Tillotson HS carb

[hohchainsaws]

I’ve got a Tillotson carb that’s off a jonsereds saw (i know totally obscene) but it’s the same as the carb on my super xl so I figured someone here could help, what happens is the saw idles great, but bogs extremely when I hit the gas, the funny thing is it sometimes will rev up and run wot great, and spins at the rpm I want, most times it just bogs. Different screw adjustments dont change anything either I ’m totally stumped   Anyone have any ideas what might cause this? The spark checks out good and there are no air leaks, just replaced crank seals and base gasket. Any help is appreciated thanks  

[edju1958]

What model # HS carb are you using on your saw that came off the Jonsered?Have you tried a new fuel filter?

[chainsawfever]

Have you been through the carb at all and are you able to pressure test it? Maybe something in the carb that's keeping fuel from flowing like it should? Does the saw react when the low jet in screwed in or out?

[xl130]

Mar 13, 2021 20:26:33 GMT -5 hohchainsaws said:

I’ve got a Tillotson carb that’s off a jonsereds saw (i know totally obscene) but it’s the same as the carb on my super xl so I figured someone here could help, what happens is the saw idles great, but bogs extremely when I hit the gas, the funny thing is it sometimes will rev up and run wot great, and spins at the rpm I want, most times it just bogs. Different screw adjustments dont change anything either I ’m totally stumped   Anyone have any ideas what might cause this? The spark checks out good and there are no air leaks, just replaced crank seals and base gasket. Any help is appreciated thanks  

In my experience that is usually due to the low screw being too lean. Try opening the low screw little by little as your hitting the throttle.

What is the HS model number?

[hohchainsaws]

I believe the carb is a Tillotson Hs 101a, i have been into the carb all seemed well, sprayed everything down with spray, removed the needles sprayed them out, let that dry and installed new kit (needle, diaphragm, fuel pump, etc...) the only thing in the carb I didn’t touch was underneath the plugs on the diaphragm side, Could there be something under there causing my issue? The carb pressure and vac tested it’s flying colors. I sprayed through the needle screw holes and got it coming out the inside of the carb in the middle and engine side of the butterfly’s, like it should. Unfortunately giving it more fuel on the low side did not work the bog still continued and when I let off the throttle it was way to rich and died right out, that being said maybe I can richen it up and turn the idle screw way in because I don’t think it’s currently interacting with the contact plate on the throttle plate shaft. That being said the low end mixture screw will be about 2-2 1/2 turns out which seems way to rich

[chainsawfever]

Mar 14, 2021 19:04:19 GMT -5 hohchainsaws said:

I believe the carb is a Tillotson Hs 101a, i have been into the carb all seemed well, sprayed everything down with spray, removed the needles sprayed them out, let that dry and installed new kit (needle, diaphragm, fuel pump, etc...) the only thing in the carb I didn’t touch was underneath the plugs on the diaphragm side, Could there be something under there causing my issue? The carb pressure and vac tested it’s flying colors. I sprayed through the needle screw holes and got it coming out the inside of the carb in the middle and engine side of the butterfly’s, like it should. Unfortunately giving it more fuel on the low side did not work the bog still continued and when I let off the throttle it was way to rich and died right out, that being said maybe I can richen it up and turn the idle screw way in because I don’t think it’s currently interacting with the contact plate on the throttle plate shaft. That being said the low end mixture screw will be about 2-2 1/2 turns out which seems way to rich

Could it be something else in the saw?  Sounds like you have been all through the carb and it checks out.  Do you have another known good carb you could put on the saw just to rule out another issue in the saw itself?

[hohchainsaws]

The only thing I can think of is that is the coil or points and condenser, I checked the spark with a new plug it had great blue spark maybe the coil is on its way out or I don’t have the points set just right. I think I’ll look into that next

[xl130]

How many CC’s did the Jonsered have? Possibly it is oversized for the Homelite? I’m not familiar with that HS model possibly it’s a perfect fit....?

[edju1958]

I think XL130 might be onto something.I believe the HS101 is a carb meant for 80+cc saws.What was the model of the original carb that was on the SXL? You can swap carbs from one brand to the next & they might bolt up perfectly,but what you need to compare is the size of the venturi in the carb.If you're putting a carb from an 80+cc saw onto a 58cc saw there's gonna definitely be a difference in the size of the venturi.You might be able to compensate with the adjusting needles,but you're playing a guessing game which could result in running the saw too lean & burning it up.Sometimes finding the size of the venturi is next to impossible.

[chainsawfever]

I guess I might have read your first post wrong. I thought you meant this carb was on your jonsered saw and not on a Super XL.

[xl130]

Mar 15, 2021 15:51:56 GMT -5 chainsawfever said:

I guess I might have read your first post wrong. I thought you meant this carb was on your jonsered saw and not on a Super XL.

Lol yeah....,totally missed that one too. If it’s on a saw that it’s meant for and you have properly tuned the carb and you’re still having problems then I’m gonna have to say that I’d be stumped the same as you are.....

[hohchainsaws]

Yes the carb is off a jonsereds 801, it’s a 4.9 cu in 80cc saw, I had the carb wrong to it is a Hs 101 c I previously said it was a 101a, I tried different settings and even a different carb and no luck, totally stumped is there a good forum for jonsereds saws I can find some stuff on arboristsite but nothing recent (within 3-5 years) or even close to similar to my problem thanks anyways 

[edju1958]

You should be able to go on AS to the chainsaw stickies section where they're brand specific & get someone there to advise you.

[fossil]

The 101C carb has an 11/16" venturi and the typical SDC or HS carbs on Super XL's had a 9/16 venturi.

That's a significant difference but I don't think that's your problem (or all of your problem). It sounds more like an ignition problem.

I had a saw do exactly what yours is doing. The plug wire was damaged and it didn't have enough carry power for high RPM's. I would check the plug wire to make sure it's not shorting out or is broken inside the insulation.

I would also check the points to make sure they are clean and gapped properly.

I would also unscrew the plug wire from the coil, trim about 1/8" off the end and screw it back in to see if that helps.
Check that you have good contact at the plug end as well.

[fossil]

Quite a few well worn HS carbs have badly worn throttle shafts. You can't tune that out. Wiggle the shaft to make sure it tight.

[hohchainsaws]

I’ve tried switching carbs no luck just bit the bullet and bought a new coil, supposedly tested good, thanks for the info on the Hs carbs wiggle around the throttle shafts but that didn’t seem to be the issue for me, I’ll know to check for that on other trouble saws