Husky 238 Needs Help

[Agrarian]

This one has me stumped. My 1987 Husky 238 that I fixed up from an ebay win is giving me headaches. Basically it will not idle at anything less than ~3200 rpm but it is spec'ed to idle at 2700. And when I give it full throttle, it makes a lot of smoke (I run 40:1 93 octane gas with Husky premium oil) like it is too rich and the sparkplug is very black. In addition, the high adjust screw seems to make little difference, even when screwed all the way in.

I did a top end rebuild using the original piston and cylinder. I replaced the crankshaft seals, ring, wrist pin bearing, gaskets, rebuilt the carb, replaced the the air filter, gas tank breather, the gas line, the gas filter and added a new NGK plug. Everything else was cleaned up to a fairly spotless state.

It has 165psi compression. I have pressure and vacuum tested it three times and it always holds 10psi / 10"h2o for minutes. And I do pull the starter cord while doing this.

I have replaced the carb with a known good one and replaced both the coil and the electronic module with known good ones. Neither helped.

I thought I was on to something when I found the carb pop-off pressure was 20+ pounds on the original carb but fixing that did not change anything. It uses a Walbro HDA-34A carb, and I have adjusted the metering lever so that it is flush with the carb body. And as I said above, another carb acts the same way.

I visually checked the manifold block and it looks ok. I plan to do a pressure test with the block in place just to be sure.

I removed the gas filter and did a pressure test on the gas line to the carb and it was fine. I ran it without an air filter - no difference. I ran it with the gas cap cracked open - no difference.

So, as I said, I am stumped. What am I missing?

 

[gomoto69]

Possible that flywheel key is sheared and/or missing? Just guessing because you seem to have covered just about everything. Maybe fuel somehow got contaminated?

 

[RedFir Down]

I plan to do a pressure test with the block in place just to be sure.

This may be creating an air leak, causing your troubles.
Let us know what happens, Im curious.

 

[HiOctane]

Your 238 should have a governor on it,that can make your saw run rich at WOT ,thats why closing HI doesnt seem to make difference.You should not fell the richness in the cut .At idle @ 3200 ,does your saw seems to run too rich or starving for gas ?Does the idle seems steady ?

 

[Agrarian]

Possible that flywheel key is sheared and/or missing? Just guessing because you seem to have covered just about everything. Maybe fuel somehow got contaminated?

I thought of that too after I wrote this thread. Got all excited because it seemed it could explain a lot of things. But no, the key was in place and the flywheel was tight.

I'm going to have to use the rope in the chamber trick to stop the crank from turning when torquing the flywheel nut from now on. I ended up snapping off a small piece of the lowest cooling fin on the cylinder with my screwdriver wedge.

 

[Agrarian]

Your 238 should have a governor on it,that can make your saw run rich at WOT ,thats why closing HI doesnt seem to make difference.You should not fell the richness in the cut .At idle @ 3200 ,does your saw seems to run too rich or starving for gas ?Does the idle seems steady ?

Yes, the idle seems fairly steady but at that speed the chain is turning (700 rpm above spec).

I was not aware of a governor on these saws - how is it implemented?

I just finished rebuilding 3 246's and one 242, all of which behaved normally as far as the high speed adjust and all are built on the same crankcase, same coil and use similar carbs. On these other saws, I could find the sweet spot on the high adjust but I can't do that on this one. One difference in these saws compared to the 238 is that they use a different carb that has a pressed in main jet/check valve whereas the Walbro 34a uses a capillary screen check valve. I believe that should only potentially cause problems when transitioning from full throttle to idle which is not my problem.

My guess is that it is too rich based on the amount of smoke at full throttle and the oil weeping from the muffler. With the tach on it, when I give it full throttle initially it goes to about 13K but then almost immediatly goes down to about 9K and sound really labored with lots of smoke.

Please keep the ideas coming guys because I am flummoxed.

 

[Agrarian]

Possible that flywheel key is sheared and/or missing? Just guessing because you seem to have covered just about everything. Maybe fuel somehow got contaminated?

I just made up this fuel yesterday with a fresh bottle of Husky oil. I want to say that it is not likely.

 

[gomoto69]

Sounds like carb issue but replacing with a known good one all but eliminates that. I was just going to suggest trying another coil but re-read your post and you've already done that! Have you evwr had this saw run right, or was it a basket case when u bought it? If so, maybe it has the wrong flywheel or something, timing wrong? I replaced a crankshaft in my kx250 years ago, wouldn't run after. Finally discovered flywheel keyway was in the wrong spot.

 

[Agrarian]

Sounds like carb issue but replacing with a known good one all but eliminates that. I was just going to suggest trying another coil but re-read your post and you've already done that! Have you evwr had this saw run right, or was it a basket case when u bought it? If so, maybe it has the wrong flywheel or something, timing wrong? I replaced a crankshaft in my kx250 years ago, wouldn't run after. Finally discovered flywheel keyway was in the wrong spot.

I agree about the carb sounding like the problem but durned if I can figure it out. Since other carbs do the same thing I was thinking that this could be a carb setup issue. So I have started playing with the metering lever height to see if it makes any difference. So far I have only tested it being set 0.010" too low thinking too much gas was being forced into it but that made no difference. Next I am going to try setting it 0.010 too high - maybe gas isn't filling the high metering circuit.

This was a basket case when I got it and I have never had it running correctly but it only required an upper end rebuild. But taking your advice, I checked the part number stamped on the flywheel and it is for a 238. Cross off another possibility.

 

[gomoto69]

Running out of things to cross off bud! I was thinking the same thing on the metering height adjustment, i know some carbs call for a height below flush, but i couldn't find a spec for your carb anywhere. I might throw another plug in it, every once in a while new plgs are bad, longshot at best! Do you have another saw you can try your fuel in? Again, longshot but bad fuel from the pump has been known to happen. Maybe unhook your kill switch?

 

[Agrarian]

The Walbro HDA carbs are set flush with the body of the carb which has always worked well for me on my other saws which all use HDA's. Setting the metering lever 0.010 lower did not improve it either. What is strange is that the saw has its best high speed performance when the high speed needle is all the way in (closed) but still acts like it is rich.

In some developing news, I decided to rebuild another carb but this one was an HDA-98 which is the one used on the 42/242/246 and uses a main jet with a mechanical check valve. I could only make a few adjustments (getting late with neighbors) but I think I may have hit on something. The prior carb I had tried was also a 34A so it had the same capillary screen check valve and main jet. Maybe this older style carb needs different tuning? Anyway I'll continue the battle tomorrow (got the week off!).

 

[Agrarian]

Well the carb seems to be the problem. With a rebuilt HDA-98, the saw performs normally as far as carb adjustments go although small adjustments seem to make more of an effect than the other saws in my sig. I don't think I will be using any more of the HDA-34's since two of them gave the same problem.

On a slightly different note, does anybody know what the max unloaded rpm of this saw is? And can anyone confirm that 2700 rpm is the idle speed? The Acres site does not list it and my 1985 operator's manual does not specify it.

 

[HiOctane]

Yes, the idle seems fairly steady but at that speed the chain is turning (700 rpm above spec).

I was not aware of a governor on these saws - how is it implemented?

I just finished rebuilding 3 246's and one 242, all of which behaved normally as far as the high speed adjust and all are built on the same crankcase, same coil and use similar carbs. On these other saws, I could find the sweet spot on the high adjust but I can't do that on this one. One difference in these saws compared to the 238 is that they use a different carb that has a pressed in main jet/check valve whereas the Walbro 34a uses a capillary screen check valve. I believe that should only potentially cause problems when transitioning from full throttle to idle which is not my problem.

My guess is that it is too rich based on the amount of smoke at full throttle and the oil weeping from the muffler. With the tach on it, when I give it full throttle initially it goes to about 13K but then almost immediatly goes down to about 9K and sound really labored with lots of smoke.

Please keep the ideas coming guys because I am flummoxed.

The governor is 5031 765 01 on this page. There is a "star clip" holding it. http://www.jackssmallengines.com/Jacks-Parts-Lookup/Model-Diagram/husqvarna/30668/404

 

[Agrarian]

The governor is 5031 765 01 on this page. There is a "star clip" holding it. http://www.jackssmallengines.com/Jacks-Parts-Lookup/Model-Diagram/husqvarna/30668/404

I never thought of that as a governor since it is just a brass jet that limits the fuel flow to the high adjust needle. But the diameter is very small compared to the drilled hole in the HDA-98 carb that feeds its high adjust so I can see where it would limit the maximum possible additional fuel that could be added by the high adjust. Wouldn't that make it more of a limiter than a governor though? Or is there more going on here than meets the eye?