Hot Rod 25hp 2-stroke Merc Sea-Pro Jet Build

[eric2381]

How shallow would you say it sits when just drifting?

[Positrac]

Originally Posted by eric2381

How’s the unit performing for you so far? Thanks for the write up

I've got a bit of a fuel issue. If I'm cruising along and crack the throttle the motor runs great at WOT for about 10 seconds then cuts back about 10% for a split second then runs WOT again for another 4-6 seconds then cuts back another split second. It will run like that all day and if I cut the throttle back it runs fine. So its like the bowl is running out of fuel.

I've cleaned the carb a couple times, rebuilt the fuel pump, ran without the fuel filter to see if it was the issue, adjusted timing, etc... So far I haven't found out what the issue is. The main jet on the 25 and 30hp models are the same part number. Carbs are the same as well as fuel pumps. I've ran it lean and rich and that doesn't stop it from bogging at WOT. Plugs have been changed and all fuel lines checked for obstructions or leaks. Pumping the ball doesn't change anything. The fuel filter is staying full so it has to be in the carb but its hard to tell what is actually happening in there.

My next step is to put the restrictor carb gasket back in and if it runs fine then I know its getting too much air compared to fuel. I could then keep the open gasket in and try to open up the jet to get more fuel.

I'm actually a bit stumped at this point. Plugs are not showing that it is running lean. Its just running out of fuel at WOT.

Other than that its the right motor for this boat. It goes plenty fast enough and being only 134lbs is over 50lbs lighter than anything in its power range. I cruised over stuff the other day that I would have touched in my old 380 and its on step in a matter of feet. From a stand-still I can get it on step in 6" of water without touching.

Once I get the WOT issue fixed it will be great. If anyone has another idea what the issue is I'm all ears...

[Positrac]

Originally Posted by eric2381

How shallow would you say it sits when just drifting?

4" maybe with a couple tanks of fuel, myself and a bit of gear.

[Positrac]

Originally Posted by ehrgeiz

27mph downstream or upstream?

On my Honda GX390 mud motor setup with the Stryker 420 I was about 16-18km/h upstream into a bit of headwind.

Downstream I was getting 25-28 km/hr.

2 guys w/ gear.

Sorry, I missed this one.

I've had it on a calm section or river where loaded light with just a tank of fuel and I've averaged 27mph up and down. So, 29 down and 25mph up river. At 29mph down river when running not far off shore I can say that's as fast as this little boat should go. You're screaming.

[eric2381]

Well Shoot. That’s too bad to hear you’re having troubles. I don’t know what to suggest, it sounds like you’re well on your way to sorting it out.

I’m definitely interested in one of these units for the future when I’m not working all the time. A four stroke engine would be nice. But, like you say, the weight comes with it.

[eric2381]

4” drifting is great. And it’s lightweight to push off if need be anyways.

[Tannerdog]

Saw your comment on running it rich and lean. Does that mean you have been changing main jets? My thought is even if you are on spec for the 30hp you may want to go with a bigger main jet.

[Positrac]

Originally Posted by Tannerdog

Saw your comment on running it rich and lean. Does that mean you have been changing main jets? My thought is even if you are on spec for the 30hp you may want to go with a bigger main jet.

No, I haven’t touched the main jet yet. But when I open up the fuel/air mixture screw so that it runs rich it seems to bog a bit faster. There is no other jet to buy other than a high altitude jet which won’t work at only 2000 ft elevation. I’m just going to use the next size up number drill and drill out the jet a thou or two for starters. I’ve got a pin vice I can put the drill in and rotate it by hand. It’s just brass so it will be easy to drill.

If it doesn’t help or really messes things up a new jet is cheap and easy to get. I’m really thinking this is where my problem lies.

[Tommy]

Maybe try welding tip reamers. That would open the jet then you could slowly increase in size.

Tommy

[GStyler]

Originally Posted by Positrac

No, I haven’t touched the main jet yet. But when I open up the fuel/air mixture screw so that it runs rich it seems to bog a bit faster. There is no other jet to buy other than a high altitude jet which won’t work at only 2000 ft elevation. I’m just going to use the next size up number drill and drill out the jet a thou or two for starters. I’ve got a pin vice I can put the drill in and rotate it by hand. It’s just brass so it will be easy to drill.

If it doesn’t help or really messes things up a new jet is cheap and easy to get. I’m really thinking this is where my problem lies.

Be sure to let us know how you make out with this.
I've bought the same motor as you ( a 2010). It's sitting at my Dads in ON. Need to get around to shipping it to myself. And I also need to order the Jet leg.

When looking for information on converting to 30 HP, I didn't see anyone else mention having any issues like you are mentioning. Some guys didn't even need to adjust the timing, as it was already advanced to where it needed to be for the 30 from factory.
Like you said, the main jet is the same part number on the 25 and the 30. Shouldn't have to modify it.

I had the opposite problem on a 2012 Mercury 3.5 HP 4 stroke. Once warmed up, the thing would not idle at all. I had to leave it at half throttle - in gear and start it. not the most fun thing in a canoe. haha.
I left ethanol gas in it too long. It turned into boogers, and must have gummed up a passageway. With all the EPA regulations, that carb has tons of tiny passages for preventing unburnt fuel emissions.
I pulled that carb apart a dozen times cleaning all the tiny passageways with wires, spraying brakleen and other dissolvers, blowing with compressed air. I even gave it a bath for a day in an ultrasonic cleaner. No improvement at all. the passageways are cross drilled through the body at all sorts of angles, making it impossible to get a wire down them. I was about to throw the motor in the lake.
I finally gave up on that carburetor and ordered a brand new chinese knock off off of ebay - hoping maybe the chinese knock off had less EPA features than a genuine one. haha. It was the most excited I have ever been to order something made in China. I bolted that thing on, fired it up, and the motor idles beautifully!
Now, i'm not suggesting you need to order a chinese carburetor. A new OEM carb would have worked fine as well. And again, I had the opposite problem of not idling A 30 hp carb should have bigger passageways than a 3.5. ...but maybe there is a passageway clogged up in there somewhere.

If drilling out your main jet doesn't work and you still can't figure it out, we could meet up and we could bolt my carburetor on your motor to see if it works any differently. Or it could help eliminate or confirm the carb as being the problem. ( I also wouldn't mind seeing your setup, as I have to get my boat set up eventually as well).
Unfortunately, it will be another month before I go to Ontario to visit and ship my motor to myself. So, it might be a bit chilly to go do any testing by the time it gets here. haha.

Graham.

[Positrac]

Thanks for your thoughts Graham.

The fact the motor runs beautifully for 10 seconds at WOT after cruising then cuts back slightly tells me it’s running out of fuel in the carb. Float level could come into play but the float level is not adjustable like some small carbs are.

I’ve ordered a couple new main jets as well as a new 30hp non-restrictor carb gasket. I’ll open up one of the main jets a couple thou and test it. Bogging on a 2-stroke dirt bike at wot is a sign the main jet is too small so maybe…

I’ve got a few more things to check and try so I’ll defiantly get back with what it was once I get it figured out. Time is running out for this year though. I’m hunting my next days off then back to work for 7 so it will be almost 3 weeks when I next get to try it out. Depending on what’s on my plate it may have to wait for the spring.

[Adamsarich09]

Hi, I have a Stryker 420pro and I have a new merc25jet on it. I am wondering how you think your motor compares to the 4 stroke merc? I would like more performance but don’t really want to go 200+ pound motor. Thanks a lot

[GStyler]

Originally Posted by Positrac

Thanks for your thoughts Graham.

The fact the motor runs beautifully for 10 seconds at WOT after cruising then cuts back slightly tells me it’s running out of fuel in the carb. Float level could come into play but the float level is not adjustable like some small carbs are.

I’ve ordered a couple new main jets as well as a new 30hp non-restrictor carb gasket. I’ll open up one of the main jets a couple thou and test it. Bogging on a 2-stroke dirt bike at wot is a sign the main jet is too small so maybe…

I’ve got a few more things to check and try so I’ll defiantly get back with what it was once I get it figured out. Time is running out for this year though. I’m hunting my next days off then back to work for 7 so it will be almost 3 weeks when I next get to try it out. Depending on what’s on my plate it may have to wait for the spring.

Positrac, I've been meaning to give you an update on my motor that I finally got the Jet leg for and installed on my Solar 420 Strela.

Because of your issues, I wanted to try mine out as the factory 25 HP first before converting it to 30HP to make sure everything worked fine. So I ran the motor in the red deer river above Glennifer (1000 m above sea level). I had none of the issues you described. I put a Tiny Tach on the motor and it was at about 4800 rpm at full throttle.
I then converted it to 30 HP and ran it in the Bow river (which is at the same elevation). And again, had no issues. The RPM increased to 5050 rpm at full throttle.
I am not sure how much performance I gained by the conversion, because I had a lighter load on the second run. But, the acceleration seemed better, and the top speed on flat water was a bit faster.

One thing I did not do that you did was open up the exhaust pathways. And I am running the stock Outboard Jets Liner, Impeller and Intake for now.

I still need to play with the transom to fine tune the motor position a bit. The intake hits the floor on pin position 1 and 2, so I am running on pin 3 position - which I think is forcing me to run the motor a bit lower than recommended to avoid sucking air into the intake. I would like to get it at least one more pin tilted down, so I can raise the motor up a tad. But think I need to add a spacer in between the transom and the riser to move the motor back some. I've seen some guys cut the floor back a bit. No way I am going to mess with that.

Sorry, I still can't help diagnose your problem. But I thought you might want to know that I have the exact same motor as you - converted to 30 HP, with all stock parts, and I am not having your issue.

[GStyler]

Correction... 5250 rpm after the conversion