Hard Starting 68S Motor w/PMO 40s

[Jim2]

I bought this car a couple years ago with a 68S motor which is stock except for PMO 40 carbs. The carbs are in the range of 12 years old however they don't even have 100 hours of running time on them. They are clean, no damage, and still look fairly new.

I've driven the car about three times since buying it two years ago but now want to use it.

I have difficulty getting it started, and the symptom is just like it needing a faster accelerator pump squirt. The PMO site states that one throttle stroke should squirt .6cc per nozzle. I've measured and adjusted each carb, all the nozzles are flowing and measure .6cc each. The problem however is no matter how fast I kick the throttle I can't keep it running beyond 5-10 seconds. I then key the throttle another 10 times and fire up with a little throttle and I can modulate it at about 1500 rpm but shortly dies off, and continual kicking the throttle barely keeps it running. Repeat cycle about 6-8 times before I can get it hold fast idle.

I taped cardboard covering the velocity stacks to act like a choke, pump the throttle a few times and it fires up and runs fine but the cardboard makes it bog if I rev it, just as expected.

Once the engine is warm, it idles, runs, and drives perfect.

My experience from messing with carbs years ago suggests I need larger orifices in the pump nozzles, but I hate to drill them as I can't go back.

The fact that the squirt volume is adjustable is irrelevant, because it takes a couple second for the full .6 cc to discharge, I can kick the throttle faster than that resetting the diaphragm, but the squirt is only injected by the spring under the diaphragm. I feel I need a *faster* higher volume squirt, not a longer quirt at this low flow rate.

Before I go drilling the accel pump orifices has anyone got some feedback for an alternate solution I'm overlooking?



Excuse the red box.
edit: and the red fan...

[toddu]

How many pumps of the peddle before cranking over? What size idle jets are you running? If my car sits for a week or more, it's a bit of a chore to start, maybe 3 attempts of peddle pump then crank, but then starts.

Todd

[Jim2]

Todd, idle jets are 55

3-4 pumps and it will not fire at all. 6-8 SLOW pumps holding the pedal to the floor for about 3 seconds between each pump, and it will fire up. 6-8 fast pumps have about the same effect as 3-4 fast pumps, no fire at all, or just a few strokes is about it.

[Gordo2]

I would start my troubleshooting by assuming that the carbs were setup right when they were installed - i.e. shouldn't need change setup / configuration.

Then I would move to cleaning - beginning with the idle jets and the idle air control jets.

Good luck, Gordo

[Jim2]

This summer I disassembled the carbs to clean out old gas and any debris, replaced fuel filter, added a FPR, adjusted float levels, adjusted idle mixture, synchronized them, etc.

Like I say, after it's run for just a minute or two life is good, it will idle and drive fine. Warm restart is good. After it's cooled off then I'm back to square one.

It's like I need an enrichment system like that found on DCOE side draught, mikuni, delorto etc.

I'm almost positive that drilling out the accel pump nozzles will help, I'm trying to avoid it because it's not reversible due to the nozzles being aluminum. Can't solder them up like a brass jet.

[Jim2]

I do wonder if PMO dude offered different size nozzles. There's no mention of any alternates on his site, give me the distinct feeling there was only one size, only the pump stroke being adjustable.

[1QuickS]

PMOs have float bowl sight glass. Check fuel levels in float bowls before attempting to crank. If fuel levels are low then let fuel pump run until fuel levels are good. Then depress accelerator pedal to the floor & hold for a two count & repeat. Then hold throttles partially open & crank. It will take some time for fuel to be drawn into the idle circuit; it drains empty once engine is shut down. The squirt amount is fine at 6 ml/stroke.

Important to review idle mixture & air flow adjustments: I assume you performed a "Lean Best" idle mixture adjustment & checked idle air flows with drop links disconnected. I also assume you checked for air flow balance at 3000 RPM.

55 idle jets are fine for your 2.0S using 40mm PMOs.

[SoyRacer]

When you rebuild PMO carburetors they now send along I the kits updated accelerator pump cams with a more aggressive profile. I've only seen any improvement on 40s (coincidence . . . .). I might have a pair so I'll check. No promises
Good luck.

[Tomsherman]

I agree with Gordo2.
55 idles should easily get the job done for a 2.0 This engine could be failing to jump up nicely on the idle circuit. S cams with their high overlap exaggerates idle issues. After your adjustment procedure how many turns out on the idle mixture adjustments do you end up at ? Ideal would be between 1.5 to 2.5 turns out. More than 2.5 you are too small idle jet or clogged and will have lean transition. My initial thoughts are this is a global problem not necessarily the carbs, especially with ultra reliable PMO's

Have you checked your timing ? many times carbs are blamed for ignition issues. It has happened to me for before. Overly retarded timing at startup/idle has symptoms very similar to described. Make sure breaker plate in dizzy is in good order and mech. advance is working without sticking.

Richard at PMO is extremely helpful so do not hesitate to contact him.

Poor idle or start in general assuming engine worked well in the past:
valve adjustment / low compression.
weak spark.
Retarded timing.
too cold / fouled / over gapped plugs. Iridium type heat up and clean quickly. highly recommended.
clogged idle jets. clogged progression holes.

[1QuickS]

The "new" accel pump cam is actually the cam from the 1969 911T & 914/6 Webers. It has the same total lift or squirt output as the other cam but it occurs earlier in throttle shaft rotation. I know since I provided the info for Richard to use a few years ago.

[Gordo2]

Another thought, you may want to consider how old the fuel is...

If it's been in the tank for a while - that could be the source of your problems.

Gordo

[Jim2]

Tried to reply a half hour ago guys but my mac cratered. I'll be back in an hour two using my phone.

[Joe Bob]

I seem to remember three stabs of the pedal. Anyways, send a fax request to PMO. They don't answer the phone or email IIRC....

[Jim Dunham]

I have the EXACT same problem on my 3.2L converted to carbs in my 1972 911. I'm pulling my hair out to figure out why the cold start is SOOOO tough/long to accomplish. This is my second car with this issue so anxious to solve.
Will dive into idle circuit based on these comments.

[jmz]

Listen to Paul. 1quicks

[snbush67]

My motor (3.2SS with 46 PMO’S) likes five full slow pumps, turn the key, then gently add slight pressure, barely pressing on the pedal until it catches (which is within 1-2 seconds) and revs to about 2200 rpms, then release pressure while setting the throttle knob above 1500 rpms until smooth idle (smooth idle usually within 30 seconds to a minute).

I have the new accelerator pump cams and have the screws backed all the way out with two or three threads remaining to get full range of motion. I’m not sure if the pump jets are the same in the 40’s as the 46’s or 50’s. Fuel pressure set at 3 PSI.

Still working on a slightly rich (12.5 AFR) at light cruise situation, but running smooth and powerful with very snappy throttle response.

[al lkosmal]

What is your fuel pressure set at? Carbs like 3.5psi or so, if I remember correctly.

[Jim Dunham]

I'm at 3 psi but I've decided fuel pressure at cold start is not important. What is important is to see the float level 1/2 way in the sight glass for both carbs to prove that fuel is there. I also have checked that the accelerator squirters are working. The comment earlier that the idle circuits may not be "filled with fuel" is intriguing to me and something I'll explorer further. Will try snbush67's suggestions too since I'm same displacement and same 46 PMO's. Curious if snbush67 has 36 chokes like mine.

[Arctic Rat]

Jim,

Not sure if this is relevant to your situation. My 2.2 with weber 40idas had a similar hard starting problem. This was due to my points having worn down and not gapping enough to provide a prolong spark for cold start. Warmed up the engine ran just fine, idle was a little off but otherwise ran strong. Not sure if a timing or points issue may be contributing more to the issue than a carb problem.

Best of luck

Joe D

[Jim Dunham]

Thanks Joe, I do recall Richard at PMO telling me "90% of carb problems are ignition". I've swapped out CD boxes, switched to Pertronix, checked plugs/wires/cap/etc. and have seen no positive change but you are right - it's always there to validate. We did measure coil current/voltages at Key On/Start/Run to verify strength. Starts/Runs great once warm.