High Speed Jet (Fixed Jet)

[Stihl-Pioneer]

Just wondering does Stihl make only certain size jets(.062,.064,and .074) to fit that carb or do they have an assortment like every .001 or .002? So if you wanted say a .070 you could get one.

 

[Tzed250]

Just wondering does Stihl make only certain size jets(.062,.064,and .074) to fit that carb or do they have an assortment like every .001 or .002? So if you wanted say a .070 you could get one.

Other models have different sets. MS440 has .64-.66. MS460 has .66-.70, so they can be obtained.


.

 

[Bill Becker]

Jets: (not all are available in all countries)
.46 = 1121 121 5601
.52 = 1121 121 5602
.56 = 1120 121 5600
.61 = 1123 121 5601
.62 = 1122 121 5603
.64 = 1122 121 5604
.66 = 1128 121 5605
.68 = 1128 121 5603
.70 = 1128 121 5602 (installed in my MS460)
.72 = 1122 121 5602
.74 = 1122 121 5607 (installed in my 066)
.76 = 1128 121 5604
.88 = 1124 121 5609
1.04 = 1124 121 5604

Carburetors with fully adjustable fuel mixture screws:
044/046/MS440/MS460 = 1128 120 0624 with .70 jet
064/066/MS650/MS660 = 1122 120 0621 with .64 jet

Dual port muffler covers:
044/046/MS440/MS460 = 1128 140 0801
064/066/MS650/MS660 = 1122 140 0800

 

[Tzed250]

Great post!!!

 

[Eccentric]

Great post!!!

I agree. Just gave 'em some rep. He's now within sneezing distance of another nova. Somebody give 'em a bump...:agree2:

 

[gemniii]

.

A few weeks back there was a discussion about the high speed jet, called the fixed jet in a Stihl IPL, and its role in tuning the carburetor.

A little research shows that the US bound MS660s are equipped with a Walbro WJ-69 carb. The IPLs that I have show a .64 jet as standard, with a .62 jet optional for high altitude operation. After porting my 660 I found that the H needle needed to be 1.25 turns out to get the saw to four-stroke. I figured a new jet was needed. I ordered the 1122 121 5607 .74 fixed jet from the dealer. This jet is found in the WJ-76 carbs found on saws not headed for North America.

When I disassemled the carb I found a somewhat unpleasant surprise. The saw had been shipped with a .62 jet. EPA strikes again.

I thought I would share a quick how-to for replacing this jet.

.

THANKS - After I got my recent 660 (snellerized and a mild muf mod by Brad) and was asking about potential power increase by adding a DP muffler I told by mntgun

never changed jets, never heard of anyone who had to change jets. You would only need to change jets if you ran out of adjustment on the H screw.

So I guess if I put the DP cover on that saw it might open it up enough to need another jet. The process seems simple and the cost is low.

I really like being able to squeeze more power out of a box with incremental mild mods.

 

[Tzed250]

THANKS - After I got my recent 660 (snellerized and a mild muf mod by Brad) and was asking about potential power increase by adding a DP muffler I told by mntgun

So I guess if I put the DP cover on that saw it might open it up enough to need another jet. The process seems simple and the cost is low.

I really like being able to squeeze more power out of a box with incremental mild mods.

It is not so much a "need" thing as it is optimizing the tuning parameters. Different jets will all allow the saw to be tuned correctly, but only one will put the needle in its "sweet spot".


.

 

[Tzed250]

I agree. Just gave 'em some rep. He's now within sneezing distance of another nova. Somebody give 'em a bump...:agree2:

Got him!!!!

 

[roger m]

what would the reccomendation be on a fairly new ms 460?,i just purchased the oem dual port muffler cover and the carb tool to remove the plastic stops,just haven't had the time to work on it yet:msp_confused:

 

[struggle]

per sent as well. Great info and more to think about as always with this site

 

[Tzed250]

Pull the limiters, trim the tabs, then re-tune. If the final position of the H needle is more than 1.25 turns out then it may be time to re-jet.

 

[bushwackr]

ok maybe someone can answer my question. Ive been workin on my 46m. When I got it it had a 044 carb on it , the only reason I found that out is when I went to use it , I cut thru a chunk of wood and set the saw down for a second to move blocks or something pick up the saw touch the throttle and it would die. I went to the dealer saw checked out good but wrong carb. I got a used one I cleaned the carb, rebuilt it. Installed it and I set the high and low screws to what it says on the air cleaner cover to start with. It says 1/4 low, 3/4 high, I set it like that it would only start when choked. I played with it to get it close so its a cheap trip to the dealer to set high, low rpm. The high screw at 3/4 sounds a little bubbly so it must be kinda close, but the low speed screw has to be at least 3/4 from seated to run. I think is at prob 1 1/8 where it runs nice. Does the fixed jet play into the low speed mix as well. the carb has the .68 fj , would goin to the .70 fj from the 44 carb help me or just mess up the high setting?

 

[mdavlee]

Don't worry about the 1/4 turn stuff. Most like around 1 turn on both screws. Get it to run right if its under 1 1/4 I wouldn't worry about it if its running right and tuned right. If you can't get it to 4 stroke at wide open then you need a bigger jet. There's not much difference between a 44 and a 46.

 

[bushwackr]

Ya the saw runs nice now , and wont die when throttled after a cut. I had to try it out after the carb was replaced. I will prob just runner

 

[sigafreddi]

Tzed250,

I put a dual port muffler on my stihl ms 460, and then retune the carb, H needle 1 1/2 turn, and Low needle 1 turn.

It runs correctly, four stroking at 13200rpm with a .68 fixed jet (h16a carb), but i will try a .70 fixed jet.

like you said, the H needle adjustment will be about 1 turn with .70 jet, but i don't know for Low needle !



Thank you for your help.

 

[bushwackr]

ok pretty much saw as mine. Them Im prob pretty close then. Thanks

 

[Tzed250]

Tzed250,

I put a dual port muffler on my stihl ms 460, and then retune the carb, H needle 1 1/2 turn, and Low needle 1 turn.

It runs correctly, four stroking at 13200rpm with a .68 fixed jet (h16a carb), but i will try a .70 fixed jet.

like you said, the H needle adjustment will be about 1 turn with .70 jet, but i don't know for Low needle !



Thank you for your help.

The fixed jet will not affect the L setting. Let us know how it turns out.

 

[one.man.band]

1/16 Turn of HS Needle = 1 Jet size

from what i have read so far in this thread:

Tzed250 saw:

original jet size = #62 = 0.62mm with a HS needle setting of 1-1/4 turns out

new jet size = #74 = 0.74mm with HS needle set at 7/8 turn out

i like math
so,

going from size 62 to size 74 = 6 jet sizes larger (62, 64, 66, 68, 70, 72, 74)

and

turns out from seated:

1-1/4 to 7/8 = 1.25 - 0.875 = 0.375 (turns difference) = 3/8 turns
and
3/8 = 6/16

Since, he went up 6 jet sizes, and reduced turns out by 6/16......

Therefore:
1/16 Turn of HS Needle = 1 Jet size

 

[HARRY BARKER]

The jet was $5.99.

No power gains. The correct mixture is still the same, it is just delivered with the needle in a different spot. The carbs are engineered to work with the needle @ ~1 turn.

.

and who told you that??

 

[one.man.band]

missed the 'other' thread about jets.

i realize that carb bore and venturi size create vacuum of fuel delivered through/from HS jet. the faster the intake air charge through carb, the more vacuum over the jet orifice to deliver more fuel. the original jet size was delivering enough fuel at 1-1/4 turns.....and, after larger jet 7/8 turns ....the end result was the exact same amount of fuel. although the original jet size amount of turns out, was more than the 'factory' recommended....can't see the difference in fuel the saw sees in WOT operation. the channel between the high speed need seat and the high speed jet remains the same size, and would seem to dictate the amount of vacuum of fuel in both jet sizes, with fuel flow being equal. if part throttle operation was poor, with the smaller jet size, (which couldn't be tuned out with the LS needle) i could see reason for change.

i'm missing the point, i guess.