Tecumseh Hh120 Walbro Carb Trouble
Posted April 10, 2013 - 09:55 AM
Anyone familiar with the Walbro LME carbs as used on Tecumseh HH engines?
I rebuilt the carb Sunday and got this tractor running for the first time in at least a decade. No fuel leaks in the maybe two or three minutes I had it running. I had about 15 minutes to work on it last night and I was hoping to set mixture screws a bit better. Unfortunately, as soon as it was running I had fuel spraying out of one of the holes marked in the picture. It was hard to see but I'm pretty sure it was the top hole marked with the green arrow in the pic. That little hole has a small brass plug with a tiny hole in the middle that I assume is a vent?? The hole with the red arrow has nothing in it and appears to be rough cast so I don't think its missing a plug. My obvious thought is maybe the float level is set too high but I didn't have fuel leaking Sunday when it was first running. I'm going to check the float the next time I get to work on it but I just thought I would get some more experienced opinions ahead of time. It appears to be in the idle fuel circuit so I would assume there should be fuel there???
Anybody run into this before?
- JRJ said thank you
Posted April 10, 2013 - 12:12 PM
Ok, that top hole (green arrow) is supposed to be a solid brass plug. they have a dimple in the center that looks like a small hole but it is not. That brass plug blocks off the idle circuit fuel passage, they installed the plug after the drilled the passage out. These plugs should come in the rebuild kits but they do not.
The hole on the side is the bowl vent, it does not connect to the idle fuel passage at all. It sits in a little well at the highest point inside the base of the carb (highest point above the float) so if you stick something in this hole it should go into the hole around 1/4".
So if it comes out the top, you will need to plug that hole somehow. Find a plug, JB weld, or drill and tap?
If it comes out the side hole, either the float is adjusted to high, the float has a hole in it, or the needle is sticking.
Hope this helps, and I hope it is an easy fix for you! Good luck!
- New.Canadian.DB.Owner said thank you
Posted April 10, 2013 - 02:41 PM
I figured asking what each passage was for might be too much to hope for but the members of this site really are a wealth of knowledge.
Hopefully I won't need to work late tonight and I can diagnose it a bit further. It was fairly dark but it sure looked like it was coming out the top hole. I'll update this thread when I fix the problem.
- IamSherwood and chris m have said thanks
Posted April 10, 2013 - 03:18 PM
Ok good luck!! I still don't understand why these brass plugs are not available? It would make cleaning the idle fuel passage so.... much easier to clean.
Posted April 10, 2013 - 09:23 PM
On the plus side, I've confirmed the hydro unit is functional.
Edited by Canawler, April 10, 2013 - 09:26 PM.
- chris m said thank you
Posted April 10, 2013 - 09:52 PM
Hmmm. I wouldn't give up on that carb just yet. If it were me, I would take it off for a thorough soaking and cleaning. I have a feeling (like you said)that the small passages may be blocked. the idle passage you can take the mixture screw out, take the bowl off and spray carb cleaner from the idle fuel passage down near the main jet, and it should come out were the low speed mixture screw threads in.
I also have a feeling you might still have gunk inside the main jet and possibly one of the small holes inside the throat of the carb is plugged. There is one next to the hole were the low speed needle sticks through in the throat It is on the back side of the throttle butterfly plate, That is for the idle circuit also and if plugged will cause your symptoms also.
I would get a full can of carb cleaner and just blast every small hole you see. Remember to look all over the carb for passages. there is even one on the flange that mounts to the engine.
Just take your time and clean and clean again! good luck! I hope you can get it fixed in time for the weekend
Posted April 11, 2013 - 08:11 AM
.....for passages. there is even one on the flange that mounts to the engine.
What would that passage do? It would just be blocked off by the gasket and if not the gasket by the heat isolator plate.
My big concern with the carb is the messed up threads for the bowl retaining nut. There's not really a good way to fix that. The nut is literally only grabbing a half thread at the most. I think it's tight enough not to leak but the next thread could break off at any moment. The pot metal is so corroded and brittle it won't take anythng to crack it. The mounting flange was so warped that I had to file the ears extremely thin just to get the throat anywhere near sealing. It wouldn't surprise me if one of the ears would break off.
I'll still mess with it tonight if I get a chance but I don't see this tractor making it to plow day. Not really a big deal as I was only going to park it in the show area anyway.
Edited by Canawler, April 11, 2013 - 08:12 AM.
Posted April 11, 2013 - 08:55 AM
If you feel the repair is over your head or afriad to mess it up even more, pull it and send it to Mark at Carb Rescue. He will first access it and tell you what he thinks, he could then possibly repair if repairable. He does do a lot of fabrication of parts, he siad he could weld the crack that my LME carb has if/when needed.
I agree, its sound like there is still clogs in there somewhere. Did you unscrew the main jet from the center? If you did, you will need a replacement jet, you can never get them back in properly and lined up as they are screwed in then drilled at factory.
Posted April 11, 2013 - 12:15 PM
Did you unscrew the main jet from the center?
No, I remembered reading something about that on here.
Posted May 24, 2013 - 08:25 AM
After plow day I didn't really mess with it until two weeks ago. I figured I would really pull it apart so the nozzle came out. It already had a service nozzle so I was good there. When I tried to drill that little plug out of the idle passage as mentioned above, the plug just pushed down into the fuel passage. I ended up having to drill the hole one size larger so the plug would fall out. Surprisingly, a second plug fell out. It would have been blocking the idle passage. With this and the service nozzle, apparently someone has been deep inside this carb before. :-) The throttle shaft hole was also wallowed out pretty bad so I drilled it out and made a temporary bushing out of copper tubing.
Of course I assumed that after sealing up the hole all would be well. Unfortunately there was no change. It required heavy choke to run and none of the adjustments made any difference.
After doing a lot of digging I finally figured it out. In an earlier post I mentioned the threads for the bowl nut were stripping out. I ended up having to remove one of the two gaskets just to get to the point where the threads would grab. It turns out that screwing the bowl nut in just that little bit of extra thickness of the gasket was enough to partially block the angled fuel pickup hole. I used some of the Permatex thread repair compound and added the second gasket under the bowl nut and then everything worked as it should.
I drove the tractor around a bit and took it to a show last Saturday. The carb has been working good but the engine started smoking pretty bad as I was loading it up to come home but that'll be a project for another day....
So if your Walbro carb won't run off the choke, make sure you have a gasket above and below the bowl so the nut isn't threaded in too far. I guess they're serious in the manual when they say you HAVE to use two gaskets.
- sacsr and speed005 have said thanks