1983? Johnson 35HP lacking power/torque :

[Mullerhawk]

Hi,

Yesterday I bought a 4.40m long boat (V-bottom that weights about 200KG) with a 1983 (I think - could not make out
The exact model) 35HP Johnson Seahorse with pull start, long rig and remote throttle (looks like this:
http://www.youtube.com/watch?v=8OxnGMghZwI)

When test driving the boat and starting I made sure it was not pre-heated but dead cold. It started right away with
Some choke (2n pull) and idled really nice without excessive smoking or strange noises. When pulling out from the harbor and hitting the gas it kind of delivered power a bit slow. And at full speed it feels like it's not revving as much as it should. I would describe it as missing out on power. At full throttle the engine sounds, feels and runs good. But it's lacking power. The boat only went about 16-17knots (the boat should do about 23knots with a 30HP, and probably around 25-25 with the 35HP).

But the boat was in really nice shape, and the engine ran smooth so I bought it anyway.

My first impression was that the boat maybe should have had a short rigged engine to start with. But that would not explain the loss of about 10knots in top speed. I also checked the propeller and it's in really nice shape (new last year). The sparkplugs are new; it's a CDI engine with power pack so there is no ignition to fool around with. Another thought was that the throttle cable did not open the carb fully. But after checking under the cowling it was.

So, now the question is what could cause this the lack of power/revs and still have the engine run smooth overall?

- Could it be worn out pistons/rings?
- Could it be worn out reeds?
- Could it be just a dirty carb?
- Could it be wrong CAM timing (shouldn?t that cause misfiring?)

Thankful for all the tips'n'tricks you can give me. I want this baby running smoothly .

 

[Bosunsmate]

Re: 1983? Johnson 35HP lacking power/torque :

if you take the airguard off the front of the carb you will gain a bit more horsepower.
It could be the top four regarding your problem, it should definitely whip any other boat doing 17knots when on the boat you describe. Do a link and sync on it, theres a past forum on it here somewhere. One of my cylinders has bad compression and the other is only ok yet i still get up around 25knots on a fibreglass boat of your boats size
Its pretty hard to get the cam timing out to far on these unless you break a flywheel key.

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Ok,

So it is supposed to be an air guard on this model? It is definitely missing on mine. It's just the carb and open space in front of it. I'll try to get my hands on a compression tester to see how the cylinders are doing. How many PSI's should a healthy cylinder show?

You don't think the long rig, or wrong type of propeller could cause the engine not to rev out fully?

Link-and-sync - Is that not primarily for a multi carb boat?

 

[Bosunsmate]

Re: 1983? Johnson 35HP lacking power/torque :

Yep most people have removed the airguards a long time ago, they are meant to be a silencer.
Link and sync- well i did it on my single carb35, but quite a while ago, theres a marks on the cam where the carb butterfly/throttle should line up with on opening, closing
I cant remember the PSI but it should be on a forum here somewhere.
4.40m sounds not too long to me, whats your props pitch? Someone will comment on that

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

I have no id?a about the props pitch. But I will check that and the exact model of the engine next time I'll go out there.. But first impressions is that it is a standard black aluminium prop.

I will dismantle the carb from the engine at the same time and give it a thorough cleaning and also see if the linkage is engaging correctly with the CAM. One of the problems Im noticing is that play between no throttle and full throttle is just a couple of cm's on the remote throttle. So hopefully it's just a matter of adjustments to get those extra RPMs that I need.

 

[Chinewalker]

Re: 1983? Johnson 35HP lacking power/torque :

The silencer does not give or take any horsepower - old wives tale...

Compression numbers should be on the far side of 100PSI in both holes, with no more than 5% variance between cylinders.

If the motor checks out as healthy, then I would look into the propeller selection. Sounds like it might be over propped (too much pitch). Going down in pitch a little will help with acceleration and should help top speed as well.

 

[Bosunsmate]

Re: 1983? Johnson 35HP lacking power/torque :


Heres the prop specs on mine,i get good top end and hole shot with below 100psi, i think mine a (currently) like 90/75psi

 

[likitvi]

Re: 1983? Johnson 35HP lacking power/torque :

Check also fuel filter, supply and state of your fuel pump.

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Thanks everybody!
+
Likitvi: Could the fuel pump really restrict the power output in that manner? I mean, it runs fine through the RPM range. It's just "sluggish" compared to my 1987 15HP for example. There the acceleration comes on quite fast. This is more mellow and suttle, but still runs fine. Just to make sure though. Can you force petrol into the engine with the bellow on the hose?

 

[2manband]

Re: 1983? Johnson 35HP lacking power/torque :

Thanks everybody!
+
Likitvi: Could the fuel pump really restrict the power output in that manner? I mean, it runs fine through the RPM range. It's just "sluggish" compared to my 1987 15HP for example. There the acceleration comes on quite fast. This is more mellow and suttle, but still runs fine. Just to make sure though. Can you force petrol into the engine with the bellow on the hose?

You can do exactly that. When you're experiencing the problem, try squeezing the primer bulb. (not hard, just as you would when priming the motor) If it's a fuel pump issue, pumping the primer bulb will usually cause it to clear up for a few seconds.

Your 11 pitch prop doesn't seem to be too unusual for the type of rig you're describing.

 

[emoney]

Re: 1983? Johnson 35HP lacking power/torque :

If what you're saying is you're concerned the motor may not be right shaft size for your boat, then yes that would cause a "sluggishness" if the cav plate is spending all it's time underwater. It's easy to confirm with a tape measure: measure the transom from the top to the very bottom of the hull and then measure the outboard's leg length as there's only 3 options there (15", 20" or 25").

I will add, however, that the compression test is very important. I've had motors run "perfectly fine" on one cylinder, outside of a whole lack of power of course.

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Emony: I will meassure tonigh unless it's pouring down as it does right now. Got to luve the Swedish autumn *not*. I will also buy a compression tester to make sure that the engine is performing mechanically sound.

I?ve been reading up upon changing pistons and so forth. If it turns out the pistons and the bore looks good (looking ahead) but the rings are worn out. Is it enogh to hone the bore and change to new piston rings to get better compression. Or am I looking as a complete change of piston/rings?

// Michael

 

[Haffiman]

Re: 1983? Johnson 35HP lacking power/torque :

Emony: I will meassure tonigh unless it's pouring down as it does right now. Got to luve the Swedish autumn *not*. I will also buy a compression tester to make sure that the engine is performing mechanically sound.

I?ve been reading up upon changing pistons and so forth. If it turns out the pistons and the bore looks good (looking ahead) but the rings are worn out. Is it enogh to hone the bore and change to new piston rings to get better compression. Or am I looking as a complete change of piston/rings?



// Michael

If the engine has more that some 3-4000 running hours, you may stat worrying about 'worn' piston rings. They may loose some tension over time, but not that significant either. If engine runs smoothly, idling is even down to 650 in neutral, do not worry about internal condition.

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Well, found the problem in the middle of pouring rain. We checked fuel pump, carb and compression (110psi on both cylinders).

The problem was that the remote throttle was REALLY sluggish. And where the throttle cable is connected into the engine (Gear throttle control) (part nr.83 part nr: 0387634 on a Johnson J35ECTS (Mine is a Belgian made J35BALCTS) was hardly moving due to corrosion. And the CAM adjustment was WAAAAY off - about 1 inch ahead of the throttle linkage.

I tried to loosen it up by spraying oil and moving it back and forth with a pliar. It worked for a while until part of it broke off . So now I need a new part for a staggering $138 (found old ones for arount $40 on eBay).

Problem is with this part it seems like I have to lift the whole engine block to be able to remove this part. Does anyone have experience with this part?!

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Well.

To quote myself. There was no big problems removing the gear throttle control once you removed the tiller gear and axle and the internal throttle arm. The gear itself was stuck like hell but after some much needed violence it was removable by pushing it up the throgh the axle hole on the engine.

From my meassurements there seems to be little differens from the 50?s and forward to this gear. So I boght a salvaged part for another OMC engine that should fit.

More to follow when it goes back into the ocean...->

 

[Haffiman]

Re: 1983? Johnson 35HP lacking power/torque :

You may be a bit mistaken. When mentioning ' cam adjuster' are you referring to the stopper on the link/rod from carb back to the vertical arm?
If so, the stopper may well be about one inch off the arm at idle.
Correct way to adjust, after idle and pick-up (roller -cam) has been adjusted is to shift engine into forward (not running).
Then give full throttle and adjust the stopper until carb is 99.9% open. When reverting back to idle, the stopper should be well off the vertical arm.

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Well. What I meant was that when engine is at idle with gear engaged. The CAM roller is off sideways from the marker on the CAM plate. On my 15HP 1987 Johnson you were supposed to align the CAM wheel with the marker on the CAM plate when throttle arm on the carb starts moving. On this engine I passed the marker by one inch before the throttle arm on the carb started moving. This could hardly be right?!

 

[Haffiman]

Re: 1983? Johnson 35HP lacking power/torque :

How the mark on the cam and the roller aligns at idle is of very little interest. That setting should just be: When roller and mark aligns, cam (carb) should start to open. With a light boat and low pitch prop, engine 'high' (little back-pressure), it might be a bit distance between mark and roller. The bigger the 'resistance' gets, more power need to be applied(timing advanced) and they will come closer to align up. On a working engine in good condition and correct propped, I've never experienced that carb has yet started to open at lowest possible idle setting in gear, around 700.

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

Hmm. So when Im in neutral - shouldnt the carb be juuuust slightly open? Im not 100% sure how to align the linkage on this engine. On the 15hk it was quite straight forward since the CAM roller was the only thing opening up the throttle on the carb. And it was rolling on a CAM plate that was bigger on the end than the beginning.

So best way is then to check the alignment is?:

when throttle is in the bottom (CAM plate cannot move any further): Adjust the carb so it's just fully open (by moving the small screw on the horizontal arm that connects to the carb. Is that the correct method?

Another strange thing is that the CAM wheen does not touch the CAM plate in the beginning. It's up in the air about 3-4mm. Im not sure if thats any issues. Mabe I should do a Youtube film to show?!

 

[Mullerhawk]

Re: 1983? Johnson 35HP lacking power/torque :

My prop is a 10.3*13 for previous questions about pitch. Im not sure if that's a standard prop?