Stihl MS250 Won't Run at Full Throttle

[Stillrunner]

I have a Stihl MS250 with a Walbro WT 215 carb. Engine starts and idles great. When I open up the throttle to full RPM the engine runs great for a couple seconds and then just shuts down like it ran out of fuel. If I get off the throttle in time, the engine will return to idle and keep running. I also have an Ebay purchased $12 carb. With this carb installed, the engine idles/runs/ and holds top RPM, just fine. I'm looking for any advice/ideas as to the problem here. Assuming it's the Walbro carb and wondering if a rebuild kit might fix my problem or of I need a new (Stihl/Walbro) carb?

Thanks in advance.

 

[pioneerguy600]

A rebuild kit will not fix that problem, I have encountered this same problem with the 025`s and rebuilding the carb and resetting /adjusting the metering lever has not corrected the fuel starving condition.

 

[HarleyT]

Go through it completely and correctly, just reuse the old gaskets and diaphrams, see if it runs better.

 

[Chainsaw Jim]

The only way to know for sure is to spend a few bucks on a k20-wat kit and try it out. If it doesn't work then save the kit for the new carb you purchased in case it ever needs rebuilt.

 

[eg1l]

My MS260 with Walbro carb had the same problem. Found rust at the tip of the high speed needle. Once cleaned and adjusted, it ran just fine. Might be worth a shot adjusting the high speed needle if your carb has one.

 

[pioneerguy600]

These 025 carbs doing this has just happened to me this month, I have 3 of them now that won`t work so they are langushing in the NFG can right now. I just put new replacement carbs on the 3 saws and they are back to work so the first time I get a spare minute I am going to pull the welch plug and take a look below. On one of the carbs I did notice rust on the end of the high speed needle, the other two were clean. A trip through the USC did not help these 3 carbs but the other couple dozen carbs I put through have worked fine so there may or may not be something going on under the welch plug.

 

[lambs]

I am working on an MS250 right now that runs pretty well on full throttle if you can get it there. But it bogs badly when you give it throttle, and it will idle well for a few seconds then just shut off. I replaced a flattened fuel vent hose assembly with the old style 025 fuel vent, and while I had the carb off, I trimmed the H limiter to allow another 1/8 turn, pulled off the carb side plates, and attempted to clean the carb. Not sure how well I did that, I was just working off youtube video. I didn't get any crud out of it. Fuel line and filter look great, and I was able to easily pull fuel from the tank by attaching a syringe to the fuel line. When I got it reassembled, it ran as before. I'm thinking I need to pull the carb again, remove the L screw, and clean that jet thoroughly.

There is no separate impulse line on this saw; it looks to just be pulsing through a little opening at the back of the carb that matches up on the gasket to the intake boot.

I have an 021 that had just had a new carb put on it when I bought it. I haven't even run it. The carb that came off it is a Walbro WT503, and I assume the new one was too. This carb has a L and LA adjustment, but the H is fixed.

The 250 has a Zama C-10.

I'm thinking about swapping the carbs to see if that solves my problem with the 250, and if so, then I'll know I either need to clean the carb better or order a Zama / Chinese carb.

Will the carbs swap out?

 

[a. palmer jr.]

I've always liked Walbro carburetors but lately on Stihl saws I've been replacing them with Zama carbs and have had great results. The Ebay Zama carbs are more adjustable than the Walbros. I've put them on the small to mid Stihl saws but haven't put them on anything bigger than a 361.

 

[lambs]

Thanks, but my question is whether or not I can temporarily put the Walbro carb from my 021 onto the MS250 to eliminate a carburetor problem as the root cause.

I'd like to know if it should fit properly before I remove two carburetors.

 

[HarleyT]

Yes, the saws are basically the same, the carbs should swap easily.
The air filter setups might need to swap with them.

 

[lambs]

Excellent! Thanks, Harley, I'll give it a try.

 

[Okie]

You say you have two carbs, you can install one and the problem goes away and you want to know if the other carb is bad???
Ronnie Milsap can see the answer to that question. the answer is YES
I have not been into a 250 carb but I've had good luck when I know for sure the problem is in the carb by giving them a ultrasonic bath using 50/50 vinegar and hot water.
I've removed welch plugs by using air pressure to blow them out, (I can re-use them if they come out with air pressure) or remove them then go to Napa and get a replacement if not in a kit. (I can reform welch plugs (concave) on a piece of leather and a round drift punch just using hand pressure.
I don,t normally remove welch plugs unless I've tried everything else first, like lots of cleaning and using Tag wire to clean the little passages. I've had a few that had issues such as yours and found the sintered carb filter or screen was restricted with gunk. The gunk not readily visible.

I also only use low pressure air not over 20psi or you can blow out or cause welch plugs to leak using high pressure air to clean a carb.

Seems patience is main thing when working on carbs, especially the small ones.

 

[logeeland]

I have experienced issues recently at full throttle and the issue is the tank vent is clogged or broken. Replaced the vent and it then runs great!

 

[lambs]

I have experienced issues recently at full throttle and the issue is the tank vent is clogged or broken. Replaced the vent and it then runs great!

Already switched out the tank vent for the older style from an 025. The original vent hose was pinched by the carb.

 

[lambs]

You say you have two carbs, you can install one and the problem goes away and you want to know if the other carb is bad???
Ronnie Milsap can see the answer to that question. the answer is YES

Actually, I did not say that but thanks for your thoughts on how you have handled carb issues in the past.

 

[HarleyT]

I think Okie was just confused, he thought that you were the original poster.
He only talks in blue words when he needs a Xanax...

 

[Okie]

I think Okie was just confused, he thought that you were the original poster.
He only talks in blue words when he needs a Xanax...

Yep, did not notice the hijacked thread and the subject changed.
Need another Xanax.

First post :Stillrunner ask this: I also have an Ebay purchased $12 carb. With this carb installed, the engine idles/runs/ and holds top RPM, just fine. I'm looking for any advice/ideas as to the problem here.

One carb run good and the other don't. He asks does he have a bad carb issue?
Yes or NO
Ronnie Milsap says YES.
Dr. Phil don't know yet.

 

[Chris-PA]

It sounds like only the L and idle transfer circuits are bad, so you are looking for something that affects only that part of the carb. Possibly a blockage in the L jet, or just the L needle set wrong. Or yet another ZAMA C1Q with a bad check valve.

 

[HarleyT]

Well Lambs, the highjacker's feelings are hurt, as well as Ronnie's, and they are offended and need counseling....

Stihlrunner is troubled by opting out the cheap way, and buying cheapass aftermarket junk, and wanted to know if a new kit would cure his Walbro, or he should order a new carb {Walbro}, or he should be content
with being called Ronnie Milsap......
So a round of medication for the house is in order!

 

[lambs]

Yep, did not notice the hijacked thread and the subject changed.
Need another Xanax.

First post :Stillrunner ask this: I also have an Ebay purchased $12 carb. With this carb installed, the engine idles/runs/ and holds top RPM, just fine. I'm looking for any advice/ideas as to the problem here.

One carb run good and the other don't. He asks does he have a bad carb issue?
Yes or NO
Ronnie Milsap says YES.
Dr. Phil don't know yet.

No worries, Okie. I guess I did hijack it a bit. It just seemed to me much the same issue so I joined it with my question about whether the Walbro on my 021 should match up with the 250 which has the Zuma.

Based on responses I will be trying the transplant later this week. It seems simple to just buy a new carb for this 250, but it would help if I can prove that is really the issue. I'm not nearly as experienced as some of my friends here on AS so I often look for your advice. Well truthfully, you're probably all more experienced than me....this is the first 2 cycle carb I've ever opened up!

Thanks, all.

p.s. Is Ronnie Milsap still around?