T700 Align 91H tune issue

[jiberjaber]

So I have run quite a few tanks through this engine on my 700 now, must be approaching 20 as of tonight.

I ran it 2 turns out for the first 4 or so tanks then leaned it in over the rest of the flights. I ended up with about 41 clicks (6 clicks in from 1.5 turns) on the main and 52 clicks (about 1.5 turns plus 5 clicks) on the mid.

There was no real science behind this other than this was the point at which it was just starting to get hot when flying. I didn't think there was as much power as there could be - there was loads but it bogged when pulling a climb in to a stall turn or an aileron tic toc for example.

So I remembered the littlerotors tuning guide, which I took to the field tonight. I started with 1.5 turns on both main and mid and tried that out for size. This was fine until about half tank and there were heat and lean running. I have checked the fuel filter, this has a bit of muck in it, which I cleaned out.

I backed off the main to 1.5 turns again and made the mid 2 turns. Filled up and flew, fine loads of smoke and I proceeded to lean out the main needle again, 3 clicks at a time with a fast forward run to see what effect was. This was still producing bogging. I got down to main 44 clicks (3 clicks in from 1.5 turns) and mid at 55 clicks (7 clicks in from 2 turns) the engine was red hot - finger burning in fact! Again at half a tank of fuel it was running lean. If I let it cool down and then take off, there was good smoke and then after a short time it started to lean again. These settings are richer than I was running previously.

My immediate thought was that the clunk line might be shot or the engine might be rubbing on the clutch bell. So I packed up and headed home to take a look.

I have dropped the engine, check checked the muffler bolts and head bolts, all tight. Popped off the head, no damage in there.

Popped out the tank, inspected the clunk no deterioration there so decided to replace the green align fuel tube on the exterior with some thick walled QuickUK stuff just in case there was a pinch point somewhere it goes through the frames.

I have also blown through the carb, all clear. I am at a bit of a loss what was causing the lean running at half tank.

Other than what I have done, any other ideas on what could be contributing to the running issues? The only thing I haven't changed is the clunk line, but I could blow in to this without any leaking.

Background info:

Engine Align 91 black head with OS No 8 plug
Muffler MP6
Fuel MT Coptamix 20%
Cyclic pitch 8 degrees
Collective pitch 12 degrees.


Thanks in advance

[electricsceadu]

i would change the clunk line it could be collapsing in causing a loss of fuel to the carb

[jiberjaber]

i would change the clunk line it could be collapsing in causing a loss of fuel to the carb

Yes interesting idea, but only at half a tank? This was why I thought it might be a bad clunk tube as that is where the clunk starts to be out in the air. Maybe I should just put some normal non-quk stuff on there I think I have some thin wall which isn't clunk but not far off the Align stuff.

[Steve]

Someone on here a while back (might have been Stuart) had a problem with a TRex 600 running lean which he finally traced down to some flashings or a tiny split on the moulded joint of the fuel tank which was letting air onto the system.

Also, maybe you're running too much pitch for the head speed (you haven't said what that is) which might cause bogging - might be asking too much of the engine? Might need less pitch or more head speed or both. I'm sure plenty of others will advise as well.

[Steve]

Is the fuel pickup nipple half way up the tank? If so, could be drawing air in there somewhere once the fuel gets below that level.

[jiberjaber]

Cheers - I thought that too about the air leak.... I have had it all out this evening, so will take it up the field early doors and see what the score it. If it is not right then I have the rest of the day to fettle and test. I was tempted to fit the clunk to the outer hole for easier access but didnt bother in the end as the clunk couldnt reach all corners and could get stuck behind itself.... hmmm well hopefully its fixed, but if not then I will be moving the clunk access for sure! LOL

[0h5h1t]

have you checked the pressure feed line from muffler jason. Also, i had to seal the clunk and blanking bung on my 700 tank using two part epoxy to close the leaks in the end.

hope you get it sorted mate.

[jiberjaber]

I tried a pressure test on it this morning, it withstood more pressure than you get when you release the pressure valve on a YS50, so I am hoping it will be OK. I'll give it a try this morning and see how it fairs.

[jiberjaber]

Anyway, back from the field, after half a tank it leaned out again. So I pulled the clunk and replaced it. I pressure tested the tank with fuel using the fule pump... all good... but then half a tank and guess what... lean again!

However one guy on another forum mentioned having to use epoxy to seal the clunk bung in to the tank. I decided to try tilting the heli whilst it was running at the half tank lean point.

Tilit forward and the bung is covered, keeping the end of the clunk in the fuel still but covering the bung, the heli richened. Tilt back to expose the bung and the heli leaned.

So I can only think it has something to do with either the new clunk I have fitted or the actual bung the clunk goes on to or the sealing plug.

Is this what you experienced Karl?

[Made2Fade]

I too very recently experienced a leak from my bung... i used a little silicon to get the bung to fit better. Seems its a bit of a problem. Mines been faultless for a few gallon and only developed the leak recently. Hopefully its all sorted now.

[jiberjaber]

OK, I will use some silicon first before the epoxy route. I have a bubbless clunk en route, so I want to be able to take it out in the near future

[t-rex pedro]

My tank leaked so I moved the outlet bung to the outer hole with the blank in the middle. I also keep the tank full of fuel as the bungs can dry out and perish. Once mine was sealed it has stayed that way and that's using a pressurised YS.

[jiberjaber]

did you have to make the clunk longer when you used the outer hole?

[t-rex pedro]

No as it can wedge itself and get locked in the corner if it's too long. It's no different to the plumbing on the 600.

Edit: it's also much easier to remove the tank with the outlet bung in the outer hole. It's a bitch with the bung in the middle. I'd refit the bungs, leave it full of fuel and leave it overnight then see if you still have a leak.

[jiberjaber]

Doh - too late it's in and silicon'ed LOL... will swap over when my bubbless clunk turns up. Going to leave it overnight and see if the leak has stopped tomorrow.