Help unlocking an MS170
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Fixed jet carbs channel the main circuit thru a single dedicated fuel jet, flows faster, smoother, unimpeded and consistent direct to the nozzle. (some here don't realize the 'fixed' jet is re-sizable/replaceable. The jets are about 8 bucks each and screw straight in)
An experienced operator will tell ya that the fixed jet setup gives more 'pep' over the rev range compared to the usual twin adjustable carb. The 'rod jammed in a hole' main circuit on a twin jet carb is coarse, ragged and agricultural compared, with the fuel belching and squirting inconsistently from around the holes perimeter...
Twin adjustable jet carbs 'do the job' and that's it..
Like I said, do some back-to-back carb swaps then come see me..
An experienced operator will tell ya that the fixed jet setup gives more 'pep' over the rev range compared to the usual twin adjustable carb. The 'rod jammed in a hole' main circuit on a twin jet carb is coarse, ragged and agricultural compared, with the fuel belching and squirting inconsistently from around the holes perimeter...
Twin adjustable jet carbs 'do the job' and that's it..
Like I said, do some back-to-back carb swaps then come see me..
willsaw4beer
Addicted to ArboristSite
So it's a bad thing my 026's have a 194 instead of the fixed jet carb?
Trigger Man
Addicted to ArboristSite
I don't know? I was always told a fixed jet carb on a chainsaw was not as good as a adjustable jet. Why would pro saws come with one if they were a bad thing?
Saw Dr.
Junk Collector
So you suggest that we keep a few hundred jets around for all of the different carbs we have? (I have seen, at most, 3 sizes available in the IPL's) This way when the seasons change, and it needs a slight adjustment, or when you go to help a buddy up at the cabin, you get to strip the carb off 3 or 4 times just to get it to run right? And on modded saws, you get to put a few top ends in it because it siezed while you were trying to get it up to running temperature with a lean mixture?
Enjoy your stock saws with fixed jets. Even if yours makes .01 more horsepower than mine, I don't care. A sharp chain will level that discrepancy. Technically the fixed jet carbs may be more efficient, but they're highly impractical for most of the folks on here.
Saw Dr.
Junk Collector
breymeyerfam
Addicted to ArboristSite
but....... unless you have a pile of different fixed jets laying around, modding a fixed jet saw sucks.
My work saws are stock 200T, 020T and 335XPT. One of my 335's is ported and runs awesomely with an 020T fixed jet carb. The twin jet carbs can't touch a properly jetted fixed jet carb for consistent performance on any of these saws. Note these are all small highly-strung screaming little monsters. I don't think I've ever seen a fixed jet carb on a 'big' saw.
With a fixed jet carb, the 200T goes off like you wouldn't believe. Again, the stock WT walbro adjustable carbs are a notch below on performance. I've swapped all sorts of carbs around on all these saws, the fixed jet carbs are impervious to altitude/weather variations, they always hold a consistent tune and rarely ever 'play-up'.
If you think the saw is screaming too lean up top, then simply slam in a larger jet. From memory, the 020T fixed jet carb had a .50 jet. I replaced it with a .53 to tame it down a bit..
Tzed250
Addicted to ArboristSite
Saw Dr.
Junk Collector
That's what I'm asking. Nevermind 2' MSL or 4000' MSL. Stoichiometric mixture is 14.7 parts air to 1 part fuel for ideal combustion. This varies a little, but if the ratio and volume coming out of the business end of a carburetor is the same across the rev range, then the performance will be the same for fixed or variable jet. I'm surprised that the hotsaw guys haven't found out about this fixed jet thing.
I'm glad his fixed jet carbs work for him. I'll continue to use them for parts in my shop.
The ONLY good thing that I can think of about fixed jet is for troubleshooting. If it does not run right, you can't "tune around" the issue. It must be repaired, be it seals rings or whatever.
Of course extremes in altitude has some affect, but twin jet carbs suffer a lot more than a fixed jet carb, I can go from sea level pruning blocks to a 2500ft altitude block the next day and the fixed jet carb won't even miss a beat, will just keep on keeping on whilst my twin jet saws will be farting and fluffing until you re-tweak them. I can tell some of you 'experts' have had no experience with fixed jet carbs.
Wasting your time quoting me stoichiometric mixtures, percentages, ratios, volumes, digits on paper, etc.. etc.. it's all theory and bluster in the real world, I'm talking about every day use on the practical side of things, I couldn't care less what the academics have to say, anyone telling me that twin jet carbs are an 'improvement' are talkin' thru holes in their heads.. I know myself that fixed jet carbs are a better choice for my work saws.
But carry on, as you were..
Wasting your time quoting me stoichiometric mixtures, percentages, ratios, volumes, digits on paper, etc.. etc.. it's all theory and bluster in the real world, I'm talking about every day use on the practical side of things, I couldn't care less what the academics have to say, anyone telling me that twin jet carbs are an 'improvement' are talkin' thru holes in their heads.. I know myself that fixed jet carbs are a better choice for my work saws.
But carry on, as you were..
