Stihl MS460 floods when I try to start it. Help!

[marsingbob]

I started a thread on this a year and a half ago and thought the problem might be fixed, but it isn't. I have a really nice 460 with very low hours. I have owned it for 6 or 8 years and until about 2 years ago it was competely trouble free. It idles as it should and runs great with good power. About two years ago it started flooding when using the choke. Probably does it three times out of four and the problem seems most common when the saw is cold and has not run for a few hours. It has a nasty kickback when this happens. The only solution is to remove the spark plug and flush the gas from the cylinder and (I assume) the crankcase. I always use fresh non ethanol gas.
My starting procedure is what Stihl recommends for a cold saw--put it on choke until it fires, then move it to fast idle. I am careful not to pull it again on choke after it pops. If it tries to start on the first pop it usually dies immediately--before I can move it to fast idle--and then is flooded.
I took the saw to the dealer in this area (Southwest Idaho) with the best reputation a year and a half ago and they rebuilt the carburetor and put a new spark plug in it. It started when I got it home, but quickly started having the same problem. I was frustrated and left it alone for a year. I took it back to the same dealer last fall and left a message about the problem (this is a new style dealership and I was not able to talk to the service person). They again rebuit the carburetor and put in a new spark plug. It started when I brought it home, but then had the same old problem. I took it back and they called later that day and said there was nothing wrong with it. I talked to the salesperson and he said I was probably too old and could not pull it over hard enough.
It still runs great when it starts. It is bone stock and the piston shows a little wear but no scoring. Air filter is almost new and clean. Tank vent seems clear. If I pull the plug and crank it over 10 or 12 times, then replace the plug, it will often start on fast idle.
Any thoughts or suggestions on how to fix it would be appreciated. Perhaps a new carburetor? I have done several searches and cannot find anyone having this problem with a 460 (or an 046). Any suggestions on a service shop I could take or send it to?

 

[Wood Doctor]

I just ran into this with a 460 and I think PioneerGuy600 is waiting for me to respond. The old carb was flooding the engine way too quickly and actually pumping fuel through the decomp valve and out the muffler. I replaced that old carb with a new carb and got it running. After letting it sit for a few days afterwards, it started normally: a few choke pumps until it popped, take it off choke to fast idle, and pull once or twice more. Bingo! it starts fine. Your patience will be taxed.

Note that when choked, the decomp will pop up and need a reset or your right arm or shoulder might fall off after the next pull. These Stihl 460 Mag saws usually have lots of compression.

 

[user 122190]

Put it on choke and pull before it pops. Then fast idle to start.

Basically use the choke to prime the saw.

 

[SteveSr]

I started a thread on this a year and a half ago and thought the problem might be fixed, but it isn't. I have a really nice 460 with very low hours. I have owned it for 6 or 8 years and until about 2 years ago it was competely trouble free. It idles as it should and runs great with good power. About two years ago it started flooding when using the choke. Probably does it three times out of four and the problem seems most common when the saw is cold and has not run for a few hours. It has a nasty kickback when this happens. The only solution is to remove the spark plug and flush the gas from the cylinder and (I assume) the crankcase. I always use fresh non ethanol gas.
My starting procedure is what Stihl recommends for a cold saw--put it on choke until it fires, then move it to fast idle. I am careful not to pull it again on choke after it pops. If it tries to start on the first pop it usually dies immediately--before I can move it to fast idle--and then is flooded.
I took the saw to the dealer in this area (Southwest Idaho) with the best reputation a year and a half ago and they rebuilt the carburetor and put a new spark plug in it. It started when I got it home, but quickly started having the same problem. I was frustrated and left it alone for a year. I took it back to the same dealer last fall and left a message about the problem (this is a new style dealership and I was not able to talk to the service person). They again rebuit the carburetor and put in a new spark plug. It started when I brought it home, but then had the same old problem. I took it back and they called later that day and said there was nothing wrong with it. I talked to the salesperson and he said I was probably too old and could not pull it over hard enough.
It still runs great when it starts. It is bone stock and the piston shows a little wear but no scoring. Air filter is almost new and clean. Tank vent seems clear. If I pull the plug and crank it over 10 or 12 times, then replace the plug, it will often start on fast idle.
Any thoughts or suggestions on how to fix it would be appreciated. Perhaps a new carburetor? I have done several searches and cannot find anyone having this problem with a 460 (or an 046). Any suggestions on a service shop I could take or send it to?

Pressure test the fuel inlet on the carb. It should hold 7-10psi indefinitely. If not you have a needle/seat leak to fix.

Also it may not "pop" if you aren't pulling it over fast enough. But if it tries to rip your arm off or pulls the rope out of your hand just remove the choke and pull until it starts.

 

[Wood Doctor]

Pressure test the fuel inlet on the carb. It should hold 7-10psi indefinitely. If not you have a needle/seat leak to fix.

Also it may not "pop" if you aren't pulling it over fast enough. But if it tries to rip your arm off or pulls the rope out of your hand just remove the choke and pull until it starts.

I have noticed that also ( the silent "pop"). With the new carb I now get an audible "pop" on a choke pull and it sometimes even tries to run. The old carb just plain wasn't supplying the right air-fuel mixture.

 

[marsingbob]

Thanks for the suggestions. Steve I do not have a problem getting it to "pop", it just seems to flood as soon as it does. However it does not clear out if I move it to fast idle--still tries to pull your arm or hand off. As Wood Doctor says, it has a lot of compression. I have tried to prime it with the choke for a couple of pulls, then start it on fast idle. So far not a lot of luck getting it to start, but I will try again. I am going to try to find a fuel pressure guage I can use and test the needle valve/float. I would think the valve and seat would have been replaced with both of the carb kits the dealer installed, but who knows.

 

[user 122190]

Thanks for the suggestions. Steve I do not have a problem getting it to "pop", it just seems to flood as soon as it does. However it does not clear out if I move it to fast idle--still tries to pull your arm or hand off. As Wood Doctor says, it has a lot of compression. I have tried to prime it with the choke for a couple of pulls, then start it on fast idle. So far not a lot of luck getting it to start, but I will try again. I am going to try to find a fuel pressure guage I can use and test the needle valve/float. I would think the valve and seat would have been replaced with both of the carb kits the dealer installed, but who knows.

They are not to just be replaced, but also adjusted. When I rebuilt my carb, I left the valve and seat since I didn't have the tool to check or adjust.

Here is the tool(s). Use the correct one for your carb. I do have them since doing my carb rebuild. They are inexpensive and can be had via Ebay.

 

[cookies]

Sounds like the needle lever is set too high opening it too long or the diaphragm is the wrong version causing the same issue.

 

[marsingbob]

I was thinking I should replace the carb, but now I am wondering if maybe I should replace just the needle and seat (if the seat is replaceable). A new oem carb is around $85 and the saw is certainly worth that and a lot more if it fixes the problem. I am certain an oem carb kit is a lot less. The entire saw looks almost new and I am certain it has low hours (probably less than 50 or 100 hours at most). It runs great once it starts. Assuming I am able to check the fuel pressure and it is holding pressure at the needle valve, is there any reason to replace the carb? I am familiar with car carbs where things like worn shafts can cause air leaks and problems, but this is a very simple carb and it seems very unlikely that wear is causing this problem. It sat unused for a few years before I bought it. Maybe corrosion? The choke appears to be a simple valve on the opening to the carburetor and it works freely and closes completely. Is there anything more than that to a chainsaw choke?
A reply to my earlier thread suggested a timing issue. Possible even tho the saw starts and runs great? Checking the timing is probably beyond my ability so I will need to find a shop if that is the problem. I can rebuild or replace the carb mysef.
Once more thanks to all of the suggestions. They are all appreciated.

 

[cookies]

If you have fuel coming from the muffler after only a couple pulls its over fueling badly. Most carbs use what I call a level with the body lever height. I simply use the flat edge of the carb end cover, i set them where a hair of light shines past and the cover does not touch the lever.

 

[SteveSr]

Thanks for the suggestions. Steve I do not have a problem getting it to "pop", it just seems to flood as soon as it does. However it does not clear out if I move it to fast idle--still tries to pull your arm or hand off. As Wood Doctor says, it has a lot of compression. I have tried to prime it with the choke for a couple of pulls, then start it on fast idle.

Are you sure that the fast idle / part throttle position is actually being locked? If you ground start the saw your boot toe might hit the throttle trigger and knock it back to regular idle where it will be hard to start... especially cold.

So far not a lot of luck getting it to start, but I will try again. I am going to try to find a fuel pressure guage I can use and test the needle valve/float. I would think the valve and seat would have been replaced with both of the carb kits the dealer installed, but who knows.

The needle gets replaced but the seat remains in the carb. carb cleaner or toothpaste on the end of the paper q-tip swab shaft will clean/polish the seat.

a BIG thing to check is that when the carb was rebuilt that the metering lever height was checked and set correctly. The new levers in the kit are NOT adjusted and MUST be after installation. The techs SHOULD know this but these days no telling! I usually reuse metering levers but I ALWAYS check them for proper setting. Never know what monkey might have been in there before.

 

[gtb]

I have same issue with my MS460 as describe. Kickback is fierce. Sounds like a common problem.
Is the ignition timing adjustable?
My MS660 fires up cold no problem.
Any advice is appreciated.
Thank you.

 

[gtb]

Put it on choke and pull before it pops. Then fast idle to start.

Basically use the choke to prime the saw.

I tried this procedure a couple of times with no luck. I leave the saw for short period and it fires up.

 

[Canyon Angler]

Put it on choke and pull before it pops. Then fast idle to start.

Basically use the choke to prime the saw.

I generally put my saws on full choke, then slowly pull the rope past TDC 3 or 4 times, then move the switch to "RUN" then start them. I almost never use "Fast Idle" on any saw, ever.

 

[user 122190]

I tried this procedure a couple of times with no luck. I leave the saw for short period and it fires up.

MS880 works well this way. It is a beast to pull over fast and floods if left on full choke. Peoples gots to figure out what works for Them and Theirs.