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I have a Bolens 1656 with a Tecumseh 16hp OHV engine. It runs pretty good and I have gone over everything I can to get it properly tuned. It does seem as though it smells worse than it should. What I mean is that the exhaust smells strong. It's significant enough that my wife notices the strong exhaust smell on me and my clothes after I've used it, and I can tell it's stronger than it should be. My belief is that this strong smell would indicate an overly rich fuel mixture. I've adjusted the low speed mixture screw and the idle speed screw, however there is no high speed mixture screw. The carb is a Walbro and it has a fixed high speed mixture jet.

Two questions:

Am I correct in thinking that this is a high speed fuel mixture issue? I've checked everything else and this seems to be the most likely cause.

If this is caused by too rich a fuel mixture and the high speed mix is non-adjustable, what do I do? Can the carb jet be replaced with an adjustable jet, or would I have to replace the entire carburetor?
 

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If the spark plug looks a nice tan or brownish color,I'd say the mixture is adjusted OK..if its sooty or carboned up it could be running too rich,a clogged air filter is about the only thing that can richen the fuel mixture on a non adjustible carb ,or a float level that is set too high..

Just about every older engine I own of "flathead" design with the valves in the block,smell like that,they have fairly low compression ratios,fairly rich jetting,and were built long before "emissions" were any concern..
and its just the nature of the beasts...older carbed cars smell the same too,even when tuned perfectly..about the only way to eliminate it I know of would be a catalitic converter,then it'll stink like rotten eggs or sulpher instead!...
 
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