p.j

I have been trying to tune my first gas engine G-26 with Ralph mods. It would start great but I could not get any good rpm. I eventualy tryed bending down the lever for the inlet valve so it was flush with the carb body because I thougth it was a little high. Well the engine runs much better know-- low 7s with 18/6w and nice idle.

My question. Should the throttle valve be wide open at full throttle or is it ok if it is only partly open. When my engine is at max rpm my throttle valve is about 80% open. Do I need more tuning or is this normal?

Thanks P.J

karolh

Considering that your engine came from Ralph, I would suggest that you contact him directly for advice regarding your query, as to the best of my knowledge all engines from him are run and tuned before being sent out.

The rpm you quoted on an 18x6W is about normal if the engine is being run with the stock muffler which is quite restrictive. Fitting a less restrictive muffler should show an rpm gain of about 800.

Ralph's number is 928 635 2455.

Karol

Tired Old Man

My Feedback: (1)

A little off won't hurt anything but it sounds more like a linkage problem rather than tuning. Adjust the length to get things to open right. Leaving a butterfly partially closed is akin to opening the slide barrel in a glow carb only a little bit and expecting full power.

Every gas engine from Ralph is tuned for performance at his location, which is about 4,000' (+/-) above sea level. It should go without saying that each engine should also be re-tuned for the final location it will be used at, by the owner.

arobatx

As for the throttle valve in the carb, it is pretty normal to be hitting near max RPM well before the valve is near full open. In fact, some have claimed that slightly over-opening the valve produces minor, but noteable RPM increases. I've tried it, and haven't seen this to be true, or at least not significant enough to mess with. You'll want your linkage setup correctly first, like Pat said above.

Make sure full stick position is fully open on the valve. Make sure throttle down stick position ALONG with your trim lever fully down, fully closes the valve, but doesn't bind the servo. You can then set your throttle trim to neutral, and use the travel adjustment in the radio to reduce the amount of throttle down travel to the point where you like your idle. Once you have tuned the carb for your surroundings, which again like Pat said is different pending elevation, temp, pressure....etc, read your max rpm. For example, let's say you are getting 9000 rpm at full throttle. Then, using a tach, set your throttle stick at 1/2 with the engine running....If you have a throttle curve function in your radio, adjust the half stick position so that it reflects approximately half of the highest RPM reading, in this case, about 4500rpm.

This will make the throttle stick to RPM feel very linear, and small stick adjustments will be reflected in RPM at all positions. In my personal opinion, I usually edge the half stick position up a few hundred RPM from half....on mine in this scenario, you'd read approx 4800 at half stick position, which is simply a personal 'feel' preference.

If you are using the APC 18x6w prop, it is a bit heavy, and you won't see the best performance out of it. The 26 makes good consistent power around 9000rpm, so 'tuning' your prop and exhaust selections accordingly will have significant affects. In the 18" size, the 26 can spin the Mezjlik carbon prop at approximately 9000rpm, but only with a less restrictive muffler. Or, the APC 17x6 works well, and can run close to 9000rpm, but again, you will need to toss the OEM muffler and run something less restrictive.

Chad