1987 YAMAHA 150 plugs not firing

[mailman1]

The engine starts and idles perfect. It will not get over 4000 rpms and top end is sluggish. Two of the plugs are wet but are not brown like the other 4. The top left and bottom right are like new. Any help?

 

[easygo0]

Re: 1987 YAMAHA 150 plugs not firing

have you actually ck to make sure you have spark at cylinders.ck coil wires not shorting out or disconnected.how about correct prop for application? bad gas try running on 3 0r 6 gal portable tank with fresh gas.that motor i belive had a problem with screw heads in fuel pumps rusting and plugging jet in carbs just a few possibilities you can ck before major concerns like cdi.good luck

 

[vinney]

Re: 1987 YAMAHA 150 plugs not firing

Check the fuel pumps on that engine. There are three low pressure fuel pumps on that engine. There are diaphram kits or replace the entire fuel pump. If the primer bulb will not get hard and when it idles there is raw fuel on the top of the water check your fuel pumps for bad diaphrams.

 

[mailman1]

Re: 1987 YAMAHA 150 plugs not firing

The engine starts and runs fine but I can't get over 4000rpms. It does not stall or sputter. When I said they were like new, I meant they were clean after being used, like not firing. Could the carbs be not sending fuel to these pistons?

 

[vinney]

Re: 1987 YAMAHA 150 plugs not firing

You need to inspect your fuel pumps for a bad diaphram,

 

[Ray Neudecker]

Re: 1987 YAMAHA 150 plugs not firing

First step is to take a timing light and see if plugs are all firing. If so, you have a fuel restriction problem. The plug description would have me looking at the carbs first.

 

[bruce537]

Re: 1987 YAMAHA 150 plugs not firing

Hello<br />I had the same thing and it was the plug caps.<br />It is not uncommon for Yamaha wires to have bad caps and sometimes the coil itsself<br />Take a multi tester put it on resistance.........unplug the wire from the plug....put red lead in cap and ground the black you should get between 750-850 thru the wire with cap on.<br />If you get 0.........unscrew the cap from the wire and check the wire the same way........the wire to the coil should be around 3.2.........if you got nothing and then got around 3.2 thru the wire, just replace the cap.<br />If you check the wire and get zero, then replace the whole wire and coil assy.<br />The wires and coils are about 135$ each, so check them carefully.