Yamaha 115 V4 cylinder 3 problem

Help!


Hello all can anyone help me with the following??
I had to replace 1 cyclinder number 3 in my yamaha v4 2-Stroke 115 1986. It was bought this way as it overheated. All the hard work is done but it wont run??? Spark is ruled out and it is also getting healthy fuel.

Compression.... I have 105 on all other 3 cylinders and 93 PSI on number 3 the one causing all the trouble. This cylinder was running after i replaced the piston and is now not its very od! Dont no what to do with it and the summer is coming. I did not rebore the cylinder just but a standard size back in as no damage was caused to the walls of the cylinder however it did require a hoaning. Its basically runnig fine now on 1 2 and 4 and number 3 is kicking in and out.

Thanks in advance
Daragh - Ireland.

Re: Yamaha 115 V4 cylinder 3 problem

You are losing spark or you have a fuel problem for the cylinder not to fire.
You need to start testing things like your Yamaha service/repair manual says.

If everything tests good for spark then look for the fuel problem.
You will need a spark tester, ohm meter, Peak reading voltmeter made especially for these motors or a multimeter with a DVA adapter

Re: Yamaha 115 V4 cylinder 3 problem

Great, thanks for that. Its not spark I have established that much did all the tests known to man, replaced coil etc

I was thinking of checking fuel but if it was fuel would it not effect the other cylinder as the bottom carb feeds them both?

could carbin build up be also adding to the problem?

Kind regards,

DC

Re: Yamaha 115 V4 cylinder 3 problem

What tests did you do and what ohm and voltage readings did you get on the charge coils,pulsar coils and any other tests you did. this info will help others see what is going on so they can help.

Where any of the tests run while motor was running and cylinder not firing?

Re: Yamaha 115 V4 cylinder 3 problem

Basically I used a spark testers at night with the boat running on all 4 leads. In the dark you can see the spark easier so I was trying to make it easier for myself. Aslo a friend of mine also has a Yamaha 115 so I borrowed his coils to see if it made any difference, but it didnt. I then moved on to timing to see if it may have been slightly out, but it wasnt. I replaced all the plugs just to rule out the ovious but still no joy.

I then took readings with my multimetre in OHMS with the motor runnig on 3 I cant remember the readings it was a week or so since I did it but they where all consistant in all four. Have you any idea what they should be and I can do it again? Whats important to note is that all four are giving the same reading, but number 3 is cutting in and out every sixth power stroke or so even with the same reading as the rest. Its actually more of an irregular fire rather than a mis-fire.

Pritty sure I have spark ruled out. My way of thinking is that the spark was fine before she over-heated, however it was taken a sunder and put back together. I took photos of the ignition system at the time before I began to ensure I put it all back togeter correctly.

I bought a manual online its not a genuine Yamaha one. But all the tests above are listed in my version.

The joys of boating... Think you might be onto something with a fuel problem.

Re: Yamaha 115 V4 cylinder 3 problem

A multimeter will not read ohms on coils while motor is running.Ohms need to be read while wires are disconnected
Your manual should give the the ohms and minimum voltage reading needed for proper operation on all of the different components. voltages are taken with a peak reading meter or a meter and a DVA adapter to get the proper reading to compare to specs in manual.
An inductive tach and timing light can be used to help see if the is intermittent spark problem but will not pin point the sorce of problem like a DVA reading will.

Here something that kind of explains the use of different tools and what they are used for while checking these ignitions.

http://www.outboardparts.com/troubleshooting/printguide.htm

Re: Yamaha 115 V4 cylinder 3 problem

Turns out it was the carbs. They needed to be cleaned and balanced. Thanks for all the advice.

DC