Ms310 running issues. Totally confused!

[slowcar281]

I was given a complete ms310 that was deemed trash. I tore the entire saw down, cleaned and rebuilt it.

I cleaned the stock cylinder and removed the transfer. Installed a meteor piston, caber rings, and new bearings. New oem impulse line, crank seals, fuel line and fuel filter. Pressure tested the saw and it holds 8 psi and vacuum just fine. Double and triple checked the intake boot for wear.

I bought an OE carb kit for the oem hd21c carb and installed that.

I cannot get this thing to idle properly. It’s up and down constantly. You can’t get the idle to calm down at all unless you richen the L screw so rich that it smokes at idle and full throttle acceleration is poor. Even with the H screw turned all the way in, it will only rev to 12,500 rpms. It just runs like crap overall, but starts just fine. I was shooting for stock specs of 13,000 rpms. The muffler is completely stock.

I talked to our small engine mechanic at work and he had a brand new walboro hd19 sitting on the shelf. He told me to take that and try it.

SAME EXACT PROBLEM. Runs no different.

Anyone have any ideas? I checked the coil gap and made sure the flywheel key wasn’t sheared.

I’m out of ideas other than buying a new oem carb and trying that. Dealer said they are 80 dollars, but I’m not convinced that will fix it.

 

[cscltd]

Replace Fuel is usual issue, put u replaced that?
muffler screen or muffler plugged?

 

[slowcar281]

The screen is perfectly clean. Fuel is fresh 89 octane non ethanol.

 

[jltrent]

If it pressure test then it sounds like a carb to me. Also check the impulse close. I have a pile of saws laying around as it usually gives me the advantage of testing a for sure good carb to eliminate that.

 

[slowcar281]

As I mentioned before, the impulse line is brand new along with the fuel line. When I pressure tested it I used the impulse line to introduce pressure/ vacuum

I just find it hard to believe that a rebuilt carb and a brand new ( still in the box) carb could produce the same symptoms.

 

[67L36Driver]

Spark timing? Check to see if you sheared the flywheel ‘key’.

 

[slowcar281]

Spark timing? Check to see if you sheared the flywheel ‘key’.

please read the first post. I checked that along with the coil gap already.

 

[grizz55chev]

Sure sounds like an air leak causing lean run to me, even though it holds vac. Those are all the classic lean run symptoms. Have you checked the compression? Might be a case where excessive squish has the comp so low that it can't produce enough pulse to work the pump side of the carb.

 

[slowcar281]

That’s one thing I have not done. I’ll borrow a compression tester and test it today. It definitely passes the “ drop test “ it gradually drops down if you let the saw hang by the pull rope

 

[grizz55chev]

That’s one thing I have not done. I’ll borrow a compression tester and test it today. It definitely passes the “ drop test “ it gradually drops down if you let the saw hang by the pull rope

After market cylinders are notorious for excessive squish which will have a negative affect on compression, might run, just not well!

 

[slowcar281]

After market cylinders are notorious for excessive squish which will have a negative affect on compression, might run, just not well!

I’m using the oe cylinder

 

[lone wolf]

I was given a complete ms310 that was deemed trash. I tore the entire saw down, cleaned and rebuilt it.

I cleaned the stock cylinder and removed the transfer. Installed a meteor piston, caber rings, and new bearings. New oem impulse line, crank seals, fuel line and fuel filter. Pressure tested the saw and it holds 8 psi and vacuum just fine. Double and triple checked the intake boot for wear.

I bought an OE carb kit for the oem hd21c carb and installed that.

I cannot get this thing to idle properly. It’s up and down constantly. You can’t get the idle to calm down at all unless you richen the L screw so rich that it smokes at idle and full throttle acceleration is poor. Even with the H screw turned all the way in, it will only rev to 12,500 rpms. It just runs like crap overall, but starts just fine. I was shooting for stock specs of 13,000 rpms. The muffler is completely stock.

I talked to our small engine mechanic at work and he had a brand new walboro hd19 sitting on the shelf. He told me to take that and try it.

SAME EXACT PROBLEM. Runs no different.

Anyone have any ideas? I checked the coil gap and made sure the flywheel key wasn’t sheared.

I’m out of ideas other than buying a new oem carb and trying that. Dealer said they are 80 dollars, but I’m not convinced that will fix it.

Sure sounds like a bad carb but the new Walbro should have corrected it. What is the compression reading? I cant but help wonder if you have an air leak after where you tested it like at the boot ,try some grease on the boot connection.

 

[slowcar281]

Sure sounds like a bad carb but the new Walbro should have corrected it. What is the compression reading? I cant but help wonder if you have an air leak after where you tested it like at the boot ,try some grease on the boot connection.

The first pic is after 5 pulls
2nd pic is 10 pulls
Engine is completely cold

Are you taking about where the intake boot goes to the cylinder? I can put some grease around it to see but I’ve pressure tested the saw more than once. Tested once after running like crap and then tested again to verify no air leaks. Still same issues

 

[cookies]

U put the piston in backwards? lol I had a ms290 do that same crap, it had a very slightly deformed crank seal that was very hard to see but it held vac/pressure in testing but leaked when running. Saw would crank and run but I had to keep adjusting the L needle to get it to calm down after blipping the throttle. Try keeping it adjusted fat on the low side and lean out the high needle to the edge of 4 stroking and then cut some stuff and see if it calms down and settles out. If not I would take it all back apart again to look at everything very closely including the fuel hose, filter and the sealing between the intake and carb and the impulse barb pressed into the cylinder and if the impulse hose is flowing..seen more than one aftermarket one have flashing in them plugging them off or not fit tight,

 

[lone wolf]

View attachment 1008872
View attachment 1008873

The first pic is after 5 pulls
2nd pic is 10 pulls
Engine is completely cold

Are you taking about where the intake boot goes to the cylinder? I can put some grease around it to see but I’ve pressure tested the saw more than once. Tested once after running like crap and then tested again to verify no air leaks. Still same issues

Yes was that pressure tested with boot connected and carb mounted?

 

[lone wolf]

Pressure test while moving both crank ends up and down while watching the tester.

 

[grizz55chev]

I’m using the oe cylinder

10-4, could only be an air leak then.

 

[slowcar281]

U put the piston in backwards? lol I had a ms290 do that same crap, it had a very slightly deformed crank seal that was very hard to see but it held vac/pressure in testing but leaked when running. Saw would crank and run but I had to keep adjusting the L needle to get it to calm down after blipping the throttle. Try keeping it adjusted fat on the low side and lean out the high needle to the edge of 4 stroking and then cut some stuff and see if it calms down and settles out. If not I would take it all back apart again to look at everything very closely including the fuel hose, filter and the sealing between the intake and carb and the impulse barb pressed into the cylinder and if the impulse hose is flowing..seen more than one aftermarket one have flashing in them plugging them off or not fit tight,

Haha, nope the piston is in correctly. I double checked the impulse barb to make sure it was seated in the cylinder before putting it together

Yes was that pressure tested with boot connected and carb mounted?

Yep. All I did was remove the plug and start pulling.

Pressure test while moving both crank ends up and down while watching the tester.

I’ll try that as well when I get back home.

I still feel like it’s a fuel delivery issue. I called around several places. Got prices from 97 dollars for an oe carb all the way down to 55 dollars all for the same part. Im gonna pressure test it one more time and closely look everything over again.

 

[lone wolf]

Haha, nope the piston is in correctly. I really checked the impulse barb to make sure it was seated in the cylinder.

Yep. All I did was remove the plug and start pulling.

I’ll try that as well when I get back home.

I still feel like it’s a fuel delivery issue. I called around several places. Got prices from 97 dollars for an oe carb all the way down to 55 dollars all for the same part. Im gonna pressure test it one more time and closely look everything over again.

Well that certainly could be the issue but why with the new carb did it still act up? Dunk that saw in a bucket of water while pressure testing.

 

[slowcar281]

Well that certainly could be the issue but why with the new carb did it still act up? Dunk that saw in a bucket of water while pressure testing.

That’s a good idea. Never even considered that before!