My neighbor dug out a really old Hornet mini bike with a 2.5 hp Tecumseh engine that he wanted me to take a look at. I've been known to refurbish small engines and clean a few carbs but I'm no expert. The engine is a model H25-25162H and the carb is a simple gravity fed bowl/float design. The fuel fed down from a detached tank through one of those 90 degree elbows into the carb. The engine itself was in great shape, a lot of carbon deposits on the cylinder head and valves but they cleaned up great and the cylinder is nice and smooth. I took the carb down and broke it down and cleaned it. I replaced all the gaskets, including the bowl gasket and the needle valve and seat and yes, the little groove side went in first. The carb has two of the punch out plugs and I opted not to mess with them until I saw how everything else worked. So I put it all back together and got everything ready to go. Most of the linkages were missing and what was there were homemade replacements. I worked all that out, although I'm still unsure of a couple of things, the needle valve that runs though the bowl nut and the needle valve on the side of the carb, I don't know how many turns the factory set position would be for either of them.
The engine will start up without any trouble and runs very strong but it bogs down and stops after 3 or 4 seconds. Great compression though. So.....I noticed a very bad leak about the carb. I immediately suspected the bowl gasket and indeed it could use a little more tightening and I did that but the leak did not stop. It was not coming from the bowl gasket, it was just running out of the carb, out of the air cleaner/choke opening and coming out of the little hole near the top of the carb on the side opposite from the fuel inlet. What I discovered was that the leak started after bowl filled with gas, I could open the air cleaner/choke opening and look inside and see that the carb was completely filled with gas until it ran out of the air cleaner opening. Basically it seemed that there was an issue with the float not causing the needle valve to close and fuel just kept coming in. The float was in very good condition, it was level and the new valve and seat went in with no problem so I don't understand why that would not be stopping the inflow of fuel once the bowl float rises.
Let me add that the original small square tank had several cracks and was useless. I had temporarily connected a larger generic new plastic fuel tank. I replaced the fuel line and added a fuel cutoff and a little basic non-fuel pump inline fuel filter.
So, a couple of questions...Would the fact that I had this temporary tank positioned up higher that the original tank create more gravity pressure, enough overcome the float and keep the inlet valve open? Also, during this time I didn't have the fuel cap tightly secured, I wouldn't think this would matter but does the carb rely on a vacuum created by the sealed fuel tank to slow the fuel feed? These both seem a little far fetched to me. Hopefully someone a lot smarter than me will have some troubleshooting suggestions.
Yes, I know this model carb is selling new for about $30 bucks, but that would just be giving up.
The engine will start up without any trouble and runs very strong but it bogs down and stops after 3 or 4 seconds. Great compression though. So.....I noticed a very bad leak about the carb. I immediately suspected the bowl gasket and indeed it could use a little more tightening and I did that but the leak did not stop. It was not coming from the bowl gasket, it was just running out of the carb, out of the air cleaner/choke opening and coming out of the little hole near the top of the carb on the side opposite from the fuel inlet. What I discovered was that the leak started after bowl filled with gas, I could open the air cleaner/choke opening and look inside and see that the carb was completely filled with gas until it ran out of the air cleaner opening. Basically it seemed that there was an issue with the float not causing the needle valve to close and fuel just kept coming in. The float was in very good condition, it was level and the new valve and seat went in with no problem so I don't understand why that would not be stopping the inflow of fuel once the bowl float rises.
Let me add that the original small square tank had several cracks and was useless. I had temporarily connected a larger generic new plastic fuel tank. I replaced the fuel line and added a fuel cutoff and a little basic non-fuel pump inline fuel filter.
So, a couple of questions...Would the fact that I had this temporary tank positioned up higher that the original tank create more gravity pressure, enough overcome the float and keep the inlet valve open? Also, during this time I didn't have the fuel cap tightly secured, I wouldn't think this would matter but does the carb rely on a vacuum created by the sealed fuel tank to slow the fuel feed? These both seem a little far fetched to me. Hopefully someone a lot smarter than me will have some troubleshooting suggestions.
Yes, I know this model carb is selling new for about $30 bucks, but that would just be giving up.
