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First 290 rebuild and it wont start

JSharpe

JSharpe

New Member
Joined
Sep 13, 2021
Messages
3
Location
Lilburn, GA
Hi guys, I have been reading on here for a while as I rebuilt a MS290 I had. The original cylinder/piston was scored pretty bad. I went ahead with a 390 piston and and new cylinder. I did not use top shelf parts, but don't think that I used bottom of the barrel either. My problem is that I cannot get the saw to start. I have fuel, and spark. I thought the spark was weak so I installed a new coil. The H/L screws are turned out 1 turn each to start with. The idle screw may be not right as I have messed with it. I checked the compression thinking that maybe the cylinder did not seal to the base well. I did use Motoseal. It has 150psi with rings that really not have been seated by running. I thought this was pretty good. The flywheel is new as the old one sheared a key. I have also rebuilt the carb. I feel like it might be getting flooded, but not sure. Am I missing something? Anyone have any suggestions? I have read about impulse line issues.....thoughts? I have rebuilt several hotrod small block chevys and fords, so this type thing is not a big deal, but I am stumped. Thanks in advance.
 
Vintage Engine Repairs

Vintage Engine Repairs

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3,442
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back to basics :)

Close both carb screws to stop fuel coming in, take plug out and make sure it’s dry.


Add a small amount of fuel to the plug hole and re attach plug.

set the saw to high idle (not choke!) and pull over until it runs for a few seconds.

Try this first. Small steps so you don’t jump over a problem.

Compression (above 130psi)
Spark (strong blue)

Fuel (at the right ratio)
Air (at the right ratio)
Spark timing (check key is not sheared)
Clear spark screen (if present)


So far, the points in green are confirmed correct? Black is unknown?
 
JSharpe

JSharpe

New Member
Joined
Sep 13, 2021
Messages
3
Location
Lilburn, GA
back to basics :)

Close both carb screws to stop fuel coming in, take plug out and make sure it’s dry.


Add a small amount of fuel to the plug hole and re attach plug.

set the saw to high idle (not choke!) and pull over until it runs for a few seconds.

Try this first. Small steps so you don’t jump over a problem.

Compression (above 130psi)
Spark (strong blue)

Fuel (at the right ratio)
Air (at the right ratio)
Spark timing (check key is not sheared)
Clear spark screen (if present)


So far, the points in green are confirmed correct? Black is unknown?
Thanks. I will give this a shot. I assume the spark timing is correct. The flywheel is new. The old one is the one that had a bad key.
 
Vintage Engine Repairs

Vintage Engine Repairs

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Messages
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Thanks. I will give this a shot. I assume the spark timing is correct. The flywheel is new. The old one is the one that had a bad key.
The first pull of the rope of an incorrectly torqued flywheel can shear the key and you wouldn’t have any idea it’s happened.

I’d double check just to confirm that it’s not sheared and tick it off the list. 5 minutes is all it takes :)
 
cookies

cookies

ArboristSite Guru
Joined
Nov 26, 2020
Messages
621
Location
Crawfordville
on those 029/039/290/390 saws the flywheel key fits like a wore out whore in the crank, every single one I have removed had 2-3 degrees of rotation making it easy to install the flywheel incorrectly and shear the key off. What I do is center punch mark where the key is on the face of the crank snout and the flywheel so during assembly I align the two dots.
 
sled_22

sled_22

ArboristSite Operative
Joined
Oct 22, 2020
Messages
161
Location
WI
Check the metering valve in the carb. I'd suspect you're flooded.
Set it level with the base of the carb. Often times this is forgetten after a carb rebuild with a new needle.
 
Old2stroke

Old2stroke

Never too many toys
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Jan 24, 2016
Messages
954
Location
Ottawa, Canada
Is the new coil an OEM module? I have had problems with AM units from China where the timing was too retarded to even start and some made good spark with the engine turning over fast with the plug out but produced no spark at slower cranking speeds with the plug in. That being said, MAKE SURE IT ISN'T JUST FLOODED before getting side tracked by other issues.
 
Pioneer

Pioneer

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Jan 1, 2005
Messages
686
Location
Winnipeg
Make sure the key on the new flywheel is in the same position in relation to the magnets as your old flywheel.
I actually had a new crankshaft for an MS 250 with the key slot cut in the wrong position, so don't take it for granted that the new flywheel has its key in the right position. It's also possible to run the flywheel without any key at all, many people do it when they want to advance the timing a little.
An ignition out of time situation is just one of the problems you can run into.
 
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