Another Gastester Update

GIBSON · GIBSON's Garage

After all of the comments here recently on the advantages of the Gunson Gastester I finally got mine in the mail yesterday.
My 73S has 115 miles on the rebuild so I was anxious to be sure I had it set up properly. I've been adjusting MFI systems for years by feel and sound, not the best way to do it.

I set up the Gastester, warmed up the car to 180, checked the initial reading and it was so lean I'm not sure how the car ran.
The Gastester is set to 2% to start, as soon as the probe went in the tailpipe the numbers dropped and stabalized at around .1%.
I adjusted the idle adjuster on the pump and brought it up to around 6% then set the main rack adjuster to around 7% at 3K rpm. It runs great. There is some slight backfiring on decel but no flat spots, great transistions and a good idle.
I had to adjust the air by-pass screws to bring the idle down after adjusting CO but they were too far out anyway.
I also noticed that with the car less lean my idle engine oil temp never got above 180 after an extended idle.

So, I will never again try to set up a MFI system without one of these testers. I'm sure there is some error in the readings of this inexpensive machine but I know I'm running better than before.
It's set a bit rich but I think these cars run better that way anyway.

If you've been thinking about getting one, do it. I got the basic version because I have a pertronic points replacement device and don't need to check dwell.

Bruce Herrmann

CraigD · 04-17-2002, 07:57 AM

I'm curious, would a gas tester help setup a carb system?? Seems like a more accurate way to set the idle mixture. Has anyone used this setup for adjusting carbs??

john walker's workshop · 04-17-2002, 08:08 AM

carbs are still a "by ear" thing. the only reason for a tester would be to pass smog.

Early_S_Man · 04-17-2002, 08:50 AM

Sounds great, Bruce!

About that backfiring on over-run ... you may want to check the operation of the rpm speed switch to see if it has failed???

I don't know if you saw the five or so threads last May and June about the failures of those switches ... but here is one that lists them at the end.

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=8074&highlight=mfi+warning

GIBSON · GIBSON's Garage

Warren, I forget. Is that RPM transducer connected to the
switch on the left stack? I've tested the switch by depressing the button and noting that the rpm cuts-off and then goes back up. I have adjusted the linkage so that at idle the switch is just engaged (an audible click). So, I know that the switch works.
Seems like those transducer modules used to have a green sticker on the side of them that indicated something, I can't remember what. Mine has the sticker.
Is there a chance that this is causing the backfiring?

Early_S_Man · 04-17-2002, 11:08 AM

Bruce,

I wasn't referring to the Mocroswitch, but rather, the 'module' that the factory has called ALL of the following in various years' publications ... Rpm Transducer, Speed Relay, Speed Switch!!! Here is a '69-vintage schematic that I scanned from an InterEurope manual, printed, colored with map pencils, and finally rescanned:

The modules were coded with the colored stickers to designate different versions used in carbed 911T applications vs the MFI version ... different rpm operating points!