Why Does My Honda TRX400 Lose Power?

When you have a Honda ATV that loses power, you might need to do a compression test on it, and maybe even go further and do a leakdown test. 

Partzilla's resident powersports pro John Talley livestreams on our YouTube channel every Friday at 3pm Eastern for Q&A sessions. In this edition, John was asked about a Honda TRX400 that lost power, and what could be done to solve the problem.

Honda ATV power loss leakdown test

Honda ATV Power Loss

I have a 2005 Honda TRX 400 that for some reason the motor lost power. What can I do?

John Talley: Well, when you say it lost power, is it still running? Is it smoking? Start with the basics. Do a compression test on it and see if it bent a valve or something else has gone wrong. If the compression test shows that she’s down something under 75 or 80 pounds, then maybe you’ll want to do a leakdown test. That will tell you if your rings are shot out, which I doubt because that usually happens over a long period of time. What you’re describing is possibly a bent valve, because one split second and that piston touches that valve and it’s not going to seal. And it might still start, but it’s going to be down on power after that. If you’re thinking it’s not anything in the engine, I guess your main circuit could be getting stopped up on the carb. But do the compression test first and if that isn’t it, then take a look at your carb. One other thing I have seen in the past, where everything’s running fine and then the bike will start losing power is actually a misfire, and that’s usually caused by either a crack in your CDI or coming off of your coil going to your spark plug, or the coil actually breaking down itself. The hotter it gets, the worse it performs until it doesn’t let the bike run at all, so just a couple of things you can look at. Compression test first, then take a look at the carburetor if it’s fuel-related, and if it’s not, head over to that coil wire or coil pack that goes to that spark plug cap. 

Buy Bike Master cylinder compression tester kit

Buy Performance Tools leakdown tester

Watch the video below to see how to do an ATV compression test.

Watch the video below to see how to use a leakdown tester.

Want to see more live repair questions answered? See more motorcycle and ATV repair questions answered here.  



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