HDA 181 Nipple?

[Gamma Woods]

I've got a Shinny 757 with an HDA 181 carb in it and it's got a bit of an issue. Takes 3 turns out on the jets to get it running right. Doesn't lean out or stumble, doesn't flood and doesn't have any performance issues at all with that many turns out, but it's annoying me. Carb has been well cleaned (USC, then carb cleaner spray shows all passages are open), needle is clean and properly shaped, carb holds pressure (but doesn't pop off). Saw has no leaks and fuel lines/tank vent/impulse are good, tried raising the lever a bit higher (out of spec now) and didn't make a difference. I'm wondering if the no-pop off (I stopped trying to pop off at 25 PSI, more than I like to put through a carb) could be related, maybe trimming the spring a bit.

But there's something else I noticed: the diaphragm I put in the carb doesn't have much of a protrusion, it's pretty much flat, and can't remember if the old one was like this or not. The HDA series wants the lever set to the outer edge, so part of me thinks it's correct and supposed to be flat (and my problem lies elsewhere), plus the images of the rebuild kits seem to be tiny nipped, but I wanted to ask around first. Does anyone know if the HDA diaphragms are supposed to be nippleless?

 

[pioneerguy600]

I have only seen diaphragms for the HDA that had the more or less flat button that rests on the top of the metering lever. If the kit did have the longer protrusion with the groove in it then the metering lever would have a fork in the top to accept the longer protrusion.

 

[rmh3481]

Didnt the HDA start out with a 'hook to' style lever? I would buy the current Walbro HDA kit from your local Shindaiwa Dealer and go from there. Raising the lever just ever so slightly will richen it up if that is what you think it needs. You need a good 4 stroke to make sure it wont heat up under load.