HELP! Running on Five

[hwy61]

Oh boy, here we go...New to me '70 911T w/2.7 isn't firing on cyl. 6. Has spark, compression, fuel, recent valve adj., 152psi compression. I'm at a bit of a loss. What am I missing? Firing order is correct, and I can see fuel(and have dripped fuel)not even a cough, has Webbers, I have checked the intake, all clear. Can cam timing do such a thing even though 4&5 seem to be firing in time? Read through this thread with interest...

Cylinder #6 doesn't fire

Wish it had a happy ending... : )
Cheers,
Pete

[Steve@Rennsport]

Pete,

That link contains a TON of good advice to follow, especially Grady Clay's.

Did you see a nice fat blue spark on #6 while cranking?

If so, did you connect a timing light to #6 and observe the light flashing while cranking?

Check that cap & rotor VERY carefully.

Remove the idle jet and main jet, drain the float bowl and blow clean air through the idle jet passageway as well as the jet to make sure its clear.

This is good for starters.

[ppickerell]

If this was a 912 you would not be complaining





JK

[1QuickS]

What Steve said with one additional check. There is an air bleed jet in the top of the main throttle body just inboard of each idle jet. These can get blocked with a bit of crud which will make the idle mixture so rich that it won't burn. If blocked then this will also allow fuel to siphon from your fuel bowl into that cylinder until fuel well is empty.

[hwy61]

I've run through it all once at least, but I guess one more time for good luck...

[1QuickS]

If the fuel gallery from the bottom of the emulsion well up to the inlet of the idle jet is blocked then no fuel will pass to the idle jet. Procedure for checking below:

Hidden gallery cleaning procedure:

There is one fuel gallery which I refer to as "hidden" and is the vertical passageway between the emulsion tube well and the idle/progression circuit gallery that runs down the outside of the carb to the idle mixture screw; this passageway requires a special procedure for blowing out/checking for obstructions, the remaining galleries are easy to verify for blockages. Follow this procedure as best you can and you will quickly correct the issue or determine if the repair must be taken to the next level where lead plugs are removed to gain the requisite physical access for clearing these galleries.

1. Drain fuel and remove carb from engine and stuff some rags in the intake ports or cover them
2. Remove top cover of carb body (high pressure air will crush brass fuel floats if introduced into the carb body via the vent pipes or fuel inlets)
3. Remove main jet assembly
4. Screw idle mixture screw closed
5. Remove auxiliary venturi
6. Remove idle jet and jet holder
7. Remove air correction jet (above the emulsion tube)
8. Remove emulsion tube
9. Clean the bottom end of the air correction jet (opposite end from the screw slotted end) and place a piece of duct tape over it; cut away excess tape with razor blade leaving the end completely covered
10. Reinstall air corrector jet and lightly seat it
11. Place a 3/16” to 1/4" dia ball bearing into the port for the main jet and lightly reinstall the main jet assembly (the eraser tip from a pencil may be used as a substitute)
12. Put on some safety eyewear to prevent fuel/debris from being blown up into your eyes.
13. Use an air nozzle and compressed air from your compressor and blow directly into the idle jet port keeping the nozzle tightly against the side of the carb to minimize escaping air
14. If the "hidden passageway" is clear from blockage then air will easily escape from the fuel transfer port that feeds into the hollow wing of the auxiliary venturi
15. If no air escapes then try the procedure on a "good" passageway to check that you have a good procedure
16. Failure to pass air indicates a tightly blocked fuel gallery which will require lead plug removal to clear it.
17. If the eraser gets stuck then install the idle jet and blow into the fuel transfer port or into the emulsion tube well while blocking the fuel transfer port with your finger. Be careful as the compressed air will shoot the eraser tip rather forcefully.

[hwy61]

UP AND RUNNING ON ALL 6 Fuel it was after all. Sneaky little blockage that finally gave up! Thanks for all the the help!

Cheers,
Pete