Race / Performance carbs

[boobie]

Re: Race / Performance carbs

A mentor of mine told me many years ago that it takes a 50% increase in horsepower to gain a 15% in speed in a boat. He may not have been wrong.

 

[Scubaproh20]

Re: Race / Performance carbs

Whats the math on 15hp to 40 ? lol , max with the 15 evinrude was 12mph, so 175% increase should be 52.5% speed increase adds to like 18mph, (that took like ten min of math lol) I'm really saddend by the idea that a 8 pitch prop is ideal i'm confident it cant be, when i'm nearly certain 40hp with an 8pitch can move a pontoon the same speed (my friend has a 35 rude with an 18' pontoon with an 8 and it does 18-20 ) what isn't adding up?

Someone please confirm my theory a long shaft on a short transom is that severe and causing all my fears that I should have put a 150 on my rowboat!

 

[levi_tsk]

Re: Race / Performance carbs

whats your wide open throttle rpm with the 14 pitch prop?

 

[Scubaproh20]

Re: Race / Performance carbs

Not sure no tach but it can't be 4500 and I could get maybe 1/2 throttle b4 hitting 4500 with the 8pitch, I also fixed a short on the vacuum cutoff switch circuit, yet untested since repair.

 

[levi_tsk]

Re: Race / Performance carbs

there are some schools of thought (me and fatzbullet for instance ) that seem to think that if you turn a little higher rpm at wot that it helps to make a motor last - especially on the older cross flows they just dont like to lug - i equate it to this: imagine carring a piano around in the back of your car ... it will shorten the life of your engine because it has to work harder to move the car right- same with an outboard when you over prop it -just happens faster because an outboard turns high rpm while your car turns a relatively low rpm - an operating rpm isnt a suggestion and its better to slightly exceed it in a two stroke than to stay below it
picking up what im throwing down?
id shoot for 4800rpm@WOT that way when you put your girl and a cooler of beer in the boat your still running about 4400-4500
and like i said before... if you wanna go faster than that get a bigger motor

 

[Scubaproh20]

Re: Race / Performance carbs

Does the gas can cap need to be cracked open a notch if so i"m a really big fool And I need to sit and think about the important things in life.

 

[levi_tsk]

Re: Race / Performance carbs

there should be a small thumb screw in the middle of the cap - THAT needs to be wide open

 

[Scubaproh20]

Re: Race / Performance carbs

There is no thumb cap its one of these tanks, I thought they were vented through the connection of the hose.

 

[Scubaproh20]

Re: Race / Performance carbs

http://www.treasurevalleyclassifieds.com/omc_5_gal_gas_cans
this is the exact type of fuel tank I use

 

[ONERCBOATER]

Re: Race / Performance carbs

yes and in the middle of the cap/filler is a valve that you must open when running the engine... you only have a single fuel line leading from tank to engine... therefor open vent. That said.... possibility for leaky fittings and connections to let in air bubbles and stall you... but if the lil ven is closed you not going far or fast.

 

[Scubaproh20]

Re: Race / Performance carbs

I re re inspected the carb after i got my carb kit after running a wire throug a port i found a mud wasp crawled in a milling oriface and died partially blocking the high speed oriface i plane out immediately and do 27mph now instead of 13 with 3 ppl thought i should do bout 35 though ill keep trying

 

[Chinewalker]

Re: Race / Performance carbs

No there is NOT a vent in the cap of those OMC steel tanks. The vent is in the male fuel fitting on the tank. The pins are pushed in by the female fitting, opening the vent. The o-rings inside the fitting can deteriorate with age/ethanol exposure. They can be replaced.

 

[Scubaproh20]

Re: Race / Performance carbs

In my search for a solution I thought i'd seen thumb screws but i think its just on merc motors, anyway I got my service manual and realized I was just in a panic of sorts when I couldn't solve the poor performance of my now awesome boat.