PMO Carb Float Level Adjustment Advice Needed
 

Anyone with PMO's care to give a brief float level adjustment lesson? The instructions that came with the carbs are a bit thin and I'd like to hear from someone who's been there done that. Note that these are not Webers and the procedure is different with the PMO carbs. Thanks to all.

news to me... interesting

Well, that was my thinking too. When I installed the carbs a while back, I talked with Rich at PMO since the float levels were not equal. He suggested that I wait a bit for the needle valves to completely seat and then if the levels still needed adjusting to follow the procedure listed in the PMO kit. I specifically asked him about washers/shims under the needle valve and he said that's not how it's done on the PMOs. It involves bending the little metal tab on the float according to the instructions. Now this seems a bit odd to me since the PMOs are an amazing piece of mechanical art and everything about them is very nice. Before I call Rich back on the phone I was hoping someone with some PMO experience could clear up some of my confusion about setting the float level.

I haven't seen the insides of a PMO carb, but as described, it sounds like the float is adjusted like most any other carb with the float/seat in the top housing. Rest it upside down, then measure/adjust the distance between the gasket surface and a reference point on the float by bending the metal tang that contacts the needle.

I don't know, but since the PMOs have an inspection window to verify fuel level, is there any way to fine tune it w/o taking it apart? Didn't the PMOs come with any instruction manual?

Sherwood Lee
http://members.rennlist.org/911pcars

The ONLY thing I fould lacking when I bought the PMOs was the documentation. The carbs are beautiful but the instructions were....thin. There are about 20 photocopied pages that come with the kit describing the conversion process from CIS to PMO including the set up procedure. There is a single page on the float arangement and how to measure what to where and the tab to bend. Suffice it to say, I think they feel that if you are putting these carbs on your car you have a fairly healthy working knowledge of the Webers they replace. I have several books on Webers and have used them in conjunction with PMO's pages to set up and dial in the carbs. The fine tuning of the float levels is one thing I haven't attempted to date since it's running "almost" perfect and haven't felt the need to take the carbs apart to bend the tab. Just seems a bit tedious to take them apart and bend the tab, then put them back together and see if the level is correct. I keep thinking there must be an easier way (i.e. the washers) to do this.

One more carb question while people are interested...
 

When I turn on the ignition key and energize the fuel pump, the sight glass for the fuel levels just fill right up to the top. Is this normal? The fuel pressure is 3.5 PSI (at least that's what the fuel pressure gauge that came in the kit says...I have my doubts as to its accuracy). Shouldn't the floats shut off the flow of fuel when the correct level is reached?

not for nothing, but any new carb I ever got needed the floats adjusted.........Ron

"The carbs are beautiful but the instructions were....thin."

When PMO was engineering prototypes, I spoke with Richard about providing documentation/service procedures for the new carb (that's what I do); even went as far as visiting the molding/casting facility where the prototype parts were being made. Nothing came of it; maybe didn't press him hard enough, although I'd have to admit that documentation funds are always scarce after spending a bunch on engineering, casting/machining and sourcing parts for this unit.

Oh well. I guess most techs find this unit similar enough to regular carbs. Still, an external float adjustment would be a definite plus. If I had to R&R the tops of my Webers to fine tune the float level, I'd be one unhappy tuner. Isn't there any sort of threaded valve seat arrangement on the carb to adjust the fuel level?

Sherwood

Thanks Ron. That's one thing I wasn't too sure about. I assumed that coming from PMO the floats would have been set. I suppose that was a combination of wishfull thinking on my part and a desire not to open up the new carbs and f... things up inside before I even got them installed.

Here's the PMO instructions
 

Here's my poor man's scan of the float level instructions...

Sherwood...as far as i can tell there is no way to get at the float valve/seat....You can see from the photos that the access points that exist on the Weber are not present.

Other side....

nobodys fault.. to my understanding, the "shipping" will disturb and carb float level..
in days of old when. . . even if the carb has been thrown around from going from one friend to another I would check the floats

and PMO is a continuous class act.. obviously your 911 is a class act, or you would not be going thru this now.. so from one perfectionists to another.. I will be installing a 2 micron fuel filter.. I believe the routine is 10 microns.. and the aids virus is 3 microns, I think, LOL..................Ron

I'm running a Racor 110A fuel filter water separator (10 micron?) but have been contemplating some additional filtration just before the carbs. Where did you find a 2 micron filter?

Gratuitious picture :)
 

...

Racor, in marine supply books.. will even go to one micron.. with a dirt alarm on them.. 10 micron is good for a pre filter

Hey Eric ... I just looked up the 110 filter.. the specs say for dirt removal "96% at 2 micron".. that's all I got now.. got in from a supply book....Ron

Thanks Ron
 

I thought it might be a 2 micron but I couldn't locate the specs online. Got the floats adjusted as per the PMO instructions - bending tabs and whatnot. Still not perfect but close. The float bowls still fill all the way up when I energize the fuel pump but settle back down with the car running. Normal??

I am now looking for the cause of a intermittant miss from 3000 RPM up. Not sure if it's carb/jetting related or my ignition. Feels like an ignition issue but the ignition is fairly new and the wires/plugs/cap/rotor are all new as well. Sometimes it cuts out sometimes it doesn't. Happens more as the engine warms up. Could this be caused by the float levels still being off slightly?

Thanks

Re: Thanks Ron
 

I find w/carbs that it's easy to tell the difference between fuel and ignition on a miss. sometimes w/hand on carb linkage and air cleaners off. a quick blast from 3k to wide open throttle. maybe holding it there at WOT for a second or 3.. if flames of flashes it kinda looks and sounds like ignition instead of fuel. good routine to pick up on a "known problem" engine..

and our electrical pope once mentioned that the Beru plug connectors can sometimes miss at higher heat than warm-up heat only.. which sounds like fun to find when testing room temp wires w/an ohm meter.. how about a timing lite rotated from wire to wire when this is happening.. I hate those Beru connectors..

I also use a vacuum machine that picks up ultrasonics from vac and exhaust leaks.. it works great. I've seen the same unit in Snap-On and other brands.. costs $75-$200 for the same unit...

Well....first thing I did was swap ignition cables with a set of MSD wires I built fron scratch with MSD plug connectors. No difference - same intermittant cut 3K RPM +. The ignition box worked 4.0 with the CIS before the PMO conversion so I'm hesitant to believe it's bad after only about 1K miles. The problem first arose after the carb conversion. So that's where I'm at. I've reset the float levels pretty close, cleaned the idle jets/passages several times, changed the plugs for a little hotter set (BP6ES), swapped ignition cables, checked cap and rotor for obvious damage. I haven't checked the coil as it is also new with the carb conversion. I have another laying around so I'll give that a whirl.

Could a piece of dirt intermittantly clogging a main jet cause a cut at higher RPM? It seems to feel like more than one cylinder being affected however.

One other piece of the puzzle - #2 requires several turns more on the air bypass screw than any other cylinder to achieve the same balance. This is also the cylinder with the vacuum port for the brake booster. Smell anything funny here?

I'll give your 3K to WOT thing a shot and see if it sheds any light. Thanks again for the insight.

I don't have hard experience with carbs on the 911.. plenty around here do.. so better to bow out on that one..

if the tach takes a sharp dive at this miss, then definately ignition problem somewhere...........Ron

I'm just a neophyte, and my car is injected. But if I were to be given the job of designing a float level window in a carb? I'd think the level should be dead in the middle of the window, with everything off. Then a dead level, middle of the road level should be right. Right? Here I go again...thinking things should be logical. One needs only to observe the current and past political scene to know that isn't so...

Hey Eric .. if you want to get logical I have the 3 soft covered Weber books/at least, and can scan anything you want.. the scanner is a new toy and I can't shrink it and still be legiable.. so I'll have to do a direct e-mail.. not confirming that being logical will solve the issue

Hey Paul .. Libya is now chairman of the UN Human Rights Commission.. maybe the UN figures it's about time for truth in advertising... screw the UN, that's logical.....
http://www.pelicanparts.com/support/...flackwhore.gif

Eric, what are you using for a fuel pump and fuel presure regulator with the PMO's? In the pic of your engine, is that the pressure regulator immediately to the right of the pressure gauge?

Thanks for the offer
 

Ron,
I've got one of the Weber books myself and as each day passes I'm learning more and more. The problem is that the PMO is a little different here and there and that seems to be where it counts. I had the carbs apart yesterday and I should have taken a few pics but I was hot on the trail of those floats and didn't get any pics. Wish I had taken the main jets/emulsion tubes/air correctors out while I was at it. Just couldn't imagine they're plugged already.

More info is always appreciated but please don't slave away over the scanner to send a bunch of files. If you see something particularly insightful, I'd love to see it. I'm at:

ericnbel@2fords.net

No dip in the tach btw- that's a sure giveaway for the ignition. I only wish it was that easy.

Break...Break....

Paul, the fuel level with the floats properly adjusted and working 4.0 are dead on the sandblasted dot in the center of the view window. Mine aren't quite perfect with the internal specs of the floats pretty damn close to PMO's requirements. I may tweek some more to get them dead on.

Bob,
Pump is stock CIS pump with a Mallory 3-20 psi bypass regulator.

BTW here's the book I'm using...
 

...

[QUOTE]Originally posted by RoninLB


Hey Paul .. Libya is now chairman of the UN Human Rights Commission..

You're kidding? You're NOT kidding? What's next? A Ted Kennedy school of driving???? :confused:

Hey Eric .. that's the Braden book.. I have more if you need greater/maybe info on a topic..
-but I kinda think, if your coil checks out, that the miss may be a pop.. so if it's not a lean adjustment on that carb, then the external gaskets to the head may be leaking.. just a thought..
- but the air screw on #2 ????
-and do you notice the "miss" thru the carb? or thru the exhaust?
-does/did any spark plug look hot, as from a lean condition?
I bet if a 911 carbhead reads all this the prob will be over...

and Paul .. Not Kidding

...do you notice the "miss" thru the carb? or thru the exhaust?

Not sure as I can only get this to happen under load while accelerating. If I rev the car in the garage it runs fine up to redline.

...does/did any spark plug look hot, as from a lean condition?

Plugs all looked uniform and a bit sooty. Switched up to the next hotter heat range plugs.


I bet if a 911 carbhead reads all this the prob will be over... Amen! Calling all carbheads.

Thanks to all for their interest and help.

the load info is meaningful.. if me I'd go after points and coil, then the box.. because you don't have any resistors in plug wires.. I hate Beru connectors

"Thanks to all for their interest and help".... it'll cost you on payback one of these days, LOL................Ron

You might check that you have a good seal between the spacer blocks and the base of the intake manifold for starters. All idle screws should be relative as a baseline. As for the miss - the float bowls need to be PERFECT. Your CIS pump might be overkill, as the carbs only need 1/3 of the pressure your pump is putting out. If your floats continue to stay flooded to the top- nothing good will come of this condition. Too much gas and it will have no where to go but out onto your HOT engine= fire! Talk to Rennsport Systems,TRE,COX Motorsports etc - all their customers have race cars with these carbs - your floats need to be persuaded within range to get the fuel level to the sand dot on the inspection window of the carb.

Good luck.

Progress!
 

My suspicions about the veracity of the fuel pressure gauge I had seem to be founded. I turned the regulator down until the indicated pressure was 2 psi and, low and behold, the float levels droped to the proper location on the sandblasted dot. I knew from previous reading that these gauges are inherently inaccurate especially when reading near the extremes. I'd like to get an electric sender to wire a gauge into the cockpit so I can monitor it from there with no hazard of fire. Any suggestions. At any rate I'll find a replacement in the meantime.

Alas, the miss is still there and I was able to reproduce it in the garage. It's not nearly as noticible just a some popping in the exhaust (not out the stacks) when I get up to about 4K RPM and beyond. While driving the effect is much more pronounced. I'm going to go through and double check the balance on all throats at 4K RPM and above to makesure I'm not missing something easy here.

Ron,
BTW, got the PDF files - thanks mucho!

Next step for you is to check the pump volumes with the vial that was included with your carb purchase. It is VERY important that each cylinder is the same. Do you have a carb synch tool?? Are you positive that each barrel is pulling the same amount of air? You are on the right path and most likely will be able to dial out the miss you are speaking about. Good luck.

Jim

Just found out that PMO has a website now. Go to PMO site and look under "support".

When I had a "rising idle" problem with mine, it was the distributor not retarding the spark enough at idle.

Good luck,
TT

What does PMO statnd for ( yes I'm new )


Michael

Wonder who's muffler is on the PMO site....
http://forums.pelicanparts.com/uploa...1065037375.gif

That looks like a Dansk.

TT

Porsche Mail Order...PMO.

what was the answer to this mystery ?