25 hp johnson running issues

[djchris]

ok back to the drawing board! took boat out after work yesterday and it ran well for about 5 minutes than started surging again......gotta be a float problem right? i will be pulling the carb off tonight after work and investigating a little more.....hopefully i can find something cause me and my brother are supposed to be going fishing on saturday....

 

[New River Rat]

I'm suggesting something now that may sound foolish (fuelish?). Since you've done everything you've done, is the tank vented properly? I've found this before on my '97 25 Johnson, as well as the connection on the tank loose.

 

[Johny25]

Surging at WOT indicates a fuel problem.......... incorrect adjusted float, high speed orifice plugged in the carb, fuel system air leak, fuel filter plugged, restricted fuel supply line, fuel tank vent or hose restricted, carburetor base gasket leak ......and the list goes on. This is why I do all my own work, that way I know what has been done so trouble shooting is easier. Who knows what that guy did or did not do?

Remember my opening comment...^^^^..... It could be any of several things. All you can do is start eliminating possibilities. Making sure the float is adjusted properly will eliminate that one. You could have debri in the carburetor again.....? Lines should be flushed good next time the carb is off. get a clean bucket that you can pump fuel into to check for gunk coming through. Just hang the line that comes off the fuel pump over the side when you have the carb removed and pump some fuel through.

 

[djchris]

Ok heres the run down on what i did today.......pulled the carb back off(don't know why i was afraid to pull it off before it only takes about 10 mins) pulled everything apart on it.....The float looked pretty good parallel to the base but what i did find is a bunch of crap (old fuel hose pieces) where the float needle or what ever it's called goes.....so im going to assume it was restricting fuel flow to the bowl. I did not put the carb back on yet but i did pull every single fuel line and any hose that has to do with the fuel system and im taking it to work tomorrow to match it up and replace ALL of it! I work on cars for a living so is automotive fuel line ok to use? we have miles and miles of it at work....

I really hope this works cause i am loosing valuable fishing time and my kids want to go but i won't take them out with a motor that is not running correctly......wish me luck!

 

[Johny25]

It sure will : ) I get all my fuel lines at the local napa and for the little primer lines I go to the chainsaw shop. This would explain why it runs great for a bit then runs like crap. Once the pieces make it to the carb each time the motor runs like crap.

Yeah and once you have had the carb off and are confident with it it's a piece of cake. Most 2 stroke outboards are really simple to work on, it is the fear that keeps people from doing there own work is all.

 

[djchris]

it's kinda funny i work on cars and can tear a automobile engine down with no problem what so ever but for some reason i was afraid to tear in to my outboard....i do think i will be doing all my own work from now on.....

 

[djchris]

Well it seemed to be just fine today....was out for about 4 hours and ran the motor for about 2 hours and never missed a lick.....so i think it's finally fixed......i had to put a differant prop on cause i dinged up my original prop so the boat is a little under propped. the boat planes extremely fast with a 11p prop on it but can only run half throttle cause im afraid im gonna over rev the motor.....according to my gps i was getting about 23 mph at half throttle and one time i went full throttle and it jumped to 28mph but didnt stay there long again afraid of blowing the motor up.....i really need to get a tach......

anyways the motor ran great and now i can get on with the rest of my plans for this boat.....

 

[Johny25]

Yes a tach is worth the $50 or so. You can usually here when you are really under propped. If you get toward the top end of the throttle and the engine revs but the boat does not seem to go any faster then I guarantee you are under propped. If you want the best performance get a tach for an RPM reading, plus the GPS and we can get you the best prop that will get you best performance. The correct prop can be worth 2-3mph top end and in some cases even a better hole shot.

My 30hp johny turned an 11pitch at 6300rpm. Was great out of the hole but was way underpropped at WOT. I ended up with a 14 pitch New Saturn Solas that out performed the 11, 13, and 15 pitch props. And the stainless steel does make a difference in performance on these mid range engines so don't let others tell you it doesn't matter on a smaller hp motor. But you have to be careful not to hit things with the SS or you can damage your lower unit.

 

[djchris]

When i had it at wot it did seem to keep picking up speed but i think i hit a rev limiter or something. is there such thing on a outboard? As far as SS i prolly will be going with aluminum due to the fact that 4 out of the 5 lakes i fish are real shallow and almost every tourny i have done at those 4 lakes someone chucks a prop.....i would rather replace a prop than a lower unit.....however i do plan on adding a jackplate and tuning the engine setup to get the best performance out of it as well as being able to run shallower......

 

[Johny25]

I believe most of the newer outboards have rev limiters but not back in 89'. Unless you are pushing upwards of 1300-1500 lbs I can't imagine your not over revving with an 11 pitch. What is the model of your boat anyway?

 

[djchris]

2008 tracker grizzly 1448 w/ side console....2 batteries, trolling motor, gas tank couple rods and a big *** tackle box....and me (210lbs)

Im pretty sure it's over reving but i swear it acted like it had a rev limiter.....im not leaving this prop on just wanted to try it cause my original prop is a lil chewed up....it's a 10x13.....i couldn't believe how quick the 11p would get the boat on plane and keep it there all the way down to a quarter throttle or so....i mean crawling speeds and it was still on plane......shocked the hell out of me.....

I had this motor on my last boat which was a alumicraft bandit 17ft and it ran great on it till the last time i had it out last year which resulted in all the work i had to have done to it......but it would push the alumicraft about 30mph. that boat needed some transom work and i didn't feel like fixing it so i bought the tracker brand new left over.....got the motor back from the mechanic and put it on and it wouldn't run so i took it back to him with the motor on the boat and he found that the upper crank seal was bad and the crank case gasket was also bad....got it back the second time and it wouldn't idle but would run wot and the lil tracker would scoot.....gps said 39mph but don't think that was right might have been a glitch or something....anyways you only asked what boat the motor was on and i told a short story...sorry

 

[Johny25]

hey no worries I like talking about my boats and motors too so I know where you are coming from =D>

Yeah the 11 pitch is surely not enough prop with that light setup you got. Here are some stats of what I found out on my boat : )
Ok my 1988 johny was originally a 25hp but I did the carb and intake mod to make it a 30hp. So my RPM range is 5200-5800 now instead of the 5000-5500 of the 25hp

Ok my boat is a 14ft Lowe V hull with an 88' 30hp Johnson. I tested 3 props with my new Tiny Tach today and here are my results. I run with what I will call a heavy load 25% of the time and a light load 75% of the time. When the wife and second son go out with us is the heavy load, about 250 lbs heavier than the light load (that includes the 2 extra seats I have to put in the boat). Engine specs are 5200-5800 RPM at WOT.

10X13 aluminum OMC prop
Heavy load (gross weight 1,150 lbs) =5450 RPM at WOT
Light load (gross weight 900lbs) = 5700 RPM at WOT

10.5X11 aluminum OMC prop
Heavy load =6010 RPM at WOT
(didn't even bother with light load due to high RPM at heavy)

10.13X11 stainless steel Cabela's (brand new ugh...)
Heavy load =6290 RPM at WOT
(didn't bother with light load again)

THEN I GOT GPS READINGS with the new props (minus the 11 pitch's that was way to low of a pitch)

Heavy load at 1,100 lbs
10X13 stock aluminum 25.7-26.4 mph 5550rpm
10X14 Solas stainless 27.4-28.2 mph 5500rpm
10X15 stock aluminum 25.2-25.7 mph ?

Light load at 875lbs
10X13 stock aluminum 28.0-28.5 mph 5840
10X14 Solas stainless 29.6-30.2 mph 5680
10X15 stock aluminum 27.8-28.1 mph ?

Now who is telling stories :lol:

 

[djchris]

those are great numbers and thank you for the info......i just had me and my 2 brothers on my boat today and with the 13p it wouldn't barely move.....than we stuck the 11p on and it seemed to run pretty good once i got on plane.....didnt bother with getting a gps reading but i would guess we were moving at around 23 or so with the 11p....we are not small people either....250, 250 and 210, a cooler and fishing gear prolly totalling 100lbs.....had the weight limit on the boat a little over the max but it did well......

 

[Johny25]

Your RPMs were probably fine with the 11pitch with the heavy load in the boat. I know when I had my 11 stainless on my boat it would jump on plane really fast which was nice but the over rev was of high concern due to the damage it will do to the motor long term and possibly short term.

 

[djchris]

this may be a silly question but how does changing the carb and exhaust allow you to safely rev your engine at a higher rpm?

 

[Johny25]

Carburetor and intake manifold, it allows more fuel and air flow creating more HP and a higher RPM. I have a whole thread about this mod that you can do on iboats. Here is the link if you are ever interested in getting a few more ponies for around $100-150 bucks : ) It is good for about 3-5mph top end. But the biggest difference is how well it does with a heavy load after the mod.
https://forums.iboats.com/showthread.php?t=532265
It is a really easy mod to do and the results are very good for the money. What you have is a de-tuned 30hp motor with that 25. You have the perfect year johny to do the mod. All you need is a carb and intake off of an older 35hp or a post 84' 30hp

 

[Johny25]

I am sure you can run your 25hp at 5800 rpm like the 30hp but your HP band is completely different. The 30 puts out 30hp at 5500 rpm and the 25 puts out 25hp at 5250 rpm. So going to 5500-5800rpm with your 25 will do you no good because you won't even be putting out 25hp at that rpm. As you go past your peak HP rpm range you will lose HP.

 

[djchris]

so when you see the rpm range that means thats where your making the most power? and what years older 35 hp? i have a 1978 35 hp that needs a lower unit.....would that work? o and what guy wouldn't want a lil extra power! lol

 

[Johny25]

Yeah I believe you can put that carb and intake right on your 89' and make it a 30hp. Does it look like the 78' carb and intake will fit?

See in 78' they weren't making 35hp at the prop. Johnson didn't start rating HP at the prop until 85' so the 84' and back 35's were rated at the flywheel/crank so they were closer to 30hp. After 85 they renamed the 35 a 30 in order to keep up with the foreign outboards that were putting out the labeled HP at the prop instead of the flywheel like J/E and mercs.

And yes the RPM range will represent where your engine will produce peek HP and perform best.

 

[djchris]

yes the whole engine looks almost identical to my 25hp......don't know if i wanna do that or not being the 25 hp now runs great and i was always taught don't fix something that ain't broke! lol......know anywhere i can get a lower unit for a 78 35 hp?