74 Merc 1500 Spray Seafoam in bottom carb and it almost dies- No effect top 2 carbs

[supervetteracer]

It's a 74 Merc 1500 tower of power. The motor seems to run fine. Perfectly even compression on all holes. Starts and runs well. But when I sprayed some seafoam on the carbs something off happened. When I hit the lowest carb it almost kills the motor. But when I hit the upper two carbs it feels as if it has no effect at all. Are these carbs working? Shouldn't it have equal effect on all carbs? What could cause this? Do I have a LOT more power waiting to be discovered?

Thanks,

[milkdud]

Im guessing your lowest carb has the idle jet a bit rich or spot on. Introducing more fuel (seafoam) richens it too much and it drowns and looses RPM.

If the upper two speed up or barely no affect when you hit it with fuel (seafoam) the idle jets may be a bit lean. Make sure all your idle jets are turned out equally and sharing the load at idle. The 1500's like to run a bit rich on the idle jets so it accelerates proper.

Your hi speed jets are fixed so you should not notice any more HP.

If its running good, you might not want to change much.

[CrayzKirk]

The lower carburetor might have more of an effect due to the transfer of the excess fuel from the lower bearing to the upper bearing. I've used storage seal on my 1350 and 1500 and it had the biggest effect on the bottom carburetor. I was never able to stall the motor as the instructions indicated. Maybe if I had three hands so I could spray into all three carburetors at the same time...

It just smoked A LOT...

Kirk S.

[supervetteracer]

Got it. So this doesn't mean that my other two carbs are not working. Cool. Just thought I would check. Everything is running fine in that department so I think I'll not screw with it. Perhaps I'll take it out again tomorrow. It's such a FUN boat.


Thanks

[vtboy]

just run it use good gas and oil

[Glasstream15]

Use fresh 93 gas or 89/90 NonEthanol gas. And mix the oil at 40:1. That's 1 pint to 5 gallons instead of 6 gallons. Those old InLines run great that way and the ignitions are easily capable of handling that ratio. The motor will thank you.

[vtboy]

use the highest non- ethanol gas over 93 your wasting your $ but any pump gas mixed holds water this will kill your engine
use good oil , cheap oil leave deposits and will kill perforance, my thoughts