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Fuel and Exhaust Systems

The fuel system requirements for most small engines are pretty simple, which means there is not too much to be concerned about when repowering. If fact, the primary thing you need to know is whether your old system has a fuel pump or not and then match the new one up accordingly. Simple, huh?

Actually, the bigger problem is in cases where you do not have an old engine to start with or if you are building that "special project" from scratch. In those situations, here are the primary things to consider:

Where is the fuel tank mounted in relation to the carburetor?

If the fuel tank is mounted directly to the engine, chances are good that a fuel pump is not required. If the fuel tank is located remotely, but within a foot or so of the engine and is mounted up higher than the engine, chances are good that a fuel pump will not be required.

For all situations where the tank is mounted remotely and has a distance to the engine greater than about 18 inches, a fuel pump will likely be required. For situations where the fuel tank is mounted level with or lower than the carburetor on the engine, a fuel pump will likely be required.

Assuming that you should find an engine that has a pump where none is needed, it's usually a non-factor since you can just bypass (not use) the fuel pump altogether.

Should you find an engine that meets all other criteria with the exception of needing a fuel pump, you may be able to install a low pressure (typically 3 PSI or less and preferably adjustable) electric pump. Check with a local automotive parts store for availability.

Also, if you have access to a method of tapping into a source of crankcase pressure on the new engine, you my be able to use one of the vacuum style models shown to the right.

Exhaust System Considerations

Since we've already mentioned the exhaust system as an important factor in several other places, you are likely by now wondering...what's the big deal? Here's the story:

The first and foremost concern is that the older "Flat Head" style engines have been mostly out of production for several years now and unfortunately, there are literally hundreds of thousands of these engines (most major brands) that are just now wearing out. This can be crucial situation for a couple of reasons. Some of the newer replacement OHV style engines have the exhaust ports located on the opposite side of the engine from the flat head counterpart, which means:

  • Your existing OEM supplied exhaust system or muffler will not fit and cannot be re-used and a "bolt on" replacement may not exist.
  • Even if the new engine comes equipped with a muffler or exhaust system, it may be located in a position that will not work for the application.

The good news is that many of the smaller engines powering rotary lawnmowers, pumps and such, this is often not an issue. On the other hand, if you are repowering a riding mower or commercial product, you would do well to get as much information together as you can.

The second part of the equation has to do with the fact that some of the larger engines are often sold without an exhaust system provided by the engine manufacturer. In these cases you are generally expected to re-use your old system or purchase a new one from the equipment manufacturer. This can be a tricky and difficult situation if you are repowering with a different brand engine or one of a different size range.

The bottom line in regard to exhaust systems and mufflers is that even if you select a replacement engine model that has been specifically recommended by the engine manufacturer, it may be a perfect match for all other factors, but there isn't any specific guarantee that it will be suitable for your particular application. If you are repowering with a different engine brand, be sure to do you homework and be aware that there may be some fabrication required.

As mentioned elsewhere, the best bet is that when possible, select a replacement engine of the same brand, size range and family. Otherwise, do your research, ask questions and/or contact us if you need additional advice.



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