Walbro WT526 Trouble

[dougand3]

Walbro WT526 Trouble
Working on an MTD 31cc tiller - which is a good engine from my experience.
Replaced fuel lines, purge bulb, pickup.
Rebuilt carb with K10-WAT kit. New diaphragms, gaskets, needle assy. Screen clean. Replaced big welch plug but not small one.
The trouble: Cold starts are awful. 50 pulls with choke- gets flooded. 50 pulls no choke - no fuel. 50 pulls half choke - no fuel. Priming cyl with mix gets it to start after 5 pulls. Once hot - starts REAL easy with a half pull. And runs great on throttle up and WOT. Resarts great every time until it cools for 15 mins.
I tried a makeshift high idle setting and no difference.
What should I try next?

 

[alexcagle]

Sounds like your choke isn't closing all the way to me. Make sure the choke flap isn't bent, and theres no missalignment or debris restricting the lever movement to close the choke completely.
It should "pop" after one to five pulls with the throttle halfway open. If it doesn't have a throttle lock, then you will have to use one hand to yank start, and one hand to hold the throttle halfway open.
Now; I don't know you or your capabilities, so dont get offended, -but just know that two strokes seldom start and stay running on the choke position. They aren't like automobile carburetors.
Stop immediately after the "pop" and take the choke off completely.
Then with the throttle still locked halfway, pull it and it should start and run. Then after a brief warmup, just blip the throttle to unlock the throttle lock (if it has one) and return to idle speed.

Obviously; Make sure and keep tines safely away from anything that they could be a danger to.
If there is still an issue, check the basic high and low speed mixture settings in the specs.

 

[HarleyT]

Put up the MTD model numbers off of the tiller.

 

[AVB]

If nothing else Doug you can bring it up to my shop during the week and I see if I can help you figure out whats going on that little Mantis style tiller. May need to leave it so I can run diagnostic tests though.

AVB

 

[dougand3]

Thanks, alex and Harley.
Lack of good choke makes sense. It's a slider choke plate, not part of carb. And it has a non-original air filter box on top of carb - so, a FrankenTiller set up. I'll check it over and see that when choke is closed, I don't find unwanted air avenues.
Model # 21A-120R000 Yard Machine 31cc.

Thanks, AVB. I'll keep slugging away at present and keep you posted.

 

[HarleyT]

 

[HarleyT]

Primer bulb hooked up correctly?

 

[HarleyT]

Also you might want to look at the reed plate gasket, just look at the surface without removing the reed plate. You may see the cracks/breaks. If you remove the reed plate, it could break then.

 

[dougand3]

Thanks for info, Harley.
I examined choke plate assy better and the choke shutter mounting plate looks a little warped. With choke shutter closed, air must be sneaking in between carb body and mounting plate. I put a carb gasket between the 2 and it seals well now.
Now on cold start - Full choke gets a burp on 1 pull, running on half choke 2nd pull.

It's kind of like a Poulan 1800, Micro XXV, etc with the slider choke set up.

Thanks for pointing me in the right direction, guys.

 

[alexcagle]

 

[rmh3481]

Make sure the muffler is open and free flowing. Remove all screens.

 

[alexcagle]

Then after It's clean, If you don't want to risk having the grass and leaves catch on fire next march, put the spark arrestor screen back in.
They serve a purpose or they wouldn't be there to start with.
Not trying to be a "b-hole", but, advising people to remove a safety feature is probably not a good idea.
I have an old Tecumseh chainsaw that I scare the kids on my block at Halloween. It's dark when I fire it up, and it blows out a few good sparks every time I rev it up good. It has a straight pipe for a muffler though. You can see the piston through it; - so its probably not a good comparison to modern muffler....

 

[CrufflerJJ]

I have an old Tecumseh chainsaw that I scare the kids on my block at Halloween. It's dark when I fire it up, and it blows out a few good sparks every time I rev it up good.

Are the sparks from droplets of burning fuel, or burning chunks of carbon, or...?? Just wondering.

 

[alexcagle]

Carbon. Red hot from combustion

 

[CrufflerJJ]

Thanks!

 

[AVB]

Thanks for info, Harley.
I examined choke plate assy better and the choke shutter mounting plate looks a little warped. With choke shutter closed, air must be sneaking in between carb body and mounting plate. I put a carb gasket between the 2 and it seals well now.
Now on cold start - Full choke gets a burp on 1 pull, running on half choke 2nd pull.

It's kind of like a Poulan 1800, Micro XXV, etc with the slider choke set up.

Thanks for pointing me in the right direction, guys.

View attachment 516807

To me it is more like some of the Ryobi, MTD, and Troy-Bilt trimmer setups.

Look like someone was being cheap and used a Homelite air cleaner box instead of the MTD air cleaner/muffler cover. That would explain why you had the air leak as that choke and plate weren't design to hold an air cleaner. I have replace several of those new versions of the cover with the older style when the trimmer had one those carburetor that the internal enrichment choke systems. Once that enrichment fails either you need a new carb or convert over to the shutter style choke; that was before carburetor prices started coming down as it was cheaper to change over.

 

[dougand3]

those carburetors that have the internal enrichment choke systems.

Never heard of those. How do they enrich?

 

[AVB]

It called the simple start system among other names; Zamas . You flip a lever to start which pull the plunger off the port opening. This opens a passage directly to metering chamber and this fuel is metered via a port into carburetor venturi.

If this lever s left in the flipped position it will gradual flood out the engine thru this additional enrichment. These are spring loaded normally to auto shut off as you pull throttle lever. The problem arises when these passages become plugged with oil or trash and can no supply the extra for start up thus requiring cleaning or replacement; although you can hand choke these carbs to start the engine.