Lins

Ok, so I had a small prop strike while taxiing in last night, and damaged my wooden prop. My replacement prop is a 26x10 instead of the 26x12 that was on there. I know it is a minor difference, and might not even affect anything, but do gas engines usually go richer or leaner when down sizing the prop? The reason I ask is because I am still leaning out the engine as it is almost broke-in, and it is also going a bit rich in flight as well. I just want to know if I should leave it as is, or make a larger adjustment, cheers!

By the way, yes I will check the run out on the prop shaft!

AW Extra 260 75cc/ZDZ 80 RVJ

Tony Hallo

I would think that you will happier with the 10" pitch, might have a bid more prop noise however. Conventional wisdom would say re-adjust the needles, I would be interested in knowing how much it did change.

Tired Old Man

My Feedback: (1)

Changes in pitch present problems when tuning. A higher pitch spins lower on the ground than it does in the air. What is does in the air determines the required state of tune, so ground tuning is only close at best. I imagine you'll need to tune leaner but the amount will be subjective and not something to be guessed at on the ground. Normally as an engine spins faster it becomes leaner if only the prop is changed. Of course that depends on how it was tuned before, and as you noted that process had not been completed.

his brings up a point. Gassers are not glow engines and should be tuned for peak performance during the first engine run. There is zero benefit from rich break in running. In fact, there is some detriment from breaking in rich. Hopefully that was not the reason final tuning had not been accomplished.

Lins

It was tuned on the ground before flying, and then followed the manufacturers recommendations for richening high needle to allow for higher rpms in flight, however rpms were low and obviously rich throughout the rpm. High needle seems close now, but still a slight burble when running low rpm. I'll just lean the low again and see how she does next flight.

What detriment would there be to running rich aside from running reliably and fouling the plug? Thanks for the replies.

av8tor1977

My Feedback: (6)

A loss of power, along with the possibility of carboning up the ring(s). When they get carboned up and stick, then the blowby gasses overheat the piston skirts, burn away the oil protection, and then the engine seizes. All in all a "bad" thing.

AV8TOR

Tired Old Man

My Feedback: (1)

Beats running hot.

pe reivers

It is hard to tell if leaner or richer settings are needed. As a precaution, with more prop load tune the engine slightly richer before running, then adjust for best power again.
Having said that, A few weeks ago I completed power curve test runs on an 80cc engine on just one single carb setting. I got a lucky tune. There is just no telling what to do and do it right the first time. Engine timing, rpm range and carb size related to engine displacement have a large say in this, as well as some "fingerspitzengefuehl" which comes with practice.

Flatspin-RCU

Pe...that engine wouldn't be a DJ80 would it. The reason I ask is there are not many 80cc to 90cc singles out there. I have a DJ80 I purchased from SDShobby. After only one flight the next time I started it, it seized and I sent it back to China (but will never do that again) They are sending me a new engine but I have to pay another 50 bucks for return shipping. I know, buy cheap buy twice, Any precautions I should take when I receive the next DJ80nc. I broke the first one in slowly with short runs to temp and then letting cool etc. Pennzoil air cooled oil and 32 to 1 mix. Thanks for any info

Ron

captinjohn

If you have any photos of that seized engine....would you please post them? Thanks Capt,n

pe reivers

No, MVVS80.
I won't mess cheap engines again.

nonstoprc

My Feedback: (90)

You may need to check the highest RPM with 26x10 and make sure it does not over-spin the engine.