My Yanmar Won't Start!

Your Yanmar tractor has faithfully started every time you needed it but, suddenly, without warning, the engine will not fire. What do you do?

Don't panic! A solid 75% of the tech support emails that we get started with something that could have been an easy fix and turned into something more serious by a hasty mechanic. Jumping around, randomly changing things, and trying things, is only going to complicate the troubleshooting later on.

We have had customers disassemble injection pumps, pull off cylinder heads, destroy engines with starting fluid, all while trying to fix a very simple contaminated fuel problem. 

These Tips Assume:
 - The engine is turning over. If it is NOT turning over, check this article.
 - The tractor was running normally when you parked it. If the tractor overheated or stopped unexpectedly, please contact us for other tips. 

Is the engine turning over fast enough? Since diesels do not have spark plugs, they require the engine to spin over relatively quickly in order to build up the necessary compression to ignite the fuel. This is especially true when the engine gets older and has less compression than when new. If the starter sounds slow, try putting the battery on a charger or jumper box. 

Fuel Supply. This is probably the biggest problem with the Yanmar tractors and, really, any diesel engine. Diesel engines need a steady flow of quality fuel in order to run. To test that you have a good flow of fuel, remove the fuel hose that goes into the injection pump. Let that fuel run into a gallon jug and be sure you have a steady stream for at least 10-20 seconds. It is not uncommon, if there is a restriction, to get a stream of fuel that quickly tapers off. If your fuel flow is low or blocked, work your way back up to the tank, removing hoses, until you find the restriction. It might be the fuel filter is clogged or even the outlet at the bottom of the fuel tank. 

Fuel Quality. Diesel fuel can get contaminated with water through a leaking fuel cap, through a contaminated source, or even just condensation. Water will settle to the bottom of the tank and quickly get sucked into the system. Your engine will not run on water and, to make things worse, water can also cause your injection pump to rust and stick. Water will also allow tiny microbes to grow in the thin layer between the fuel and water and these little critters are highly corrosive. Keep your fuel clean and add a biocide and stabilizer if you are going to be storing your fuel for over a few months. If you suspect water or contaminated fuel, drain the fuel tank, replace the fuel filter, and flush the fuel lines.

Air Intake. Another common problem is mice or rats (or even mud daubers) building nests in the intake system of some models. They like the dark, warm air cleaner housing and intake tubes. If you tractor has been stored for several months it is always a good idea to pop off the air cleaner lid and check for visitors before trying to start the engine. 

Exhaust Blockage. It is not that uncommon for Yanmar mufflers to get clogged when an internal baffle separates and covers the exhaust tube.  If this happens while the engine is running it will produce very thick, black, smoke and a massive reduction in power. If it happens after sitting it might just make the tractor hard to start. 

These steps will find 90% of the problems that you will have with your Yanmar starting. If the tractor will not start after checking these things then it is time to move onto more advanced troubleshooting. We will be updating this article soon to include those.