Force 120 carbs

[cfstar18]

Hi All,

I hope I can get a simple answer to this. I have an 18 ft Nitro fish and ski with a 120 force tracker and it runs decent, but not as fast as I would like. I get about 35 MPH / 4900 RPMs WOT with two guys and a load. I have a friend with the identical boat and prop that gets 45 MPH and 5200 rpm with the same load. My boat sat for two years..is it possible that this is a CARB issue? Do they need to be rebuilt? At times it dosent like to idle espicially after i have been running it all day, but I always get it going. Almost like I need to warm it up every time even if it has only been off for a min or two. My friend turns his key and his boat will idle..mine I have to warm up everytime. The carbs look like they are opening all the way too. Please let me know if you have any ideas...thanks..new to this boating thing.

 

[jerryjerry05]

Re: Force 120 carbs

What pitch prop do you and your friend have? At those rpm you can go down in pitch say from a 19 to a 17 maybe a 15.Post the pitchs you find.
Bad performance at low rpm could be the air screws need adjusting,the carbs need cleaning.Water in the fuel.The return fuel system in the block is clogged.
Jerry

 

[cfstar18]

Re: Force 120 carbs

HI,

Thanks for the reply. We both have 20" props (original) laser II. The recommended WOT rpm for our boats is 4900 to 5250. He is getting it with top speed and I am not. Please let me know where to start. I really don't think it is a pitch issue. THanks

 

[Frank Acampora]

Re: Force 120 carbs

No two boats are identical! What is the load in his and what is the load in yours? Is your flotation foam waterlogged, making your hull way heavier? Is his engine Jacked up on the transom just a bit higher than yours? What condition is your prop in? How about your fuel pump? Is it delivering the amount your engine needs at full throttle? Does your hull have a hook or rocker in it from sitting on the trailer? How dirty is the bottom? There are SO many variables between identical hulls: If they add up, significant differences in speed can occur.

On an 18 foot bass boat, I would expect a bit more than 35 out of your 125 so start with the outside and check all the obvious speed stealers, then go back to the engine. Start with a compression check to see if there is any obvious damage, then change the plugs. After that check the timing and ignition system. Set the idle speed to 700-750 RPM in forward gear in the water. Then as a last resort, fiddle with the carbs.

Whenever an engine starts to give problems it is a natural impulse to mess with the carbs. Unless they have a proven problem, they should be the LAST thing to touch.