limited rpm from 40hp 1990 2 stroke yamaha

I have just fixed all the carby issues on my boat and motor.

Wandering what the motor should rev to? seems to max out at 4000rpm. have checked to make sure getting full throttle. is this normal or any ideas?

1990 40hp yamaha 2 stroke 3 cyl engine.

All help greatly appreciated.

Re: limited rpm from 40hp 1990 2 stroke yamaha

My 1999 manual states 4500 -5500 RPM for my C40TLRX.
I think that you still have carb problems or you are over propped.
Check this out

http://www.yamaha-motor.com/outboard/products/perfbull.aspx

or try this one if you are having a problem finding the 40 hp motors

http://www.yamaha-motor.com/outboard/products/perfbull.aspx?ls=outboard

Re: limited rpm from 40hp 1990 2 stroke yamaha

This motor has the original prop on the motor so i would say not over proped

Just wandering how you check the lead resistance and coils on this motor as the lead is part of the coil? could a faulty lead/coil cause engine not to rev?

have checked spark on all cylinders throws good spark using spark tester. but wandering if could be breaking down under load?

Re: limited rpm from 40hp 1990 2 stroke yamaha

You should be able to check resistance of the secondary of the coil by installing one lead into the plug cap and the other to ground.

An inductive timing light will help you see a miss fire on a plug wire.

Your plugs will help you see if it is running lean or rich, but if you still have a problem with a cylinder running lean because of a carb problem it will wipe out a piston by running it that way.

A manual and the proper meter will let you test the electronics even at load, but it is not easy while you are running WOT and testing.

I have been told that if you think your carbs are clean enough and still have a problem to go through them again and again to make sure.

I had a high speed miss on my motor for quite a while, but it was due to someone drilling out the jets allowing too much fuel into the cylinders. It still ran over 5K, so I would be very careful running yours since it will only get to 4K

Re: limited rpm from 40hp 1990 2 stroke yamaha

Have rechecked carbies all good. checked and made sure timing is correct and advancing all good. checked fuel pump diaphram etc all good. Checked spark all cylinders firing well.

original prop still fitted to motor

can any one think of anything else this could be.

jumps out of a hole well and gets to 4000rpm but won't go past 4000rpm.

Re: limited rpm from 40hp 1990 2 stroke yamaha

we are not sure what type of boat and load you are running, along with what prop. Did this motor and boat ever run properly?
you are not saying how you are testing any of this , so we do not know what is going on.
Do you have a manual and are you testing things like it says and with the proper test equipment?

Just saying it is good does not mean a whole lot.

have you checked your fuel delivery system with a pressure/vacuum gauge to see if it is starving for fuel or sucking air?

Re: limited rpm from 40hp 1990 2 stroke yamaha

99yam40 i do have a manual and have checked as per.

Have removed the carbies again checking everything to make sure all clear. Have checked fuel pump diaphragm and there are no holes etc. checked timing as per manual and checked to make sure making advance as per manual. checked spark with spark tester all ok.

I have not checked the fuel system with a vaccuum guage as yet but will do.

It is a stacer 444 4.5meter aluminium boat.

hope this clarifys for you.

Re: limited rpm from 40hp 1990 2 stroke yamaha

What 99yam40 is trying to find out is, was this motor running fine and just quit working all the sudden? Or did the problem develop over a long set of no use. While troubleshooting have you taken any output reading on your coils or the cdi to see if they are to spec.
If the carbs were trashy when you checked them first, they may still have something in them you can not see.
I always use a clear glass jar to catch some gas out of the hose that hooks directly to the carbs, not the engine or filter. Hold the glass to the light and swirl you a tornado in the jar ,all trash will go to the point in the tornado.
If your fuel lines under the hood are original they may be deteriorated and releasing small bits of rubber [you cant see] back in the carbs.

Re: limited rpm from 40hp 1990 2 stroke yamaha

Here is something on fuel from the frequently asked questions part of the forum

http://forums.iboats.com/showthread.php?t=283363

What kind of voltage reading did you get when testing the pulser coil output, charge coil outputs, and the CDI outputs? What kind of meter and DVA did you use?

What did the timing light show the timing set at at idle and WOT?

You never answered the question, Did this boat and motor ever run properly? or is it you do not know if it ever has because you just got your hands on it, or maybe you just put the motor on the boat?

Like Turn2 said give us some history on what has been going on with this motor if you have had it for some time and what all you have done

Re: limited rpm from 40hp 1990 2 stroke yamaha

Sorry

The boat has never run right since i have had it. It has been in the family for a long time. My wifes Grandfather bought the boat new in 1990. it has run fine at some stage but i have had it for the last 2 years and has not.
(I went out once and can remember the boat performing as i would expect)

The boat sat for 5-6 years before i got hold of it. as i said done very low hours for the age of the motor.

I went through and rechecked coils and looks as if no.3 coil has an open circuit on the secondary side. Am waiting on a test unit to double check and see if i pick up wot 5500rpm.

Will let you all know when have done this test.

I have carried out full carby rebuild changed all fuel pump diaphragms and gaskets cleaned out the fuel system replaced the fuel feed line and primer.
obviously replaced spark plugs.

The boat shop replaced the CDI unit and said they had tested the coils????????. refer to my other post to do with the carby issues.
Yamaha 40hp Lacking Power

Again thanks to all will post back once coil replaced.

Re: limited rpm from 40hp 1990 2 stroke yamaha

I take it that this motor is not a US motor, you never gave a model # and since you are using meter measurement and the word carby I would say you are not located in the USA.
read #9 on this post it helps us a lot to know everything .http://forums.iboats.com/showthread.php?t=250876

Does your manual say if the plug caps are replaceable? My 1999 manual says that Canadian and European specs for spark plug caps are 4.0-6.0 K ohms but give no specs for the US so I take it mine are not replaceable, but yours maybe. Make sure the black wire on the coil is grounded good and has no corrosion on the connector.

I thought you said the spark was good

What kind on meter are you using to take your measurements and what is the test unit you are speaking of that you are waiting on?

"The boat shop replaced the CDI unit and said they had tested the coils????????."
Did they do this like they cleaned the carbs and fuel system?

Did you get the old CDI unit from them that they took off? It may be a good unit still and even if it is not the wiring connectors might can be used to make a test harness.

Did you read the tread on testing the fuel delivery system? are you sure it is not sucking air?

Re: limited rpm from 40hp 1990 2 stroke yamaha

This is not an american model.Australian... Model 40 HEO/ 6H4L / 406722

It does have good spark when testing at idle. Using spark tester it jumps the max opening of that tester. but secondary is certainly testing as faulty compared to the other coils.

Have checked all connectors and replaced any coroded ones.

I have been over the fuel system and checked for fuel leaks as per post. all testing ok no air bubble formation and pump creating vacuum.

The plug leads are not replaceable it is a replacement coil. I have a friend at a boat shop that is supplying me with a coil for testing purposes.

The meter is a fluke automotive meter.

Yes very hesitant with them testing coils etc. The cdi unit on the boat is new but i have not paid for it as it did not fix the problem...

Re: limited rpm from 40hp 1990 2 stroke yamaha

Good to hear you did not have to pay for the CDI, they are lots of $$$. around here they charge you for anything they put on.

I take it it is a pre mix motor and not a oil injected one.

What readings did you get on the different coil secondaries to make you think one is bad?
This type of info is what helps others when they do searches and read your posts.

I was wondering about if the the spark plug caps were replaceable, not the secondary wire itself.

Did you get peak voltage readings on the pulser coils, charge coils, and CDI outputs?

If the new coil does not fix your problem you will need to get these at the problem RPM.

Re: limited rpm from 40hp 1990 2 stroke yamaha

the motor is oil injected. (precision blend model)

coil number three is open circiut the other 2 i can get 6ohms resitance.

no the spark plug caps/leads are intergrated into the coil there is no way of replacing a cap/lead.

If it still plays up after the replacment coil i will take these readings at problem rpm's but am pretty sure this coil will fix it. will let you know when i know.

The only thing that i am concerned about is the motor will run all day at 4000rpm no problems. and is running very smooth. In the car world if it dropped a cylinder it would run rough so unsure if boats work the same?

thanks heaps for all your help.