misfire issue

[ideas113]

Hi from down town Brisbane Australia
any suggestions on piston4 not firing
Engine = 130beto

symptoms
engine running rough
remove leads one by one, no change when can4 lead is off
Swaped Spark plug betwwen 3 & 4 = No change
replaced can4 coil = no change

that's the easy stuff out of the way, any suggestions please

[CallalaJohn]

I'm definetely no expert, but here are my thoughts. Have you thought of the lead running from coil to plug. You probably thought of that already but give it a go. Take it easy. John.

[ideas113]

Cheers John thanks for the thought, the lead is not seperable from the coil, so in this case both the coil and lead is new..

happy days

[99yam40]

Need to make sure the compression is good on all cylinders and then check spark with a spark tester.
Pulling plug wires off while motor is running can cause the spark to jump internally and hurt the coils or other parts.
If all that is good the you have a fuel problem

[ideas113]

Need to make sure the compression is good on all cylinders and then check spark with a spark tester.
Pulling plug wires off while motor is running can cause the spark to jump internally and hurt the coils or other parts.
If all that is good the you have a fuel problem

Thanks, here's hoping for an easy fix

[ideas113]

Thanks, here's hoping for an easy fix

Checked Compression, 1 = 9.0 bar, 2= 9.0, 3 = 8.7 and 4 = 8.5, spark action afirmative on all 4 pots....
That leaves fuel, as you say. Since fuel system is not my thing, any suggestion would be appreciated.
In anticipation of a filter question, Primary filter is a Racor 10um with water seperator, Yami engine mounted filter serviced recently

[99yam40]

Have you checked fuel pressure and vacuum?
How old is the fuel and is there water or trash in it or the carbs?

[ideas113]

Thanks for the reply,
no check on fuel pressure + vacuum, but will do
fuel is less than 30 days in the tank,
no water showing in seperator bowl of Racor filter or on the engine filter bowl,
as far as debris, tiny bit of fine in Racor, none in the engine filter, Can't say for Carb bowl as i have not opened the carb.
I'm struggling a little with fuel flow issues as i can achieve 5500 RMP at WOT, any thoughts?
cheers
Rob

[99yam40]

Check fuel pump for leak if that motor uses #4 crankcase for pulsing the fuel pump. I am not sure if it does, but it is something to look at to be sure. A leaking pump diaphragm will cause a cylinder to run rich.
Other than that pull and clean the carbs , if it running lean because of plugged jets the you will hurt a piston

[robert graham]

If you can run 5500RPM's at WOT but motor is rough at low speed/idle, then possibly plugged up low speed carb jets? Carbs ever been cleaned?

[ideas113]

Thanks for the info guys, much appreciated, I will go after the carbies, as that makes sense to me. I have had the boat for two years, during that time I have not had the Carbs serviced other than idle speed adjustment. I can handle disaasembly and rebuild no problem but the actual setting up of the carbi is something i will need to read up on, where do I look for that info?
cheers

[99yam40]

Get your hands on a Yamaha service manual for your motor it will pay for itself in saving you time and trouble trying to find info other ways

[ideas113]

Thanks folks,
I have manual in hand, intend to strip and clean carbi, check fuel pump. Will post outcome once completed and test run, time frame dependent upon "domestic managers" approval of funds

[ideas113]

Ok. Domestic manager is pleased, no cash required.
I am pleased, it's fixed.

I did not see anything in the slow speed jet when removed but if it was blocked it may have been dislodged during removal of the jet as it was difficult to get the jet out.
After a good clean out and check over including removing the High speed jet port cover to see if there was fuel in the bowl (there was). At initial test the result was not great however I have reset the air flow metering screw, noting that at 1/2 a turn outwards the engine revs pick up and the intermittant misfire is eliminated.
So, having reset the idle speed I think we have a fix.

Thank you to you folks for your assistance.

Happy days

[BazzaDee]

I had a similar issue last weekend coming back from Tangalooma, just died on me when we backed off for traffic!
I had wanted to clean and adjust carbs for sometime, as it was hard to start, required manual choke for first start (even though auto choke was working and adjusted fine!) and would run fairly rough at idle, missing etc.
Carb #4 had debris in main jet which fell into my hand as I removed the blanking screws! Cleaned carbs out, reset float levels from 19.5mm to 17, assembled, adjusted timing, sync carbs, adjusted pick up.
This motor was serviced prior 1 year previously, I could not believe every setting I checked required adjustment! I thought I had the wrong manual, checked and rechecked I was on the right track.
Primed and first kick she burst into life!
There ya go, no money, just some time and loads of reading and she is best she has ever been!
Cheers,
Bazza