Johnson Engine Problems

[evrgladesbasser]

Hey Everyone,

Just had a first time ever problem with my boat. While on the water it was taking a long time to get my boat up on a plane. The rpms stayed low while trying to get on a plane, between 1800 and 2200, once on a plane the boat would open up and run great at around 5500rpm. My gut feelings about this were these:

1. I have a prop problem

2. Engine is not geting good fuel

3. Compression problems

4. Fouled spark plugs

After inspecting the prop I found no issues or defects. When I pulled the plugs I found that all four appeared to be fouled with a lot of oil (very black) on them. I did a compression check, all four cylinders have 114-116psi in them.

So my questions are these... Do you know if these compresions are normal? Would the spark plugs being that gummed up cause problems geting up on a plane? How often do your plugs foul out? And I haven't pulled the carbs yet, can I run regular carb cleaner in my fuel to help clean up whatever may be in there?

Thanks for your replies they are much appreciated.

p.s. this is a 1991 Johnson 115hp, 4 cylinder 2 stroke pushing an 18ft nitro.

[Nitrofreak]

Mine is a 90 but the same exact configuration, did you have extra people with you this time out?

[evrgladesbasser]

Yes I was fishing with a partner I usually fish alone. However, I have fished with a partner before and not had this problem....

[Nitrofreak]

I am not trying to be offencive but was your partner heavier than anyone you have ever had on the boat and did he or she bring a lot of tackle with him or her and maybe a cooler or something heavy?

The reason I ask is because this boat is very sensitive to weight distribution I found that out the hard way my self and if you were to shift some of the weight to the front it plains much faster and I too thought I had a problem but your boat is like mine and it sits deep in the back and I even put a predetor prop on mine and it helped the top end a lot but did nothing for the launch to get on plane with extra weight on board,    Since then I have been experimenting with different trim angles on the launch and that has done a lot

[jbh3]

I would start with new plugs. You should also look into running a cleaner/fuel stabilizer additive regularly. Seafoam, Startron, Marine Stabil are all good options. Your compression numbers sound good. JMHO.

[Way2slow]

Your compression is good.

If you let it idle very long while getting back to the ramp a loading, the plugs are going to be black. To check the plugs, you need to be running at WOT for a couple of minutes and then while still holding it at WOT, cut the switch off. Take the cover off, trim the motor all the way up for easy access and then check the plugs. They should be a medium brown color then.

18ft Nitro + 115 = Under powered. Tracker may have only rated that hull for a 115 but that's not enough motor for an 18' boat

Are you running a Stainless or Aluminum prop? A stainless steel prop would help bunches, just don't get a four blade Renegade, those motors don't like Renegade props. It's also very easy to have a rolled edge on a prop and it look fine to the eye, but won't come out of the hole for anything. The Sport SE 300 hydrofoil would help a lot also.

Make sure you are getting the motor fully tucked in also. If your motor has the trim stop pin to limit how far it trims in, make sure you have it in the most inner position. (I guess it does have power tilt and trim)

As for cleaning the carbs, you could have plugged mid jet but don't waste you're money on anything that runs through the carbs to clean them, it's not going to do anything for you. To clean what needs to be cleaned, the carbs MUST come off and be taken apart. Then be sure all orifices are open by using tooth picks or other small objects. If you use numbered drill bits, only use the backs, do not run the cutting end through the orfice, .0005" can cause you problems.

[evrgladesbasser]

@ Nitro- Yes I was carrying more weight than normal.. A partner with more gear, full livewell, and fuel tank 3/4 full ( I usually only fill to 1/2). So I'm thinking what your saying makes sense now. So the question now is how do I solve this? Would a prop with a different pitch really get me up on a plane better? I just looked right now it's a 13x19.

@ Way2slow- I always tuck the engine fully when I take off then trim up when I get on a plane. Never had an issue til now. Lets say I'm a bit underpowered, if I use a different prop am I going to get better rpms during the hole shot? As I said the rpms are only running between 1800- 2200 during take off. Once it finally plains (if it does) the engine surges and the rpms go up to 5500. The manual states operating rpms should be 4500- 5500rpms.

I usually dont run top end at 5500rpms, usaully 4800- 5000. 5000 rpms puts me between 35- 40 mph and thats fast enough for me. 5500 rpms moves the boat at about 45mph which is to fast for me (I'm just a wuss i guess).

So.... where do I go from here?

[Way2slow]

First I would get me a Raker II prop. I think you will still be good with a 19" pitch since your rpm is about right. It actually will not hurt the motor if your turn it 5,700 rpm. It will do that all day long with no harm to the engine. Just never run it at a steady rpm between 5,800 and 6,200. Those motors develope a harmonic in that rpm range that can cause the crankshaft to break. The only reason they limit it to 5,500 rpm is that's already about 300 rpm over the peak power band for the porting so turning it any more accomplishes very little. They overturn them a few hundred rpm past the peak so it takes the strain of the engine and gets a little better fuel economy.

You've gotta realize, you have a lot of boat and a little motor, it's going to get over loaded very easily. You can launch out of the hole with just you and minimal load but throw a couple of hundred extra pounds and it's going to strugle, sometimes to the point you may have to ask the passanger to step two the front of the boat until it lays over.

I think you will pleasantly suprised if you get a Raker II and add the Sport SE 300 hydrofoil. Just the Raker II may give you all you want.

The reason I suggest the Raker II is they are vented so it gets the hole shot rpm up higher than the old raker. A vented prop creates a controlled cavitation that lets the motor spin up to 3,500 - 4,500 rpm coming out of the hole. This is where you peak torque band is and the motor pulls a whole lot stronger. With an unvented prop, (most all aluminum and some stainless) the motor gets bogged down at 2,000 - 2,500 and has a hard time making rpm to get above that. Vented props is why you hear big V-6 boats coming out of the hole and it all of a sudden sounds like a turbo charger or something kicks in.

If 40 mph is where you're comfortable, that's where you should run.  Those that have a 75 mph boat and don't know how to drive it are the ones the get hurt.  For me, 60 - 65 is my prefered cruising speed.  The boat is very stable, the bow's up and riding nicely, it's up on the pad and just kinda skipping along on the chop.  A very comfortable and pleasant ride.  When mine starts hitting  70 or more, you have to pay attention and drive, no sitting back relaxing.

[Fishing Rhino]

Aha!  It may have been the first time you've had this problem, but you finally got around to telling us the rest of the story.

It was also the first time you had that much fuel, a full live well, and a heavy partner with a lot of gear.

I've got a Z7, which is 18' 8", with a 150, and it has the same problem with a fuel tank more than half full, empty live well, and a second person in the boat.

The motor will turn up over 5000 rpm and still not get up on a plane unless the passenger sits forward on the step to the bow.

I've got a vented prop.  Someone suggested removing one of the "plugs" to give the prop a better "bite".  So I removed one.  Nothing happened.

Having read some of the prior posts, I have to wonder if the vent plugs are causing cavitation, and therefore robbing thrust from the prop.

I mean, the nose is in the air with the motor trimmed down to the max, and backwash slopping over the transom.

I'm wondering if plugging those vent holes would be an improvement.

I'd hate to think what it would be like with a 115 on the transom.

I'm considering a hydrofoil.  They look goofy, but so what, if they work.  A couple of fellows told me they cured the same ailment in their boats.

[Way2slow]

Forgot something, The Rakers only come in even pitch sizes so you will need to figure out if you want the 18" or 20". The 18" will give better hole shot if it does not rev you over 5,700 rpm.  A 20" raker is going to be similar to a 19" aluminum on top end rpm, but will launch out of the hole better

Fishing Rhino, if you're spinning over 5,000 rpm and still sitting in the water, you're vent holes are probably too large and allowing too much cavitation. The motor height may not be just right and letting it suck air from the surface, the SE Sport 300 will cure that problem. Especially if you're have a problem with the prop blowing out just as the boat starts to lay over. When I had one of my 300+ hp hotrod motors on my my Stratos 285 Pro, I could not run a stock prop the motor would blow the prop out at layover. The SE Sport 300 would always keep that from happening. I didn't need it with my custom tuned props but the it helped hole shot so much, I'd leave it on anyway. Yes, they do look dorkey as all get out, but it sure did make that 285 come out like it was shot out of a cannon.

[Fishing Rhino]

When the nose starts to come down on plane, I back off the throttle some.  Not much, but enough to keep the boat from suddenly jumping forward, about 4000 rpm.

Leaving the throttle there, once on plane, I trim the motor up, until the rooster tail is not quite as high as the motor.  At that point, the motor will be turning just over 5000 rpm, and the boat will be doing 48 - 50 mph.

I then back it down to the 4000 range and cruise in the low 40s. 

At that speed, if I put the throttle in the corner, the boat rockets forward, gets to about 56 mph, and the warning horn sounds, so I back it down.

It helps to understand that for years I was used to 8 or 9 knots in my lobsterboat, and for the past three with either a paddle canoe or one with a trolling motor.  So it's all very dramatic to me.

My only gripe is getting the beast up on plane.  Other than that she behaves herself.  In a fair size chop, I trim it down, and increase the speed 'til it stops pounding.

It's amazing how forcing the bow down smooths the ride.  I know, I know, there are limits beyond which you can bury the nose in a wave.

Hopefully the hydrofoil will be the cure.  It's a pain when the boat falls off plane with the motor turning 3000 rpm.

[evrgladesbasser]

First I would get me a Raker II prop. I think you will still be good with a 19" pitch since your rpm is about right. It actually will not hurt the motor if your turn it 5,700 rpm. It will do that all day long with no harm to the engine. Just never run it at a steady rpm between 5,800 and 6,200. Those motors develope a harmonic in that rpm range that can cause the crankshaft to break. The only reason they limit it to 5,500 rpm is that's already about 300 rpm over the peak power band for the porting so turning it any more accomplishes very little. They overturn them a few hundred rpm past the peak so it takes the strain of the engine and gets a little better fuel economy.

You've gotta realize, you have a lot of boat and a little motor, it's going to get over loaded very easily. You can launch out of the hole with just you and minimal load but throw a couple of hundred extra pounds and it's going to strugle, sometimes to the point you may have to ask the passanger to step two the front of the boat until it lays over.

I think you will pleasantly suprised if you get a Raker II and add the Sport SE 300 hydrofoil. Just the Raker II may give you all you want.

The reason I suggest the Raker II is they are vented so it gets the hole shot rpm up higher than the old raker. A vented prop creates a controlled cavitation that lets the motor spin up to 3,500 - 4,500 rpm coming out of the hole. This is where you peak torque band is and the motor pulls a whole lot stronger. With an unvented prop, (most all aluminum and some stainless) the motor gets bogged down at 2,000 - 2,500 and has a hard time making rpm to get above that. Vented props is why you hear big V-6 boats coming out of the hole and it all of a sudden sounds like a turbo charger or something kicks in.

If 40 mph is where you're comfortable, that's where you should run. Those that have a 75 mph boat and don't know how to drive it are the ones the get hurt. For me, 60 - 65 is my prefered cruising speed. The boat is very stable, the bow's up and riding nicely, it's up on the pad and just kinda skipping along on the chop. A very comfortable and pleasant ride. When mine starts hitting 70 or more, you have to pay attention and drive, no sitting back relaxing.

First off thanks for the great info I really appreciate it. I did some online searches for the Raker 2 with little luck. I found the regular Raker quite easily though. Do you have a good site you buy parts from?

What you mention about the "bogged down" motor sounds like my exact problem.

My thinking is to go with the prop with less pitch (the 18P), since this is what will give me more hole shot power. I already have a hydrofoil so hopefully a good prop will help. The prop on there now has no writing on it besides the size so I have no idea what it is. Again, thanks all for your input.

[Nitrofreak]

That is some great info guys and thanks and I was wondering the same thing.

Evrgladesbasser, I am like you in the same respect that I don't run my boat that fast either but I have had it to wide open throttle only once just to see how it really is and loved it but the conditions were perfect to do that and most of the time they are not.

But like you I would love to get on plane much faster with some added weight and I have been looking for the prop that gives the underpowered boater a chance at doing so and thanks to way2slow and rhino I think we have finally found an answer.

Rhino,

A friend of mine has a fin on his boat that helps him with a lot of different issues he had on his boat but he has a 150 on his. My question would be to you is do you think an underpowered boat would plane faster with a foil?

Way2slow,

How would one determine which one would be better if they both get you on plane faster? and does either one effect idle speed more than the other for instance I load my boat by driving it on the trailer is this prop going to make it faster at idle too?

[Way2slow]

Raker II's are fairly new and you may not find good used one for sale in those.   Most dealers will give you a price break on the raker II's, I bought one last fall for my son's boat for $425.   If you don't want to dig that deep into the piggy bank, find you a good 18" pitch V-4 Raker for $200 - $250.  It should do a good give you what you want.  Just be sure it's in very good condition, it can cost $175 to have one reconditioned, so you haven't saved a dime if you get a dinged up one.

Idle rpm should not change, idle speed should not see a noticable change. I drive on also and run 26" and 28" rakers, and don't have a problem.

When I'm wanting to wipe that Cheshire Cat grin off those Triton guy's faces, I run one of my fun motors with a 28" @ about 6,500 rpm. The rest of the time I run my Evinrude DFI motor @ 5,900 rpm and a 26".

If you want hole shot, always lean toward the smaller pitch prop. It's always better to over rev a motor a couple of hundred rpm than to load one down a couple of hundred below recommend max rpm. Two stroke motors DO NOT like to be loaded down at WOT. It's just the CrossFlow OMC motors, they can't handle rpms between 5,800 - 6,200. So, on stock motors, stay below that.

I would never run a prop that does not let the motor turn the manufactors Max recommended rpm with my normal load. If I'm 200 rpm low, I'm going to a smaller prop. Each pitch change usually gives you about a 300 rpm difference at WOT and as I said, it's better to over rev 100 than to load one down 200.

[Nitrofreak]

Way2slow,

Thanks again I really do appreciate the info and I will print that off so I have it with me when I start looking for a prop.

I was looking for some info last night on the web and since you guy's have proven my theory that this boat is underpowered, I wanted to ask you all if it would be possible to step up to a 125 or a 150, Thinking more along the lines of a 125.

I am not seriously considering it right now but in the future if something should happen to the engine and is too expensive to repair then I will want to make a change.

She may be old and she may be a little slow but I love this little nitro.

[evrgladesbasser]

Thanks to everyone who helped solve my issues. I ordered and received a new prop for my boat. I went from an aluminum 13x19 to a SS 13x17. I have water tested it two times with a lot of weight in the boat. I am very happy with the results. My boat comes out of the hole much quicker now, it gets on a plane within a few seconds. My rpms are still running within the manufacturers recommendations at 5200 WOT. Way2Slow I really appreciate your input, I looked into the Rakers you recommended, but they were a bit out of my price range. I went with a Stiletto Advantage (at about $250) and I am very happy with it thus far. Thanks again everyone.

[shortbasser]

Way2slow,

Thanks again I really do appreciate the info and I will print that off so I have it with me when I start looking for a prop.

I was looking for some info last night on the web and since you guy's have proven my theory that this boat is underpowered, I wanted to ask you all if it would be possible to step up to a 125 or a 150, Thinking more along the lines of a 125.

I am not seriously considering it right now but in the future if something should happen to the engine and is too expensive to repair then I will want to make a change.

She may be old and she may be a little slow but I love this little nitro.

The Coast Guard sticker next to the throttle lists the max HP for your Nitro. My guess would be 150.

Here is a link to a good source for props new and used. I have been having my prop work done there for a long time. http://www.murphyspropellers.com/.

Shortbasser

[Nitrofreak]

Shortbasser Thanks that is what I was looking for and thanks for the web info!!

[Fishing Rhino]

I've posted elsewhere that my planing problem has been solved.  The prop was too small, with too little pitch.

It would turn 5300 without getting up on plane with another person in the boat, unless they moved forward.

Went to a larger prop with a 23 inch pitch.  It will only turn 3200 plus or minus when squatting before getting up on plane, but it now gets up on plane without hesitation.  It will also cruise on plane at 2300 rpm, and properly trimmed it will do 50+ mph in the mid 4000 rpm range.  Wide open, it will top 60, but starts doing some funky handling things that will take some getting used to.