Ms 880 carb question

[singinwoodwackr]

I have an 880 in the shop…first one I’ve worked on. Mainly needed a good cleaning.
the carb was full of crap so did a basic sonic tank and reassemble with existing kit parts as they were in great shape.
pulling the needle valves I found tiny o rings…wasted, of course (2009 saw).
I didn’t have anything that small in 3 different kits so ordered some.
new kit had something close so…
saw runs well.
but…should I find some OE Walbro rings for this thing?
I can’t find the specs on the oe rings but have a message into Walbro in AZ.

main reason for the question is I can’t get (manual spec) 11,000rpm without dialing the H screw in more than 1/2 turn. That doesn’t seem right to me.

muffler mod making it a dual port so about double the OE opening in total.
new, OE air filter, new fuel filter.

 

[Vintage Engine Repairs]

Does the main jet have a bypass drilling in it?

 

[singinwoodwackr]

Does the main jet have a bypass drilling in it?

Haven't looked. First time with this big a carb
What did I look for?

 

[Vintage Engine Repairs]

Haven't looked. First time with this big a carb
What did I look for?

All good, look for a drilling in the top of the brass main jet. If it’s there it’s allowing fuel past the high speed screw and thus you get less adjustability from it.

4th bullet point down

 

[singinwoodwackr]

Ah, so similar to the echo 590 carb...acts as a governor, right?
I tried modding one of those by plugging with JB marine weld. Worked...

 

[singinwoodwackr]

All good, look for a drilling in the top of the brass main jet. If it’s there it’s allowing fuel past the high speed screw and thus you get less adjustability from it.

4th bullet point down

View attachment 1074295

This carb doesn't have those springs either. Should I order them?
Owner said someone had done some "work" on the saw in the past.
Limiters are gone.

 

[trains]

This is from the service manual.
they have a fixed jet in the system as well.

copy paste below.

Starting with the high speed
screw H (1) against its seat, open
it counterclockwise, 1 full turn
on Tillotson carburetors or 1.5
turns on Walbro carburetors
– this is the basic setting.
: Starting with the low speed screw
L (2) against its seat,
open it1 full turn
counterclockwise
– this is the basic setting.
– Warm up the engine.
The setting disc 5910 893 6600 may
be fitted on the screwdriver
5910 890 2304 to aid adjustment.
216RA470 TG
1
2
: Push the screwdriver (1)
5910 890 2304 through the
opening (arrow) and the preinstalled
limiter caps on the high
speed screw (H) and low speed
screw (L).
Adjust idle speed with a tachometer.
Adjust specified engine speeds
within a tolerance of ± 200 rpm.
1. Adjust engine speed with
idle speed screw (LA),
to 3,300 rpm onTillotson
carburetor or 3,500 rpm on
Walbro carburetor.
2. Turn the
low speed screw (L)
counterclockwise or clockwise
to obtain maximum engine
speed.
If this speed is higher than
3,700 rpm, abort the procedure and
start again with step 1.
3. Use the
idle speed screw (LA),
to set the engine idle speed
again, to 3,300 rpm on
Tillotson carburetor
or 3,500 rpm on Walbro
carburetor.
4. Use the low speed screw (L)
to set engine speed to
2,700 rpm.
5. Use the high speed screw (H)
to set the maximum engine
speed to 11,000 rpm.

 

[singinwoodwackr]

This is from the service manual.
they have a fixed jet in the system as well.

copy paste below.

Starting with the high speed
screw H (1) against its seat, open
it counterclockwise, 1 full turn
on Tillotson carburetors or 1.5
turns on Walbro carburetors
– this is the basic setting.
: Starting with the low speed screw
L (2) against its seat,
open it1 full turn
counterclockwise
– this is the basic setting.
– Warm up the engine.
The setting disc 5910 893 6600 may
be fitted on the screwdriver
5910 890 2304 to aid adjustment.
216RA470 TG
1
2
: Push the screwdriver (1)
5910 890 2304 through the
opening (arrow) and the preinstalled
limiter caps on the high
speed screw (H) and low speed
screw (L).
Adjust idle speed with a tachometer.
Adjust specified engine speeds
within a tolerance of ± 200 rpm.
1. Adjust engine speed with
idle speed screw (LA),
to 3,300 rpm onTillotson
carburetor or 3,500 rpm on
Walbro carburetor.
2. Turn the
low speed screw (L)
counterclockwise or clockwise
to obtain maximum engine
speed.
If this speed is higher than
3,700 rpm, abort the procedure and
start again with step 1.
3. Use the
idle speed screw (LA),
to set the engine idle speed
again, to 3,300 rpm on
Tillotson carburetor
or 3,500 rpm on Walbro
carburetor.
4. Use the low speed screw (L)
to set engine speed to
2,700 rpm.
5. Use the high speed screw (H)
to set the maximum engine
speed to 11,000 rpm.

Right...I have the manual. Problem is, 11000 can't be reached without turning the H screw in to less than 1/2 turn out.

 

[Vintage Engine Repairs]

Ah, so similar to the echo 590 carb...acts as a governor, right?
I tried modding one of those by plugging with JB marine weld. Worked...

Hmm not technically a governor, it’s just a means of ensuring adequate fuel supply when prying hands start fiddling. Either way, if yours does have that drilling, 1/2 turn out isn’t surprising as it’s getting metered fuel via that bypass jet.

Not all carbs have those springs no. Some do while others don’t.

Sometimes the screw limiter tabs act as a means of maintaining the needles position too. Others use rubber mounts as well.

It’s best to check the walbro site by searching the model of carb.

 

[singinwoodwackr]

Hmm not technically a governor, it’s just a means of ensuring adequate fuel supply when prying hands start fiddling. Either way, if yours does have that drilling, 1/2 turn out isn’t surprising as it’s getting metered fuel via that bypass jet.

Not all carbs have those springs no. Some do while others don’t.

Sometimes the screw limiter tabs act as a means of maintaining the needles position too. Others use rubber mounts as well.

It’s best to check the walbro site by searching the model of carb.

I sent Walbro an email and got a reply today but too late to reply back...they had closed.
I'd love to see a full schematic of this WG12-13 carb. Closest I've found is a WG8 and it is quite different.
I'll call them in the morning.

So, my concern with a half turn...or a bit less...and leaning the saw out too much is unfounded due to that hole allowing more fuel in? I just don't want to hand the saw back not fixed correctly.
Worst case, new carb for around $130. We're working out trading saw work for some of his fresh pork so it works for me

 

[trains]

This carb doesn't have those springs either. Should I order them?
Owner said someone had done some "work" on the saw in the past.
Limiters are gone.

yeah, springs help keep the needles in place, so get them, tho it depends on if the carb had them, does your carb have the polymer housing around the needles ?
if so, then they came with springs, and then the rubber seals seat below them in the housing.
if there is no polymer housing, but just ally carb, with limiters, then the ipl and sm show no springs on those.
hope that helps.

 

[singinwoodwackr]

Hmm not technically a governor, it’s just a means of ensuring adequate fuel supply when prying hands start fiddling. Either way, if yours does have that drilling, 1/2 turn out isn’t surprising as it’s getting metered fuel via that bypass jet.

Not all carbs have those springs no. Some do while others don’t.

Sometimes the screw limiter tabs act as a means of maintaining the needles position too. Others use rubber mounts as well.

It’s best to check the walbro site by searching the model of carb.

Walbro's site was useless for this carb. Very disappointing. And, the reason I sent them an email.
Hope to talk to a tech tomorrow

 

[trains]

Right...I have the manual. Problem is, 11000 can't be reached without turning the H screw in to less than 1/2 turn out.

since it already has a fixed jet in the system, I dont see that as a problem, your getting the rpm, saw is performing correctly, if you could not get it to drop to that rpm, then I would expect a problem.

 

[singinwoodwackr]

yeah, springs help keep the needles in place, so get them, tho it depends on if the carb had them, does your carb have the polymer housing around the needles ?
if so, then they came with springs, and then the rubber seals seat below them in the housing.
if there is no polymer housing, but just ally carb, with limiters, then the ipl and sm show no springs on those.
hope that helps.

Yup, poly housing.
Needles are looser than I like with just those little o rings

 

[trains]

Yup, poly housing.
Needles are looser than I like with just those little o rings

Get them springs .

sent you a pm

 

[singinwoodwackr]

Pics....

Hard to judge these things without a proper schematic

 

[Vintage Engine Repairs]

Yes, your carb has a bypass jet (2). It’s not surprising you have to lean the H screw to around 1/2 out from seated to get your 11,000 rpm. It’s being fed by (2) the bypass jet that you can’t meter.

1: H fuel supply metered via H screw
2: Bypass jet for H speed fuel supply
3: Main nozzel fed by 1 & 2 with check valve
4: Low speed jet (feeds idle & progressive drillings)
5: Welch plug covering idle & progressive drillings
6: H speed screw (controls fuel to 3)
7: L speed screw (controls fuel to 5)

 

[Maintenance supervisor]

Just fyi , sometimes a hamfisted screwdriver turner can waller out the tiny aluminum seat that the needle sits in by forcing it into the housing to hard or if the needle is loose it'll damce around in the seat . Essentially you have to setthe needle in farther to offset the larger hole.
Carb might be shot, I would see if you can get another one to test on the saw. There's knock offs of those carbs for about 50$ ,just for testing.
The MS880 was also rev limiter coil too, so it would be better to era on the side of safety and not burn up a 1500.00 saw over a 150.00 carburetor.

 

[SteveSr]

Yup, poly housing.
Needles are looser than I like with just those little o rings

This is an EPA carb. There should be o-rings, backing washers, and springs against the washers. The EPA objective is to keep air from leaking around the screw threads of the needles upsetting the mixture / calibration of the carb needles.

 

[singinwoodwackr]

Well, hitting walls, lol
Talked to the walbro dist the Walbro guy suggested. He has the o rings but not the needle springs/washers.
Got a short pts list from "Bob" showing what would work but distributer guy doesn't show them . He said this is a Stihl only carb so they would have parts. Talked to my local gal and her schematic doesn't show the springs, just the limiter caps. It is possible those caps do the work of the springs in keeping the needles in tight.the saga continues....