Poulan 4900 carb question

[MarkPrice]

I have a a 4900 and I am trying to find a new Carb for it.
From the online parts diagrams there are two Tillotson carbs listed: HS-168A and HS-176A.
What is the difference and can they be interchanged?

 

[BlackSmith]

@Cut4fun will probably know Mark, and welcome to the house...

 

[MarkPrice]

Thanks BlackSmith

 

[MasterBlaster]

Welcome to the TreeHouse, Mark!

 

[MarkPrice]

Thanks for letting me in.

Hello All

 

[BlackSmith]

Both carbs use the same rebuild kit and gasket kit but there may be a difference in mounting holes or linkage. Do you have the old carb..?

 

[MarkPrice]

Yes, The saw sat in the basement for about 20 years and the tank HAD gas in it, now it is liquid gunk!!
If I get the tank cleaned out I might try to rebuild the carb, the P & C look great.

The saw was the first one I started logging with out in Montana back in 1980. I ran it for about 10 years before I switched to buying Stihls.
I would like to clean it up, probably just set it on a shelf but I like them all to run.

A new carb might be a lot easier and cheaper in the long run considering the how much gunk might be in the old carb.

Looks like the HS-168A is going to be hard to find but the HS-176A is still available.

 

[Magnus]

I don't think you need a hole carb. Have a look first and see what is bad.
Usually they clean out nicely.

Well I used Berrymans Chem-Dip to clean out the gas tank and wow did it work great.
Based on the results I ordered a carb rebuild kit.
Now I just have to wait till it arrives then put the stripped carb in the utlra sound tank and see if I can get the saw running. I'll let you all know how it goes..

From what I could find out the difference between the two carbs (Tillotson HS-168A and HS-176A) seems to be the 176A has a governor valve and the 168A does not, does that sound right?

 

[Magnus]

Ultra sonic cleaner will loosen up all gunk in every channel inside carb. If you do that get an RK Kit so you can open/replace Welch plug. Under this is a filter that usually get stuffed with crap after a good bath or if they blow crap in to carb,

 

[Tree09]

Good tip there

 

[Cobleskill]

Do you use sealer when putting Welch plugs in ?

 

[pantheraba]

Good discussion...it led me to this video....addresses/avoids the sealant question....good demo of how Welch plugs work.

 

[Magnus]

Do you use sealer when putting Welch plugs in ?

No, not if its new and I get it in correct.
Yes, if I reuse old one. I seal it with epoxy glue.

 

[Bart]

I was chasing this very issue a while ago. Seemed that gas tolerant epoxies cleaned up with alcohol, so hence were vulnerable to most normal pump gas due to the ethanol content. I did a Marc-Antoine MS200T leaking accelerator pump mod and my JB weld rubbered up after a while. I reapplied and knock on wood so far. I'm pretty strict about alcohol free premix, maybe that's keeping the jb weld alive.

What epoxy is your trusted friend to use? thanks

Also, edit, what are your thoughts on the nail polish approach in the Stihl manuals? or Briggs manuals,, can't remember.

 

[Magnus]

I tried lots of fuel and heat graded epoxy with alcohol and various alcohols, no problem.
I think the other stuff in you gas is the issue, acids, benzene etc. Its what I figured out testing here.

I run Aspen as most do here, no fat acids or benzene, nothing aggressive. So I have no issues with fuel system at all unless its wear and tear on the parts.
Dissolved lines, membranes clogged up carbs... I miss out on all that. Thankfully I have some customers that still use gas from station. If not I probably forget more, faster...

 

[Magnus]

I used nail polish/paint sometimes to seal if I was unsure it will hold. Now its mostly epoxy and reused welsh plugs.

 

[Bart]

Last time I used nail polish on the welsh by the idle jet passages chamber I found it peeling later on. Which epoxy do you use?

Do you think its worth the pain to do the O ring in the 200T accel pump? $140 Canadian for a new carb.

 

[Tree09]

Acetone is far cheaper when you buy it from a hardware store vs nail polish remover!

 

[MasterBlaster]

But you can look pretty in your shop!!!

 

[Bart]

Butch, did you realize your avatar could be construed as doing a rim shot after your one-liner?

 

[MasterBlaster]

 

[Steve Mack]

I didn't quite get that at first.

 

[Magnus]

Last time I used nail polish on the welsh by the idle jet passages chamber I found it peeling later on. Which epoxy do you use?

Do you think its worth the pain to do the O ring in the 200T accel pump? $140 Canadian for a new carb.

I use several depending on what I do. Liquid epoxy not so much but on carbs I do.
I get it in autoshop store, cheep, its the application thats important more than the brand of epoxy.
Clean and then sort of twirl it so it bites, nut sit on top of surface.

No, it runs better with system plugged IMO.

 

[Bart]

Rim shot is a drummer thing. Ba-dap-splash after the joke punch line or some such. I used to be in a band and grew up with my drummer buddy. Next trivia - what's a paradiddle? Hint LRLLRLRR don't try to pronounce it. My buddy ended up a professional jazz drummer to this day. Paths in life.

Thanks for the info Magnus. I've got some Loctite gas tank patch epoxy I'll use next time round. I was particular about getting to stick like the twirl thing you mentioned.

auto spell switched Loctite to lactate 5 times on me.. quietly when you look somewhere else just when you think you commanded autocorrect to leave your typing alone!!!!

 

[Magnus]

With some training and experience you can do wonders with cheaper stuff.
Heating it to 50c after it started harden make it harder. More heat harder epoxy. But it has disadvantages too as everything..