I would like to conduct an informal poll of those of us who have tripowers on modified engines, to see what size center jets everyone is running. I am contemplating experimenting with bumping up my center carb jet size from 63 to 67 or so, to see if I can improve performance while on just the center carb. A recent article in Hemmings about the Bobcat treatment stated that they would install size 70 jets for this very reason (they also say that the carb was "reworked", I don't know what that means exactly). I know OMT recommends 70-63-70, which is roughly what I have now (69's in the outers, .040 389). I would like to know if anyone increased the center jets, why they did it, and their (hopefully) positive results. I guess I'm most curious about those of you with 389/400 motors. Thanks!

I would like to conduct an informal poll of those of us who have tripowers on modified engines, to see what size center jets everyone is running. I am contemplating experimenting with bumping up my center carb jet size from 63 to 67 or so, to see if I can improve performance while on just the center carb. A recent article in Hemmings about the Bobcat treatment stated that they would install size 70 jets for this very reason (they also say that the carb was "reworked", I don't know what that means exactly). I know OMT recommends 70-63-70, which is roughly what I have now (69's in the outers, .040 389). I would like to know if anyone increased the center jets, why they did it, and their (hopefully) positive results. I guess I'm most curious about those of you with 389/400 motors. Thanks!

So you are using a 65 tri-power?

Tom V.

I increased the jet size on my 65 tri power center carb from 063 to 065. My 389 is mildly modified. 030 over and a crane single pattern power max cam. The reason I did is that I noticed the spark plugs were indicating a lean condition. Since I installed the larger jets The plugs are now reddish tan indicating normal combustion. It also reduced the engine tempurature from 190 to 185. No plug fouling experienced. Did not increase the size on the end carbs. Hope this helps.

Yes, Tom, '65 is correct. A recent inspection of my plugs showed them to be dark reddish-orange, so I may not be as lean as I think.