Tuning carb with fixed high jet...ideas?

[16gauge]

Recently won an 026 Pro on eBay. Good price and runs great...but it has the fixed H jet. It seems just a little rich at WOT. I am at 550 feet above MSL where I live and think it would be way rich at the altitude I can cut Tamarack.

Any ideas other that replacing the carb with a fully adjustable model? I'm thinking about increasing the mix ratio from 50:1 to 36:1. Anyone have experience with this? Thanks

 

[skwerl]

Yes. Swapping jets and guessing at which one will work (after buying them in advance and waiting a week for delivery at the local Stihl shop) is a total PITA. I never could get mine the way I wanted, removed and replaced the carb so many times I could do it blindfolded. Finally cut my losses ($20+ on jets, plus weeks of time and several hours of ruyn time with a saw out of adjustment) and tossed the fixed jet carb. Found a used adjustable carb from a fellow ASite member for $35.

But by the time I swapped carbs, the saw was already half burnt up from running lean. I bought a Husky 346XP and gave away the 026.

 

[saxman]

I agree with the previous post. I had the same issue with my fixed jet MS260. After I opened the muffler up I needed some adjust-ability on the high side. I purchased a new adjustable carb from lakeside on this forum. After I installed it and made the necessary adjustments the saw starts, idles, and runs GREAT. I would recommend biting the bullet and changing the carb.

 

[timberwolf]

Dump the fixed jet carb if possible, but right now going to more oil in the mix might make the problem worse. The oil needs to go through the jets too, more oil is less gas.

 

[16gauge]

Dump the fixed jet carb if possible, but right now going to more oil in the mix might make the problem worse. The oil needs to go through the jets too, more oil is less gas.

Thanks for the recommendations to replace the carb. I am probably going to do that...but I am soliciting other possible solutions short of replacing the carb with a fully adjustable model. Others here may benefit from the topic. As I stated in the post, the saw is running a little too RICH at 550 ft, it would run more rich at altitude...right? My thinking is that increasing the 2 cycle oil ratio (actually lower gas to oil ratio) would lean things out nicely but I would like the benefit of the experienced menbers on this site before I try anything that may be "dead wrong".

 

[TimberPig]

Thanks for the recommendations to replace the carb. I am probably going to do that...but I am soliciting other possible solutions short of replacing the carb with a fully adjustable model. Others here may benefit from the topic. As I stated in the post, the saw is running a little too RICH at 550 ft, it would run more rich at altitude...right? My thinking is that increasing the 2 cycle oil ratio (actually lower gas to oil ratio) would lean things out nicely but I would like the benefit of the experienced menbers on this site before I try anything that may be "dead wrong".

Yes, richening the fuel/oil mix will lean the air fuel ratio received by the engine, but the effects are very small. It will only make the air fuel mix about 1% leaner, which is not likely enough to be significant.

You are correct that as altitude increases, it will effectively richen the air fuel ratio on your saw. This is assuming temperature stays constant. If the temperature is colder than where you started, that will do the opposite and lean the saw out. Depending upon the difference in elevation, and the temperature change involved, you may end up way rich, no net change, or even lean if the altitude change was small and the temperature change was large. The best possible solution for you, is to round file the fixed jet carb, and pick up a 3 screw adjustable carb. Stihl admitted the problem and went back to the adjustable model, so there is no reason to make your life more difficult by staying with it. With the fully adjustable carb, there is no worry of running rich or running lean, you simply adjust it for where you are running it at as needed and move on with life. For the cost of a used fully adjustable carb, I would save myself the headaches of the fixed jet carb if I were you.

 

[timberwolf]

I totaly miss read, oops, Most often too lean is more a worry with the fixed jet. One other solution is to open the muffler up a wee bit at a time. If the saw is running to rich opening the muffler up will lean it out and give it some pep also.

You wiil want to go at it slow, just drilling out the muffler 1/16 at a time and retrying.

 

[pbtree]

but I am soliciting other possible solutions short of replacing the carb with a fully adjustable model.[/QUOTE]

Face it - there are no other practical or effective solutions - dump the fixed jet joke and pick up an adjustable - you will never look back...

 

[stihltech]

fixed jet

Do a search, it has been covered.

 

[bugfart]

I vote muffler mod as suggested.
If you do decide to go carb-swapping, you're still good.

But what-ever works for you - still does in fact work. No shame in trying the muffler mod first in the name of science.

Sounds like you're still able to richen it up if you go further than originally desired. It makes winning it even better. Really free!

 

[stihltech]

muffler

I looked back to the original post and see that it runs a little rich a WOT. DO the muffler mod. I found that the rich 026 was right on the money after the mod. Cheap and easy to do.

 

[16gauge]

Nice rim sprocket

I looked back to the original post and see that it runs a little rich a WOT. DO the muffler mod. I found that the rich 026 was right on the money after the mod. Cheap and easy to do.

I'm likin' your avitar stihltech. Looks like the setup I need for cuttin' big weeds. RS rocks!

 

[buck futter]

Good info guys,
The richer oil mix is always a good idea, I personally think 40:1 is a decent compromise but that has been beat to death. The muffler mod is a great idea a well and will help you with issue.


Now you said it was a pro model which I believe should have a compensating carbeurator. However, it is always a good idea to have more than one good air filter so you can always have a clean one to put on. Even if the filter on there looks good you don't know how old it is or how much use it has seen. Buy a new one and do all of the other recomendations. The cumulative effect may put you in the ballpark. Also you will have lost nothing and if you are still not quite happy keep your eye open for a adjustable carb.

Buck