a VW forum recommended 45 pri idle, 55 sec idle, 125 pri fuel, 175 sec fuel, 165 pri air, 190 sec air as a starting point at high altitude (I'm at 6,000'). With that setup the car had much more power (buttometer) and was much more responsive around town. Cool, now I'm happier about the $$ put into this old car, but after 5-10 minutes on the interstate for the first time, the AFR spikes lean again and she starts running rough. I think it feels like it's just not quite getting enough fuel. I limped it surging slightly to the exit (60 mph) and shut it down to cool off as the problem seemed to happen once it got hot under the hood. Coolant temp was good. As I was sitting there I was thinking it felt the same as when I took it to the autocross and it wanted to die after a few laps and was hot before I built the engine, but after I had swapped to the 32/36 carb. Never had this problem with the original 32adfa carb. Maybe it's this carb. After it cooled down a bit it started up (still had to floor it) and I ran my errands in the next town over, but it started running rough halfway and then died as I got back into town (12 miles) off the interstate. Cooled down and then drove home fine.
- I have since swapped to a 55 pri idle and 145 pri fuel jet trying to correct the lean when hot condition, but that was just shooting in the dark and didn't help, so I put my fuel gauge back on with a long enough hose to run it into the cockpit and took a run. I still had 2.7 psi at startup and it stayed there +/- 0.2 as it warmed up and I started my trip around town. As I started on a highway and the engine got hotter and went lean it was still between 2.1 and 2.5 psi varying a little on acceleration. I guess I don't know how low is too low to start causing issues.? At one point it dropped to 1.6 for a split second, but was above 2 for the most part as it started to run rough and lose power / surge as I headed home.

So now I'm stuck. Pulled #1 spark plug and it seems to verify the afr. Black carbon around the outside from running rich at startup and tan middle from running lean, but I'm no spark plug palm reader.

https://drive.google.com/file/d/1Y_CWWD ... p=drivesdk

https://drive.google.com/file/d/1Y_H-2X ... p=drivesdk

I'll break out the timing light again and recheck that. Do I need to bump fuel pressure up just a little to get to 3 exactly? It's been a several months but the last time I pulled the new fuel filter it was fine. I checked the float when I installed it, but it may be worth reviewing that to make sure I'm not starving it for fuel, which is what it seems like. I'm about ready to put my old 32 adfa back on to rule out something other than the carb or go back to the low power original jetting and get it on the interstate to rule that out. Help please

[Nut124]

What kind of a fuel pump do you have?

Note that ignition problems can read lean when un burned fix with oxygen hits the sensor. Lean has a particular harsh, sharp exhaust note whereas rick is round and softer.

[jon8christine]

Had to take my sound insulation off to check. It's a Mr. Gasket #12S.

[Nut124]

That pump, if in spec should be OK.

To try to figure out the problem, fuel or spark, try to me methodical:
- Quick WOT pulls thru the gears, up to as fast as you can sanely handle. Does the engine pull hard beyond 6500/90mph? I would do this on a quiet interstate upon entry. What does the AFR show?
A quick run WOT thru 1st, 2nd and 3rd will validate top end jetting.
- Uphill highway, long slow WOT pull. This will validate max fuel delivery under sustained max HP pull.

There are three possible issues likely, I think:
- Jetting, going lean at top end
- Fuel delivery, bowl going empty
- Ignition problems

Need to sort it out.

When these engines run well, they are sweet!.

[jon8christine]

Spent the day yesterday testing, tuning and driving.
Timing is still at 36 deg @ 4,000 rpm, so I left it.
Ended up with 60/55 idles, 145/155 mains and haven't messed with the air jets yet 165/190
The fuel float was at 17mm and only had roughly 1mm travel, so I tweaked it to 18 and 2mm travel per the manual
I increase fuel pressure at the regulator to 3.5 psi
Readjusted the mixture screw and ended up at 1 turn out

Driving through town afr was 11-12 at 2,500 rpm, and 12-13 at 3,500
On the first long wide open pull on the highway it pulled hard to 5,000rpm and started sputtering at 5,500. Looking down, fuel pressure was down to 1.5. afr was all over the place. After sitting in the driveway for a few minutes making some notes I started it back up and fuel pressure was right back to 3.5, after being low all the way home through town and afr was in the high 13s after being spiked lean on the way home.

The common theme during all the tuning seems to be fuel pressure below 1.5-2 seems to produce the lean condition and sputterng/loss of power. This happens after driving for 5-10 or so minutes, depending on how hot the engine was to start with. This did not happen with the original 32adfa carb. Drove it 180 miles from Utah to Wyoming when I bought it with no issues. This loss of power and sputtering and even dying issue was happening at the auto cross before I built the engine when it got hot, so is it a vaporlock issue or a fuel pump issue? If I pinch off the fuel return line at idle fuel pressure jumps about 1.5, but I haven't tried running that way.

What fuel pump are you guys running? Racetep.com recommended the Carter 4070

[18Fiatsandcounting]

The common theme during all the tuning seems to be fuel pressure below 1.5-2 seems to produce the lean condition and sputterng/loss of power. This happens after driving for 5-10 or so minutes, depending on how hot the engine was to start with.

I believe Nut124 is on vacation for a couple weeks, so you're stuck with me.

It does sound like a fuel starvation issue. Vapor lock is not common on Fiat spiders, but you are at 6000' elevation and it might be really hot where you are. Vapor lock can happen, but I'm not thinking this is the issue. I've only seen it once on my spider (mechanical fuel pump) when I was climbing the mountain pass from Death Valley and it was 5000' and around 120 degrees outside. Editorial comment: It was insanely hot, and this is one of the stupider things that I've done....

Couple things:
1. The float travel should be more than 1 or 2mm. Going by memory here, but I thought the total float drop (distance between needle valve closure and the float hanging down) should be more like 8mm or so. I'd check that spec again, against what you have.

2. Any chance the fuel line from the tank is partially plugged? Plugged metal screen on the end of the pickup tube in the tank, or a fuel filter somewhere that's clogged? If fuel is moving fast enough from the pickup tube up to where you are measuring the pressure, the fuel pressure should not drop very much under WOT. Could be a restriction, or maybe your pump just isn't up to snuff?

-Bryan

[jon8christine]

Thanks Bryan, the 2mm travel is at the needle, float is much more. The rubber fuel lines are newish, but I'll pull the line and run fuel into a gas can see if there's any apparent restrictions. I did order a new Carter pump to rule that out.

[18Fiatsandcounting]

Sounds good. Check that there's not a small air leak between the pump and the tank. Even if it's not big enough to leak gas, it can prevent the pump from pulling as well as it should.

Also pull the pickup line / sending unit in the tank and make sure it's not clogged. Be careful removing those 6 tiny nuts as they're easy to strip. Or drop into the tank...

One other thought: Any chance your tank is building up a slight vacuum when you're pulling lots of fuel out of it? It could lead to fuel starvation at WOT. Try loosening the gas cap and see if that helps at all.

-Bryan

[jon8christine]

Thanks for the suggestions.

The fuel pump feed line is good, no air leaks.
Pulled the line at the carb and ran a quick test... roughly 24 gal per hour from the pump with no bubbles or surging.
Pulled the intake/ sender from the tank and there was no screen, just a 1/4" metal line that did have a little junk in the end, but nothing like, holy cow that's my smoking gun, and a plastic return tube.
Cleaned it out and retested anyway and got about 27 gal per hour, which is significantly less than the 60 gal per hour the Carter pump is rated at, but it still seems like plenty (I think it's only consuming 10 at WOT) and I can't see that being the problem, but will swap it anyway for $60.
I'll make a run with the gas cap cracked to see if that helps in the meantime...

[jon8christine]

Well I would have never guessed, but replacing the fuel pump with the Carter 4070 seems to have fixed the issues with my 32 / 36 setup. It's also a perfect fit in the trunk. Two of the mounting bracket holes lined up perfectly with two studs, just had to buy two rubber grommets for sound isolation and that made for a nice quiet pump.

https://drive.google.com/file/d/1ZwtXvQ ... p=drivesdk

I timed this new pump and it produced about 47 gal per hour, so significantly more than the old Mr. Gasket. Once I fired up the engine I was concerned that I was seeing 6psi (my literature reading says Webers want 3 and maybe up to 4psi fuel pressure), but it was running fine. I tried adjusting my Jegs 1-4 regulator, but it wouldn't really do anything. Cranked the screw all the way out, nothing. Cranked it all the way in, very little response... Still 6 psi. This fuel pump was supposed to be self regulating to 4 psi...

Took it for a drive and my first reaction through town was, my engine just woke up and has more power, enough to notice and push me back in the seat like a modern car. Acceleration from about 2,700 to 4,000 where I shifted was very good. As I drove through town I looked down and my AFR gauge was pegged rich at 10. It was reading 14 when idling and warming up. Hmmm, my jetting / tuning is probably all messed up as it wasn't getting enough fuel before... either that or fuel's now pushing past the float, but at idle at the stop sign it bounced lean and idles normal and didn't seem like that.

I headed up the hill to the highway and it pulled hard to just past 4,000, then not as hard up to 5,500 where I shifted. Took it down the highway 8 or 9 miles and it still read rich, AFR at 10 the whole way. Fuel pressure never dropped below 2.7 and was steady. 75 mph was about 4,000 rpm and it didn't want to pull past that very well... Could only hit 80 going down a hill, but no surging or fuel starvation issues. After about 8 miles the AFR gauge spiked to - - -, which is lean for it I think, but after I got to the overlook to turn around and take some notes it didn't come back on at all when I started the engine back up. Can running rich burn them out / plug the oxygen sensor?

Anyway, car started right up and ran well all the way home with no stumbles. I'm pretty sure it was running rich as my fuel gauge noticeably dropped on that short drive. Very happy, now just need to go back to jetting and fix it up right, I think...

[70spider]

I know this thread is a year old but I thought I would bump it.
NUT124 you said

Assuming your SCR is on the high side, I would try to avoid running any lean as it will increase cylinder temps. I hear these engines make best power at 12.5 AFR. I do not like to see anything above 13.5 at load for fear of detonation. At low speed cruising I will be OK with 11-13 AFT.

Why so rich? Detonation? According to "science" 14.7:1 is ideal.
I have been trying to dial in my carb for my 1438 so I installed a wideband O2 sensor gauge. With that in mind these are my numbers: Idle - 13.20, 2000 rpms 14.1, 3000 rpms 14.50, 4000rpms 16.8, 5000 rpms 14.50. These readings were taken in the driveway, not under load. I know my 4000 rpm number is high so I was going to increase the secondary main by 1. So are these to high? Should I richen up the jets and get hotter plugs, so I don't foul them?