ORIGINAL: summerwind
ORIGINAL: freakingfast
Most Webras sold in the states don't like more than 10 percent nitro. You can buy some FAI (zero nitro) fuel and dilute the mix down it you cant find 5 or 10%. Even try the FAI by itself There will be little or no power advantage to running higher nitro and a head shim in the Webra, just costs more to run. Fuel, glow plugs and engine load are your controllable tools.
If that engine has an old plug in it, start out with a fresh one like an OS #8, Enya #4 or #3.
that's wierd, back when we first started using the Webras, guys like Kirkland, Jim Martin, Ron Chidgey and even Phil Kraft found that it didn't perform on FAI fuel like it did with 5-10% nitro.
guess we had run these all wrong. but i guess you were there in the late 60's so like the old saying goes,
learn something almost new everday
That's why I said "try" some FAI. Some Webra engines really have a tough time with 15% like the speed 55 gt black head (discontinued) ringed speed 35 (discontinued) or the newer little power house speed 36. These engines when run on 15% either beat clearance in the rod end which lowers the compression (some think it's a long break-in) or it out right snaps the crank at the pin or port. Even on tuned pipes the 55 and 36 engines run great on 10% and break in quickly (the ringed 35 takes a while). The 55 runs fine on 0% IF the rod end is not already hammered.
I's better to start low nitro and work up. When the engine has less power, surging or blowing plugs on more nitro after opening up the high speed needle and even trying a colder plug, that's a pretty good sign you've gone over the nitro limit. When it's cold out you may get away with the higher nitro, so if it's running bad when it gets hot you know what you need to do.