Day Two of Porsche Ownership: Tuning Weber Carburetors

One thing that I have learned from buying multiple air-cooled Porsche is that a certain amount of deferred maintenance and adjusting is necessary to set your new Porsche up for your driving style is necessary.

The Throat of the Weber Carburetor

In my case there were three primary elements to address with my new 1968 Porsche 911HR (Hot Rod) as identified in the Day One Inspection Article.

1. Adjusting the hand brake light sensor

2. Tuning the Weber Carburetors.

3. Replacing the Spring Plate Bushings.

The hand brake sensor adjustment was an easy fix and I was no longer staring at a glowing alert light. The other two fixes would require a mechanic as they were beyond my ability.

First Visit to the Mechanic

use a mechanic, Bruce for my air-cooled Porsches that is the type of mechanic we all want to find. He is a former Nascar mechanic, but his true love is working on Air-Cooled Porsches starting with his 40-years owned Porsche 356. He requires his customers to be referred to him because he wants Porsche enthusiasts. His shop is non-discrete but you don’t go to Bruce for the coffee and donuts in the waiting room. You go to Bruce for his expertise in keeping these old Porsche on the road.

After living with my new ’68 for a week or two, I made a list to have Bruce take a look at that included four primary items.

1. Tuning the Weber Carburetors.

2. Inspecting the Spring Plate Bushings.

3. Adjusting the shift linkage.

4. Identifying the oil leaks.

Bruce kept my ’68 for a couple days and then called saying the car was ready for pick-up with the report that it is solid car with a strong engine even though the rebuild is old, but not with many miles on it. (Approximately 15,000 miles on the rebuild that was completed about 12 years ago.)

3-Stacks of the Weber Carburetors

The first job was to tune the six Webers. Bruce started by asking where the car came from. The car was out of Rhode Island that is sea level while Asheville is approximately 2,200’, while my house is 2,800’ and most of the driving throughout the mountains is probably 3,000’ -4,000’. This change in altitude where the air is thinner will have the Webers running rich since the air fuel mixture is off with heavy fuel entering the venturi within the velocity stack when the air is thinner. This alone could be the reason for the fuel smell coming from the exhaust.

Mechanic's Notes on Weber Airflow

Airflow Meter

The next step was to measure the airflow of each carburetor to balance all six. As you can see from Bruce’s notes, the carburetors were not balanced as measured with the airflow tool. The jets were cleaned and adjusted and then the six carburetors were balanced for a 1 ½ airflow measurement. The next step was to synch the linkage of the carburetors. The left bank was opening earlier than the right bank. The Weber Carburetors were now tuned for the mountains of the Asheville area.

The inspection didn’t stop there. The points cleaned and timing adjusted. The plugs were also cleaned and gaped. Everything was off so Bruce just brought the engine back into spec.

An inspection of the Spring Plate Bushings confirmed the clunking and squeaking that was being heard from the rear suspension. The car is lowered so my initial thought was that there was wheel rub, but his was not the case. Bruce measured fender height at all four corners and the right rear was riding lower than the other corners and a visual inspection of the bushing indicated it was worn and needed replacement.

The dogleg shift from first to second is tricky to get used to but Bruce also confirmed the syncho is worn but with his adjustment of the linkage and my better understanding of how to make that move from first to second, it wouldn’t be necessary to replace the synchos at this time.

The oil leaks are more troublesome with leaks coming from the front and rear of the engine seals, the cam housing and transmission tail housing. The hope is that since the last owner was a light user of the car, that they seals dried out and since I will be a heavy user of the car that as they get lubricated they may tighten up and start sealing better. This will have to be watched along with regular oil level checks.

A general inspection of the vehicle also identified that the front wheel bearings were loose and needed adjustment; a common problem in an early-911.

Mechanic Notes on Work Performed on Porsche 911HR

As soon as I jumped in the car, I noticed right away how smooth the engine was under acceleration. Though the sound of the popping and throaty roar of the maladjusted Webers sounded cool, it just wasn’t right. I was now driving in confidence.

The next step will be to replace the Spring Plate Bushings. Bruce doesn’t stock or generally source the parts so an order was put into with Elephant racing for new rubber bushings. The next installment will deal with this fix.

Shakedown Run to Asheville River Arts District

Read about the initial diagnosis at this blog post:

Day One with Your Air-Cooled Porsche: https://www.airbrigade.com/post/air-cooled-porsche-purchase-inspection

Tags: Day 2 Fixes, Weber tuning, Mechanic Inspection of Air-Cooled Porsche Purchase