running 140 hp without air silencer

[warrior1]

is it a bad idea to run the engine without the cowl and airbox silencer?
i was doing some tuneup work and took off without them on.
i achieved a max speed of 53 MPH. when i returned and to the dock and put them back on, i couldnt get over 51 MPH. is this because of a ram air effect?
will this cause the engine to run lean?
it sure ran like hell and sounded great.

 

[Walker]

Re: running 140 hp without air silencer

I'm gonna say its fine, but not a good idea to run without the cowling on. You could injest some water that way. Can't see how it would lean out your mixture though. The carbs are venturi type cards and the more air the goes thru the carb throat the more gas the venturi tube flows. Now with the airbox and the cowling off its theoretically possible to force enough air the outstrip the capacity of the venturi tube but I doubt you could reach that point with a factory setup. Maybe some of the guys that used to run the hot little hydros can shed some more light on this.

 

[Bindernut]

Re: running 140 hp without air silencer

Most two-cycle engine airboxes have a little more restriction compared to what the carbs can flow and will cause a difference in air/fuel ratio when installed or not installed. Do your tuning with the airbox installed and you should be good. Yes, it will cause a lean mixture running without it...possibly enough to damage the motor. Probably not, but possibly...be on the safe side. It's better to foul a few plugs than burn down an engine!

 

[Joe Reeves]

Re: running 140 hp without air silencer

It would help if you either listed the model number or if absolutely sure, the year of that 140hp.

If it should be a loop charged model, then yes, the carburetor face plate is an absolute necessity. There is a thick gasket attached to the face plate that presses against the carburetors. Without that assembly, the engine runs lean.

 

[warrior1]

Re: running (1979) 140 hp without air silencer

Re: running (1979) 140 hp without air silencer

1979 sorry about that. i try to include year whenever i ask a question.

 

[Dhadley]

Re: running (1979) 140 hp without air silencer

Re: running (1979) 140 hp without air silencer

Yes, we used to find that in some cases the airbox on a crossflow (now we're talking crossflow here, not looper) was restrictive. Also some motors could use a little more air intake. We'd do all kinds of things like take the front plastic decal mount off, drill a hole behind it and space the plastic piece out so it'd get more air in the cowl.

We'd remove the air intake plate under the carb in the lower pan. Only a good idea on a race boat. With the plate gone it's real easy to injest water.

We'd open up the intake under / behind the rear handle on the hood.

Some guys even ran a hose from the hood into the boat with an in-line blower. Kinda like the ducted Sea Drive that came along years later.

Naturally you'll need to check the jetting and possibly rejet to compensate for more air.

Again, we're talking crossflow. Screwing with the air intake on a looper is a good way to ruin a perfectly good piston.