STIHL 038 - Tillotson HK-29a - please help!

[SimonSaysSaws]

Hello Everyone,

I have recently purchased a used a Stihl O38 AV Super. The top end appears to be in excellent shape, the piston and cylinder look excellent on inspection and the compression is about 155 psi cold. The previous owner had problems with the fuel system and carburetor so that is the focus of things here right now.

I have replaced the fuel line and the fuel pickup/filter, spark plug and thoroughly washed out the fuel tank. The carburetor is a Tillotson Hk-29a. The impulse line connects to it flush on piston-face of the carburetor. I bought a carb kit (Tillotson RK-32-HK) from my local Stihl dealer. After thorough cleaning of the carb I re-assembled using the new gaskets and needle in the kit. When I put it back together and tried to start it, I did get a few sputters and fires but mostly it was heavily flooded. I think that I didn't get the needle/seat re-installed correctly so I am now in carb tear-down round two.

I am a little baffled right now with what was supplied in the carb kit.

1. First there is what appears to be a gasket that goes between the carb and the air filter (first picture), however the inner diameter of the gasket is smaller than the diameter of the carb (by a ~2mm). Has anyone experienced this? Do I just widen the gasket somehow to match the carb inner diameter? Do I even need that gasket?
2. Second, there appears to a redundant gasket that goes on the diaphragm side of the carb. Second pic, right hand side. The one on the left is identical to what came out of the carb. Is the right one truly redundant or perhaps for a slightly different carb version? Or do I just stack the two together? Or leave it out?
3. If I can't get this carb set up, does anyone know a suitable replacement carb for this saw? My neighbour said there is a zama carb maybe?

Huge thanks to everyone here. I learn from you all every day.

 

[Mad Professor]

Do you have the metal washer and sleeve in place on intake side of carb?

Match up the gaskets/diaphragm in the order they came off. Kits may have gaskets for more than 1 model of carb.

Make sure needle and seat are in good shape and properly installed (spring, metering lever height)

The gasket is for HK42A carbs. My shop manual lists this carb for 038S. I can't remember the carb # for the plain 038. It has a smaller venturi.

A Bing 48A125A and 48A101c carbs came on 038M and will fit, rebuild kits are more expensive.

the 038 ipl has the Bin g carb and the tillotson HS tech info should help you trouble shoot

 

[ballisticdoughnut]

I've got a old Stihl parts list for the 038 it lists a HK42B?

 

[Mad Professor]

 

[a. palmer jr.]

Hello Everyone,

I have recently purchased a used a Stihl O38 AV Super. The top end appears to be in excellent shape, the piston and cylinder look excellent on inspection and the compression is about 155 psi cold. The previous owner had problems with the fuel system and carburetor so that is the focus of things here right now.

I have replaced the fuel line and the fuel pickup/filter, spark plug and thoroughly washed out the fuel tank. The carburetor is a Tillotson Hk-29a. The impulse line connects to it flush on piston-face of the carburetor. I bought a carb kit (Tillotson RK-32-HK) from my local Stihl dealer. After thorough cleaning of the carb I re-assembled using the new gaskets and needle in the kit. When I put it back together and tried to start it, I did get a few sputters and fires but mostly it was heavily flooded. I think that I didn't get the needle/seat re-installed correctly so I am now in carb tear-down round two.

I am a little baffled right now with what was supplied in the carb kit.

1. First there is what appears to be a gasket that goes between the carb and the air filter (first picture), however the inner diameter of the gasket is smaller than the diameter of the carb (by a ~2mm). Has anyone experienced this? Do I just widen the gasket somehow to match the carb inner diameter? Do I even need that gasket?
2. Second, there appears to a redundant gasket that goes on the diaphragm side of the carb. Second pic, right hand side. The one on the left is identical to what came out of the carb. Is the right one truly redundant or perhaps for a slightly different carb version? Or do I just stack the two together? Or leave it out?
3. If I can't get this carb set up, does anyone know a suitable replacement carb for this saw? My neighbour said there is a zama carb maybe?

Huge thanks to everyone here. I learn from you all every day.

I put a Bing lookalike on my 038 when my Tillotson went bad, ran great after that. I bought it on ebay for around $12, I think

 

[VincentFR]

My 038S comes with a HK42B and i don't have a gasket between carb and air filter.
I recently replace the HK42B by a HE19A => https://tillotson.ie/shop/he19a-carburetor/

 

[SimonSaysSaws]

Do you have the metal washer and sleeve in place on intake side of carb?

Match up the gaskets/diaphragm in the order they came off. Kits may have gaskets for more than 1 model of carb.

Make sure needle and seat are in good shape and properly installed (spring, metering lever height)

The gasket is for HK42A carbs. My shop manual lists this carb for 038S. I can't remember the carb # for the plain 038. It has a smaller venturi.

A Bing 48A125A and 48A101c carbs came on 038M and will fit, rebuild kits are more expensive.

the 038 ipl has the Bin g carb and the tillotson HS tech info should help you trouble shoot

Huge thank you to all. Mad Professor, yes the metal washer and sleeve are in place on intake side of carb and look good. The documents you sent help a lot, thank you.

I am making SOME progress here. The saw will start now and idle very roughly but I can't get it to accelerate without it dying. When this happens I have to let it sit for about 30-60mins before starting again, making me think its flooded. Based on this it seems like I have the high/low jets out of whack. When I re-assembled the carburetor (HK29a) I followed the Stihl manual guideline of turning both screws all the way in, and then backing them both off 1 1/4 turns.

Do you have a good logical way to sort myself through this carb set-up?

 

[cookies]

try the H needle at 3/4 of a turn out as a starting point

 

[Brushwacker]

Sounds like your passage ways may have some obstructing. I remove all the old parts that are being replaced with the kit and the adjustment screws and spray carb cleaner through all the passage ways , lightly blowing air through the passage after the carb cleaner. Some times I use seafoam or wd40 before and sometimes also after carb cleaner letting it soak to loosen up any build up or clog. I don't let regular carb cleaner soak long, might dissolve more then the crud I am trying to clean. There is a tiny hole in front of the throttle butterfly, when spraying carb cleaner opposite hole inside the carb u should see spray exiting through this ( the idle circuit where fuel is fed into the engine during idle with the throttle closed). The other side the throttle butterfly in the middle is the high speed hole, like wise spray should come out spraying the opposite hole inside. You should be able to figure which holes match up experimenting. Protect your eyes from carb cleaner when using it.

 

[rmh3481]

Check the order that the carb diaphragm and gaskets are in. On the pump side the diaphragm goes down first followed by the gasket and then the cover. On the metering side, the gasket goes down first followed by the diaphragm and then the cover. Also, check your lever height.

 

[Mad Professor]

Huge thank you to all. Mad Professor, yes the metal washer and sleeve are in place on intake side of carb and look good. The documents you sent help a lot, thank you.

I am making SOME progress here. The saw will start now and idle very roughly but I can't get it to accelerate without it dying. When this happens I have to let it sit for about 30-60mins before starting again, making me think its flooded. Based on this it seems like I have the high/low jets out of whack. When I re-assembled the carburetor (HK29a) I followed the Stihl manual guideline of turning both screws all the way in, and then backing them both off 1 1/4 turns.

Do you have a good logical way to sort myself through this carb set-up?

When it won't restart is the plug wet or dry? And does it have spark?

If it has spark and plug is dry, will a little bit of mix in the carb (1/2 of thimble) get it to pop/fire?

Sometimes hesitation off idle means the low carb setting is too lean. If you have spark and it pops with some mix try turning out the low carb screw ~1/8-1/4 turn see if that helps. Usually this won't prevent saw from at least popping if trying to start again.

If you don't have spark there could be a short in the wire from the coil to the on/off control switch (ohm meter helps here), a short in the coil wire, or a problem with the coil. Inspect those and check the coil/flywheel gap, should be ~ 0.010".

The coil wire can get pinched between the tank housing and top cover If the AV mounts are worn or the coil wire is not routed properly. Check insulation in this area.

If you have spark could still be a carb issue. Either flooded (wet plug), or not getting fuel (plug dry). If plug is dry and it pops with a little mix added, check the fuel line well when you have the carb out. Bend it back and forth to look for small cracks that are not easily seen, and also check that the tank vent is not plugged (small line from the tank housing inside carb box.with two small screws inside).

If none of the above time to go into the carb again.......

 

[cookies]

It sounds like hi is saying it will now idle but if he tries to rev it the saw floods and then if it sits a half hour it will start and idle again. To me it sounds like the needle lever is set a hair too high or the extra matching gasket in the kit was of a different thickness or even the wrong size button on the metering diaphragm. I have in the past simply adjusted the needles in further than stock settings to adjust out the over fueling from a miss set needle lever or improper thickness gasket. I start with the h needle all the way in and adjust the L side to idle well and engine revs quickly to mid throttle before fuel more delivery is required..heII some saws/carbs barely need any H side until they get to the top of their max rpmvbefore it becomes noticeable.

 

[stihltech]

I believe this carb has the plastic spacer where the inlet needle is installed. Stihl discontinued these for a reason. The plastic seat eroded as did the jet holes in the spacer. Check for correct reassembly. I no better, you would be better served by Bing a big or Zama carburetor. If you find a Bing in good shape, make sure he lever height is correct. It can be adjusted by changing the depth of the needle seat. Cured a lot of them doing this.

 

[a. palmer jr.]

The Tillotson that was on mine had a plastic piece holding the inlet lever and was worn out to the point that the lever pin wouldn't stay in place. I just didn't want to mess with fixing it so a new Bing lookalike was what I used.

 

[SimonSaysSaws]

Thanks all. The latest update on the 038S is that I got myself a Mityvac 8500 and pressure tested the carb. It won't hold pressure. I was able to make a set up with tubing to isolate the needle and seat and the needle/seat itself actually does hold pressure so I can say now that it leaking at the gasket between the carb body and the plastic spacer that holds the needle/seat. And this is the new gasket. I tried the old gasket again, it was slightly better but still leaking. The metal surface on the carb isn't in great shape despite my carb cleaner and scrubbing and I assume that is the problem. I spent three hours on this tonight at my kitchen table and I am ready to bang my head into the wall, so I think I am just going to get a new carburetor for this thing. Unless anyone thinks a ANOTHER new carb kit with a different gasket or lightly sanding the metal surface is a good idea? (I suspect it isn't)

VincentFR above mentioned a Tillotson HE19a as a replacement. My stihl dealer couldn't get that for me so I will have to try some online places for it.
These Bing look-alike carbs that people are talking about, pardon my stupidity here, how do I find one of these? Is there a decent cross reference guide for these? Just search eBay for a carb for a 038 Av Super?

Simon

 

[cookies]

can you set the carb body on a section of sandpaper on a flat surface to deck it ?

 

[Mad Professor]

Thanks all. The latest update on the 038S is that I got myself a Mityvac 8500 and pressure tested the carb. It won't hold pressure. I was able to make a set up with tubing to isolate the needle and seat and the needle/seat itself actually does hold pressure so I can say now that it leaking at the gasket between the carb body and the plastic spacer that holds the needle/seat. And this is the new gasket. I tried the old gasket again, it was slightly better but still leaking. The metal surface on the carb isn't in great shape despite my carb cleaner and scrubbing and I assume that is the problem. I spent three hours on this tonight at my kitchen table and I am ready to bang my head into the wall, so I think I am just going to get a new carburetor for this thing. Unless anyone thinks a ANOTHER new carb kit with a different gasket or lightly sanding the metal surface is a good idea? (I suspect it isn't)

VincentFR above mentioned a Tillotson HE19a as a replacement. My stihl dealer couldn't get that for me so I will have to try some online places for it.
These Bing look-alike carbs that people are talking about, pardon my stupidity here, how do I find one of these? Is there a decent cross reference guide for these? Just search eBay for a carb for a 038 Av Super?

Simon

https://vepetersen.com/ tillotson USA distributor

1-800-537-6212

HE19a , Out of stock, expected in April $34 USD + shipping

From Ireland, real deal not Chi-Com

 

[Patrick1903]

@SimonSaysSaws any luck yet with a replacement carb?

 

[sledhead34]

Sounds like your passage ways may have some obstructing. I remove all the old parts that are being replaced with the kit and the adjustment screws and spray carb cleaner through all the passage ways , lightly blowing air through the passage after the carb cleaner. Some times I use seafoam or wd40 before and sometimes also after carb cleaner letting it soak to loosen up any build up or clog. I don't let regular carb cleaner soak long, might dissolve more then the crud I am trying to clean. There is a tiny hole in front of the throttle butterfly, when spraying carb cleaner opposite hole inside the carb u should see spray exiting through this ( the idle circuit where fuel is fed into the engine during idle with the throttle closed). The other side the throttle butterfly in the middle is the high speed hole, like wise spray should come out spraying the opposite hole inside. You should be able to figure which holes match up experimenting. Protect your eyes from carb cleaner when using it.

its critical to get the fuel metering correct at the needle and seat and spring holding pressure when rebuilding the carb and diaphragm engaged .one screw up here and its bananas set that high speed 3/4 out and low speed the same,make sure you make or replace gasket with factory style gaskets next to impulse side of the cylinder and carb ,these leather punch pliers are the cat ass for making gaskets harbor freight

 

[stihltech]

As far as the original carburetor with the plastic plate THROW IT!. The plate warps and wears which is why Stihl discontinued them. Yes you will need to buy from an outside source for the Bing. Too bad I liked them the best.