Johnson "70mod"

[hupiveneilija]

Hi!
Off the shelf, made for dellorto 40mm.

[ferdthe4]

very interested to see if the carb stacks and slight enlargement helps much

[hupiveneilija]

To me it seems that throttle response is better everywhere. These should be little shorter to gain more up top. But, we have had very hot here for a long time and it still goes like before on cooler days despite putting one step smaller mainjet!

-J-

[PIP]

sorry to ask this late in the thread, but for a stock 49 ci motor, in racing, should use a 059 jet? is that sea level? also, 19 degrees tdc? thanks a lot.

[71yella]

PIP, we just pulled the 54D jets out of a stock 20" motor and went to install new55D jets thinking it would be an increase ,turns out I think they were drilled? A .059" machine bit fit perfectly, but 19 deg was too much and it lean stuttered on top, backed of to 17 and now it turns up 6350 with a 22 raker, for what its worth? this is on 1656 Havoc aluminum boat, 52mph

[PIP]

any idea the elevation? thanks a lot.

[71yella]

We are in central Arkansas, I dont know the elevation but its hot(90s) and humid now.

[ferdthe4]

odd that it didn't like 19 deg of timing pretty sure that's what my 1992 70hp 56ci was factory, as well my 1987 70hp, I believe even the older 75hp 49ci was set at 19deg factory. Wonder if you outta run an even bigger jet and try 19 deg, maybe not idk?

[71yella]

Well we struggled to break past the 6000 mark until installed a jackpate, now its about as high as it can run and not blow out so we can go back to jetting and timing, like PIP said 19 seems to be the magic number?

[ferdthe4]

If you read through past post on here you'll see the op has tried going past 19 and has had some issues, I may be wrong I think he is running 20 deg now or maybe he is back to 19. I know he tried 21 maybe 22 and chewed up a piston. Hopefully hupiveneilija chimes in on his results. Now granted he may be running 20 or 21 but he has done some port work runs a prop and low water pick up that let him raise his motor way up and is up in the rpms with his motor.