My ms500i wont start unless I squirt a little gas down the intake. Then It starts first pull and runs fine when im using it. But if I shut it off and let it sit for 15 mins it won't start back up, Unless I squirt more gas down the intake. Doesn't matter how many times I push the primer bulb. Any help would be much appreciated
Ms500i wont start
- Thread starter jjensen36
- Start date
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Is the primer working? Look at al the normal chainsaw issues first (fuel lines, wiring, filter fuel, compression, spark, etc.)
Still just a saw.
Check electrical connections.
A couple things I have found- bad grounds and bad temp sensors. Grounds tend to be under the flywheel.
Two temp sensors- one under flywheel and one in switch. This is where putting it on the diagnostic computer works well. It will show this up quickly.
Just a for instance, Had a 500i no spark. Computer showed failed generator. bad ground and temp sensor way off.
Checked grounds, no difference.
Replaced generator. Temp sensors now read normal and spark returned.
Lost ground through the generator.
Still just a saw.
Check electrical connections.
A couple things I have found- bad grounds and bad temp sensors. Grounds tend to be under the flywheel.
Two temp sensors- one under flywheel and one in switch. This is where putting it on the diagnostic computer works well. It will show this up quickly.
Just a for instance, Had a 500i no spark. Computer showed failed generator. bad ground and temp sensor way off.
Checked grounds, no difference.
Replaced generator. Temp sensors now read normal and spark returned.
Lost ground through the generator.
The saw runs perfectly fine when you get it started. The issue is getting it to prime up so that it will start. It has great compression, No issues with spark, has a new fuel filter. All the electrical connections seem to be fine. Nothing loose or broken
What starting sequence do you use?
I make sure it always has gas in it then I pump the primer bulb minimum 8 times and pull the cord. No matter how many times I repeat this process it won't prime up and start. But when I squirt gas down the intake it fires up first pull and will run flawlessly all day as long as I don't let it sit for more than 15 mins off or else I have to squirt more gas down the intake to start it back up
Can you feel if the fuel is pumping when pressing the primer? You aren't holding the throttle on by chance, are you?
It pumps fuel. I can see it squirt gas back through the return into the tank after a few pumps
And you are not holding the throttle trigger wide open when n pull starting, right?
No I do not hold the trottle when starting it. I have tried holding it a few times but it doesn't help nor hinder when starting
It is my understanding that the pump on the 500i just pressurize the injector. I believe it is not like other saws where it will deliver fuel into the cylinder.
Once the starter is pulled the chip with its sensors will adjust the right fuel and air for starting.
There might be a problem with the cold start with the chip. You do say after it starts there are no issues.
Could be a short or problem with the wiring, or. A visit to dealer that has good reputation can just look at the wire, switch or chip. Maybe hooking up to their computer will reveal.
Good luck, Patrick
Need to take it to a dealer and get him to put in on the computer. Chances are it will not show a fault.
Could be leaking back past the check valve in the fuel pump. I have replaced those that just wore out.
Could be leaking back past the check valve in the fuel pump. I have replaced those that just wore out.
Just worth mentioning, saw purge bulbs just take air out of the carb, it doesn’t squirt fuel onto the engine
First thing that needs to be done is perform the complete fuel system troubleshooting procedure which can be found in the MS500i service manual.
Thanks for that information. Don't own anything with a purge bulb other than snow blowers.Just worth mentioning, saw purge bulbs just take air out of the carb, it doesn’t squirt fuel onto the engine
All good mate
Just worth mentioning, saw purge bulbs just take air out of the carb, it doesn’t squirt fuel onto the engine
I guess there is three versions of that. On most saws, weed eaters, blowers, you are just filling the carb and bypassing excess to the tank. Usually trouble shooting if the primer will squirt a solid stream back to the tank it is OK.
Then you have some versions where you are actually squirting a stream of fuel straight in to the barrel. Not many of those, but I have a B&S lawn mower and old Robin weed eater that work that way.
On the MS500I you are pressuring up the fuel injection system, or making sure it is purged of any air, however you want to look at it.
If it is leaking back when sitting then you have a primer issue I would think.
We fix these somewhat regularly, and I'm sure we would be called parts replacers.
But, you start with what is most likely and go from there.
Sometimes the diagnostic program will pin point the problem. Usually not.
I’ve repaired a fair number of TS and MS500i’s at this point. I can say with utmost confidence the fuel system troubleshooting procedure must be done and followed exactly to the letter. On the MS500 the MDG doesn’t really tell you much, the TS500 has much better diagnostic capabilities. Based on what OP is describing I’d say that saw very likely has a problem with the fuel pump. The troubleshooting procedure will verify this.
I pressure/vac tested all of the lines and the primer bulb and it seems that the injection valve or the injection module was leaking. So I have another 500i that I just swapped the injection module with and put both of the saws back together and now they both start right up and run. I'm not sure what the cause of all this headache was but it seems to have magically disappeared for now. I will have to let them sit for a day or 2 to see if the issue is gone for good
That’s a good sign, however I would still perform the factory test procedure. There’s a specific way the fuel system components must be tested to identify problems. Could have been a fluke I suppose but I always like to know what the exact problem is. If the injector is leaking the problem will likely return.
I finally decided to do some more tinkering on the 500i and swapped all the electrical components from a different one that starts up and runs fine to the one that won't start. And the starting issue has now swapped saws. I now fully believe it is not a priming issue, but something with either the computer or the ignition sensor. Thanks for all the help!
