Smelly gasoline fumes in the cockpit indicate a healthy carb mixture? My tech says '69s were not adjustable to lean out. Do I have to live with a headache and bloodshot eyes after every ride?

 

You should consider a tailpipe AFR sniffer and check the AFR ratio.

 

With the SU carbs HD8s richer or leaner can be achieved by thinner or thicker needles and can also be changed (somewhat) by raising or lowering the float !

Now Strombergs require needle and jet changes and if you want to gain a bit of performance with strombergs, try decreasing the top spring strength, opening up the vacuum tube that feeds the diaphragm above. Older strombergs have an adjustable needle centring nut at the base, make sure there is an audible click when the needle drops to the base, if not adjust again.

 

Thanks, the techs did just that, but they used parts out of a TR6 to lower the labor and parts costs. Car is running at altitude now w/o me smelling like petrol after half hr run!

 

Hello felinecat,
Metering Needles and Jets don't have to be replaced to alter the fuel mixture for either type of Stromberg carburetor. The later type that has a movable needle in the air damper can be adjust up and down to alter the mixture. In the earlier type, where the metering needle is fixed in the air damper, the mixture can be altered by adjusting the Jet up and down from below the fuel bowl.

Using a weaker Damper Spring on its own is not the maker of surefire performance improvement. For any given engine vacuum, the air damper rises more with the weaker spring. The amount of fuel that can be sucked from the fuel bowl is contingent on the clearance between Metering Needle and Jet and the speed of the air traveling over the bridge of the carburetor. As the height of the air damper will be greater with a smaller opening of the butterfly when using a weaker spring, the speed of the air over the bridge will be slower and therefore, less fuel will be sucked into the air stream resulting in a leaner mixture. When changing to a different rated air damper spring, it should be done in concert with selecting a compatible metering needle.

Hello ebrand,
It likely that there was a contemporaneous fix of a fuel leak when your mechanic swapped the parts from the TR6 Strombergs. A rich fuel mixture doesn't result in a fuel smell inside the the car. Irrespective of the fuel/air ratio, the mixture is being sucked into the cylinders of the engine and burnt there or in the exhaust, not hanging around to permeate the cabin.

Regards,

Brent

 

Well, I don't doubt that the task changed as they messed with the top-end rebuild. But whatever they did, there are no longer fumes or nasty smells driving me out of the cockpit..either gas or exhaust. But with these animals, you never know what might rear its ugly head, requiring yet another 'intervention' during the upcoming driving season.

So thanks Brent...I am definitely keeping this thread to show my tech!

Regards,

David

 

My '70 OTS has fixed needles and non-adjustable jets...They are the CD 2 carbs...I found that a gas smell was due to leaky "O" rings on the jet tube. Not obvious, unless you run your hand across the underside of the carbs..These rings are very suseptible to leakage, when aged. Pretty easy to replace.
Edward