Hello,

I've got an ASP 75 i've been trying to tune in on my test stand. It has a carb I am not familiar with. Seems like its got two needle valves. I am assuming the extra one is for the low end. Trouble is, I don't have the factory manual for this engine and can't seem to find the right combination to get it full power/then idle with good transition. Anyone have experience with this engine? Anyone able to quote me the settings from thier ASP manual? Or other good trial and error plan you engine experts can divulge?

Horizon hobby sez this engine is discontinued and no PDF manual is available on the internet.

Thanks

A Magnum or SC 75 would be pretty much the same but they have been discontinued also.

The High speed needle runs at about 1 turn. Don't know about the low speed. The needle in the center of the throttle arm is the low speed and the one on the other side of the carb is the high speed.

There is a idle speed adjusting screw on the back side of the carb and on this version, I think it's kept in place by a jam nut.

Enjoy,

Jim

Royce,

I'm not sure that those older ASPs will be noted in the history books for the quality of their carburetors, but to get your carburetor in the ballpark...

Attach a piece of clean fuel tubing to the carb fuel nipple, and with the barrel just slightly open you should be able to just blow a bit of air through the carb. Open the barrel while blowing into the tube, and the resistance to air pressure should decrease markedly.

If you can't blow air through..open the LS needle slightly and try again until you can. Remember....JUST PERCEPTIBLE air flow with the carb barrel slightly open.

Now...after removing yourself from the motor, attach everything else and start the engine.

Set the HS needle for maximum rpm, then richen it 2-300 rpm.

Close the throttle to idle, and pinch the fuel line (1 or 2 seconds) and note what happens to the rpm at idle. If idle speeds up with the pinch...lean the LS screw 1/8 turn

If the motor does not increase rpm, or starts to die with the pinch....richen the LS screw 1/8 turn.

(Allow the motor to run at WOT for a few seconds to clear out before returning to idle, and making LS adjustments)

You should get a just-perceptible rise in rpm the brief pinch/release of the fuel line at idle.

Go back and re-tune the HS needle for 2-300 rpm rich of peak.

This will get you pretty close, and the motor should transition from idle to full power fairly smoothly. If the motor tends to smoke and sputter a bit when accelerated...lean the LS needle slightly. Conversely, if the motor seems to cut out briefly when accelerated...richen the LS needle slightly.

It usually takes a bit of going back and forth to get the needles set for best operation at all speeds.

Good Luck,

'Race

Thanks guys for the run down. I'll take this to the stand today and give it a try - Can the carb on this engine be replaced with a more reliable, efficient and modern after market substitute? I don't like to throw things away, and would like to make this a reliable power plant if possible. However, time and effort vs expense of a modern replacement would take its toll eventually.

Normally the carb on the latter ASP's are very good. The 75A was one of the later 75's. There shouldn't be anything wrong with it? Just do like ED said. These carbs actually give less trouble than the after market Perry carb which plugs with lint very easily.

Enjoy,

Jim

Thanks Race! Worked like a charm.

Anyone able to recomend a pitts style mufler for this out of produciton engine? I've looked on Tower and can't find one. Holes are 32mm apart - center to center.


Thanks again for the set up routine.

Alright Royce!


Glad it worked out, and of course there's NEVER a charge for the consultation..<GGG>

As for Pitts-style mufflers, check the SLIMLINE brand. They're nice quality and should work well on your motor.

Good Luck.

Race