Starving Under Load? Options

[kenshapiro2002]

Just brought the green machine back from CT this afternoon. After filling her up, she started to starve under load (trying to accelerate above 3,500 RPM...getting up a hill, etc.) so badly at one point I had to pull off the highway...she was dying. After sitting for 10-15 minutes, she fired up and was alright for another half hour. Then it all repeated. After the second rest she made it all the way back to Baltimore and ran beautifully for 90% of the time. I could sense a little starvation once in awhile.

I'm a shade tree mechanic at best, but my guess is that even though the seller (A Porsche tech) said the fuel tank was amazingly clean and needed nothing after being stored for 20 years, the fuel filter was getting clogged, and perhaps sitting for a while let things "settle". The seller suspects points. Any opinions?
Thanks in advance,
Ken

[Kirmizi]

http://www.carburetorclinic.com/weber_tech.htm
Try there, in addition to searching this site.
Mike

[nycchef]

http://www.carburetorclinic.com/weber_tech.htm
Try there, in addition to searching this site.
Mike

this worked for me..eventually





A copy of my carb tuning method post for Trekkor, a few years ago.

Assumptions: the carbs have the optimum jet and venturi package (good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good.

Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist.
Start and warm up the engine.
Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin igntion wrench to snap them off.
Turn the mixture screws all the way in and then 5 half turns out.
Turn the air bypass screws all the way in.
Turn the idle speed screws out til it just touches, and then in 5 half turns.
Put on your hearing protection and start the car.
Use your STE and find the barrel that pulls the most. We'll call this one baseline.
Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter)
Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels.
Go to the other carb and do the same thing.
Snug the jamb nuts on the air bypass screws.
All six (or four)barrels should pull the same amount of air at this point, if not repeat air adjustment proceedure.
Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance.
Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm.
Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest rpm, then turn it in 1/4 turn.
Do the same with the five other mixture screws.
If you have to turn the mixture screws more than two turns either way, you've got the wrong jets.
Recheck side to side and individual air balance, adjust as needed.
Road test the car.
If you get snapping and poping out the intake, it's generally a lean condition.
If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich.
If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets.

That's a rough, five minute draft of my carb tuning proceedure, hope it helps!

If it goes good it should take about 45 minutes, if not about three years.

PK

Another good tip: If you think you have a lean cylinder (idle jet plugged) you can back out the jet carrier a half to one full turn and the engine should stumble, if it doesn't change theres a good chance the jet is clogged. This primarily applies to the 3 barrel carbs, as the 2 barrel IDF's have a different type idle jet set up.

Don't diminish the value of correct ignition timing, and valve adjustment, it makes a difference. Also make sure your linkage is dead nuts the same length.


--------------------

Perry Kiehl

several mid engined Porsches
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