2 Stroke Carb

[lefty]

I can never figure out these 2 stroke carbs.

Timmer Model:316.79190
Serial: 1E128DB0924

Walbro Carb: WT798
Another Number on the Carb: 1008
Made in Mexico

My brother dropped off a trimmer this weekend. Compression is between 90 and 100 and I have good spark but no start. Smells like crap and he reports it hasn't run in years so at this point, I'm thinking fuel delivery. A new Carb is $40 but you can buy a new trimmer for about twice that. So I figured I saw some kits for like 6 bucks but just trying to make sure I'm on the right track. I can never figure out which numbers I should be using to look up parts. I found a rebuild kit on Amazon Prime for $5.99 which fits WA and WT series carbs. Can I assume I'm on the right track? For 6 bucks, I'm willing to take a crack at this for the experience.

Also, on a side note, I think it may be time for me to pick up some adjustment tools. I've seen a bunch on the internet but it seems you get what you pay for. This particular carb has screws that are recessed into a shoulder and have a flat side. Others I've seen are splined. The biggest complaint about low priced tools I've found is that the bend and strip. I'd be willing to pay for quality but was wondering if anyone knows of a set that is reasonably priced and covers at least a few different types of carbs. My apologies for posting a tool question in the technical forum but it seemed germane to the topic.

Thanks.

[38racing]

i bought this set
https://www.amazon.ca/Carburetor-Peyou- ... =carb+tool

[lefty]

i bought this set
https://www.amazon.ca/Carburetor-Peyou- ... =carb+tool

Awesome. Thanks 38.

[creia]

Yes-fuel delivery problem. That carb will be all plugged up with the left over deposits from the fuel that was still in it years ago. At the least, it will need a complete disassembly and a very thorough cleaning, new fuel lines, and clean out the fuel tank real well. It is definitely worth trying a cleaning and rebuild. A few years ago, my son got my old Homelite chain saw going that that was in the same situation as your trimmer, which had not run since the late 1980's! A good cleaning (ultrasonic) and fresh fuel and it ran good. What was most surprising was that the ORIGINAL carb diaphragm (I bought the saw new in 1985) was still good and pumped fuel! I thought it would have been cracked and stiff after all those years.
Michael

[lefty]

Am I reading the numbers correctly? Can I assume that a carb kit made for the WT series will fit my Carb? Does the "1008" number have any meaning?

[KE4AVB]

The Wt-798 kit is the K20-WAT Kit unless you just the gasket and diaphragm then it is D10-WAT. If I remember correctly the other number is a date code.

With the compression between 90-100 you're in trouble as most 2 cycles I have found will need 100+ to even hit. Before buying a carburetor kit or carburetor see if it will even hit when direct primed; fuel mix added the cylinder. If not then check the cylinder condition and for a struck ring.

[Fulltilt]

Generally, the first thing I do with any hand held two cycle is pull the muffler and inspect the cyl, ring/s , and clean the carbon out of port if needed. Stick a penlight in the plug hole to aid inspection if needed.

[lefty]

So I was able to get her to pop off by squirting a bit of mixture directly into the cylinder through the spark plug hole...nicely if I may say. A good solid rip.

Pulled the muffler and checked the exhaust port for carbon. It was very clean. There is a good bit of carbon built up on the top of the piston that I can see from the plug hole however...may be an issue down the road?

So I think, correct me if I'm wrong, that I should be attacking the carb now. On the subject of the carb, I learned about the primer side recently from KE4 on another post and the check valves that are involved over there...but what about the fuel supply side? Should I have a nice free flow over there or is there a similar setup with check valves? When I blow into the fuel nipple lightly with my mouth I get resistance and hear a squeaking sound. My gut tells me that it should flow smoothly through there and I have a blockage. Am I wrong?

Thanks.

[KE4AVB]

Yes the carburetor is likely candidate.

As for fuel flow it depends if assembled then will be resistance to that must be over come and that is the metering needle. It hold until you approach 9-10 psi. In a normal operating engine the impulses from engine pulls in the metering diaphragm which open the metering needle to allow fuel flow. Also during the impulses also operate the carburetor's internal fuel pump. This just a couple flaps on the fuel pump diaphragm. Their positions vary from carburetor to carburetor but below is an example of these flaps. These flaps operate much like check valves themselves.

[lefty]

So let me try to understand. I'm guessing that because I can clearly see the movement of fuel through the lines when I pump the primer that the check valve there is working in at least one direction. And the fact that I don't see it flow in the opposite direction when I release the bulb that the valve is working, at least preliminarily speaking.

On the fuel supply side, if I'm not mistaken, the diaphragm acts as the valve? So with the carb disassembled, I should not meet any resistance on that side?

Forgive me if I'm off base here.