Yamaha 60FETO , hits RPM wall @ 4000rpm

[timberman]

Hi all,

I have a problem with my 1994 60hp yamaha FETO, it wont go beyond 4000rpm and its not a prop related issue.

I have this problem since day one but never noticed untill I had installed an RPM gauge.

If you open throttle to WOT it shoots out of the water (150kg boat and a 15pitch prop, should need a 21 pitcher normally) and directly stops reving up around 4000rpm, at this moment i have around 20% throttle left but that wont make a difference on rpm level.

What Ive checked and done so far:

-Checked compression on all 3 cyls, all seemed fairly good (need to check again if you guys want to hear exact pressure).
-Changed fuel pump and cleaned out fuel system and cleaned carbs (used carb cleaner and compressed air, cant be the issue)
-Changed all 3 spark plugs.
-Replaced CDI unit, bought used one from ebay but didnt make a difference.
-Checked ignition timing with timing light, idle at 7degrees ATDC, WOT 21/22 BTDC degrees according to manual found on the internet.
-Measured coils underneath the flywheel and the resistances all look normal according to manual I have.


What should I check next? I was thinking to replace the sparkplug cables just to make sure.. Also, can it have something to do with the ignition coils? Im quite clueless
what to do next..

Any help is much appreciated!

Thanks in advance!

 

[99yam40]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

If the motor has good compression, spark, and proper timing, then you are left with fuel/air ratio, it has to be correct for proper firing of cylinders

Testing compression is simple and you should give all the #s when posting to help us.
Testing timing and spark on each cylinder with a timing light at the problem RPM should be simple also.
fuel pressure/vacuum testing the fuel system will show if there is a supply issue.

If all of that is good then you are back to the carbs or a vacuum leak some where

Of course this all also depends on that the motor is not overloaded, set up properly, and propped properly

But you have told us every thing is good

a DVA and meter will be the best way to take readings to chase down any electrical problems

 

[mphelle8vld]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

Since you were unaware of a problem until you installed a tach, are you sure it is set correctly? Can you rent or borrow an optical tach to check your installation?

With that light boat and prop, maybe you're just up against the rev-limiter.

 

[timberman]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

Thanks for your quick replys,

I then probably should start by making sure the rpm reading is correct, I will borrow an optical
tacho to check out and be 100procent sure.

@99yam40, will try the suggestions you said. I will check the compressions and post the the
Specific values.

About checking the problem rpm with timing light, I havent checked it by actually having full throttle on the water
,just by checking it with all the plugs out and using the elec starter and putting the linkage to WOT.
Should I do the timing procedure again on the water?? I dont have a testprop so I guess thats onyly method to make sure..

I wil look for a fuel pressure/vacuum tester and test the fuel system.

Im sure the motor is setup correctly, atm it has the wrong prop mounted (15pitch) which should get this
motor easy on its 5.500rpm WOT. Its getting the same RPM with a 23 pitcher I have.. only little less hole shot but it proves its definitely not prop related.

 

[timberman]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

Today I checked my compressions again and resynced all my linkages (had some play) since I noticed some problems with it, not sure it will effect
my WOT rpm problem but it seems to idle better and has a better gas reaction, tomorrow we will try her in the water again.

My compressions: Cil1: 100PSI , Cil2: 105PSI , CIL3: 99PSI
The manual I downloaded says: 853kPa, this is roughly 123PSI. Are the compressions still good enough? The engine is 17 years old of course..

Also one more question about setting the correct timing, my manual states that the advanced timing should be
22 ? 1 BTDC, in the timing procedure of Joe Reeves he says: set the spark advance to 4? less than what the engine calls for.

Should I set the WOT timing at around 18 degrees BTDC? At this moment I have it set as told in the manual, 22 degrees.

Hope to hear from you guys! Thanks in advance!

 

[99yam40]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

pressures are ok as long as they are even, or within 10% of each other is what I have always heard.
I would stick to the timing in the manual.

Is this the same motor that went under water and you added plastic to the cam to get the throttle plates to open completely?

 

[timberman]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

Yes 99yam40, thats correct its the same engine. I added some nylon to the gascam for it to open fully, now they go all the way flat as supposed.

EDIT: Oh I see I made a thread about couple of months ago http://forums.iboats.com/showthread.php?t=484780&p=3277454#post3277454
As today Im still not sure why the original state of the cam wouldn't let me open it fully, the only way was to add the plastic.

 

[99yam40]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

I wonder if it was a cheap way for Yamaha to detune a larger HP motor to a 60, if it was then there maybe other things are different also, like jets to change the amount of fuel along with the amount of air it took in.
Just a thought

 

[timberman]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

Interesting thought 99yam40, Ive read that the 60/70 engines share the same type carburators so its possible that they reduced the HP's that way.

Today Ive got some progress! Ive got about 5000rpm at WOT, still the engine is missing some power and it has some kind of bogging at WOT (not sure how to describe in english).
At a certain moment at the lake I had around 80% throttle when suddenly the engine had some boost and it accelerated for 1 sec and then stopped running, I looked behind and saw my fuel-tank fell
on his side so the engine couldnt get fuel.
Now my thought is, at the moment it accelerated suddenly without moving the throttle it was running leaner and ran better and actually got the full HP's.

So maybe it is the fuel/air ratio..? Running to rich?

I also have made a video where you can hear the engine at WOT and see the rpm, hopes it helpes to diagnose the problem a little better: http://www.youtube.com/watch?v=n1fjWf4OflA

 

[99yam40]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

What did you do to get it to 5K instead of the 4K as before?
To enrich a cylinder all you have to do is spray a fuel oil mix into the carb, but
The only way I can think of to lean out a clinder for testing is to pinch off the fuel line to the individual carbs one by one with a needle nose pliers while under way, to see if maybe just one cylinder is the problem.
Too much fuel would come from too big of jets or floats not sealing off needle and seats causing too much fuel into carb maybe.
Or maybe some one has put 70 carbs on instead of the 60s, maybe that would explain your linkage problem

Mt C40TLRX was a used motor when I got my hands on it and a previous owner had drilled out the main jets to a larger size, probably to try to make a 50 out of it.
it took me a year to finally find that problem. It was getting too much fuel and missing just at hard acceleration and WOT.
It would run a lot better if I had the cowling and silencer off and run into the wind if i ran with the wind it ran poorly

 

[timberman]

Re: Yamaha 60FETO , hits RPM wall @ 4000rpm

Hi 99yam40, (late reaction cause of some network problems)

The 5K rpm I now have is probably because I did a link and sync at the carbs and ignition advancer arm, I had some play in the arm that changes the timing and I just resynced the carbs according to the manual. Im not sure why Im getting
better rpm but Im guessing its because the ratio between openening the valves and adjusting the timing wassnt correct, still at WOT you here some bogging and Im thinking its running to rich..
Good Idea to try it without an airfilter without the cowling, I will try that to and see if it makes a difference.

What you say about the carbs and jets, I will get a parts list and compare the carbs and jets to check out it are the correct carbs. Will post it here if I see anything strange.