60 hp on a 20 ft pontoon = 13mph @ wide open???

[mstrud]

Ok, i have a 1986 60 hp evi on a 20 ft fiesta toon. I recently put three carbs on it from a 70 hp evi. It fires up a lot easier then it ever has before (maybe cuz two of the previous carbs had full length cracks in the high speed nozzles). but WTF??? i only can achieve 13 mph on my gps. in my estimate i oughtta be hitting at least 19-20mph with a 60hp two stroke, led alone with 70hp carbs. Am i way off in my expectations or is a cylinder not firing or what? I havent tested the spark on any of the cylinders. I just dont know what to think. also the motor works great, but im still loosing fuel pressure (every hundred feet at wide open itll stall without ball pumping), even though every inch of fuel hose in the motor is brand new with brand new clamps and i can assure you there's no leak whatsoever between the tank and motor. Im in desperate need of some perspective. Please enlighten me anyone...

 

[mstrud]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

ps. it aint the ball.

 

[SgtMaj]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

In my opinion (which doesn't count for much), the two problems are one and the same. If you're losing Fuel pressure at WOT, then you're also losing HP.

You may have a good fuel line up to the engine, but I would follow it from there all the way to the cylinder and make sure it's good (not clogged, or partially clogged, which would be my guess) all the way to the cylinders.

Other thought, might be far off in left field... tank might be sealed too well, creating a vaacum at WOT that reduces fuel pressure.

 

[F_R]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

One "forgotten" tool these days is a fuel pump pressure/vacuum gauge. Shouldn't be expensive and is a big time saver diagnosing problems such as that.

 

[tashasdaddy]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

clogged vent in gas tank? link n sinc? sucking air, fuel system?

 

[kenmyfam]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Ok, i have a 1986 60 hp evi on a 20 ft fiesta toon. I recently put three carbs on it from a 70 hp evi. It fires up a lot easier then it ever has before (maybe cuz two of the previous carbs had full length cracks in the high speed nozzles). but WTF??? i only can achieve 13 mph on my gps. in my estimate i oughtta be hitting at least 19-20mph with a 60hp two stroke, led alone with 70hp carbs. Am i way off in my expectations or is a cylinder not firing or what? I havent tested the spark on any of the cylinders. I just dont know what to think. also the motor works great, but im still loosing fuel pressure (every hundred feet at wide open itll stall without ball pumping), even though every inch of fuel hose in the motor is brand new with brand new clamps and i can assure you there's no leak whatsoever between the tank and motor. Im in desperate need of some perspective. Please enlighten me anyone...

How did it run before you put the 3 replacement carbs on it ???
Has it ever run what you would consider "properly" and if so what was properly.
Fuel issue must be diagnosed and fixed.
Beyond that you also need to analyse the set up. (prop diameter and pitch, motor height, trim settings etc) and how about a compression check to boot !!!
You say the motor works great but then tell us you have a fuel issue and it wont go fast enough ??
Any idea what rpm you are getting at WOT ???

 

[emdsapmgr]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

The WOT performance sounds like the carbs are running out of fuel. The engine is consuming more fuel than the pump can replace. If you can get it to run properly by constantly priming the fuel hose bulb, I'd check the pump. Do you know if the engine is getting to full rpm (5500)? What is the prop pitch? Should be an 11 (or 13.) Are the new carbs adjusted properly for opening fully when at WOT? Some carb throttle plates will open so far, they start to close again-reducing airflow. Is the link arm advancing the spark fully as the throttle advances?

 

[Silvertip]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

You have answered you own question! If you have to pump the primer bulb repeatedly to keep it running you have a fuel starvation problem. If the fuel tank has a anti-siphon valve they are known to stick thus restricting fuel flow even though the bulb seems to be able to draw fuel. Those 70 HP carbs may have the float levels set too low. But the prime suspect is the fuel pump. Lastly, you may also have 21 year old pontoons that have water intrusion. If they are aluminum they may have drain plugs in them. Trailer the boat and pull the plugs. If you can't tell whether the engine is running on all cylinders, at least pull the plugs and check them. Bone white and wet = not firing. Plugs should be light tan after an extended wide open run. Lastly, the weight of the pontoon has more to do with it's speed than it's length. Some of those older 'toons were really heavy.

 

[steelespike]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Poor fuel supply?? Are you sure all the connectors are good? They can sometimes not leak fuel but will suck air.Of course you may have a bad fuel pump.Solve the fuel supply problem.Get back to us with the Prop demensions and motor rpm at speed.With a proper setup you should be in the 20 to 22 mph range.Perhaps more.

 

[samo_ott]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Sounds like a fuel pump issue but everyone knows that already. Are they steel or aluminum pontoons? Some of the old ones are steel and weigh a ton.

Btw, my 16' aluminum pontoon boat does ~13mph with a 1966 18hp on it.

 

[DJ]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Forget MPH. What is the RPM?

The wrong prop will perform very poorly, eat fuel and kill the engine.

 

[ezeke]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

If you did not make note of Silvertip's mention of the anti-siphon valve, you probably should.

"If the fuel tank has a anti-siphon valve they are known to stick thus restricting fuel flow even though the bulb seems to be able to draw fuel."

 

[HighTrim]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

As said the Anti Siphon valve is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a ball, spring, and a ball seat. Remove it, clean out the inner components converting it to a straight through fitting. Hopefully that cures the problem. If you find that fuel is running back down through the valve, you will need to replace it, although the primer bulb should prevent this from occuring.

But I feel you answered your own question as Silvertip said, if pumping the primer bulb picks it back up check that the carb floats are properly set or arent defective,failing fuel pump air motor diaphragm ,leaky or dislodged pulse hose between crankcase and fuel pump,etc...

 

[PW2]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Forget MPH. What is the RPM?

The wrong prop will perform very poorly, eat fuel and kill the engine.

Absolutely. If you're not getting the proper RPM, you might have an engine problem. If you are getting the proper RPM, you might have a prop problem, or depending on the design of the hull (whether it wants to plane or not), you may be simply running into the physics of max hull speed.

 

[BillP]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

If helps to benchmark how fast it should go...I have a 20' MonArk toon with 50hp 4 stroke. It gets 19.5 mph (gps) with two people and 30 gals of gas. It does 14 mph with 6-7 people and all the stuff for a day on the water.
The motor has a standard lower unit and not the bigfoot type with gear reduction and big prop. Your boat should run about the same.

bp

 

[ShellBack101]

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

Re: WTF??? 60 hp on a 20 ft pontoon = 13mph @ wide open???

I would be curious to hear what you find is causing it. I have a 1996 Crest Pontoon 22ft with a 50hp Johnson. It was running rough so I sent it to the dealer for a Link and Synch, when I got it back it wouldnt get back up to RPM and couldnt get more than 12-15mph out of it @ 4000 rpm. Not sure what the dealer did but he insists that it is set up right. Before I sent it in I was getting 20mph, 5500 RPM but rough idle\
KEEP US POSTED

 

[samo_ott]

Re: 60 hp on a 20 ft pontoon = 13mph @ wide open???

Aren't anti siphon vales only on built in tanks? Many smaller engine pontoon boats have just a couple of external tanks, so it depends on his tank(s) whether this is the issue or not.

 

[Harker]

Re: 60 hp on a 20 ft pontoon = 13mph @ wide open???

I've got an 18' pontoon with large pontoons and a 25hp Honda...I get 13mph gps with three of us on it. I think I need to re-prop though cause 4500 is all the rpms I can muster. Good luck on yours.

 

[mstrud]

Re: 60 hp on a 20 ft pontoon = 13mph @ wide open???

Ok, so... i havent checked the cylinders yet. i did check the linkages and yes at WOT the carbs are wide open. The toons have no water in them, are made of thin aluminum there are no lifting strakes or anything like that, no furnature on deck other than a console. as i said there are no leaks in the lines at all, vent's clear. I did try running it with the fuel pump disconnected electronically. the boat ran much like it normally does. WOT is too slow, and it begis to stall every 100 ft, however the ball never really got as firm as it normally would, though it did get firm nonetheless. So i'm thinkin there may be a problem there. Anyone care to verify that? Also i dont run the VRO i've heard about getting lone fuel pumps for cheap. can anyone fill me in on this conversion? Where to find these pumps? The exhaust doesn't impress me as being any richer then anyother two stroke so i dont really think any cylinders aren't firing.

 

[mstrud]

Re: 60 hp on a 20 ft pontoon = 13mph @ wide open???

And again the carbs are immaculate. Perfect condition off of an 86 70hp evi fresh rebuild, floats are brand new and perfectly flush.