Snowblower Forum banner
941 - 960 of 977 Posts

·
Premium Member
Joined
·
1,491 Posts
The go cart guys will use different emulsion tubes and main jets. Not to mention intakes and exhausts. I dont see them messing with the low speed jet. I am not an expert or someone who frequents those board much. But when I do, I do not see any talk about the low speed jet. I know you can buy larger low speed fixed jets. So maybe some people do. But it seems far from the focus. Maybe becuse they run them as fast as they can go and are not too interested in the idle speed. Most people only run their snow blowers on high and only throtthle down when they pause to do something else.
I have purchased after market carbs and had to mess with them to get them to work right because they are not exact replicas of what it is replacing. To say it is simple ignores murphy's law. You neet to have some understanding of physics and how carbs work for you start changing things. Sometimes it is simple and sometimes it is not simple.

If you have a new Honda and you have stock jet that is surging. It should be simple to try a few larger jets and optimize the mixture or get it close enough. Preverably get an adjust able jet and be done. I agree, you dont have to understand alot if all you need to do is what is in that instructional video above. You can just change parts and gauge it by the sound of the engine.and done.
 

·
Registered
Joined
·
329 Posts
One hour later.....

Its an air screw.
All it does is add air if you screw it out and make things leaner.
How are you even adjusting that?
Most don't even have a slot for a blade.
A few have a black cap on there to prevent you from playing with it and making things worse that was 15 years ago and I have not seen one with a slot in long time
 

·
Registered
Joined
·
329 Posts
f you have a new Honda and you have stock jet that is surging.
OK be specific here now.
Unloaded its just sitting there hunting speeding up slowing down?
Or doing this until you have a load on?
That's a lean low side issue.
You can tell if you choke it a little and the hunt goes away. ( or feed it some gas from a propane torch to richen it up )

Hunting can also be caused by a governor not adjust properly ( I will post some detail on how to fix that shortly )

High side hunting can happen too but your load must decrease with the engine RPM so the machine does not stall out completely from being too lean.
That's hard to do on a snownblower.

Here's an Onan linkage that shows the speed and sensitivity adjustments.
Its the same for all governors but Onan makes it easier to see.
Font Parallel Triangle Diagram Drawing
 

·
Registered
Joined
·
329 Posts
The pilot jet controls the amount of fuel its the wet bit.
All that screw does is meter a tiny bit of extra air/fuel from the metering chamber....
You selectively can pass more mixture from one pick off port to another, but this does not materialy effect fuel mixture because you can't get more fuel.
Not enough to tell you passed a fart in the wind.
Follow the carb circuitry from the wet side of the jet into the mixing chamber.
The jet meters the amount of fuel you have and that screw can't change it.
Look into the bore back side of the carb you can see its little brass tip.
 

·
Registered
Joined
·
329 Posts
Except for the fact you're pulling most of the air around the butterfly so opening the screw results in a richer mixture.
Its a very tiny pick off.
Look at one...Your restricted from making much difference there is only so much fuel available and you are selectively moving it from the front pick off to the very most rear.

Try this take a jet from a lawnmower or GX160 and put that in there and see how much difference it makes.
Take a bigger one from a 212 or 223 and try that. more fuel...
The pick offs just don't pass enough volume to make a material difference thats is why have a jet.
Most engine don't even have a slot to let you turn that.
 

·
Registered
Joined
·
18 Posts
What does turning it in do?
There is a bypass air circuit (bypasses the throttle plate) that the pilot bleeds fuel into. When you turn it in, you lower the fuel added to the air bypass. So to your question, it leans out the pilot fuel-air mixture. You normally adjust this first for best idle/vacuum then move onto the main jet. In my particular case, I don't mind having my pilot too rich for my high elevation since it makes starting easy in cold weather and I don't spend much time at idle. My goal was not to be lean at WOT and make more power at my elevation. That meant, in my case, to drop my main jet down one size.

I would never recommend drilling out jets since they are cheap. You're not gonna hurt anything as long as you don't run an engine too lean. On the flip size, more fuel doesn't mean more power and too much fuel can wash down the cylinder walls leading to wear/carbon fouling.

There are a lot of resources out there to help reading spark plugs. After you've run your machine at WOT doing actual work, let it cool down and pull the plug to read it.

I made an error in my last post, I said 2.5 turns out on the pilot but meant 2.0 turns out.
 

·
Registered
Joined
·
19 Posts
I recently upgraded my HSS724 to a #78 jet as I'm within 100ft of sea level. With the machine warned up, full throttle RPM is at about 3700, so within spec, but my idle is close to 2800 and that's way above spec. I tried adjusting idle via the screw but it was already backed out all the way. Now I can certainly understand the importance of ensuring the full throttle RPM is within spec, I'm not so sure I understand the implications of a fast idle beyond fuel economy. Are there any? Can I just leave the engine as is?
 

·
Premium Member
Joined
·
1,491 Posts
I recently upgraded my HSS724 to a #78 jet as I'm within 100ft of sea level. With the machine warned up, full throttle RPM is at about 3700, so within spec, but my idle is close to 2800 and that's way above spec. I tried adjusting idle via the screw but it was already backed out all the way. Now I can certainly understand the importance of ensuring the full throttle RPM is within spec, I'm not so sure I understand the implications of a fast idle beyond fuel economy. Are there any? Can I just leave the engine as is?
Short answer is yes. You did not say if you went larger or smaller with your jet size. Just make sure you are not too lean. Check the plug apperance after running for a while to determine that.
 

·
Registered
Joined
·
5,159 Posts
I tried adjusting idle via the screw but it was already backed out all the way.
Setting the idle involves both the throttle and idle set screws on the carb (not the pilot jet screw) and the adjustment up at the throttle lever. I only have it for the HSS928/1332. Hopefully the HSS724 is similar, only with the integrated choke the lever clearances are likely different.
 

Attachments

·
Registered
Joined
·
19 Posts
I went from a 75 to the 78, so I'm not surprised idle increased.

My first read through manual didn't show any adjustments at throttle lever. A second read though does see reference to a throttle stop screw when idle screw is insufficient, so I'll check that out next. Good to know though that if I can't fix it, it's fine too.

Thanks all for the help!
 

·
Registered
Joined
·
1,136 Posts
For what its worth I just rebuilt a Tecumseh hmsk100 carb yesterday and had to adjust the main and idle jets.

From idle to about 2800 rpm the idle jet had a huge effect and main little. At 3600ish the main jet had a very noticeable effect but I still had to rev it to really get a feel of it's behavior.

That being said my predator 420 with the OEM pilot jet and richer main jet although I feel the pilot is a hair lean still runs far better than that Tecumseh.
 

·
Registered
Joined
·
2,005 Posts
For what its worth I just rebuilt a Tecumseh hmsk100 carb yesterday and had to adjust the main and idle jets.

Full idle to I'd guess around 2800 rpm the idle jet had a huge effect and main little. At 3600ish the main jet had a very noticeable effect but I still had to rev it to really get a feel of it's behavior.

That being said my predator 420 with the OEM pilot jet and richer main jet although I feel the pilot is a hair lean still runs far better than that Tecumseh.
For what its worth I just rebuilt a Tecumseh hmsk100 carb yesterday and had to adjust the main and idle jets.

Full idle to I'd guess around 2800 rpm the idle jet had a huge effect and main little. At 3600ish the main jet had a very noticeable effect but I still had to rev it to really get a feel of it's behavior.

That being said my predator 420 with the OEM pilot jet and richer main jet although I feel the pilot is a hair lean still runs far better than that Tecumseh.
2800 idle ? wayyyyy to high
 
941 - 960 of 977 Posts
Top