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Old 07-10-2015, 12:36 AM
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Need help with RedMax trimmer

Hi, I have a RedMax string trimmer that won't start. I know it has spark because I tested it with an inline spark tester and I also held the plug to ground and saw spark at the plug tip. On the spark tester with the window, the spark jumps a gap larger than the SE gap setting normally used for engines of this size.
Compression is 130psi, which I know is adequate. I cleaned the carburetor, and still could not even get the machine to even cough once. So I replaced the carb with a brand new one, and still it gives me nothing when I pull the cord.
I checked the flywheel and the shear key is intact, so the timing shouldn't be any issue. The only thing I have left to try is crankcase compression.
My question is this: would a trimmer with a crankcase leak fail to even try to start? Would I get absolutely nothing from the machine when I pull the cord if there is a leaking seal or gasket in the crankcase? Is this a common problem for Redmax?
I should mention that I do not know the model number. This is an older, "all metal" unit. Thanks!
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Old 07-10-2015, 12:39 AM
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Also, starting fluid sprayed directly into the carb throat doesn't get the trimmer to do anything either.
I sometimes get one "pop" out of it every 30 pulls or so, but never anything more than that.
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Old 07-10-2015, 06:36 AM
zo6 zo6 is offline
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sounds stupid but ive had the vent hose to the fuel tank gunk up and it wont allow it to start.
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Old 07-10-2015, 08:22 AM
dboyd351 dboyd351 is offline
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Is the plug wet when you take it out? Could be so flooded it won't fire. On the other hand, you didn't mention checking the fuel lines or filter. Doesn't sound like you have determined whether you are getting fuel to the engine.
I'd replace the fuel lines and filter, pull the plug, pull it over about 20 times, let in sit for 15 minutes or so with the plug out, install a new plug and try it again.
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Old 07-10-2015, 08:43 AM
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ilike2mow ilike2mow is offline
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I had this issue and the spark plug gap was too small
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Old 07-10-2015, 09:20 AM
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Thanks for the replies. I did replace the fuel lines and filter because the fuel lines were nonexistant and the old filter was loose at the bottom of the tank when I got the trimmer. Remember, it does nothing even when I spray starting fluid into the intake, so I don't think it's fuel related. It's not flooded because I am aware of that situation. I've pulled the plug several times to allow the unit to dry in the sun after pulling the rope to discharge any liquid fuel in the cylinder.
The only comment that has me thinking is the wetness of the plug. It feels damp, but it never gets soaked, as I expect it should. That's one reason why I installed the new carb. I wanted to rule out fuel flow.
The fuel is good, it is premix Stihl fuel from a can, and it runs all of my other equipment. I think the problem is not an easy fix, which is why I went as far as to pull the flywheel to check the shear key (timing). It's also why I'm now thinking that this may be a crankcase leak or something like that.
Still doesn't explain why it won't pop with starting fluid, though. Maybe the spark isn't strong enough despite it passing three spark tests? I will look into how to test the coil with a multimeter (I know it can be done), or may just buy a new coil to rule it out. $$$
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Old 07-10-2015, 09:34 AM
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Forgot to mention, the plug is gapped at .025
I do that for all trimmers. I use .030 for mowers. I'm sure there is some variation between different models, but this rule of thumb should at least get a machine running.
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Old 07-10-2015, 02:01 PM
Uncle Knuckle Uncle Knuckle is online now
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Quote:
Originally Posted by Wacker Mechanic View Post
Hi, I have a RedMax string trimmer that won't start. I know it has spark because I tested it with an inline spark tester and I also held the plug to ground and saw spark at the plug tip. On the spark tester with the window, the spark jumps a gap larger than the SE gap setting normally used for engines of this size.
Compression is 130psi, which I know is adequate. I cleaned the carburetor, and still could not even get the machine to even cough once. So I replaced the carb with a brand new one, and still it gives me nothing when I pull the cord.
I checked the flywheel and the shear key is intact, so the timing shouldn't be any issue. The only thing I have left to try is crankcase compression.
My question is this: would a trimmer with a crankcase leak fail to even try to start? Would I get absolutely nothing from the machine when I pull the cord if there is a leaking seal or gasket in the crankcase? Is this a common problem for Redmax?
I should mention that I do not know the model number. This is an older, "all metal" unit. Thanks!

You've covered the basics. To answer your first two questions, yes. A leaking crank seal can cause an engine to fail to start because the air/fuel mixture is not being moved up to the cylinder due to lack of crankcase pressure (primary compression). I recently had to put a crank seal in a blower for this very condition and if I can find the old seal I'll post a picture for you.

To answer your third question, no. This is not common but it does happen from time to time.

To diagnose you will need a pressure and vacuum pump to properly test the sealing ability of the crankcase, some way of blocking off the intake & exhaust ports and an adapter to apply pressure/vacuum. Sometimes the adapter fits in the spark plug hole and sometimes it is installed in place of the carburetor. Depends on the machine. If the leak is too large, you won't be able to build any pressure or pull a vacuum. There are more specifics but I won't go into that detail now.

Did you check the exhaust port for being blocked by carbon? How about the spark arrest screen? I also had a catalytic muffler plugged and if I can find it I'll post a picture of that one, too.
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Old 07-10-2015, 04:37 PM
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Breezmister Breezmister is offline
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Quote:
Originally Posted by Wacker Mechanic View Post
Still doesn't explain why it won't pop with starting fluid, though. Maybe the spark isn't strong enough despite it passing three spark tests? I will look into how to test the coil with a multimeter (I know it can be done), or may just buy a new coil to rule it out. $$$
Did you put a new plug in it ?
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Old 07-10-2015, 05:25 PM
Uncle Knuckle Uncle Knuckle is online now
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I found the parts I referenced in my previous post. The first picture is a crank seal and it should be only one piece. With a leak this large there is no way the air/fuel mixture can make it to the combustion chamber. I did as you did and added extra "fuel" directly into the intake and not even a hint of of a pop.

The second picture is a catalytic muffler that was plugged up to the point that the engine would no longer start. Turns out these little engines really do need to breathe.
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