1979 911sc HELP

[sturkph]

my father and i ran across this 911 at deal.. we have rebuilt motor.. fuel distributor has been rebuilt professionally.. we have had the car running a few times.. found some air leaks.. repaired them.. ran good.. he cranked it one morning while it was cold.. and before it could even catch a good spin it blew the airbox apart.. we have been catching hell trying to fine tune this car... any suggestions.. any tricks of trade we may be missing..???? we are mechanics, yet new to this type car..

[Oh Haha]

Did you repair or replace the air box? it will run like craaapp until you do. Install a pop-off valve in the box to prevent future problems.

[sturkph]

the airbox had a pop off in it... the box was weak from a fire the car had sustained from previous owner.. we had to replace fuel lines on car... i am looking for a box now.. cant stand the $500 price of new one..we are having trouble adjusting air/fuel mixture.. timing... and so forth.. any tricks???

[pete3799]

Don't even try to adjust anything till you replace the air box.

[sturkph]

No doubt I have to replace it now. But before it blew apart we couldn't get it right. There is a possibility it was leaking. Would that have caused the popping back. And surging going down road? Even a very minor leak?

[j911brick]

Even a small crack in the air box will make it impossible to tune. If the leak is large enough it won't run at all. You cant have any leaks between the air box and the air flow sensor. You need to start with the basics: compression/leak down. test fuel pressure. It must be exact and you will need a special CIS fuel pressure tester.

[Oh Haha]

How did you set the fuel mixture. Yes, it would have been wrong with an air leak but you said the fuel distributor was rebuilt.

Surging can be caused by a lean or rich condition.

[boyt911sc]

Originally Posted by sturkph

my father and i ran across this 911 at deal.. we have rebuilt motor.. fuel distributor has been rebuilt professionally.. we have had the car running a few times.. found some air leaks.. repaired them.. ran good.. he cranked it one morning while it was cold.. and before it could even catch a good spin it blew the airbox apart.. we have been catching hell trying to fine tune this car... any suggestions.. any tricks of trade we may be missing..???? we are mechanics, yet new to this type car..

This is easy to fix!!!!! Provided you know where to look and apply the appropriate tests to evaluate the result/s. You need to determine the fuel pressures, first and foremost, for fuel injection troubleshooting. Followed by air leak or vacuum tests. You need decent ignition sparks and a fully charge battery too. Do not tinker or touch the mixture screw at this point. Leave it as is for the meantime. You don't need it to be precisely set to get the engine running unless it was set off the chart!!!!!

You are mechanics and should be able to do the diagnostics with no problem. PM me and I'll walk you through the whole procedures. Avoid the guess work and it is fun to do CIS diagnostic.

Tony

[Gunter]

sturkph,

Get the Bentley SC Repair Manual and read about the Bosch K-Jetronic CIS and how to check the system and components.

Vacuum leaks have to be eliminated plus system- and control pressures warm/cold have to be right.

Post some pictures from all around the engine so we can see the lines, connections and components and get the Bentley.

[racingredsc]

Be sure you check the intake boots ! More common than a cracked box. I have a bottom box w/pop-off valve installed posted under 911 classified.