Johnson 75 hp Slow to pick up power

[fromtheriviera]

Hello,

I have just bought my first motor boat with a 75HP Johnson motor
ref: BE75ECCA

It starts up ok and sound like its tuned perfectly however when I put it in gear , I put the throttle on full and my 4.5 meter long Rocca (about 560 kg) does not pick up speed very fast. As if I had a 2 HP not a 75 HP ?

Wierd thing is that as the boat picks up speen and the revs get higher, it actually works well and fast..


I have been told that it could be the spark plugs are not the right ones ?

I according to some web sites I need to put L77JC4 or QL77JC4 plugs.

Not sure what plugs are on it right now but they look brand new to me .

I will try to find some new pluggs this weekend but if anyone has any other ideas what could cause this please send me a line ?

I the automatic choke was left on it would drown the engine no ?
If it was the carburator it would not run well out of gear or when going full speed ?


Could it be that the propeller is too small if its not the orriginal one ?

If the oil mixture is not correct would this happen ? What is the right oil mixture 2% or 4% ?

: confused:

 

[jonesg]

Re: Johnson 75 hp Slow to pick up power

"I the automatic choke was left on it would drown the engine "

yes and foul the plugs.
Look at the plugs, they can give good indication of whats going on.

Get the manual too.

www.outboardbooks.com

 

[jtexas]

Re: Johnson 75 hp Slow to pick up power

"If it was the carburator it would not run well out of gear or when going full speed ?"
Not necessarily. You have 3 carburetors, each with two jets (one hi-speed, one low-speed). A clogged low-speed jet has no effect at high speeds. And, that motor will idle on two cylinders just fine, but struggle when you put a load on it.

Champion QL77JC4 at .030 is the best plug for the motor. If you've got the correct cross-reference from another manufacturer, and they're in good shape, it's not causing your immediate problem. I'd still replace whatever's on there soon as I could get around to it though.

back to basics.
Compression test -- compression on the worst cylinder should be within 7% or so of the best. I'd expect upwards of 130 on that motor.
Spark test -- spark should jump a 7/16" gap on an inline tester.
Fuel, should be fresh 87-octane gasoline, mixed in a 50:1 ratio with TCW3-certified oil (that's 2% oil).
The fuel tank needs to be free from water and debris.
If you have good compression and spark on all three, the fuel line holds pressure, and the fuel is clean and fresh, a carb rebuild might help. But it's possible that the motor is making all the power it can, but there's an issue with the boat.

"...Wierd thing is that as the boat picks up speen and the revs get higher, it actually works well and fast..."

Actually, that's normal. When the boat starts moving, the stern digs in, pushing a bow wave out in front. The motor has to push the boat to the top of the bow wave. During this time the engine is heavily loaded, so it takes some time to develop power. Once the boat has climbed out of the hole, the bow falls and you're on plane.

If the motor is trimmed out too far, it digs a deeper hole and takes longer to climb out. If you have power trim, start with the motor trimmed fully in until it's on plane, then start trimming out, until further adjustment causes a decrease in RPMs.

If you don't have power trim, there's a thrust rod on the mounting bracket that can be adjusted in or out. It's a trade-off between top end speed and hole shot.

The antiventilation plate should be even with the keel (or an inch or so higher), with the motor in neutral trim. Any lower causes excess drag and slows you down.

A prop with lower pitch will get you out of the hole faster, but will slow down your top speed somewhat. Just be sure to use a prop that lets the motor turn 5000-5500 RPM at full throttle.

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

Thankyou both for your precious advice. I have printed out your suggestions and will start working thorugh them.

The plugs are correct ones.
I would bank on the slow jet being clogged but I do not want to start to take the carbs apart until I have too. So I leave this till last for now.


Choke wise I am not an expert and I can see that there is a kind of solanoid controllng this and I don't know how it works. I will try to get a manual.

I took the air filter appart and found that there is no filter in it. Is that normal ?
I would have expected to find an air filter like a car.. But if it had too much air coming in would this not drown the engine enven when in neutral ?


I will see if I can find a mechanic to check the compression.

Lastly I read in some formums that the propeller can slip ?

So will get back to you all soon hopefully with some good news,

thanks again,

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

I have just found out that my motor is a 75HP stinger and therefore was designed for racing. So the prop is not a standart propeller size. Does anyone know what the best propeller size is to fit on this engine so that the motor revs up sfrom start. I have a 12.5 x 15 and it still does not push the boat out of the water for the first 30 seconds. Then once the engine revs get higher it takes off like a torpedo..

Any suggestions for best prop size would be welcome.
You can see my boat motor at:
http://picasaweb.google.com/antonio...key=Gv1sRgCIfbw6TRycjgrQE#5321658942707803842

Here is a you tube video of the same motor.

http://www.youtube.com/watch?v=yK-mqvISlGw

 

[mrcj001]

Re: Johnson 75 hp Slow to pick up power

Sounds like a high speed prop......

You could use something has simple has Smart Tabs on you boat to help it plane faster.

http://www.nauticusinc.com/

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

Hi,
My boat does have some tabs. One on each side. They seem to have been installed more or less paralell to the bottom of the boat. Will maybe try to increase the angle so the hang a bit lower.

 

[jtexas]

Re: Johnson 75 hp Slow to pick up power

I would bank on the slow jet being clogged but I do not want to start to take the carbs apart until I have too. So I leave this till last for now.

If you suspect dirty carbs, don't run the motor until the problem is resolved. Your motor gets its lubricating oil from the fuel, so any cylinder starved for fuel is not getting proper lubrication.

Don't be intimidated, these carbs are remarkably simple devices.

I took the air filter appart and found that there is no filter in it. Is that normal ?
I would have expected to find an air filter like a car.. But if it had too much air coming in would this not drown the engine enven when in neutral ?

Outboards don't have air filters, as airborne dirt & dust is rare on lakes rivers & oceans. More air means a leaner mixture (less gas more air), more power but a hotter combustion chamber, shorter engine life between overhauls.

I will see if I can find a mechanic to check the compression.

It's a very easy procedure, buy a compression tester for less than what you'll pay to have it done once. Like I always say, "never pass up an opportunity to buy a new tool."

Lastly I read in some formums that the propeller can slip ?

If the propeller slips, the engine revs up while the boat slows down.

...75HP stinger and therefore was designed for racing.

you sure about that?

12.5 x 15 should give you super hole shot on a 14 foot 1200 lb boat with a properly running 75 hp motor. Unless you have too much weight in the stern, the motor is hung too low on the transom, or the trim angle is wrong.

What is your RPMs at WOT?

How about some pics?

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

Thanks for your comments.


Here are my comments.
I will be honnest , I am not sure how to measure the rpm . Where do I connect a rev counter ?

Compression. Can you recommend any cheap model and tell me what the compression should be ?

I tend to think that the engine is too low but I have been to an outboard mechanic who said it looks ok to him.

I will take some pictures tomorrow and post them for you to decide for me.

I do have 2 x 30 litres petrol tanks in the stern so could be over loaded on the stern,

I suspect the slow jet may be the problem too. I will get the crb references and send you pictures. Can I unscrew the the jets from the outside of the carb ?

He has told me to try a 13 x 11 prop. I have bought it but am waiting for good sea to test it this week.

Will post more info in the next few days. I appreciate the advise you have already given me and will play around with the engine angle too.

thanks,
bye

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

I have a few more questions I need help with.

Sorry for my ignorance but I am new to motor boats .

On this carb diagram which is the slow jet ? is it 6 or 17 ?

http://epc.brp.com/Index.aspx?lang=E&s1=c4cbfd89-8c70-4a36-a8b0-5167d6dc9f2e

Here is a side picture of my motor : BE75ECCA on the cover it says Formula E .

On this propeller website, it talks about E-TEC johnson motors. Is mine possibly en E-TEC ? If so then it talks about V4 and high performance props.

Is mine a V4 ?

Here is a list of high performance props.

http://www.evinrude-parts.com/etec_evinrude_boat_propellers.html

Might I need one of these ?

http://theoutboardwizard.bizhosting.com/_390895_v4_alum_12_75_x_23_for_hi_perform.html

http://theoutboardwizard.bizhosting.com/_394761_v4_raker_13_5_x_24_hi_perform_bow_lifter_.html

 

[jonesg]

Re: Johnson 75 hp Slow to pick up power

Not an Etec, not even remotely close by a few decades.

You've had the best advise money could buy, scroll up and see JTEXAS response again. Do a compression test and spark test, rebuild the carbs with new kits.

Compression tester and spark tester at any auto store.($30)

Adjustable($12) gap spark testers are whatya need, set gap to 3/8th inch.

Change the gear oil too and get the service manual before you blow it.
www.outboardbooks.com

Good luck.

 

[jtexas]

Re: Johnson 75 hp Slow to pick up power

You have a 1988 model 75 horsepower 3-cylinder carburetted loop-charged 2-stroke. Three carburetors, capacitor discharge (electronic) ignition.

Looks like a 15-inch shaft; the short-shaft 75hp has a 15:28 gear ratio (vs 12:29 on the other 3-cylinders). That gives you less torque (acceleration) but much greater top end. That's why I was thinking a 15" pitch prop should give you great hole shot ("hole shot" refers to the process of getting the hull up on plane). It's always a trade-off between hole shot and top end speed.

Still, I don't see why it should take 30 seconds to for you to get on plane with that prop boat & motor. 15 maybe. Or maybe with 300-400 pounds of passengers on board? Jettison the mother-in-law, see if that makes much difference.

Before you start messing with props, make sure you're getting all the HP you can get out of that motor. Changing props in the middle of engine repairs will muddy the water, so to speak.

That motor needs to run 5800 RPM at full throttle with a normal load. Closer to 6000 RPM would be better. Any less will be lugging at all throttle settings (too much fuel for the amount of RPM); any more, you'll be overreving. Either way will shorten the life of the motor.

RPM's are controlled by prop pitch, so you need to select the prop that lets your engine run at the speed you want it to run. A smaller prop puts less of a load on the engine, thus it will rev higher (around 200 RPM per inch of difference at full throttle).

This is why you'll need a tachometer when you start experimenting with props. Needs to be an "outboard motor" tachometer with a "12p" setting. If you have the factory control box, there's a 3-pin socket that accepts a ready-made tachometer wiring harness. Should see 4 posts on the tach marked IGN, SND, GND and LT. Purple wire to IGN, gray to SND, black to GND. The LT post is for the gauge illumination. If you aren't using the readymade tach harness, you'll find those 3 wires are in the engine wiring harness.

This compression tester looks a lot like the one I use: http://www.amazon.com/Actron-CP7826-Compression-Tester/dp/B000CPJM66

PSI should be about the same on all three, at most about a 7% difference between lowest & highest. I'd expect to see upwards of 130 on that motor, but way more important to have consistent readings across the cylinders.

Dialing in the optimal set-up (prop, motor mounting height, trim, weight & balance) will be a trial & error process.

 

[LIGHTFOOT]

Re: Johnson 75 hp Slow to pick up power

I've got same motor with the same problem. Its at the shop now. Would make a good big orange anchor.

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

I have posted some photos of the real of the boat.

http://picasaweb.google.com/106298816060283696541/20100811?authkey=Gv1sRgCJnYmI-el_G2fw#Also I have discovered this morning that all the solenoid petrol hoses have been disconnected from the carbs.

This is the model I have 397909.

http://epc.brp.com/Index.aspx?lang=E&s1=9a5864d7-8188-4238-9a04-affad5d64009

The part 7 primer solenoid cover is craked. That probably why it was disconnected.

My question is, could this be the problem and how do I coonect the hoses again to the carbs ?

I will try to figure it out.

Thanks for the above advice. I am looking to buy a compression tester and will post my findings.

 

[jtexas]

Re: Johnson 75 hp Slow to pick up power

Can't view your photos.......

The primer is only useful in cold starting...instead of traditional choke plates, the primer solenoid opens a valve which drains fuel into to the cylinders to enrichen the mixture for cold starts. Pushing the key in (while in the "on" or "start" position) should engage the solenoid. If you've been having a hard time with cold starts, you'll appreciate having this fixed.

Note that the model number you posted above, "BE75ECCA", indicates a 1988 Evinrude, 15" shaft, made for export to Belgium. Shouldn't be a problem...you might have a Johnson cover on an evinrude motor, or a Johnson motor on an Evinrude mounting bracket...either way, Johnson & Evinrude are interchangeable part for part, even the part numbers are the same. The corresponding model # for a Johnson motor is BJ75ECCA.

For a cheap, simple to use, yet useful digital inductive tachometer, see www.tinytach.com

 

[jtexas]

Re: Johnson 75 hp Slow to pick up power

fixed the link...

I have posted some photos of the real of the boat.

http://picasaweb.google.com/106298816060283696541/20100811?authkey=Gv1sRgCJnYmI-el_G2fw#

This should help your acceleration:
Use the screw labeled "roller adjust" in the 1st photo below to move the roller to the right, to where the "Mark" hits the roller dead center when you advance the throttle. The purpose here is to give you a little more spark timing advance *before* the carb butterflies start to open.

After this adjustment, you'll need to remove the airbox cover and make sure the butterflies are perfectly horizontal at wide open throttle. If they aren't, adjust the WOT stop screw (2nd photo).

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

Hello.
Have followed your advise and have stopped carrying heavy mother in law.

I have also invested in some tools to measure the compression and haveposted photo of my spark plugs.

They have run about 50 miles at full throttle since so i guess that could explain why they have deteriorated so much. ?

http://picasaweb.google.com/106298816060283696541/20100811?authkey=Gv1sRgCJnYmI-el_G2fw

So, the pressure measurements areas follows which I guess is not good news ?

top cylinder 7.5 x 100 kpa
middle cylinder 8.50 x 100 kpa
bottom 8.87 x 100 kpa

I guess I needed to multiply by 100 as it says on the gage ?

 

[jtexas]

Re: Johnson 75 hp Slow to pick up power

Right, read as 750-850-887 KPA, which converts to 109-123-129 PSI over here. #1 is low but probably not fatally so.

the procedure described here:
http://forums.iboats.com/showthread.php?t=158076
might recover some of the lost compression, if the loss is due to carbon build-up.

I'd try that first and if it does not help, think about pulling the head for inspection. Cylinder head removal/reinstall is not too big a deal on these motors.

Spark plugs look pretty good, maybe a little rich. But the center electrodes are not visible in the photo. How much has the gap eroded? Should be .030 (0.75 mm).

The one on the left is different, is that an NGK? Did it come out of the top cylinder? NGK makes a great sparkplug, but you really want to run champions in this motor.

The #1 spark plug does not look like it is running too hot, but nevertheless I would want to make sure the top cylinder is not overheating. To test the overtemp warning horn, find the temperature switch at the end of a tan wire high on the cylinder head. On that wire, a few inches back, is a black rubber sleeve. Peel back the sleeve and touch the connector to the cylinder head (keyswitch "on"). A steady tone should sound from the control box.

The location of the temp switch is shown below.

Also, replace the water pump impeller. Replace the chrome liner inside the pump housing, if it is scratched or scored at all.

 

[fromtheriviera]

Re: Johnson 75 hp Slow to pick up power

Hi.
I was delighted to discover that our european measurements are different from US and that the commpression is not so far off after all. You saved my engine from going into the scrap yard !!

I will read the procedure to try to recover the lost compression on the 1st cylinder.


Unfortunatley I did not keep the plugs in order when I took them off so I may have misled you a bit from my photo. What I will do is mount some new ones and run them for a while then take them off to show you again soon.

I did not realise that I had 1 NKG and 2 champions.

I will put new plugs tomorrow however for the moment I only have spare NKGs.


Next time I go to town I'll buy champions.

I will look at the gap in electrodes tomorrow too. From memory one was very different from the other two.

When I buy new sparks , are they already set at the right gap or do I need to modify them to 0.75 mm?

I was told to use Champion QL77JC4 plugs.

I have done the second part of your last mail:

" remove the airbox cover and make sure the butterflies are perfectly horizontal at wide open throttle. "

They look perfectly horizontal.

Will try to advance the throttle and test the overheating alarm tomorrow,

 

[Chinewalker]

Re: Johnson 75 hp Slow to pick up power

I might add that your motor is somewhat rare and is considered a racing motor with the 15-inch mid-section. Even if the motor does "blow up" or become otherwise non-usable, it has a fair amount of value in parts, particularly the lower unit bits. They are quite sought after.... Take good care of it!!