Help with PMO carb issue/set up

[VFR750]

Air correction jets control the top end of the mains. With 160 mains and 190 air correctors you may also be leaning out a lot at high rpm. That required some real data collection to nail down accurately. Not your described problem. But may be next.

I’m a Zenith guy, and PMO are different. But not really. Just their preference and subtle reactions to jet sizes.

It just seems you are too lean, and all the things you have fixed and cleaned up were the right things to do first.

Now that everything else is sorted, real tuning begins. And the persistence of the issue points to undersized jets.

[cabmandone]

Double check your idle jets. If you only sprayed them with carb cleaner you could still have some buildup in them. I think your issue is in the idle circuit since it cleans up when the mains come in under a load.

[andy s]

Jamie - I do not have fuel metering set up. I've only had the car a couple of weeks so I'm ust getting started with it (although I DO have a set of 50mm PMO EFI stiiing around and should just throw those on....LOL(

Mgatepi, I have not touched plugs or timing yet, but its on the list

VFR - Yea, its been in the high 30's low 40's up here. I don't want to tune it for these temps as I plan to run the car in the summer (hopefully 60's - 80's) . I agree that adding o2's will help and maybe I do in time, but i'd also be nice if I could get close so I'm more comfortable driving it now.... If you are at 60/61 and 160's do you think jumping to 60/165 will be enough?

btw, If you are a zenith guy, I may have a set or two kicking around....

Nick, I did double check idle jets but am happy to try a 3rd time to tripple check. Wilth the limited carb knowledge I have, I agree that I think its carb tuning in the idle side as the top end side felt good

best place to sort jets and stuff?

[cabmandone]

Andy,
If you don't have a wide band O2 to read AFR's I'd recommend you look into one. Have you pulled the plugs? They'll give you a decent indication of what the engine is doing. You might want to have a spare set of plugs on hand while tuning. You want the plug ends to have a brown almost chocolate milk color to them. White on the plug end is lean and black is too rich. I'd put a new set of plugs in, take the car out for a drive but stay out of the pedal. If you have some fairly flat roads, go out and drive it like you're trying to baby it so you're staying out of the main circuit. In some of the tests my brother and I did, we found his car runs primarily on the idle circuit until a load is introduced. We were running in the 50-60 mph range on the idle circuit if I recall correctly. Again, a wide band 02 would be a good investment. I'll try to ask my brother where he picked up jets for his car. He started out with a micro bit set and a pin vise and slowly made his jets bigger until he had it tuned the way he liked it.

[jjeffries]

Andy, I have a ColorTune I'd loan you. I'm in CT, could mail it.

[andy s]

Wow, thanks so much for the offer to mail it, but I'm thinking I'm gonna need one with all the stuff I have lying around..... Confirming plugs are 12mm on a 3.6, right?

[cabmandone]

The colortune is pretty cool and will get you in the ballpark. Personally I'd spend the money on a good wide band 02 with data logging. If you experience a hiccup you can plug in and see exactly what's going on real time.

[juanbenae]

Originally Posted by cabmando

Andy,
If you don't have a wide band O2 to read AFR's I'd recommend you look into one.


Again, a wide band 02 would be a good investment.

im with you cabman, but crickets from the OP on this suggestion we both provided.

a color tune is a great tool, but the AF meter will likely tell you if it is color tune ready. if it's not close the CT can only provide so much relief. I have one and only used in the past for the final adjustments after monitoring the AF meter to see where it's on & where it's off. then i jet accordingly to get it as close to good on both circuits and then use the CT if needed.


I rarely use the CT these days as the AF readings are where I want them to be and can make minor adjustments due to the fact im very familiar with what my motor and webers are telling me after a couple years of tinkering.

talk to me in three months when I take the car from sea level to 4000' and points greater when I relocate to the foothills and im crying in my hands. with the thinner air at that altitude im expecting it to require a full blown from jump re-set up with the AF gauge telling me what to address/correct. I'm expect to be a rich condition so getting the jetting/air-corrections and emulsion tubes in place with good AF readings I hope to not even need the CT. it is a pain to be removing plugs, installing the tool on six at operating temp cylinders. at least carbs provide good access to the plugs unlike other fuel delivery systems common to the 911.

[andy s]

Cab and Juan, not crickets, just slammed with running companies and other issues that can take me away from all the fun here....

I agree with you on the wide band and looked and found a double wide band Innovate double wide DLG-1 o2 kit, although I don't think it has logging.....

[VFR750]

I have two sensors. And it is interesting to see how much different the left and right can be. Never figured out why. Hence
60 on the left and 61 on the right

After doing a lot of logging and plotting data I got pretty good at predicting the sensitivity to small jet changes. Now I have my favorites and swap jets for the seasons. 165 mains in the cold weather 162 in the middle of the summer. 160 for summer with altitude (1500’ at watkins glen).

Helps to have extra jet holders. Swap is slowed by draining the fuel.

In 30-40 weather the engine will be very cold blooded. Part jetting, part fuel atomization in the cold, and no manual choke. Carb icing too!! Fun with carbs.

[andy s]

VFR, LOL, like I said above..... Why am I doing this when I can just bolt on efi.....Glutton for punishment..... Some days I think everyone who is defending "carbs or death" still runs a reel to reel for music and defends it..... LOL!!

[cabmandone]

Originally Posted by andy s

Cab and Juan, not crickets, just slammed with running companies and other issues that can take me away from all the fun here....

I agree with you on the wide band and looked and found a double wide band Innovate double wide DLG-1 o2 kit, although I don't think it has logging.....

There was no complaint from me! I totally get it.

I think this one can take information from two sensors and it has data logging capability. I put a permanent mount setup in my car made by 14point7 that connects to my laptop using Winlog which is a bit clunky but once I figured it out it's pretty decent. I wish I had gone hand held since I like to tinker with other engines and can't just take my setup out of my car.

https://www.innovatemotorsports.com/products/lm2.php

Some here have mentioned putting a single bung in the muffler to read the AFR from both banks

[juanbenae]

hope i didn't sound like i was complaining.. my girl is the only one complaining over here...

do your 3.6 headers already have 02 sensor bungs that have been plugged with the carb install? AEM makes a reasonably priced 02 sensor/gauge/sensor/11'harness that is invaluable. ive got bungs in both my SSI's collectors that i swap the sensor & plug from bank to bank a couple times a year to look in on each bank independently while i drive it. i bought a second sensor and harness that ive installed during tuning and simply switched the harness from in a minute or two left to right during tuning efforts at the tunnel coupler the unit comes with.


im not familiar with carbing a 3.6. do you keep any of the ECU stuff from the motor? does it take multiple MSD type ignition and coils with the twin plug set up?


monitoring carbs in the muffler is a stretch.

[VFR750]

No reel to reel here. But that would be a cool toy.

Carbs are old but interesting. Certainly robust in the most basic way, but fiddly. Once you know what they want life gets easier. Actually once set up, a little rich, they will run without too much else.

I would love EFI. And tuning would be a new adventure. But it’s a done deal. No need to change. My personal niche in the Porsche world is set.

[andy s]

I don't have o2 bungs in, but its easy enough as I have a mig... I'm gonna order stuff in the next day or so, but I am still intersted in trying to retune the set up by ear and syncrometer again, which I plan to do this weekend if the 60's and 165's come in and my employees don't implode...

If I have time, i will also try to really go back and detail step by step everything you all have suggested for posterity.

Also, as some point, I'd like to get back to the original point of this thread which was to detail each step to take off, fully clean up, reinstall and double check jetting for someone like me who has a set of carbs already, but they are old and dirty. All this other stuff is awesome info, but is based on putting on new stuff.

VFR, clearly I'm much older than you, cause I came from the era where reel to reel was cool.... but then again, so were 8 tracks and mullets.... Some things we should never go back to.... Add skinny jeans, Smedium tee shirts and male hairbuns to that list while we are at it.

[andy s]

Juan, this motor has dual MSD boxes

[juanbenae]

im going to quit trying to drive from the back seat then.... I do look forward to this tale growing longer while I continue to look in.


AND nobody is older than VFR.....

[andy s]

LOl, not Jaun I apprecite any and all questions as it is both a learning too which I need and I reminds me to double and tripple check everything... I'm confident its a tuning issue and you and the forum will help me figure it out.

[Gordo2]

Andy,

Sounds like you are well on your way with some great advice from other's with considerable experience here on the board.

Here's my 2¢...
- If you are reasonably confident that the previous owner had it running well with the jetting, don't feel compelled to start changing them. I assume you are running the same ignition and exhaust, otherwise all bets are off, and you may need to change some jets. If completely the same (ignition, exhaust etc.), focus on figuring out what's causing the engine to run differently than it did previously.

- Agree on installing a wideband. Everything else is just guessing for those who can't close their eyes, listen, sniff, observe a spark plug and apply their old school magic / skills to tune (there are some out there who still have those skills - but they are getting rare...). I lacked old school skills, therefore opted for the wideband / scientific approach, but it too requires a learning curver.

- Keep in mind that ensuring that the ignition is working correctly is equally as important as ensuring that the carbs are properly config'd and tuned.

Here's some info that may help in cleaning and tuning: http://forums.pelicanparts.com/911-engine-rebuilding-forum/821976-gordos-pmo-carb-tuning.html

Your primary issue sounds like it's associated with idle to main transition - which can be challenging to get just right. Stick to it and you will find the zen.

I love my PMO's for all the reasons I went that way instead of EFI - stick to it, learn them inside and out, and I'm confident you will feel the same.

Good luck, Gordo

BTW, I also have a Colortune that I've used a few times. With the Colortune, I've found that adjusting the idle mixture to get at the edge of a white to blue flame (lean best) leaves my mixture slightly too lean - leading to hesitation at idle to main transition. Meanwhile, if I go slightly richer (1/4 - 1/2 additional opening of the idle mixture screw after lean best), I still get a nice blue flame and it runs slightly richer - but smooth. I've adjusted the mixture many times by ear, and have found I can get a more consistent mixture across each carb using the Colortune - making the engine run noticeably smoother.

[Walt Fricke]

VFR - sounds like you have Webers. That's my 911 experience also (other than CIS, and I now have EFI). I had three sets of main jet holders, a miscellany of plastic cups, and the rags always got use. Great fun with a hot engine. But I had a 2 barrel Delorto on a VW 1775 beetle, and sure liked the stacked main/emulsion/AC. No spilled fuel. Which is how the PMOs are set up, right?