PT422 Running Rich Robin Engine

BobRip · Jan 27, 2008

I looked at the new spark plugs today (about 5 hours on them) and noticed that they are blackened. I can also smell gasoline while running the engine. I have not seen any leaks. I think the oil smells like gasoline. I seem to do a lot of short runs (10 to 30 minutes). The choke is operating OK. The engine starts and runs fine. The engine has about 625 hours on it. I will talk to the local Robin mechanic tomorrow and see what he suggest. His previous suggestion was check the plugs after a few hours, but that the smell is pretty normal in the winter. Does anyone have any thoughts on this. The manual says leaking float valve or jet worn. I am thinking it is time for a carb rebuild.

cqaigy2 · Jan 28, 2008

Don't forget to look for the PT gastank crud that could be keeping the valve from closing.

ponytug · Jan 28, 2008

Dear Bob,

All these are pretty classic signs of a rich mixture, except that you mention it runs well.
It could also be an engine running cold, especially if it is being run for short times when it is really cold out.

If you have the right plugs, and they are at the right gap, I would double check the setting of the jets, and make sure you have a clean air filter (I'm sure you do, but just in case...). Tuning the jets up may make you realize that they are worn, but 625 hours seems a bit short for that. A leaking float valve is certainly in the possibilities.

Without knowing how cold it has been where you are, I find it a tough call. The fact you are asking now, after 625 hours with your PT, makes me lean toward the leaking float valve, just because I think you would have noticed the effect other winters, rather than just a cold weather phenomenon of your Robbins.

Good luck!

Peter

BobRip said:
I looked at the new spark plugs today (about 5 hours on them) and noticed that they are blackened. I can also smell gasoline while running the engine. I have not seen any leaks. I think the oil smells like gasoline. I seem to do a lot of short runs (10 to 30 minutes). The choke is operating OK. The engine starts and runs fine. The engine has about 625 hours on it. I will talk to the local Robin mechanic tomorrow and see what he suggest. His previous suggestion was check the plugs after a few hours, but that the smell is pretty normal in the winter. Does anyone have any thoughts on this. The manual says leaking float valve or jet worn. I am thinking it is time for a carb rebuild.

BobRip · Jan 29, 2008

I swapped the plugs out today, and noticed that the other new plugs were not that bad. I dug trenches today for over an hour and it ran well. I think that I have just not run it long enough and hard enough lately. The Robin mechanic stated that it needs to be run at 3600 RPM (full speed) at least some of the time. I will keep you updated, but I think it is OK for now. Thanks for the comments.
Oh, it's been low in the 20's with high in the 40's. Cold for us.

woodlandfarms · Jan 29, 2008

I don't know for your application, but you can get hotter and colder plugs as needed. It may help your situation in winter (run hotter in the winter, colder in the summer).

BobRip · Jan 30, 2008

woodlandfarms said:
I don't know for your application, but you can get hotter and colder plugs as needed. It may help your situation in winter (run hotter in the winter, colder in the summer).

I put in the plug that Robin Subaru dealer in Fredericksburg VA (FSR, a very helpful guy named Butch is their tech support) recommended. So I think that is OK. This week I trenched about 160 feet of trench, with about 60 feet through a compacted gravel driveway and the machine ran perfectly. Trenching through the woods was a nightmare since I had a very narrow and convoluted path. We had to fill the trench in by hand in order to not knock over the flags for the inspector. The gravel driveway was bad because rocks would get caught in the trencher. If it had reverse I could have cleared the trencher easily. Instead, I had to get out and use a hammer and chisel to remove the rocks. This was still about 100 times easier than digging a trench 24 inches deep by hand. I now have the underground wires in and that is a relief.
The roof trusses are on and 80% of the plywood. Tomorrow the tar paper should be on and Monday the shingles will go on.