Tuning a Gas Engine to Run Slow

Community Shop Talk

| June/July 2004

Online engine conversations from Stationary Engine List

Fast-forward a couple months, and here in England we just had the first shows in May, so my husband, Jim, prepared my newly acquired Baker Monitor for her first outing. As usual, the cart design depended on available materials, which in this case was a set of four large, narrow, thin-spoked wheels that Jim's brother acquired during a family holiday in Belgium. The cart is quite stylish, as befits such a stylish engine! It's also nice and easy for me to move the engine about, too.

Show season anticipation has inspired folks to take their engines out for an airing and to tune them up correctly, which brings us to our topic: show season fine-tuning.

Recently, an engine found its way into my garage and needed a little tune-up. Getting her to run well was no problem, but it ran faster than I like. Getting her to run well at a slow speed was a bit of a head-scratcher.

Even though the throttle was closed all the way, air leaking around the various shafts and butterfly keeps the engine running too quickly. This wouldn't be an issue with the engine running at its rated speed or under load, but this old girl will spend the rest of her days lazily lumbering along at engine shows. The adjustment that had the most dramatic effect was decreasing the intake valve lift. By reducing the lift, the rpm was cut in half.

Isn't that pretty much the same as 'throttling down?' I mean, you're reducing the amount of mixture that's taken in, which seems pretty logical except the intake valve is the final word on how much is admitted.