jamessouthaus
ArboristSite Lurker
hi everyone new to the site but have found many previous threads from google searches very helpfull. looking for info on how to tune my 365sp that i have just put a 52mm big bore kit. any help much appreciated.
365sp with 52mm big bore kit tuning
- Thread starter jamessouthaus
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RiverRat2
Serio Tree Freak
Welcome Mate, If you have modded the muffler or not It would be wise to rebaseline the carb settings, so the limiters have to go!!! make sure you have at least a half tank of good fresh fuel mix, I like to start with the L @ 1 and a 1/4 turns out from the bottom and the H about a smidge over 1 full turn out, Warm it up a bit with the B&C combo you are intending to be running for the time being adjust the L till you have good snappy throttle response, you may have to adjust the idle a couple of times to keep it out of chain creep. On a fresh top end I like to tune the H a tad fat to where it four strokes out of the cut but cleans up nicely in the cut. So using short time interval WOT burst adjust H out to you hear it burbble,,, then in a smidge so it is still 4 stroking then see if it cleans up in the wood,,, Run good synthetic oil if you have access, FWIW, I mix all fo mine @ 40:1 and have never toasted a topend!!! Ohhh and keep your chains sharp and bar oil reservoir topped off....
BTW this tune is safe for any saw, stock, new top end, or any good used saw or otherwise!!!,,, Just sayin
BTW this tune is safe for any saw, stock, new top end, or any good used saw or otherwise!!!,,, Just sayin
jamessouthaus
ArboristSite Lurker
thanks mate about to have a go now
Terry Syd
Addicted to ArboristSite
James, I put one of those kits on a 365 and discovered that the carbs (Walbro and Zama) just didn't flow enough down low to give the saw the potential 'grunt' it has. I drilled out the jets on a Zama and the saw came alive with heaps of torque.
If you can find another Zama carb to send me, I'll mod the carb for you. Just contact me via the personal message function on the site.
If you can find another Zama carb to send me, I'll mod the carb for you. Just contact me via the personal message function on the site.
MCW
Somebody's talking crap here & it ain't the tree!
Where about in SA are you mate? I'm in the Riverland so 2 1/2 hours away from Adelaide towards Mildura.
Terry above certainly knows carbs
Terry above certainly knows carbs
Terry Syd
Addicted to ArboristSite
Yeah, if you send me a carb, make it a Zama. I can whip up some quick mods with the Zama that don't require me pulling the Welsh plug. I can do the carb in about 20 minutes - heck, since I have the carb apart, send me a rebuild kit and I'll put it in while I'm doing it.
I'm just starting on modding the Walbro HDs and they are a real pain. I still haven't gotten it worked out and I have to pull the Welsh plug each time to drill different air bleed/transition holes. Freakin' nightmare the way the low speed circuit is designed...
I'm just starting on modding the Walbro HDs and they are a real pain. I still haven't gotten it worked out and I have to pull the Welsh plug each time to drill different air bleed/transition holes. Freakin' nightmare the way the low speed circuit is designed...
MCW
Somebody's talking crap here & it ain't the tree!
RiverRat2
Serio Tree Freak
Good on Ya Terry!!!!
James,,,
I was going to suggest that if you find your settings open more than I reccomended it may help going to a bigger carb or re-jetting to see the full potential. But is sounds like Mr. Terry/MCW has given good advice and offered to take care of it for you so you are in good company with those two blokes
.. I have had good luck using oxy/acetylene tip cleaners to rod out jets and get a better flow... once the carb jet stuff is resolved Ii for got to mention a trick I learned on setting the L in my inital post,,,,once the saw is warmed up and idling with the 1 and 1/4 turns out L setting (I like using a screwdriver that I have an indexing mark on the end of the handle so I can keep up with where I am at) adjust the L in and out until you hear it starts to stumble/falter with out letting it die in either direction making a mental note where the sweetspot is in the middle of the stumble points. With the new sweetspot setting, then snap the thottle wide open and it should accelerate crisply. if it stumbles a bit, open L abit more an it should be spot on. I hope that helps.
Terry Syd
Addicted to ArboristSite
Those Chinese 'Zama' carbs you sent me weren't that bad. They only needed the discharge nozzle recessed to the edge of the venturi, otherwise they were identical to the Zamas I had.
And the Greenlog was a Walbro clone, you could go with either one - both had the same crap low speed circuit.
The Zamas low speed circuit is controlled by the low speed jet (plus it has the extra 'torque jet' at quarter throttle) and the low speed needle controls just the mixture at the idle port - very easy to tune.
The freakin' Walbros (and Greenlog) have a compromise low speed circuit where the needle controls BOTH the idle and the flow for the transition ports. Trying to increase the flow in the low speed circuit requires a heap of work trying to match the air bleeds in the transition ports (which requires pulling the Welsh plug each time). I figure I should be able to get it close enough that when you tune the idle that the flow for the low speed circuit should be close enough for most work - at least better than stock. Crikey, the HD-5 I'm working on has a .25mm LIMITER jet in the low speed circuit that I have to completely drill out (in comparison, my Zama is running TWO .3mm jets for the same saw.)
Fork the EPA...
And the Greenlog was a Walbro clone, you could go with either one - both had the same crap low speed circuit.
The Zamas low speed circuit is controlled by the low speed jet (plus it has the extra 'torque jet' at quarter throttle) and the low speed needle controls just the mixture at the idle port - very easy to tune.
The freakin' Walbros (and Greenlog) have a compromise low speed circuit where the needle controls BOTH the idle and the flow for the transition ports. Trying to increase the flow in the low speed circuit requires a heap of work trying to match the air bleeds in the transition ports (which requires pulling the Welsh plug each time). I figure I should be able to get it close enough that when you tune the idle that the flow for the low speed circuit should be close enough for most work - at least better than stock. Crikey, the HD-5 I'm working on has a .25mm LIMITER jet in the low speed circuit that I have to completely drill out (in comparison, my Zama is running TWO .3mm jets for the same saw.)
Fork the EPA...
SawTroll
Information Collector
The venturi could need some extra opening as well - I assume the carbs used on the xt versions will be even better, 19+mm vs. the 17.5 of the HD-12. If memory serves, the Zama is 17mm.
one.man.band
ArboristSite Guru
jamessouthaus......... take terry up on his kind offer!
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adjusting HD low circuit is frustrating. have been trying different approach with an hd298. wanted to keep it simple. when i have the transition to the high circuit working as it should, the low cannot provide enough fuel for good idle.
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adjusting HD low circuit is frustrating. have been trying different approach with an hd298. wanted to keep it simple. when i have the transition to the high circuit working as it should, the low cannot provide enough fuel for good idle.
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Terry Syd
Addicted to ArboristSite
If the HD298 has a limiter jet for the idle circuit, drill it out. Then the low speed needle will control the fuel flow to the low speed circuit.
Of course, since the low speed needle can now provide lots of fuel to the low speed circuit, the idle will quickly become too rich. The carbs need a LOT more fuel going through the low speed circuit, so getting the idle to work after bumping up the flow is a challenge. You need to provide more air bleed to the idle circuit to lean it out. Go slowly, although both fuel and air are fluids, air is compressible, so a small change in the size of the air bleed can make a big change the air fuel emulsion ratio.
If you pull the welch plug you will see two air bleed/transition holes (there are also the holes where the fuel comes in and also the idle port, forget them). The air bleed hole furthest from the idle port (it enters on the backside of the venturi) is the one you want to try and get in the ball park. I've got a couple of micro drill sets, one is in millimetres and the other is SAE. Each set has slightly different sizes, so I have more options to try.
Good luck.....
Of course, since the low speed needle can now provide lots of fuel to the low speed circuit, the idle will quickly become too rich. The carbs need a LOT more fuel going through the low speed circuit, so getting the idle to work after bumping up the flow is a challenge. You need to provide more air bleed to the idle circuit to lean it out. Go slowly, although both fuel and air are fluids, air is compressible, so a small change in the size of the air bleed can make a big change the air fuel emulsion ratio.
If you pull the welch plug you will see two air bleed/transition holes (there are also the holes where the fuel comes in and also the idle port, forget them). The air bleed hole furthest from the idle port (it enters on the backside of the venturi) is the one you want to try and get in the ball park. I've got a couple of micro drill sets, one is in millimetres and the other is SAE. Each set has slightly different sizes, so I have more options to try.
Good luck.....
one.man.band
ArboristSite Guru
thanks for pointing me in the right direction.
been experimenting with adding more air to the HD. works very well, except for idle issues. what i have found so far, found when 'air' is concerned, a 0.013 inch diameter hole size increase has a a very large effect. decreasing hole size, test, repeat.
regards
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been experimenting with adding more air to the HD. works very well, except for idle issues. what i have found so far, found when 'air' is concerned, a 0.013 inch diameter hole size increase has a a very large effect. decreasing hole size, test, repeat.
regards
-omb
Terry Syd
Addicted to ArboristSite
Yeah, working with the air bleed function in the idle circuit is a 'go slow' process.
Like I said earlier, there are two fluids going into the mixing chamber, one gas and one liquid. When there is a demand on the mixing chamber the liquid fuel can't compress to get into the chamber so its movement is slowed down, however the air can compress to get past the hole and will flow much faster - you can get the mixture a lot leaner than you wanted it to be real quick.
Here's another trick. The HD runs primarily on the High speed circuit. The designers used the nozzle placement in the venturi to adjust the fuel curve. You can move the nozzle out to the edge of the venturi to bring in the High speed circuit sooner and flatten the fuel curve up on top end.
The result you're looking for is the blending of the fuel curve from the low speed circuit with the curve from the High speed circuit. The two fuel curves are different - the low speed circuit is in the straight part of the body and the High speed circuit is in the venturi. The total fuel curve for the carb should be a lot flatter and be richer down at peak torque where it needs the richer mixture.
Like I said earlier, there are two fluids going into the mixing chamber, one gas and one liquid. When there is a demand on the mixing chamber the liquid fuel can't compress to get into the chamber so its movement is slowed down, however the air can compress to get past the hole and will flow much faster - you can get the mixture a lot leaner than you wanted it to be real quick.
Here's another trick. The HD runs primarily on the High speed circuit. The designers used the nozzle placement in the venturi to adjust the fuel curve. You can move the nozzle out to the edge of the venturi to bring in the High speed circuit sooner and flatten the fuel curve up on top end.
The result you're looking for is the blending of the fuel curve from the low speed circuit with the curve from the High speed circuit. The two fuel curves are different - the low speed circuit is in the straight part of the body and the High speed circuit is in the venturi. The total fuel curve for the carb should be a lot flatter and be richer down at peak torque where it needs the richer mixture.
one.man.band
ArboristSite Guru
think my current problem is, have too much air. so much so, that the check valve is coming into play at idle.
will have to start from square one again, if i drill. many hours spent in testing changes made so far.
amazed at how good the mid to high rpm transition with no flat spots, can actually be compared to stock.
now i know why you spend so much effort gtting the carby right!
will keep slowly plodding away until its right.
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will have to start from square one again, if i drill. many hours spent in testing changes made so far.
amazed at how good the mid to high rpm transition with no flat spots, can actually be compared to stock.
now i know why you spend so much effort gtting the carby right!
will keep slowly plodding away until its right.
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Terry Syd
Addicted to ArboristSite
If you can fit a Zama twin jet on the saw, it will be a lot easier to get the jetting close. The Zama is a much better designed carburettor and easy to mod. The Zama got a bad rap because they came jetted lean on the low speed circuit to get around EPA regs. However, the same jets can be drilled out very easily.
Yeah, setting up the carburetion is 'free' power, no grinding of ports necessary. Easier starting, nice idle, quick throttle response, great low end torque and a higher horsepower peak.
Yeah, setting up the carburetion is 'free' power, no grinding of ports necessary. Easier starting, nice idle, quick throttle response, great low end torque and a higher horsepower peak.
MCW
Somebody's talking crap here & it ain't the tree!
And another reason why the better saw builders (not many left on AS) will always get more power than somebody with a die grinder who's read a porting thread and think they know everything. I know guys who spend more time on the carby than they do on the porting and it shows.
jamessouthaus
ArboristSite Lurker
thanks guys i'm in the south east of sa. it has the walbro carb on it and seems to be idling nice and got a good throttle response still yet to try it out on some decent size wood but cut up a few lengths in the yard and went well noticibly up on power from the originall 65. are the walbros too hard to mod or should i put a zama on it if i was too get some carby work done.
MCW
Somebody's talking crap here & it ain't the tree!
First thing worthwhile is to give it a muffler mod. Will make it a bit noisier but that helps these saws out and is ready to do. Mount Gambier I gather or thereabouts?
jamessouthaus
ArboristSite Lurker
bordertown. i have opened up the exit port on the muffler a bit just bent the cover up about twice the size outlet now. and yeah is a bit louder. but still as bad as my 2100cd
