Best fuel mix for a Bunch sparker

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Best fuel mix for a Bunch sparker

Postby jerry1927 » Tue Apr 15, 2008 9:11 am

I plan to run a 1949 Bunch Tiger Aero on ignition. It is a ringed sideport that has no ball bearings but seems to have been broken in properly. Can anyone suggest a good fuel for it? I've heard castor gums up rather quickly but most synthetics have their own limitations. I'm prepared to buy a commercial methanol mix with no nitro, in the interests of cooler running. Max rpm will be below about 8000. Any suggestions? Thanks.
Jerry Wiles
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Postby loucrane » Tue Apr 15, 2008 9:40 am

Jerry,

I haven't yet done it, but I hear from good folks that you are looking the right direction with the methanol-based fuel. It can run cooler, and will probably run less time per ounce. (Those are connected ideas: the alcohol chills things nicely as it evaporates, and as it has less potential heat per unit of volume/weight, you need to flush more of it through for similar performance.)

Also, minimum of 25% castor in the fuel, with as much as 30% a decent idea until you are sure. Alcohol doesn't mix well with mineral-based oils. If everything looks good, but you suspect a tendency to varnish or gum from the castor, 1% or so of a synthetic, like KLOTZ, might keep things clean.

Some have tried a few of the highly advanced synthetic oils newly available, and speak well of them. Your Bunch Tiger was designed when castor was one of the best choices for oil. Finding a good single-weight SAE70 is not too easy, and would work best in a gasoline-based fuel - defeating your purpose to run it gently and cooler.

Luck, and let us know how things progress?
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Fuel mix for a Bunch engine

Postby jerry1927 » Wed Apr 16, 2008 12:47 pm

Lou,
Many thanks for your help and advice. I'll get the stuff and try it.
Jerry
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Location: Bradford. Ohio

fuel

Postby chiefss » Fri Apr 18, 2008 8:35 pm

I run straight methanol and castor oil 3 to 1 in my Ohlsson 60. It has a modern OS4B carb on it now but everything else is stock. Runs great and you won't believe the idle when the spark is retarded. well below 1000 RPM.
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Best fuel mix for a Bunch sparker

Postby jerry1927 » Tue Apr 22, 2008 8:26 am

Guys,
I've contacted the manufacturers of Red Max fuels and will buy a gallon of their recommended mix. It contains 12.5% castor and their propietary 62RM oil, also 12.5%. I'll holler when I know how it works.
Jerry
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Posts: 56
Joined: Sat Jan 24, 2004 2:42 pm
Location: Bradford. Ohio

Bunch engines

Postby jerry1927 » Mon May 21, 2012 7:27 am

Hi, Guys,
I've fiddled around with my Bunch and RedMax fuel but the ignition system seems to be fouled up. I never got any of my Bunches to work well but have had to set aside everything while I healed from a bad car accident (my fault.)
Does antone have a reference to all the Bunch-designed ignition engines, especially the early post-war? I recently bought a .45 that has an unusually thick head as part of the 1-piece cylinder assembly. The top 3 fins are very shallow, making the steel head about 5/16 in. thick. Everything else looks to be standard, including the PDW driving pin and the broached hole in the drive washer.
The PN is thin but the prop shaft just barely reaches through the 3/8 in thick prop and die-cast PFW. The shaft is too long to permit use of the long, 3/8 in. dia. PN with its 1/4-28 set screw.
Tim Dannels' Model Engine Encyclopedia has too few details on Bunches to help my quest.
Thanks.
Jerry
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