G16 performance loss after running for 5-10 minutes

[logan1211]

Hello all! Have an older Yamaha G16 that wouldn't start when I got it. Got what I feel is the carb cleaned well enough and replaced the fuel hoses, filter, and pump and gave her a tune up. Now she fires right up and stays running without dying after 10 minutes.

However, last night I noticed that after I drive for 5-10 minutes, the power loss is very noticeable.

GPS speedometer I hit 18 mph on a flat road after getting it put together and took it out. After doing that a few times; it wouldn't go over 11 mph.

Any tips or advice on where I should I be looking next?

[greenskeeper]

When it loses power does the engine sound normal and run correctly or does it miss or show a sign of fuel starvation or poor ignition?

My initial thoughts are a fuel pump issue, but that would probably show up sooner. Another thought is a coil issue that shows up once the coil gets hot.

[CP241]

Generally if it loses power when it gets hot its a failing ignition coil, possibly ignitor. but also could be compression related. I'd check compression cold and hot just to be sure. Adjust the valves to spec. And if all else fails try another (OEM) coil.

[logan1211]

Thanks all! When losing power; it does seem to have a little miss, just won't rev as high as normal.

I adjusted the carb just a tad yesterday and got the valves adjusted. Drove for 30 minutes and can't get it to slow down/lose power now. Going to keep an eye on it and check coil if it happens again. Appreciate the input!

[SandbaggerYDRA]

Originally Posted by logan1211

Thanks all! When losing power; it does seem to have a little miss, just won't rev as high as normal.

I adjusted the carb just a tad yesterday and got the valves adjusted. Drove for 30 minutes and can't get it to slow down/lose power now. Going to keep an eye on it and check coil if it happens again. Appreciate the input!

It was probably the valves. If there isn't enough gap, when the engine heats up, the metal in the push rods expands and it's possible that the value may not close completely which will rob you of compression, and produce a miss.