Low power

[scottessex]

I was flying yesterday and had trouble gaining altitude, I looked at the tach and I was only turning about 5800 rpm. I finally pulled the throttle back and was able to get to 6400 like normal. Huh??

Saturday it was cooler and didn't act this way, yesterday it was hot and humid in the late afternoon, would this have had a this effect?

[GyroRon]

what were the EGT readings?

[scottessex]

EGT was about 1200deg when the rpm was low.

[GyroRon]

might be too hot

[barnstorm2]

Are you running a 2-stroke rotax? I would check the plugs and see how your mixture is doing ( lean/rich ). IMHO the best way to do this is to put in a new pair of plugs run it then check them right away.

[Caribean_gyro]

if you reduce power and rpm goes up , Means he is sucking air and the mixture ratio is wrong. some time the primer bulb leack some air to the carb. I would start from basic and check carb setting and carb intake filter
ChuckP

[Chuck Irby]

Scott, it sounds like it could also be in the throttle linkage.

[scottessex]

Running 2-stroke Arrow 500cc.
Thanx for the info.

[GyroRon]

I have had weird stuff happen with two strokes before that was solved by simply putting in new plugs. The old plugs would still look just fine but the new ones worked better......

[scottessex]

Yeah I know what you mean, I used to take a BOX of spark plus with me when we would go dirtbike riding for the day.

[Ron Marlett]

If I read your first post correctly, it showed the lack of power symptoms on the first day(hot humid) and ran more like normal on the second day(cooler), is this correct?

If so, IMO I would agree with your thought on high air temp as part of the cause. If your mainjet region(above 3/4 throttle) was a little on the rich side to start with, a hot and humid day would make this more apparent as there is less air in the air due to its density. Temperature induced Air density decreases apply to air/fuel mix just like they do to wing lift. An increase in humidity also adds to this density decrease/effect.

It sounds like your midrange needle jet/jet needle combination is a little leaner so as you rolled off the throttle(nearing 3/4?) and started to enter the midrange jetting area(between 1/4-3/4 throttle) you gained horsepower with the leaner mix so the RPM increased.

What kind of prop are you running? How much pitch? How did your plugs look after the power loss symptoms were observed(the plugs tell all:)?

[scottessex]

I flew tonight for a little while, again it was humid and warm. I pulled the throttle back to give myself full power, and gain some altitude, Once I was up, I brought the throttle back to around 5800 rpm, noticed the EGT going towards 1300deg. gave it throttle and reached 6450rpm and the temps came down to below 1200deg.
If I hold the throttle in FULL OPEN, rpm drops down to around 5900, and temps go down slightly below 1200.
This would lead me to believe it is rich at wide open, but why are my temps going up when I reduce the throttle? I have a BING 55 carb.

I haven't checked the plugs yet, I will. The best way is to chop power at high rpm, shut engine off then land and check them, then I could get a proper reading at that setting, but I don't think I will try that yet, I used to check motorcycles that way, full throttle, kill engine, pull in clutch coast to stop and pull plugs. Just a little more difficult on the 'ol gyro.

Oh yeah, I am running a Warpdrive 60" 3 bladed prop.

[GyroRon]

Scott I wouldn't fly it till you get it sorted out Bro! check the needle clip position and if possible rasie the needle by lowering the clip a notch or two.

[Ron Marlett]

Yes, it does sounds like you are lean in the midrange circuit. As suggested, check your needle clip position. When was the last time the carb was stripped and all the jets and passageways were cleaned? If you can get access to one, an ultrasonic cleaning tank is fantastic for this.

You could do your plug chops with the machine tied to the ground, such as is done for a thrust test... I think this would be a much safer way to sort out a mixture issue than in the air.

[scottessex]

Yes I agree, much safer, I'll do some checking tonight, I do have access to an ultrasonic tank, I use one everyday at work, and love it. Any how, I will check out some things and get back to ya'll.

[Brent_Brown]

Sounds like a change to the needle clip will do the job for the mid range.
not sure about the high side drop in RPM?

[Caribean_gyro]

had same problem on an air comand, my findings the metering needed was close and book said is 2 1/2 turns. I suggest assume nnothing go back to basic and check needle adjustment, floats level etc.

when in doubt salute.

ChuckP

[scottessex]

I am going to check everything. I may be slightly over propped, and could possibly be over carburated.
I am only able to reach 6450rpm in flight. I will do some ground runs, check plugs, etc. and keep you posted.

[Udi]

Scott,

The mid range fuel mixture is supposed to run leaner than full throttle. The EGTs should read highest at the mid range.

A hot-humid day would make the mixture more rich, not lean (because there is less air for the same amount of fuel). The EGTs should read lower on a hot-humid day, not higher!

On the other hand, your EGTs at 1300 degrees are way TOO hot. This means your mixture is too lean.

This is conflicting information. It sounds like the problem is not in the tuning of the carbs, but something else. You may have a problem with fuel supply. Maybe it’s the fuel pump or a restriction to flow somewhere. This would explain loss of power at full throttle (the carbs bowls may be getting running low on fuel). Do both EGTs read the same temperatures?

Udi