DMSA 1592cc High Altitude Jetting

[73Ragno]

I'd like to do a quick sanity check on my carb jetting calculations.
I have a 1973 with the 1592cc engine, originally fitted with a 28/36 DHSA3. Now I have a 34 DMSA from a 1974 with a 1756cc engine. I'm in Denver and using 5500ft elevation for my calculations.

The stock DMSA jetting (primary/secondary) is Idle: 50/60 Main: 140/145 Air Corrector: 165/155
Adjusted for 5500ft per Weber, Idle: 45/55 Main: 130/135 Air Corrector: 190/180
Now, multiplying those values by (1592/1756) to match the lower displacement, Idle 40/50 Main: 115/120 Air Corrector: 170/165

Is this at least a good starting point? I feel that it's pig rich right now but I don't want to go to far the other direction and damage something.

[Nut124]

...Now, multiplying those values by (1592/1756) ...

?? Where do you get that ^^ from? No such thing. Engine displacement does not in itself require jetting changes.

Now, elevation change can affect ideal jetting. I'd abandon the (1592/1756) calc and try the default jets and see how it runs. Rich always runs OK at the expense of fuel economy.

[18Fiatsandcounting]

I agree with Nut that there is no need for a correction due to the different engine size. A smaller displacement engine will have less air velocity through the carb, so less fuel will be drawn into this airstream, and so in a way it's self correcting.

Correcting for altitude is necessary, and for 5500' what you have suggested seems a reasonable starting point:
Idle: 45/55 Main: 130/135 Air Corrector: 190/180

If your spark plugs remain black and sooty, my guess is that there is another issue: Engine too cold, wrong heat range for the plugs, not driven long enough to completely warm up, choke sticking, etc.

-Bryan

[73Ragno]

Awesome thanks guys!