Addendum: See step 9-1/2 (below) for a later detail:
9-1/2. I shoved in the clutch after pulling along the street, heading generally downhill. Engine conked. I tried to start by engaging the clutch, and though the engine rpm's came back up while in gear (and timing light began flashing) the engine died as soon as I pushed down on the clutch. I tried it again, but this time fed it some gas. It remained running after I pushed down on the clutch.
Could this be some return-to-idle thing in the carburetor?
Here I get to show my carb ignorance... If only it was fuel injection! I'll open some suggestions, but I have no experience with your carb so please consider I'm shootin' from the hip! My feeling is lean - not rich. I'm thinking it's going lean when it returns to the idle circuit.
Is the idle circuit dependent upon float level?
Can an idle jet be partially clogged?
Can some debris in the carb be covering a passageway when decelerating or nose-down?
If you set the idle speed about 200 rpm higher than normal, does it make a difference? (distributes fuel flow so not solely idle circuit - maybe?)
If too rich - any indications of black smoke at any time?
Does it blubber and die or just kinda spin down to nothing? (blubbering = richness)
Clamp or plug any vacuum hoses that are not essential for running. (Use your own judgement esp. re the servo circuit!)
Anything obviously loose on carb or related areas?
Maybe open carb and see if anything is obviously loose inside. I have had carbs that like to vibrate apart and one recently that the accel valve was inside the float chamber and the screws always vibrated loose...til I Loctited them.
Beats me -- anyone? This is a newish (less than a year) 34 PICT-3 "Pierburg" from Aircooled.net
Beats me -- anyone?
... of (as the pattern becomes clearer) after pulling for a minute or so at highish (3,000 or more) rpm?
Good question -- anyone?
It's getting where I know that simply cruising easily along on a city street will usually not cause the engine to conk. When it conks it does so on return to idle. Feathering the gas will cause it to get past the trouble. But it conks only 5%, maybe 10% of the time on return to idle.
I can try this.
Not a bit.
I have learned to predict whether the engine will return to idle or just drop to off by watching how the tach needle drops when I take the foot off the gas. When the engine is not going to die, the needle rotates smoothly counterclockwise, slows gently as it approaches idle rpm. When it's planning on conking, it drops to zero like a stone.
Well, all this thing has for vacuum hoses is brake servo and vacuum advance.
Is steering wheel considered related area? Got a loose nut there. Otherwise, nothing on the carb noted as being out of order on visual inspection.
I will do that if other smart guys like you chime in and suggest same. It being a mighty PITA -- I will get crabby and resentful and childish if I have to do it and nothing is found to be wrong.
my 76 did the same thing. the carb throtle shaft was worn and if I let go the gas pedal slowly id returned to idle ok. snap it shut and it would go past the normal idle and the engine would stop.
new carb fixed it :) but in the meantime I just adjusted the throttle stop half a turn in and it ran fine. shifted the problem to 'if I dont snap the gas shut fast, the idle stays as 1300rpm :)'
I forgot about it being a new carb, but new carbs are not immune to loosening parts or debris flopping around. I wish some carb guys would jump in here. Maybe need to bring it to a new posting!
1) Remove carb top, just when the engine had died. Note how much fuel is in the bowl.
2) remove carb top, when teh engine is idling fine. NOte how much fuel is in the bowl.
If there's no difference: remove and clean bowl bottom, main jet, idle jet, blow idle passage clean.
If there was a difference in the amount of fuel left in the bowl between #1 and #2, turn your attention to needle valve, fuel filter, fuel line.
Also, do you have a good gasket between carb and intake manifold? NO SEALANT, and NO RUBBER. Use proper, fairly thin paper or cork gasket that doesn't expand like mad.
I assume the carb was adjusted properly?
1) adjust valves
2) adjust timing
3) adjust carb throttle lever stop screw: Loosen the throttle cable. Make sure the stepped choke plate is secured UP, in the "no choke" position. Turn the lever stop screw OUT until it no longer touches the stepped choke plate, when the throttle is closed.Now start turning it in again, until it BARELY touches the stepped plate. Then turn another 1/2 turn in, and leave it there forever. The purpose of the stop screw is to make sure the throttle plate never closes fully, because then it might bind and eat a groove in the carb throat. It also allows a tiny bit of air through, what is needed for idling. AND it moves the throttle plate edge just slightly so that it clear an idle mixture hole in the throat. Barely visible.
4) set idle speed (when it works) to a reasonably normal level,
5) turn idle mixture screw in all the way (engine might die), then turn it out (restart engine with mixture screw ONE TURN open if it died) until idle speed stops climbing. Then keep turning in and out until you feel certain you have found "the spot" where idle speed has just reached it's peak and turning the mixture screw OUT no longer affects it. Turn it 1/2 turn at a time and wait for the result a little. Takes a few seconds for the engine to react sometimes.
6) turn the mixture screw back IN about 1/4 turn, you should notice a veeeeery faint drop in idle speed. Leave it there.
7) adjust idle speed from the appropriate screw to about 900rpm. (Whatever is comfortable for you. Some books say 800 but I would not let it idle too low, it steals oil from the bearings)
Thanks, Jan, for the nice troubleshooting flow chart. The carb does only have a thin paper gasket, but will re-check the seal. It was adjusted per the procedure a couple months ago, but who knows? Mixture might have slipped.
I don't have Bentley's at hand . . . does it have pictures of how to remove the top to peer into the bowl? I'll have to practice this move a couple of times so that when the engine dies while I'm on some errand on a city street I can coast over and do a curbside bowl inspection.
.................There now, was that so hard? This was in your head all this time and you finally put it up even though it's been posted in the past and is in the RAMVA archives. I copied it though so that I can use it in the future and maybe even post it someday myself so that everyone will think that I'm smart too..........lol .....
You keep saying that, but then you say the tach sinks like a stone when the engine conks out. Is the engine still spinning (and the timing light flashing) even though the tach sinks to 0?
No, the tach reflects what the engine is doing. Else I would be asking "how come my tach goes to zero but my engine does not?" The tach falls to zero, while the timing light slows to zero, and the engine falls quiet.
Anyone got a link to a schematic diagram of how something like my 34 PICT-3 carb works? Idle circuit, bowl, needle valve, idle passage . . . those things? I want to get a clear picture in my head of how the bits are connected and interrelated.
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