Carb & Fuel Flow Question

[AKNick]

This is a sore subject for me right now. Rebuilt my DA35 carb. Marked and reset the needles to exactly where they were before and my engine would not want to leave idle, could baby it up to mid range and then it would die. Classic case of an air leak, bad plug cap, or lean high.
Ran the engine with the cowl off, no air bubbles detected. Redid the connection to the carb for giggles... no help. Bad new plug maybe??? changed it anyways... no help. Tried DA factory settings 1-7/8H 1-3/8L (It was at 2-1/8H 1-3/8L) worse. Let it (my head, and the cylinder head) cool down for ten minutes.
Starts up, and does the same thing... time to richen up the HSN went to 2.5H 1.5L engine runs up to WOT but fades in and out but doesn't die. Does not feel like it's producing the power it had before the carb/tank rebuild. But it ran without dying. Said the infamous "good enough for a flight!"
Flew the next evening... all two minutes of it. Should have listened to my conscience thinking it's not acting like it should at WOT. Flying lower, powering/pulling up gently, engine dies with the wind on it's left wing along with 1/2 the runway. "Uh oh" My flying buddy watches as I wing over into the wind with the sound of silence and nature... head for the field, below tree tops and between two alders, rudder over into the landing area (not runway ha ha)- going too fast... performed two hard fast skids - one left one right. Touched down with a little bounce.... SOOOOOO lucky. I was certain my beloved 73" laser was going to become part of the forest.

Back to square one. Ran the engine on the ground and it doesn't want to leave past the mid range again. open up the HSN a bit and it did the same. Idles like a champ. Guessing it gets warm and leans out, but I cannot seem to figure out why! I was very meticulous and clean when I rebuilt the carb with the gaskets only. It seems as if the inlet needle is not opening enough or there is a blockage in the HS flow somewhere. Super frustrating when it was running great. Prior to the rebuild I also changed my tank plumbing lines + filter, new CM-6 spark plug - gapped, and the carb gasket set.

Thoughts?

 

[dhal22]

I have had carb rebuild success before (with good advice from gsn/fg members) but I'm no expert. In fact not being an expert almost forces me to mail my DA/3W in for service. That I don't mind as your engine will come back running flawlessly, which is the reason for this discussion.

 

[Bartman]

Ordered a new carb last night from DA. Should have time next weekend to play with it some more although I should figure out the comment someone made about spraying cleaner somewhere the check a check valve. Haven't tried that yet.

 

[49dimes]

I really need to change my name to "Rodney" as in "Dangerfield"....I get NO respect . lol

@Bartman I have been doing a bit of looking for you on the Bing49 carb. That carb has been a favorite on the more powerful chain saws
and guys here in the US had been getting rebuild parts from the UK. But the info I read was a bit dated "2007". Anywho...There is a guy in the United Kingdom named Gavin Carter. I discovered him on ebay when I was trying to rebuild my DL50 in late 2015. Guys think he is another "Ring" manufacturer which is true but he is a lot more than that. He is actually an engine restoration guy. He may be able to help you out with your Bing 49 carb. Here is his facebook page https://www.facebook.com/gavin.carter.395

@AKNick You described "Textbook" what problems a stuck or faulty HS jet check-valve can cause.

 

[Bartman]

Sorry if that was you that made that suggestion and I ignored it! Well, I heard it and remembered it but forgot it was you!

That carb will be a paper weight in a few days. Unless the one check valve is found to be stuck open or closed in which case I'll give it another try. I'll also look up Gavin, it's weird that the chain saw guys love those carbs!

 

[49dimes]

They do I guess. There is one thing you said that makes me believe the issue is in the "pump side" of the carb or air leak in the pulse passages , carb block or fuel inlet nipple. "fuel flows back out". Once these carbs are primed they should remain that way unless air is getting in somewhere. The fuel nipple on the carb itself could be your culprit. Guys will rotate them for install reasons only to have an air leak develop.

 

[AKNick]

@AKNick You described "Textbook" what problems a stuck or faulty HS jet check-valve can cause.

There is one thing you said that makes me believe the issue is in the "pump side" of the carb or air leak in the pulse passages , carb block or fuel inlet nipple. "fuel flows back out". Once these carbs are primed they should remain that way unless air is getting in somewhere. The fuel nipple on the carb itself could be your culprit. Guys will rotate them for install reasons only to have an air leak develop.

This all makes sense to me with my issue as well. At one point with the cowl off I witnessed a loss of prime from the carb as it sat untouched. Maybe 1/2" of air from the carb inlet visible through the tubing. I'm guessing if the HS flapper check valve is not seating like it should, allowing air to be introduced through siphoning and thus loosing prime?
I used the same style neoprene looking (black) gasket DA used, and not the tan fiber one. Is there a big difference?

IDLE:

WOT:

 

[49dimes]

Yes you can lose prime through the HS check. As far as the gasket material used the black is for our engines ( higher rpm and gasoline fuel) the tan for lower rpm engines running "heavy fuels". Thanks for posting up that video. Will answer a lot of questions guys have. You da Man . The "flow diagrams" are nice too!

 

[AKNick]

Yes you can lose prime through the HS check. As far as the gasket material used the black is for our engines ( higher rpm and gasoline fuel) the tan for lower rpm engines running "heavy fuels". Thanks for posting up that video. Will answer a lot of questions guys have. You da Man . The "flow diagrams" are nice too!

That little video has over a million views for a reason We'll take what we can get! That's for sure!

 

[Bartman]

File under "Updates"

The new carb is on and the engine is running but I'm not sure if it's been my technique or the new carb. Previously I was flipping the prop to prime the engine with the choke closed but wasn't flipping it quickly as I am now to ensure the prime charge is being sucked into the cylinder. I'm also using more of an 8-3-1 sequence to get more prime, fewer flips to circulate it and then ignition on to light it off....it's working but there's no low end, it just dies and won't recover on the way down. I'm going to pull the engine again and check to make sure the intake gasket/isolator is not leaking, I might put the old carb back on to see if technique has anything to do with that one not working but I can't keep dicking with this thing and might have to park it for a few months and work on other stuff.

Stay tuned, or don't, it's just me losing my mind over here!