PMO conversion, it's done...almost

[jtkkz]

very nice andy , you will love the sound..

I rebuilt my motor off my '74 carrera and went with PMO's as well

[oregonmon]

Very nice.

[911Freak]

Originally Posted by TWork

If the car you want to put them on is the one listed in your sig, then you're out of luck. Post-75 cars in CA are required to have the standard emissions equipment which were on the car as it was originally manufactured -- unless you upgrade the motor to that of a newer car. In that case, you have to have the smog equipment that is standard for that newer motor.

Thanks guys....That sucks, but I was afraid of that...reality bites sometimes in Ca sometimes.....

[RoninLB]

Originally Posted by ael911

I hope my 135 mains aren't too lean, but I trust Richard's judgement and I will eventually have a reputable shop double check them for me. Thanks for the advice JP911

My 135 mains are correct.

[RoninLB]

Originally Posted by Steve@Rennsport

We dyno each and every carburetor conversion (new engine or not) to ensure that the AFR's are correct and anyone doing or contemplating such things should NOT skip this critical step.

the finer adjustment becomes the more some kind of air/fuel measurement becomes necessary.

without measuring default seems to be on the rich side. Rich = cold combustion = lower power.

[ael911]

I am happy to report the PMOs are alive and the experience is a blast. Much better throttle response and the sounds are just heavenly. I did have a hiccup during the install as I found out my fuel pressure would not go any lower than 9 pounds no matter how I tried to adjust the PMO regulator. After consulting with Steve Weiner and Richard Parr, they both believed I had a kink in the return line. My options were to find the small kink, or replace the fuel pump with a lower pressure pump and re-plumb new fuel lines. Both of these options are very labor intensive jobs.

Well, my neighbor and fellow pelicanite came to the rescue. He believed the CIS pump just puts out way too much volume. The combination of the high flow volume and the resistance in the fuel hose due to natural bends and hose diameter creates the pressure to 9 pounds.

The aerospace engineer in him devised a plan to connect the flow and return line together through a ball valve. The idea of the ball valve is to be able to regulate the intake pressure as it comes in from the pump if necessary. A normal T fitting would work as well. Then plumb another line from the flow/return loop and connect a diaphragm regulator to it so the 9 pounds of pressure can be dialed down to an acceptable 3.5 pounds. From the regulator, the flow is fed into the PMO regulator and diverted out to the carbs. The return side of the PMO fuel block is plugged up as it is no longer used.

The idea was simple and it worked. We were then able to tune the carbs and get them synced up without the 9 pounds of pressure sinking the floats. I am now a very happy man and I hope this trick will help others who encounter excessive high pressures when converting from CIS to PMOs.

I also cut out some thick lexan for air filter covers. I think the beautiful venturies are too nice to be covered up under the metal rainshields.

[JTO]

Nice job Andrew! Have fun.
Troy

[JP911]

Congrats! I had the same issues with a kinked line. It made me nuts. I ended up using 2 regulators until I could replace the fuel lines.

[OZCarrera3]

Great work Andrew, I agree those PMO inlet trumpets need to be able to be seen!

So how do they drive? I was looking at getting these when I was having CIS problems a while back. Do they drive as smoothly as a good CIS, without snatchiness and hiccups on the on/off throttle changes and constant throttle?

[jittsl]

I have a quick question for those with PMOs. My Supertec built, PMO equipt 2.4 "S" spec runs beautifully when warm but is a beast to start. Usually requires several pumps of throttle get her to even fire and then it often stalls and requires me repeat the process. I realize there is no cold start setup and so I expect her to be a little hard to start but this is beyond a little hard. Does everybody else have the same issue?

Thanks in advance,

Laurie

[Steve@Rennsport]

Originally Posted by jittsl

I have a quick question for those with PMOs. My Supertec built, PMO equipt 2.4 "S" spec runs beautifully when warm but is a beast to start. Usually requires several pumps of throttle get her to even fire and then it often stalls and requires me repeat the process. I realize there is no cold start setup and so I expect her to be a little hard to start but this is beyond a little hard. Does everybody else have the same issue?

Thanks in advance,

Laurie

Hi Laurie,

Although you might speak to Henry about such things since he built your engine, I can tell you that these cars can be difficult to start if there is an issue with:

1) Low fuel pressure

2) Low float levels

3) Wrong idle jets

4) Incorrect starting procedures.

Properly set up & adjusted carbs should start right up from cold with a few pumps and only require some footwork to keep running for a few minutes before setting down to a sustaining idle. A hand throttle makes this task easier.

The only exception is if the car sits for awhile and the fuel evaporates from the float bowls. This necessitates leaving the key on (before starting) to refill them before cranking.

As long as everything outlined in #1, #2, & #3 are correct and you follow the starting drill, these cars start right up.

I hope this is helpful,

[RoninLB]

I'm 5-7 full pumps at 32F and lower on 10% E. Then I can keep it idling at 1,200 if i had to.

I can't confirm it but i think my engine fires cleaner at 10deg BTDC than at 5deg at those temps?

[JV911SYDNEY]

have weber stopped making carbs for 911s??

can only find twin carbs on their site (ie for 356, 912 etc)

thanks

[jittsl]

thanks Steve,

I'll check on the state of all of your suggestions.

Laurie

[ael911]

Originally Posted by OZCarrera3

Great work Andrew, I agree those PMO inlet trumpets need to be able to be seen!

So how do they drive? I was looking at getting these when I was having CIS problems a while back. Do they drive as smoothly as a good CIS, without snatchiness and hiccups on the on/off throttle changes and constant throttle?

Sheldon, these babies work great with no hiccups or hesitation as I have logged about 150 miles over the weekend. The response is so much livelier than the CIS. The revs are quicker from gear to gear and the sound is just incredible. I am only running 26 degrees advance at 4k so I still have some power left on the table. I plan to advance it a bit more this weekend.

On a side note, the carbs are more thirsty than the CIS. I was averaging about 20 to 22 mpg with CIS on normal driving. The carbs are yielding about 15 to 17 on semi-spirited driving. Since I do not commute with the car, fuel economy is not a big issue with me.

As for cold starts and warm starts, I followed Steve's advice and three pumps when cold will fire her right up. On hot starts, I crank the starter and floor the pedal at the same time and she'll fire without excess cranking. Best part is I still have the hand throttle so I can set her to idle at 2k rpms for warm up and it also acts as a cruise control on the freeway. I think this is the by far the best upgrade I have done for the car so far. I can only imagine what S cams and pistons will do...

Andrew

[Karaya]

ael911,

Where do those orange hoses on your blanking plates connect to? Still the heater or are you scavenging air from somewhere?

Nice work and I'm going to do my PMOs real soon.

Karaya

[silverc4s]

Andrew,
Congratulations on a great set up, and thanks for sharing the pictures and description of your issues with us here.
I would like to contribute a bit of information to your effort that may save your car from total destruction someday.
I used that same diaphragm regulator (mine was Purolator branded) on my 2.4 targa with webers some years ago. It worked well, and allowed me to get my fuel pressure set just where I wanted it.
One fine Texas morning, I went for a spirited run through the empty hill country back roads, having a great time and enjoying the wonderful car. As I got back onto more traveled roads, I noticed that I was running pretty low on fuel. Funny, I thought I had almost a full tank 40 minutes ago, that's odd. Some people driving by were honking & waving as they passed, admiring my pretty little silver car, thinks I.
By the time I reached a service station, my fuel gauge was almost on empty, and I am thinking that something is amiss.
When I stopped & exited the car, I could smell gas very strongly, and when I looked at the back of the car (engine still running) there was a pool of fuel forming on the ground under the engine!

I was sitting at the pumps, engine running - so I very calmly shut the car off and opened the rear deck. On the drivers side, the engine tin was awash in fuel, and you could see wet gas all over the intake valve cover, etc. I slowly pushed the car away from the pumps, fortunately there was a hose bib and a water hose at the side of the 7-11 store, and I was able to coast over there, close enough to reach with the hose.
Only after I was able to thoroughly hose down my entire engine compartment, and the underside of the car, did I realize how very close to complete disaster I had been, and maybe still was.

It was easy to spot the leaking regulator. As soon as I turned the ignition on, fuel poured from a small hole in the bottom of the silver disc housing the diaphragm. I was able to remove the regulator, and had sufficient length on one hose to bypass that connection fro the drive home.

It was a very nervous drive, but I made it. Later, upon dis assembly, I could see that the diaphragm had split at the center where it is riveted to a metal disc. I would never use one of these regulators again, even on a lawn mower, let alone under the deck of a 911.

You may never see this problem, but I would ask you to please buy a proper fuel pump, or get a Holley type regulator, or some other more safe & reliable solution.

[BK911]

I agree with Bill. You are regulating the pressure down with a cheap regulator, before it gets to a really nice regulator. You are also restricting flow. Let the PMO regulator do what it is supposed to do.

You have an issue with the return line. Same issue I am currently trouble shooting.

When I hooked my system up per the PMO instructions the pressure was 12 psi wide open. When I disconnect the return line after the regulator and dump it right to a gas can, the pressure is less than 4 psi. That indicates I had >8 psi drop in the return system.

Hook it up per the PMO instructions. Determine where the return blockage is and fix it.

[BK911]

Also get rid of the worm clamps. They will eat through the gas line eventually.

[ael911]

Those are heater duct hoses that run up from the SSI heat exchangers. I did the heater backdate conversion and got rid of the heater blower...

Originally Posted by Karaya

ael911,

Where do those orange hoses on your blanking plates connect to? Still the heater or are you scavenging air from somewhere?

Nice work and I'm going to do my PMOs real soon.

Karaya