036 Pro goes lean as I cut

[rd35]

My 036 Pro has this problem. When I fire it up cold it runs, idles, revs just fine. But when I start cutting with it and its temperature begins to rise it starts running lean in the cut under load. What has me puzzled is that when I pull it out of the cut and let it come back down to an idle it idles just fine. After a few seconds of idling I go back to cutting and it runs great under load for about 30-45 seconds and then begins to transition into running lean. If I stay on it and keep cutting it will start to bog down lean. If I stop cutting and go back to idle and then jerk the trigger it almost dies lean. Let it idle for several seconds and then jerk the trigger and it revs up fine again. I have not vac tested it...but I figured a vac problem would give me problems at idle. Could my fuel line be collapsing maybe? Any ideas?
Thanks

 

[merc_man]

Did you try richening the high side a little to see if it helps.
If that dont help id pressue vac test it.

Sent from my SM-J320W8 using Tapatalk

 

[rd35]

Yes I had my little screw driver in my hand while I was cutting. When it started going lean I stopped in the cut, opened the H about a quarter turn and buried the trigger again. Helped for about 3 seconds and started going lean again. Stopped, opened another quarter on the H, buried the throttle and it started 4-stroking in the cut for about 10 seconds, then cleaned up and cut like mad for about another 15 seconds then started getting lean again. Stopped to scratch my chin and think... saw just idling away beautifully....then about 15-20 seconds later pulled the trigger again in the cut and it 4-stroked real bad rich...then started the slow transition to lean until it started bogging lean. That's when I decided to shut it down before I damaged the P/C.

 

[Westboastfaller]

Very good job in your description.
That was
It's not racing so I'm positive it's not an air leak. The gas line/ filters/ carb screens ect. is a great place to start as you said. Coffee time

 

[Whiskers]

It could be a tear in the intake boot/manifold. If it’s a small enough tear it can open when pressure is applied. Also might also want to make sure the crank bearings don’t have any play allowing air past a seal under load.

 

[Westboastfaller]

Something is affecting full flow to the high side at full throttle obviously.
Your jet looks to be doing its job fine.
It's a restriction/blockage or inadequate supply.


collapsing line
Gas filter
crap behind the high needle
carb screens
Inner built up
Metering level/diagram

 

[Westboastfaller]

You got that thing fixed yet?
Come on..let's go let's go let's go!
The helicopter just fired up. Some one wants to pay you $100 an hour and your third flight.

Oh it's an 036...OK $15 an hour.

 

[rd35]

Think I’ll start at the gas filter and work my way to/through the carb. Oh and I will do a vac test before all else just to be sure. This one is a real puzzle!!!

 

[alexcagle]

Trubble in carbatooter land......

That sounds like it's got a fine accumulated debris in the internal carb screen.

Oh....wait, that's only concrete cutoff saws. LOL
I doubt a small seal leak is going to cause what you describe.
A big leak will cause high idle.
Do the simple stuff first.

All my repairs start with fuel inspection poured in a clear bowl, then flung out the back door. (not really.... )
Next, remove the fuel filter, and see if it's restricted, and pressure test the fuel hose up to and including the carb needle.
Look for a fuel line pinched or kinked.
Plug the fuel line and test the tank vent is not building up a vacuum.
Hook it back up
Fill with fresh fuel.
New sparkie pug......retest....
If none of those help, remove the carb and check the internal debris screen.
Also, depending on it's age, look for an old glue ring that detached from the welch plug because of today's fuel formulations, and may be getting sucked up to HS jet at WOT. Also make sure the hole in the pump cover isn't plugged up and keeping it from pumping well enough at WOT.

 

[Big_Wood]

it sounds to me like the pump side of your carb is struggling to feed the metering chamber. this is why it runs fine until the chamber is drained and can no longer supply the fuel needed to run at high speed. a low metering lever from improper assembly can cause that issue but unlikely if it's never been apart. i'd test tank vent, inspect the line and replace if neccessary, then replace fuel filter and carb diaphragms. the flywheel side seal are a known gremlin on these too, i replace them just because.

 

[HarleyT]

All of the av mounts in good condition?

 

[Westboastfaller]

All of the av mounts in good condition?

Yes, they all checked out.
It did however have an unusually deep scratch in the top cover.
What's your diagnosis?

 

[Westboastfaller]

Trubble in carbatooter land......

That sounds like it's got a fine accumulated debris in the internal carb screen.

Oh....wait, that's only concrete cutoff saws. LOL
I doubt a small seal leak is going to cause what you describe.
A big leak will cause high idle.
Do the simple stuff first.

All my repairs start with fuel inspection poured in a clear bowl, then flung out the back door. (not really.... )

funny.
Don't forget the Douglas tree. That stuff eats cylinders.
I'm still coughing up fur balls..no wait!

Cutoff saw specialist:
"Sorry ...it didn't go well in there.
I'm sorry to inform you the diagnosis Is chronic.
Customer: No! No! it can't be...I always run the water
Cutoff saw specialist: I'm afraid so...
Silicosis!
Customer:
There has got to be something we can do?
Cutoff saw specialist: ..er..um..10 litre flow of oxygen?

 

[Chris-PA]

Sounds like the tank vent is not flowing enough air when the engine is at rpm, so it begins to draw a vacuum on the tank and lean out the mixture. Once it shuts off for a moment the pressure equalizes and it's good again.

 

[HarleyT]

Yes, they all checked out.
It did however have an unusually deep scratch in the top cover.
What's your diagnosis?

I was thinking that a bad mount or two was putting a flex/pinch on something when you are in the cut. But if they are good then,
my guess is that the passage under the metering lever needle is partially blocked with scum, there is enough fuel able to flow until you are at full rpm and load, and the fuel isn't able to keep up then.

 

[Westboastfaller]

Sounds like the tank vent is not flowing enough air when the engine is at rpm, so it begins to draw a vacuum on the tank and lean out the mixture. Once it shuts off for a moment the pressure equalizes and it's good again.

uncharacteristic! It doesn't go back. It stays sucked up.
It races at idle and it will die about 4 seconds after the first cough unless you open the gas cap.
My Bookie just called back.
It's sitting at 300:1 odds
It would be a nice pay day.
Put you down for the usually 10?

I was thinking that a bad mount or two was putting a flex/pinch on something when you are in the cut. But if they are good then,
my guess is that the passage under the metering lever needle is partially blocked with scum, there is enough fuel able to flow until you are at full rpm and load, and the fuel isn't able to keep up then.

I see. Well this is awkward. I thought you were joking. I was joking.. don't no about the mounts or the deep scratch really.
That's what happens when you joke all the time. People don't really know. Look at Andy Kaufman.
He got a rare form of lung Cancer and nobody believed him. Rest his soul.

All right..let's get serious.
That's a good one.
Get you 5:1 on inner build up of scum. Just text it in again.

 

[Chris-PA]

uncharacteristic! It doesn't go back. It stays sucked up.
It races at idle and it will die about 4 seconds after the first cough unless you open the gas cap.

I was not suggesting a complete blockage, rather that some air still enters the tank, but very slowly (through the vent or elsewhere). It's just a matter of relative air flow rates - if the flow of air into the tank is just slightly less than the volume displaced by fuel use, then it will work as I described. The tell is the time delay, which a fuel blockage isn't going to have because fuel is not compressible, so the blockage is unlikely to get worse after a bit of running time. A partial air blockage will take time to build a low pressure in the tank and starve out the fuel flow, but recover when the engine is off, or even at idle.

The only reason I suggested it is because I have a saw that I believe is doing this now and I've been thinking about it already. A collapsing line might sorta work that way, but it was not the problem on the saw I'm having trouble with.

 

[HarleyT]

Get you 5:1 on inner build up of scum. Just text it in again.

Not sure what that means, but hey, I have been called a lot of things here by these kids.....

 

[burnses]

tank vent.....

 

[Ozhoo]

tank vent.....

Moon pie