Hey all,

Got my 914 running to the point after sitting for 15 years where I can actually drive around the block. Trying to synchronize the webers and noticed that when I put the unisync over cylinder #1, the engine's rpms rise to over 2000. Noticed the same on cylinder #6 but not as pronounced. Opening up the unisync all the way still causes the reduced air to the intake to cause the rpms to rise.

Is this normal?

I have the idle and air mixture screws at the default settings and would try adjusting but it developed an oil leak under the oil filter somewhere so have to fix that first before tuning more. This car has been 2 steps forward, 1 step back all summer. Almost there though.

Thanks for the insights.

Peter

I can't say much about the sync but as far as the leak by the oil filter you may want to check the oil pressure switch for the leak.

Do a search at the 911 pelican parts technical bbs for the info on this.
Paul Abbott is the main weber guru over there. In order to tune the
webers, you have to do things in a particular order and also have the
engine in a known state.

IIRC, first thing of all is setting valve clearances properly.
Then ignition timing.
Then with the 2 banks disconnected from each other, equalize air
flow of the 3 cyl of one bank, then equalize the 3 cyl of the other bank.
Then hook up the linkage again and get it adjusted to both sides are equal.
Then at slightly high idle set all the mixture screws (easier said than done).
Then set idle stop so that the throttle plates are over the lowest
progression hole (which is not able to be seen unless carbs are off car).

Easy

which carb tool are you using for synchronizing?

this one, i hope:



KT

Thanks for all the tips. I am using the older unisync tool. Maybe it's time to invest in a newer version.

It doesn't seem right to me that the rpms would rise when the airflow is decreased over a particular cylinder head but my "working" theory (and by working meaning only what I've learned in the last 2 months working on these webers and reading about them) is that as the air is reduced, the vacuum is increased and therefore causes more fuel vapors to be injected in to the engine. Or it could be a vacuum leak is part of the issue though I have checked for those and can't find any.

The engine was completely removed and rebuilt by a local Porsche shop so the valves are set. The carbs have been completely stripped and soaked in carb cleaner for hours. I think all the passageways are clear as adjustments can be made on the idle and air screws.

I installed size 75 idle jets that I had and that seemed to help out tremendously with my stuttering past 2500 rpms while driving. I'm going to take out the emulsion tubes and let them soak overnight and put in a extra set of F3s I have to see if that helps.

Thanks again,

Peter

Here's my carb tuning proceedure from a March 03 post:

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 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 idle, 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

NOT NORMAL

as others suggest - it's probably the tool - but ... ??

go here for starters - weber tech
\

buy a copy of Bob Tomlinson's Weber Tech Manual

buy Mike Pierce's Weber book (Pierce Manifolds, Gilroy, CA)


.

I'd add, be sure every thing else is as it should be. If you have a wobbling distributor or vacuum leaks everywhere all the tuning in the world will do nothing meaningful.

PK's write up is spot on.

I can dial in carbs in just a few minutes, thanks to him!


KT

The old style Unisyns do restrict the air intake ... the newer 'snails' are much better.

If your RPMs increase when you restrict the air, it's possible that your idle mixtures are adjusted too rich.