Husky 262, carb options, 199 instead for 87

[drf256]

120 vs 87
Venturi 15.08 vs 16.66 mm on Walbro home page....
Throttle plate 17.4 vs 19mm

So, theoretically, if one could grind the Venturi of the 120 out to 16.66, it could flow almost the same. Whether or not one would get enough speed increase to have the Venturi function is another question.

If two carbs have different bores but the same Venturi diameter, does the larger bore carb still flow more if the Venturi is the bottle neck?

We all know poisselle's law of laminar flow, where the biggest limit to flow is the tube diameter as the denominator to the 4th power. The length of the tube is much less restictive.

 

[drf256]

I'm sure the pressure drop needed to pull fuel has to do with those ratios.

How does one pop the fuel nozzLe out for playing with the bore?

 

[drf256]

This thread doesn't seem complete without a pic of the 87 vs the 120.




Sent from my iPad using Tapatalk

 

[Tor R]

So, theoretically, if one could grind the Venturi of the 120 out to 16.66, it could flow almost the same. Whether or not one would get enough speed increase to have the Venturi function is another question.

If two carbs have different bores but the same Venturi diameter, does the larger bore carb still flow more if the Venturi is the bottle neck?

We all know poisselle's law of laminar flow, where the biggest limit to flow is the tube diameter as the denominator to the 4th power. The length of the tube is much less restictive.

this is way over my knowledge.
The way I see is that venturi is 1.6mm bigger and flap is 1.6mm bigger on HDA 87 vs 120.
I dont know if the jets are different though.
The same goes to 199, I dont know if it has gains over 87 carb

 

[Tor R]

This thread doesn't seem complete without a pic of the 87 vs the 120.

View attachment 16618View attachment 16619

agree, I quoted you and placed it in the first post

 

[super3]

How does one pop the fuel nozzLe out for playing with the bore?

Push it thru into the bore. It's a light press fit.

 

[Tor R]

@super3
Most of those carbs have a tap inside the bore to put the choke flap in reset position, how do you solve this issue when you drill an 120 carb for 87 butterflys?

 

[super3]

Ball mill the divot in the choke shaft for the ball to sit into a bit deeper when in the open position.

 

[Wagnerwerks]

i am happy you got one 87, I called around a bit to check if I could get one for you with no luck. Yes, 87 carb have almost no venturi!

bodies have same dimension so changing shaft would work, there are some issues changing shaft though.
199 has accelerator pump, not sure if 120 carb have throttle shaft to support the pump, on an 198 it doesnt mather since it doesnt have acc pump.
The choke rotation has different rotation on those 199 vs 87/120, there is choke stopper in carb house. I did an 120 rebuild with 98 shafts for one of my 242 projects, thats where I spot those choke stoppers.
The only way I see is to dremmel of that stopper.

Later today I see if I can fix the throttle connections, hopefully it will be an easy fix

Do you know if the 175 has an acc pump? I found this thread while working on the same swap.

 

[Wagnerwerks]

Do you know if the 175 has an acc pump? I found this thread while working on the same swap.

It does. So other than drilling a vent hole in the cover, what's the fix for these? I want to put one on my fresh 254 but I want to make sure it's right first.

Edit. Found it. Just needs a rebuild with proper kit. Easy peasy...

 

[Tor R]

It does. So other than drilling a vent hole in the cover, what's the fix for these? I want to put one on my fresh 254 but I want to make sure it's right first.

Edit. Found it. Just needs a rebuild with proper kit. Easy peasy...

you can just another top cover from another carb who has the hole in the cover.
What modd will you do on the 254 plastic intake?

 

[Wagnerwerks]

I'm not sure yet. I'm going to try to get time to do it this weekend. I hate to hack away because it's a pretty nice saw.

 

[Wagnerwerks]

how about putting the throttle and choke shafts from one of the hda 120 or 144 carbs in

I went this route and ground out the tabs in the housing. The ball detent fit right in my 175 body so that should work fine. We'll see. I had to take a tiny bit off of the choke flap. I used a burr to cut a dent in the throttle shaft to run the accelerator pump.

 

[Tor R]

I'm not sure yet. I'm going to try to get time to do it this weekend. I hate to hack away because it's a pretty nice saw.

I went for HDA-120 on my 254's, it has bigger venturi compared to the original 35 carb.
If I remember correct the 174/175/190/191/198/199/87 butterfly is bigger then the hole in the 254 intake block by quite a bit margin also, not much meat left to the impulse channel

 

[Wagnerwerks]

It took a little grinding but I just left a little extra meat on the impulse area.

 

[SawTroll]

So, theoretically, if one could grind the Venturi of the 120 out to 16.66, it could flow almost the same. Whether or not one would get enough speed increase to have the Venturi function is another question.

If two carbs have different bores but the same Venturi diameter, does the larger bore carb still flow more if the Venturi is the bottle neck?

We all know poisselle's law of laminar flow, where the biggest limit to flow is the tube diameter as the denominator to the 4th power. The length of the tube is much less restictive.

That's a very good question, that I don't have an answer to - and there are other restrictions (and not) in play as well. Some times a change in the size of the cutout in the butterflies will make surprising differences according to my brother, but I'm no expert (he is, but not available)...

As I understand it, it is about eliminating the most severe choke point first (often the carb venturi and/or muffler outlet), and then go from there. Cylinder porting often is about getting the most "timearea" out of as little duration as possible (=wide ports, not tall ones, and sufficient blowdown) - but again I'm not the expert, so this is just a hint.

The cylinders that can gain the most from porting usually are the quads that have sufficient material to work with for widening the ports - not because they a quads, but because the divider around the middle allows for a larger total width of the upper transfers, without the rings snagging.

Lack of sufficient material to work with at crucial points is detrimental to the potensial of many cylinders.

This is how I understand it after a lot of reading and listening on the subject, it isn't carved in stone as the eternal truth.

 

[Tor R]

It took a little grinding but I just left a little extra meat on the impulse area.

i did study the intake block, knew it was a very tight call.
I have to many plans going on but I had in mind one day to make a new intake block who fit HdA 87 size carb better instead of having a very thin wall impulse channel, but with me it can go ages before I get so far lol

 

[cgraham1]

Mastermind did a thread on this a while back...

http://opeforum.com/threads/making-a-walbro-hda-199-fit-on-a-262xp.3475/

 

[SawTroll]

Mastermind did a thread on this a while back...

http://opeforum.com/threads/making-a-walbro-hda-199-fit-on-a-262xp.3475/

This is not directed at him in particular, but it isn't surprising that people that are payed to port saws are negative to alternative (larger) or modified carbs, as if they were positive to it their costumers would want it, making their job more complicated.

I have seen a lot of statements that a larger carb doesn't help trough the years - but I happen to know it often isn't true, provided the saw is opened enough at other "choke points" as well.

 

[drf256]

I have seen a lot of statements that a larger carb doesn't help trough the years - but I happen to know it often isn't true, provided the saw is opened enough at other "choke points" as well.

Exactly. On a stock 262, there is little difference between the 120/144 and the 87. On a ported one, I've seen the difference first hand.