Tillotson HS carb experts

[fossil]

i have a Tillotson HS-176 carb with governor that wants to go lean at full throttle. It starts out four stroking and moves to a lean condition after a second or two.

Here's what I know

The governor is blocked off.
The throttle shaft is not worn
The carb has been tried on two saws which have both been pressure and vac checked and both are good
The saws run fine the the 176's ungoverned brother, the 168.
New kit in the carb didn't help.
The carb was cleaned several times with a US cleaner.

Any suggestions would be appreciated.

 

[paragonbuilder]

Have you cleaned the jets manually. Sometimes that crusty stuff just don’t want to let go...
Or let it sit in some fix it fuel overnight.
Or both at this point...

 

[fossil]

@paragonbuilder

I haven't cleaned the jets but it has sat in fuel for awhile and in some Sea Foam for a week.

 

[Lightning Performance]

Clogged feed port to the flood jet. Likely black death. High pressure air might move it. Next step is to drill the port and replace the welch plug.

 

[fossil]

Clogged feed port to the flood jet. Likely black death. High pressure air might move it. Next step is to drill the port and replace the welch plug.

Would the clogged feed port be the passage under the end of the high speed needle?

 

[Lightning Performance]

Idk. Just working from my head. Not any one carb. Someone will be along shortly to answer that for you, I'm sure. GL

 

[paragonbuilder]

@paragonbuilder

I haven't cleaned the jets but it has sat in fuel for awhile and in some Sea Foam for a week.

At this point With it being stubborn I’d tear it down completely and run my micro drills thru all the passages.

 

[paragonbuilder]

Clogged feed port to the flood jet. Likely black death. High pressure air might move it. Next step is to drill the port and replace the welch plug.

Ken, what is Black Death?

 

[Lightning Performance]

Dead fuel, stale two stroke oil and melted black fuel line.

Check the bottom of an old outboard boat fuel tank.

 

[hotshot]

Not an expert, but have worked over a hundred of the HS series. About as bullet proof as a carb can be designed, if the fuel supply is kept clean.

I know you ran that carb on other saws, but double check your impulse hole in the very top gasket of that 4200 or 5200 Poulan to make sure it’s punched in alignment with the carb face flange impulse hole, not smashed off to one side, & is punched big enough to not partially block it. You can’t use that skinny ass intake gasket supplied in the carb kit either, always make a new full sized 5300-19082 gasket.

Also check the black plastic heat isolator below it, to make sure it’s got no cracks & the transfer channel is clean. Run a pipe cleaner soaked with solvent/cleaner into the impulse hole down into the crankcase, through the reed plate.

Did you test the main nozzle check valve with a short piece of tubing?...just use your mouth for pressure/vacuum. If that nitrile flapper valve is shriveled up or folded, it could be partially blocking the main jet. Flow is up through it, then checks on vacuum...as you know.

I would go ahead & replace the main nozzle at this point with a new one, as you can’t tell if it’s restricted w/o replacing it. Just remember to remove the H adj screw before you punch the old nozzle through.

Lucky that parts are still available as I just bought/replaced the diaphragms, nozzles, throttle & choke shafts on two sister HS 168 last week. Tillotson dealer VE Petersen’s in Ohio had all of the parts...although I got the last throttle shafts available until they replenish in August!

 

[Lightning Performance]

There you go. Someone in the know and Welcome to OPE.

 

[fossil]

Not an expert, but have worked over a hundred of the HS series. About as bullet proof as a carb can be designed, if the fuel supply is kept clean.

I know you ran that carb on other saws, but double check your impulse hole in the very top gasket of that 4200 or 5200 Poulan to make sure it’s punched in alignment with the carb face flange impulse hole, not smashed off to one side, & is punched big enough to not partially block it. You can’t use that skinny ass intake gasket supplied in the carb kit either, always make a new full sized 5300-19082 gasket.

Also check the black plastic heat isolator below it, to make sure it’s got no cracks & the transfer channel is clean. Run a pipe cleaner soaked with solvent/cleaner into the impulse hole down into the crankcase, through the reed plate.

Did you test the main nozzle check valve with a short piece of tubing?...just use your mouth for pressure/vacuum. If that nitrile flapper valve is shriveled up or folded, it could be partially blocking the main jet. Flow is up through it, then checks on vacuum...as you know.

I would go ahead & replace the main nozzle at this point with a new one, ad you can’t tell if it’s restricted w/o replacing it. Just remember to remove the H adj screw before you punch the old nozzle through.

Lucky that parts are still available as I just bought/replaced the diaphragms, nozzles, throttle & choke shafts on two sister HS 168 last week. Tillotson dealer VE Petersen’s in Ohio had all of the parts...although I got the last throttle shafts available until they replenish in August!

Thanks Randy.

Do you have the PN for the nozzle? I was unable to locate an IPL for the 168 or 176 carbs.

 

[fossil]

Thanks guys.

I cleaned out the carb there wasn't any gunk anywhere. All passages were cleaned out with fine wire.

I did pull the nozzle this morning and it was leaking a bit when I blew back through it. I threw it in the US cleaner and it seems fine now.
I will put it back in and order a new one once I have the PN.

 

[fossil]

Apparently the main nozzle was the issue. Runs like a beaver on steroids now.

Thanks all for the input!

 

[hotshot]

Good job there! The part number is 363-528.
Think that’s the same nozzle # that MM used after that XL-925 caused him some grief a few years back on AS. I’ll send the IPL to you tomorrow in a PM from work.

Just looked again at the HS-168 carbs, and they do have checked main nozzles...can’t remember Sheite anymore. They do not have the governor though. Note that the L & H needles are fed on the same circuit too, so adjusting one will slightly impact the other.

Remember to run the L speed adjuster screw in CW snug & then back the H out CCW a couple.

Then use a small diameter fuel line to cover the supply circuit hole & suck/blow to feel the valve seat & unseat...that sounds a lot like a Stormy Daniels method.

 

[fossil]

Thanks Randy. My 5200 came with a 168 which likely replaced the 176 at one point. The 4200 and 4400 have 168's (I haven't looked at the 4400 so that's an assumption).
This problematic 176 came on my 8500. I swapped them out last year when I took the 8500 to a GTG.

Appreciate the advice and looking forward to the IPL.

 

[hotshot]

Glad to help.

A few months back I got a HS-168 in on a well traveled 4200 that had the choke lever bent off the shaft, then I noticed the throttle plate was over traveling back towards closed again. WTF? They had even busted the throttle lever stop tab off!

Some folks shouldn’t own channel locks nor needle nose pliers.

Then it failed pressure test & I found this...small crack. No doubt an unwanted bar oil injection feature! But it’s a good runner now w/new cases & it makes the wood chips fly!

 

[fossil]

Glad to help.

A few months back I got a HS-168 in on a well traveled 4200 that had the choke lever bent off the shaft, then I noticed the throttle plate was over traveling back towards closed again. WTF? They had even busted the throttle lever stop tab off!

Some folks shouldn’t own channel locks nor needle nose pliers.

Then it failed pressure test & I found this...small crack. No doubt an unwanted bar oil injection feature! But it’s a good runner now w/new cases & it makes the wood chips fly!

View attachment 117685

Some people are hard on equipment.