fitting Stihl 088 carb to YD80 -pulse line?

[kiwigasbikes]

Hi Brand new Stu here from New Zealand. Ive been around motorized bikes for many years. But not modifying them. Ive searched the forum for my answer. I learned a whole lot of new stuff but not what I need to know.
I bought a carb for a 088 Stihl chainsaw hoping that it will work well on my small alloy framed MTB. when you see my video
View: https://youtube.com/shorts/yqZ-XRnnVbs you will see why I cant fit the std carb. also, after breaking in, Ill be porting and balancing, better bearings and seals, crank stuffing so I want a very tunable carb.
MY ISSUE- I cant identify the pulse port on the carb. on the gasket face there is a drilling, but with my jeweler's loop I can see that the hole is blind. Ive tested it with air too. The two brass tubes are obviously fuel in and return. maybe that tiny drilling in the bottom of the venturi is something to do with it? It's on the down wind side of the butterfly. where is my pulse port? I cant find any info online that will guide me.
edit: Oh and having gravity feel should mean that the primer bulb and return line are not needed. Right?

 

[Johnny_]

Hi Brand new Stu here from New Zealand. Ive been around motorized bikes for many years. But not modifying them. Ive searched the forum for my answer. I learned a whole lot of new stuff but not what I need to know.
I bought a carb for a 088 Stihl chainsaw hoping that it will work well on my small alloy framed MTB. when you see my video
View: https://youtube.com/shorts/yqZ-XRnnVbs you will see why I cant fit the std carb. also, after breaking in, Ill be porting and balancing, better bearings and seals, crank stuffing so I want a very tunable carb.
MY ISSUE- I cant identify the pulse port on the carb. on the gasket face there is a drilling, but with my jeweler's loop I can see that the hole is blind. Ive tested it with air too. The two brass tubes are obviously fuel in and return. maybe that tiny drilling in the bottom of the venturi is something to do with it? It's on the down wind side of the butterfly. where is my pulse port? I cant find any info online that will guide me.
edit: Oh and having gravity feel should mean that the primer bulb and return line are not needed. Right?View attachment 228791

Ok so.... that hole in the face of the carb IS the pulse port. It probably takes a turn that you can't see, up to the diaphragm in the top (or bottom, depending on how you look at it) of the carb. And it's not made to have air flow constantly through it, so you can't check just by blowing. It's supposed to wiggle the diaphragm back and forth, so just a tiny amount of air flows back and forth each time.
That hole down wind of the butterfly is your idle jet. It kicks in when the throttle is all the way, or very nearly, closed. Air flows over it from that notch in the butterfly, and pulls the fuel out. It is adjusted by the needle marked "L".
Hope at least some of that makes sense?

And I recall seeing on the "other forum" (I can hear Damien growling) a thread on doing a conversion with a carb like that, I'll see if I can find it for ya.

 

[Johnny_]

Ok so.... that hole in the face of the carb IS the pulse port. It probably takes a turn that you can't see, up to the diaphragm in the top (or bottom, depending on how you look at it) of the carb. And it's not made to have air flow constantly through it, so you can't check just by blowing. It's supposed to wiggle the diaphragm back and forth, so just a tiny amount of air flows back and forth each time.
That hole down wind of the butterfly is your idle jet. It kicks in when the throttle is all the way, or very nearly, closed. Air flows over it from that notch in the butterfly, and pulls the fuel out. It is adjusted by the needle marked "L".
Hope at least some of that makes sense?

And I recall seeing on the "other forum" (I can hear Damien growling) a thread on doing a conversion with a carb like that, I'll see if I can find it for ya.

Here ya are.

Stihi Carb

Seems experimenting with carbs is a fun pass time for me. Having been in the small engine trade am well versed on Walbro and Tillotson carbs. Now that the Chinese have started making clone chainsaw parts I decided to gamble 15.95 shipped on a carb for an 041 Stihl. Seemed a good choice as the...

motorbicycling.com

 

[Chainlube]

Hi Brand new Stu here from New Zealand. Ive been around motorized bikes for many years. But not modifying them. Ive searched the forum for my answer. I learned a whole lot of new stuff but not what I need to know.
I bought a carb for a 088 Stihl chainsaw hoping that it will work well on my small alloy framed MTB. when you see my video
View: https://youtube.com/shorts/yqZ-XRnnVbs you will see why I cant fit the std carb. also, after breaking in, Ill be porting and balancing, better bearings and seals, crank stuffing so I want a very tunable carb.
MY ISSUE- I cant identify the pulse port on the carb. on the gasket face there is a drilling, but with my jeweler's loop I can see that the hole is blind. Ive tested it with air too. The two brass tubes are obviously fuel in and return. maybe that tiny drilling in the bottom of the venturi is something to do with it? It's on the down wind side of the butterfly. where is my pulse port? I cant find any info online that will guide me.
edit: Oh and having gravity feel should mean that the primer bulb and return line are not needed. Right?View attachment 228791

Need a couple more pictures.

 

[kiwigasbikes]

Here ya are.

Stihi Carb

Seems experimenting with carbs is a fun pass time for me. Having been in the small engine trade am well versed on Walbro and Tillotson carbs. Now that the Chinese have started making clone chainsaw parts I decided to gamble 15.95 shipped on a carb for an 041 Stihl. Seemed a good choice as the...

motorbicycling.com

That is awesome info- thanks so much. but with a headtorch and jewellers loop I can clearly see that the pulse port hole goes nowhere !? im now stripping the brand new carb to investigate. ( I know that we both know what we are talking about- but Im looking at it and its a blind hole! )

 

[Johnny_]

I know that we both know what we are talking about

Wrong! Apparently I don't. I had one of those carbs sitting in pieces in the garage and I looked at it while I was out there today. You're right, on that specific carb that passage doesn't go anywhere. Looks to me like the pulse port might be dead center on the venturi, behind the throttle plate. Only place I can see. In which case you wouldn't have to worry about it at all.

 

[Johnny_]

headtorch

*headlamp.
And the thing you hold in your hand is a FLASHLIGHT.

 

[kiwigasbikes]

Wrong! Apparently I don't. I had one of those carbs sitting in pieces in the garage and I looked at it while I was out there today. You're right, on that specific carb that passage doesn't go anywhere. Looks to me like the pulse port might be dead center on the venturi, behind the throttle plate. Only place I can see. In which case you wouldn't have to worry about it at all.

Ahh- but its on the upwind side of the butterfy- so how can it pulse at idle?

 

[kiwigasbikes]

*headlamp.
And the thing you hold in your hand is a FLASHLIGHT.

Wot!- even if you dont flash it? - Uggh- Murican is so hard to learn.

 

[Johnny_]

Ahh- but its on the upwind side of the butterfy- so how can it pulse at idle?

Air is still flowing through there. In addition to the notch, the butterfly is never fully closed.
And now we know for sure that the pulse hole is NOT in the gasket face, and it is NOT an exterior connection, so it MUST be in the carb throat lol.