I just aquired a used quadra 35 with a tillison carb. Starts and runs to about half throttle fine.Seems to have no difference in r.p.m. between 1/2 and full throttle. Running a 18/6 prop. Seems to run a little rough all the way through.Put in new diaphram kit but not welsh plug/rebuilt kit.Wondering if it might be timing(points) or magneto gap? What are the point gap/flyweel mag gap? Has anyone run into a simmular situation?

George

George,

What is the RPM at half and full throttle on the 18x6 prop?. Most carbs are pretty nonlinear with respect to throttle position.

Ken

Don't own a tack. . . .but going by sound , seems not to differ from 1/2 to full throttle

I'm running a low time Quadra 35 with the Tillotson carb, still a bit rich, on a Zinger 18 x 8 at 7300 RM. Can peak it to 7500 if I want. Initial start settings for the needle valves are: Low Speed= 1 1/4 turns open, High Speed=1 turn open. Adjusting the low speed needle too lean for a good idle can mess up the high end. Run at full throttle at the initial settings and set the high end. Then adjust the idle for a good transition, making sure its not too lean (it will heat up and quit if it is). Then reset the high speed needle. Points and plug should be set at 0.015". The B&B Carb Adjustment Tool is handy to have as it allows adjustments from behind the prop with the engine running (see picture).

Thank's for the response Wile, I've set the carb as per your suggestion, setting the high first,low,then back to high.I'm comparing the sound with a simular Quadra I have in a Tiger Moth which is doing a nice job. The only difference between engines is the carb, the one I'm working on has a tillison, while the one in the tiger moth has a walbro.I know from previous Quadra engines I've worked with that the 1/2 throttle and up is close to the same sound but this one seems different. It doesn't have that topped out humm I get from a tuned high speed needle.I'm still perplexed with weather it's carberation or ignition, or even an air leak in the crank or carb plate.Just wondered if anyone else has had simular concerns and what they found them to be. George

George,

A tach would be a good investment. Borrow one from a friend. If I were you I would take the Walbro off the good engine and try it on the 35 if the bolt holes will align. It's very hard to diagnose by earball and without a tach.

Ken

Is possible the tillotson is bigger than stock and the engine cannot intake any more air at 1/2 throttle than wide open.

It is also posible that you are getting limited gasoline flow. If the screen is partially clogged in the carb or if the fuel line is restricted or to small, you will get this effect. In general, performance is the same with either a Tilson or Walbro carb.

Thank's for all the advice guys . . .I'll try all the obvious and post the results for anyone who encounters this type of problem.
George