What is on the roof of the 911 in you photo?

Almost the EXACT same thing Gordo2 was having. He came home a year ago, I drove the car and it would put you back in the seat to red line. This year he comes home and I say "man it's doggy". It was coughing and felt sluggish, wasn't pulling to red line like it did the last time I had driven it. When we checked exhaust temps we thought one cylinder was stinking rich. We pulled plugs, all the same. If you had one running so rich as to significantly change your exhaust temps it would show on the plugs. I'll be really surprised if the cleaning you did doesn't fix the problem. I hope it does.

One of the juicier threads lately. Thanks all. Sub'd.

timmy;

the 911 has a cloth sun roof. I bought the wreck in '88 to re-build and added the MGB GT (!) Webasto sunroof to delete the crass glass aftermarket roof it had.

Glad this little thread has given some good value to others let alone me!

I've never ever been on Pelican before but used the Dempsey book to this 3.2 engine, so thought I would give 'you all' a try! One of my better ideas....:cool:

PMO's are very rare in the UK and there are no spares at all.

Might not do the Porsche Club run tomorrow, so could well get to the carbs tomorrow, see how the wife feels.

At the last hillclimb,just one week ago, the engine pulled but not with the purpose it usually has.

The car all up weighs just 520Kg and the engine had 247 bhp, it felt well down on the day and 3 seconds short of my personal best at the track last year, pb is 46.7, race run was 49.64 and several said it sounded well 'off'.

I'm dropping pictures in as pics help the interest along (I hope)

Sometimes running to the red line in 3rd for too longs does not work out well.
http://forums.pelicanparts.com/uploa...1436040596.jpg

Resisted the temptation to take the 911 to Prescott/PCGB day out and continued with The Problem.

With the 456 bank carb now cleaner than it left PMO in 2007 re-fitted it to the 456 bank.

Let everything fill up...and the same problem!

Bit deflated, took the carb off again, stripped it and re-cleaned/air line/ look at every passage and hole.
Still puzzled why #6 is flowing 30% less than the other 5, but realised that #6 choke (and #1 choke) do not have petrol feeds as the other 4 do, no cross-drillings at all.

Anyway, after a coffee put is all back together again, filled the carbs and fired the thing up.

suddenly it runs the same on both banks with the mixture set at the PMO recommended 2 turns out.

The velocity of the gasses from each bank are much the same to the palm of my hands and the temperatures are the same too.
Not a back fire in sight/ear fall but the engine is not turbine smooth like my old 911/3.2 on injection is.

Maybe I'm expecting to much?

Full throttle blips of the engine and the engine lags behind, but it has never been good at that party trick and I think this is down to the carbs being simply too big for the engine at 50mm/38mm it needs 46mm/36 I think.

going to let it cool down now until the GP has finished (and Williams come in 1st and 2nd please) and then try it again.

Observations:
I put the colour tune on #4 pot after I replaced the carb the first time (and running rough) this morning to see why I still had the problem. It would hardly mixture tune at all.
The cylinder would 'thump' as it fired every now and then with a resulting yellow colour as the cylinder fired. did this several times as I turned the mixture screw +/- 0.5 of a turn.

The mixture screw on #6 had no effect whatsoever and neither did the air flow adjustment.

After the second re-fitting I have not tried the colour tune on any cylinder, the mixtures are all out 1.75 turns and the flow needle is max out on #6.

The engine really get hesitant at anything like 900 rpm; it will hold 900 but after a minute or so starts to fall to the point that I'm certain the engine will stop.

The balance of the cylinders are all '4.75' except for #6 which is at '4'

The carbs are 50mm PMO with 38mm chokes and are too big for the 3.2 capacity (46mm would be ideal). If I take this engine out to 3.4 then 50mm will be closer to ideal.

If I blip the engine with a good 75% throttle travel (all links clipped in place) then the engine does not pick-up instantly but certainly lags behind the mechanical input by about a second.

I helped Richard Parr a year ago in overcoming acceleration lag. Basically I substituted an IDTP cam-lever arm for the IDA type his carburetors use. The IDTP cam-lever has a steeper ramp that provides early squirt increase over that of the IDA version and helps bridge the lean gap from demand to main circuit fuel delivery. These are retro-fitable.

I typically see "4 3/4 to 5" readings when adjusting for Lean-Best at 900 RPM. Still troubles me as to why #6 is a low flow barrel. Once that is set right then 900 RPM should be achievable. You disassembled carbs and allowed butterflies to go fully closed and looked at throttle plate alignment, right? If so, and all is good there you could drill a 2 mm hole into the edge of the butterfly to provide air at idle and possible render your air adjusting screw effective. This can be re-closed if necessary with a bit of solder. This is not an unusual procedure to perform but does not answer the lack of airflow issue.

One item left to investigate is whether the fuel gallery feeding the idle jet is clear or partially obstructed. This gallery is what I refer to as "hidden" since it is almost impossible to clear by blowing through normal orifices. On the PMO I believe there are screws that plug the fuel galleries so it is a little easier to check this out than for Webers. The hidden gallery taps into the emulsion tube well and delivers fuel from there to the tip of the idle jet. You will need to remove the top cover of the carb to access the blanking screw on the top of the throttle body. It is the screw that is inboard from the idle air correction jet. The lower port is just to the side of the float bowl and is a horizontal bore.

Since you are having occasional firing of #6 (be grateful for the Colortune to help see this event) you may well have some debris that has been ingested through the main jet, into the emulsion tube well and then sucked into the hidden gallery.

I have had another go at the engine and #6 I am sure is doing nothing.

There is a spark.
There is compression (200 psi!)
Thus there is no fuel going into that choke.

The exhaust pipe (header tube) from #6 is cold to my spit, the others the spit doesn't even get a chance to wet the pipe surface, crude but proves the point.

The ign lead is continuous, I've changed the plug top and I've change the plug. The plug sparks outside of the engine and in the colour tune.

With the engine running if I block off the top small holes by the bell mouths that lead to the stainless plugs on 2/3/4/5 the engine will drop its tick over revs and uncovered restore to tick-over.

Cover the hole on #6 and nothing happens
Even remove the mixture screw, nothing happens, unscrew to the maximum the flow adjust screw nothing happens.

I simply cannot understand what is stopping fuel being drawn to the mixture/flow screws.
The plug obviously looks new BUT is not wet.

I am at a loss now, hope someone has a bright idea?

going to try to contact Richard Parr now.

Sounds like Paul may have discovered your issue. At least 90% of PMO issues are debrise/gum related, that rises to almost 100% when they used to run well.

I very much appreciate this help as I'm quickly getting irritated!

I know the hidden galleries you refer too.

Mine are plugged with a small grub screw. I removed them on the bad carb this morning and they are clear!
I drowned them with brake cleaner with the long tube nozzle passed all the way down to the bottom of the carb. Cleaner flowed from every orifice!

As I see the circuit:

The fuel is in the bowl.
Engine runs and the fuel is sucked from the bowl up the 'hidden gallary' to the top of the carb.
It passes through the top jet mixing with the air passing through the stainless plug.
It then passes down the gallery you can see cast in the carb body to the chamber with the 4 small holes in that vent to the throttle plate.
There is a cross drilling that flows some fuel to the idle adj screw.

(except on #6 and #1 cylinders where no such cross drilling exists)

The fuel sits at the mixture screw as it is shut tight until it is opened to allow fuel to bleed into the cylinder setting the fuel/air mix.

Trying to see a positive in todays garage work;

It is only #6 that is not working at all except there is a spark and I have very good compression.
For combustion I only need fuel and then I'm on all 6.

The cylinder is all ok, no leaks and very high compression pressure and a spark.

Why will fuel refuse to flow from the bowl when the #5 cylinder is shared and works fine?
This MUST be a blockage?

I will remove all the #6 jets etc and try cleaning again.

In all this cleaning I've removed all the gallery blocking screws to get cleaner down the tubes inside the body.

On the accelerator system Paul, I think these are the improved 'hatchets' I have read about?

You have made me think Paul.

Just opened the carb again and poked through all the galleries and jets.

#6 has a low air flow that cannot be increased or I can drill the 2mm hole in the plate to allow more air to flow as you suggest.

Can it be that the low flow is not enough to draw fuel in the first place at tickover?

Can it be that there is not enough vacuum in #6 to pull enough fuel through to mix and combust?
If this is the case then I will never get #6 to run (though it has in the past) at 900/1000 rpm but it might at a higher tick over?

I can't see what mechanical difference #6 has over the other 5 (inc #1 on the 123 bank that is running)

I can't get to Richard Parr without a fax.

Right, Richard named them "hatchet" due to their similarity in shape to a hatchet. They are actually IDTP cam-levers from 1969 911T and 914/6 carbs. I tried them on a set of 46 PMOs sent to me to work on by Richard. He has since incorporated them into his new PMOs along with progression hole revisions, again a function of last year's work.

Fuel blockage to mixture screw:

I see this from time-to-time. I have a procedure for the Webers (on my site) but similar procedure for PMOs is:

• close mixture screw
• remove main jet/emulsion tube/air corrector stack
• drop a small ball bearing into the e-tube well to act as a blockage of flow through the main jet
• place a bit of adhesive tape over the top of the main air correction jet
• re-assemble and install jet package into well
• remove idle jet & jet holder
• blow compressed air into idle jet bung
• look for freely flowing air to pass through the fuel transfer port in the wall where the auxiliary venturi is installed
• you can compare air flow to a "good" barrel

This test will confirm good fuel flow through the hidden gallery for the #6 barrel in the "as assembled" configuration.

Another way to blank the main jet & air correction jet would be to make a short rod that drops into the well and is just the same height as the top of the main throttle body. Use your finger to hold rod in place and seal top opening against air flow. Better plan than to drop & then re-acquire ball bearing from the bottom of the well. ;)

Your characterization of the fuel path of the hidden gallery is correct.

Vacuum below nearly closed butterflies is prodigious, plenty to suck fuel when available. Air flow does not draw fuel from mixture screw at idle, it is intake manifold vacuum that does the work.

I can supply phone number for Richard but would prefer to supply via separate email.

"May the Force be with you!"

Right!
I'll try that tomorrow.

I wont let this defeat me!!

I will send you my email address to your address on your post Paul.

Spent another 3 hours on the thing today, but some progress!

Decided to approach this issue from a different angle having poked and washed the carb yet again with no obvious debris dislodged.

Thought I would start from the heads up to the float chamber, so off with the 456 carb.

Sticky to get it free and no wonder, the gaskets either side of the insulators had dissolved!
Worst was #6 with a gap 40mm x 1mm which was where the air was getting in. Paul made me think when he said the vacuum was 'prodigious' under the throttle plate so set me wondering why this was not so on #6. Only a hole would stop the vacuum being pulled as the engine turned over.

So, it just happened I had a new set of gaskets (!) and have replaced the lot on 123 and 456.

The dissolved/dissolving gaskets came with a real Porsche gasket set when I re-built the engine 3 years ago.

anyway, it can only get the fuel tract to the same position when the egine was fresh and the carbs balanced out etc, so my hope is I'll be back in business tomorrow.

I've re-set all the chokes now to PMO start-up positions.

Will report back later...http://forums.pelicanparts.com/uploa...1436202761.jpg
http://forums.pelicanparts.com/uploa...1436202775.jpg

Did someone use sealant on those for installation? I took my intake runners off my engine of unknown mileage and none stuck like that. IIRC, Wayne's book states those go on dry. I wouldn't think that would change for carbs or F.I.

Take a hard look at that plastic spacer. As I stated earlier, your problem as initially reported was a heavy vacuum leak under #6.

This is a bit of a concern.

I installed those gaskets dry 3 years ago.
Being a hill climb car only this engine has done about 120 miles max!

In the UK a hill race is about 3/4 of a mile x 5 times a meeting and 10 meetings /year.

I use only Shell V max petrol which has ethanol.
It has been suggested ethanol will do this.

They were all the same, #6 was worse than the others.
The plastic spacers were all flat and new when I fitted the PMO's about 5 years ago, infact they came from PMO as they cover the injector slots in the heads.

I need to put the ignition parts back together, parts I changed out during trying to isolate the source.

One other niggle is the rough running followed the 456 carb to 123 bank the inlets were left in place...

I'll rejoice when it is running right.;)

https://www.youtube.com/watch?v=HC6ZnaPv9Hg

That to me would have ruled out gaskets and spacers. Still seems to me like you've got some debris in there.

I don't think I'd worry too much about the gasket getting soft. Depending on brand and material I've seen some that will soften and stick like that (not on these engines particularly but others) it just seemed odd that those gaskets had stuck like that in such a short time period.

Any progress with the clearing procedure provided in posting #31?

Just a Public Service Announcement, from the PMO site.......

"When air cleaner bases are installed, the Idle Air Inlets must not be covered. Check diagram. If the Idle Air Inlets are accidentally covered and the engine floods, remove spark plugs, disable CD and turn engine over before trying to start engine."

This cost me dearly. I got so pissed I took the 3.0 out and had a 3.8 built instead! Just adding this to remind all to watch those air cleaner bases. I'd mark them with an arrow. My .02¢

Never got that far to be honest Paul, but before the gasket discovery I went inside the galleries myself nearly to sweep them through but nothing came out. This is when I thought I would approach this from the heads to the floats instead of the other way, hence lifting the inlets.

Did the gaskets on the inlets, put the new dist cap back on, put the plugs back in and checked everything was to PMO start-up settings.

Fired the engine and let is idle at 2000 rpm for a minute. Felt the exhaust gases out of each silencer, absolutely even and sounding very much on six cylinders.

Set the tick over to 1000 while it warmed, disconnected the throttle links and set the side-to-side balance to '5' using the centre chokes as they give the most stable venture readings.
Went across all 6 bell mouths to find the fastest one and even #6 was the same as the others!!! :eek:

Bought all the 5 to match #4 and re-set the side to side to give 900 rpm because of what you told me Paul (Obedient is my middle name according to the wife).

It held 900 like a road engine.

Decided to set the mixture cylinder by cylinder using the colour tune, all but one was rich with black plugs, even #6 was black!:eek:

The mixture adjustment to get to blue from yellow is a 1/4 turn, very fine but all are blue and stable.

It purrs at 900 tick-over.

The blip 'test' gives an instant response. :cool:

Hot re-start is on the button and after it catches a light blip settles the hot engine to 900 again. Shut-off is clean.

So, 6 or 8 hours to find the problem, 20 mins to tune the carbs.:rolleyes:

So, what have I learnt here?
1
I know a LOT more about PMO carbs now.
2
Strip everything apart to find the answer not just a bit
3
Never give up.


Thank you to everyone who has help me.

Graham.

http://forums.pelicanparts.com/uploa...1436288397.jpg