#2 cylinder blowing back through carb

Hatari · Hatari's Garage

Made a short run in the 911 last evening...maybe 30 minutes. Engine came up to operating temp. and all seemed fine. At a stop sign, it made a sizeable sneeze and then ran on 5 cyls. back home not feeling good at all. In spite of a new fuel filter, I supposed that I sucked some rust into the carbs as I noticed some real nasty rust in the bottom of the tank when I rebuild the fuel sending unit a few weeks ago and the tank had been run low earlier in the week. When I got home, I lifted the air filter cannister enough to know the problem was on #2. Today, I took that bank's carb off and completely dismantled it. No rust, all jets perfectly open and the float bowls were clean. I put the carb back together and started the engine without the breather cover. Number 2 is not drawing air, in fact it's blowing fuel back out of the venturi.

What are the symptoms of a rocker arm shaft coming out of it's bores? No unusual valve noise before the big sneeze, though.

Thanks for any feedback.

Jack McAllister

rstoll · 09-02-2001, 02:43 PM

Have you done a compression check on that cylinder??

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Robert Stoll
83 SC
83 944

Hatari · Hatari's Garage

Haven't done the compression check yet. I will be doing that next (maybe in the morning).
Thanks,
Jack

rstoll · 09-02-2001, 03:23 PM

I would be tempted to pull valve cover and see what's up with the intake valve.

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Robert Stoll
83 SC
83 944

Rot 911 · 09-02-2001, 06:51 PM

Definitely sounds like the intake valve is not fully seating. Could be out of adjustment. Carbon holding it open, who knows. I'd pull the cover and take a look.

Kurt V
72 911E

Two Oh · 09-02-2001, 06:59 PM

Hatari, If you find out that you have a damaged head or valve seat and are in need of a head. Well, I have some used heads in my garage part number 901 104 306 2R if this is what you may need, you are welcome to have one. FOC.

Hatari · Hatari's Garage

Thanks for the help and offers. I'll pull the valve cover in the morning. I just did a complete top end and if anything has gone wrong, it may be a rocker shaft working it's way out of the bore.

Will post my findings in mid-morning tomorrow.
Thanks,
Jack McAllister

RoninLB · 09-03-2001, 06:37 AM

I would put a blow-by gauge on that cyl. or at least blow air in with spark plug hole adapter to air supply. Find out if that intake valve is leaking. If it is air will be blown up into carb..........Ron

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RoninLB

Hatari · Hatari's Garage

The number two exhaust rocker shaft had backed out of it's bore. I must not have put enough torque on that one or maybe the cam tower is worn a little (doubtful...I think it's my fault). I'm out the door to get a new 0.25" drive 5mm Allen socket. I'll be sure the torque is right this time. All the others have not moved since the rebuild. I'm going ahead and changing the oil since a good bit ran out anyway, so I'll check all of them while it's up on stands.

Thanks to all.

Jack McAllister

Hatari · Hatari's Garage

Got it back in and torqued to spec. Went on a short test drive and all is well. I'm glad that if it had to happen it was an exhaust rocker shaft. Looks like if it had been an intake, the engine might have had to be dropped as the working area would be tight and vision limited.

Thanks again to all.
Jack McAllister

Two Oh · 09-03-2001, 06:23 PM

Great Hatari!......My previous offer of a head is not needed! Lucky you. Aren't you HAPPY!
BTW my recent posting of my offer to you for a cyl head was a gift.
FOC= not, " Freight On Delivery"
But, "Free Of Charge"

Hatari · Hatari's Garage

Two Oh,

That kind of generosity is rare. Again, I do appreciate it and this board is a wonderful place for help, although your offer is the first of it's kind that I can remember.
Thanks again,
Jack
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