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Vanguard engine fix!

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  • Vanguard engine fix!

    I really, really dislike Briggs engines, and here's why. Mine has always stumbled, surged, popped back in the intake, been weak etc, and this has been simply characteristic of all but one Briggs I have owned. So the off season is here and I decided to tackle the situation;

    I know the engine is running terribly lean, so I make a quick check for vacuum leaks and find none, so move onto the carb. These Nikki carbs are kind of junky to say the least with their plastic emulsion tubes and slip in jets, but in my experience that's to be expected from Briggs and Stratton.

    So my findings in the carb are this. There's two different sized main jets. One is a 136 and one is a 140. This is intentional however on these engines. People say one side of the engine flows a little more air than the other, but I am beginning to think otherwise. This engine is so horribly lean, it will begin to miss at part throttle on one cylinder unless you partially choke it, then it will clear up. And I determined the miss to be on the left side by monitoring exhaust pipe temps while missing. Same side the smaller jet is on. Go figure!

    So first step is to fatten up the left side of the engine, I turn to my machinist bits and take the left side jet up to the size of the right side. And voila, the part throttle miss is gone! Also a change in the exhaust note too. It now has a smoother tone to it, more like my Kohler engines sound, a bit quieter, and definitely more power! Also exhaust temps rise about the same rate now too.

    It still however had a hard time starting and running at idle. Next was to pop out the welsh plugs on top the carb to access the idle screws and guess what I found. The right side screw was turned out less the half a turn, yes, less than half. The left was at 2-3/4. So, I set them to 2-1/2 turns, warm the engine up, and proceed to adjust the mixture screws from there. I wound up with 3 turns on the left side and 3-1/4 for the right. Most of the time when I adjust a carb and have to go pass three turns on a mixture screw I re-jet the low speed. But this is borderline, it does run good now, and very little time is spent in that low speed range. Just so long as it'll crank up and run without being a nuisance, I don't care in this case.

    So the results are an engine that now needs very little choke, makes more power, doesn't pop back through the carb, idles smooth, doesn't surge at any RPM, and transitions from idle to WOT without hesitation. Hope this helps someone else with similar issues!!!