[harry398]

I know the 254cc B&S is lean as all heck on my Ariens 28".

you know what that needs?

420cc clone. or a 389cc honda.

 

[orangputeh]

But...it's not running too lean under load?

I mean I get it.
Everyone's saying "It's good enough leave it alone"

I get it.

check the plug to determine lean/rich condition., you can always click on my avatar and ignore me if you don't want my advice buddy.

 

[ChrisJ]

check the plug to determine lean/rich condition., you can always click on my avatar and ignore me if you don't want my advice buddy.

No,
I don't want to ignore you, my response wasn't meant to be nasty or mean in any way.

 

[Russell Stephan]

I mean I get it.
Everyone's saying "It's good enough leave it alone"

It's your machine and you have to use it... If a rough idle annoys you, change the pilot jet.

There does seem to be a group of folks that hold themselves as the Central Committee of what you can and can't do to your own machine.

And why not go all-in with a intake adaptor and pod air filter? That should get the Church Lady characters abuzz.

 

[ChrisJ]

It's far from a rough idle. That I wouldn't tolerate at all.

This is the only video I have and that's not really an idle, but it's "slower" and unloaded. Also still cold at this point. Well, cool, it's kept in a somewhat warm crawlspace.

It's not a rough idle, it just wants a little more fuel when not under load, and perhaps a next size smaller jet for the main jet, maybe not. But like I said, I think it's so little I doubt I could ream the pilot jet that little.

 

[ChrisJ]

So wait,
Do the pilot jets always have a number stamped / molded into the top of them?
And where can other sizes be bought?

 

[Russell Stephan]

It's not a rough idle, it just wants a little more fuel when not under load, and perhaps a
next size smaller jet for the main jet, maybe not. But like I said, I think it's so little I doubt
I could ream the pilot jet that little.

Once off idle, the pilot jet has no bearing on the fuel mixture. Assuming all other parameters are in-tune and functioning correctly.

Street motorcycles usually have three fixed jets -- idle/pilot-or-mid-range/main and then a tapered needle which allows the main jet to come online gradually though the upper RPM range. Although they overlap a little, once beyond their fuel delivery upper limits, they effectively bow out of the equation.

A long while back we discussed your leaking adjustable needle valve for the main. Did you remove that modification?

 

[Russell Stephan]

A long while back we discussed your leaking adjustable needle valve for the main.
Did you remove that modification?

Actually, I'm about ready to head out into the garage and install my eBay copy of the adjustable needle main jet. Hopefully, mine won't leak.

 

[ChrisJ]

Once off idle, the pilot jet has no bearing on the fuel mixture. Assuming all other parameters are in-tune and functioning correctly.

Street motorcycles usually have three fixed jets -- idle/pilot-or-mid-range/main and then a tapered needle which allows the main jet to come online gradually though the upper RPM range. Although they overlap a little, once beyond their fuel delivery upper limits, they effectively bow out of the equation.

A long while back we discussed your leaking adjustable needle valve for the main. Did you remove that modification?

Yes, the night I tried it actually.
I'm running an .043 jet. OEM was a 101 which i think is .0393.

I could swear the pilot jet was still in use at 3600 RPM no load. Are you 100% sure it's not? It always seemed like it was on my adjustable Tecumseh.

 

[Russell Stephan]

I could swear the pilot jet was still in use at 3600 RPM no load. Are you 100%
sure it's not? It always seemed like it was on my adjustable Tecumseh.

It's still delivering fuel. But its percentage contribution is so small it shouldn't matter. Once again, assuming the other players in the equation are up to snuff.

 

[ChrisJ]

It's still delivering fuel. But its percentage contribution is so small it shouldn't matter. Once again, assuming the other players in the equation are up to snuff.

I don't know......
Wouldn't the engine, in theory only use 50% more fuel at 3600 unloaded than 1800 unloaded?

 

[Russell Stephan]

I don't know......
Wouldn't the engine, in theory only use 50% more fuel at 3600 unloaded than 1800 unloaded?

Welcome to the painstakingly arduous task of dialing in carb settings for perfect idle, acceleration, drivability, and top-end performance...

If it was easy, every motorcycle squid on a Summer's Friday and Saturday night wouldn't have a popping and backfiring issue on deceleration from light speed.

 

[jherbicide]

Yes, the night I tried it actually.
I'm running an .043 jet. OEM was a 101 which i think is .0393.

I could swear the pilot jet was still in use at 3600 RPM no load. Are you 100% sure it's not? It always seemed like it was on my adjustable Tecumseh.

Regarding which circuit is in operation, Its not about RPM, its about throttle butterfly opening. No load it takes very little throttle opening to get 3600rpm.

-When the throttle butterfly is closed (or more closed than open) there is a higher vacuum (lower pressure) behind the butterfly than in front of it. This sucks the fuel out of the idle circuit.
-As the butterfly opens, the vacuum shifts to the venturi.

Stolen from a previous post, here is a decent graphical picture of the two carb circuits that may help visualize how the circuits work:

Toro powermax 8/24 oe, re jetting carb.

 

[jherbicide]

Welcome to the painstakingly arduous task of dialing in carb settings for perfect idle, acceleration, drivability, and top-end performance...

If it was easy, every motorcycle squid on a Summer's Friday and Saturday night wouldn't have a popping and backfiring issue on deceleration from light speed.

Not true, popping on decel is normal for a properly tuned circuit, especially on low restriction exhaust systems. The fuelie machines can easily tune it out if their software allows for it, but on a carb it requires an overly fat idle mixture to eliminate decel popping/cackles

 

[Russell Stephan]

Not true, popping on decel is normal for a properly tuned circuit, especially
on low restriction exhaust systems. The fuelie machines can easily tune it
out if their software allows for it, but on a carb it requires an overly fat idle
mixture to eliminate decel popping/cackles

I don't know how many times I have to say this on various personal preference topics, but here it goes again... If blubbering, burbling, backfires, and popping on decel float your boat, have at it! If jumping car suspensions are your thing, knock it out of the park.

But, my personal preference is to have my street vehicles perform at their maximum, be polite, and well groomed while among other road users and those living in the community I'm traveling through.

 

[jherbicide]

I don't know how many times I have to say this on various personal preference topics, but here it goes again... If blubbering, burbling, backfires, and popping on decel float your boat, have at it! If jumping car suspensions are your thing, knock it out of the park.

But, my personal preference is to have my street vehicles perform at their maximum, be polite, and well groomed while among other road users and those living in the community I'm traveling through.

That “fix” is to enrichen the idle circuit beyond ideal. Like you say, to each their own but decel popping on easy breathing (read: short exhausts like OPE) is not a sign of mis tune, it’s the opposite. I’d rather have my idle settings right versus stopping having some harmless cackles on throttling down.

There are a ton of resources on the net that describe this phenomenon.

 

[Russell Stephan]

There are a ton of resources on the net that describe this phenomenon.

And no doubt, I've visited a few since my vehicles don't fart and burp through town.

 

[ChrisJ]

And no doubt, I've visited a few since my vehicles don't fart and burp through town.

I have a feeling your main one most certainly does burp and fart through town. Literally.

The TBI 305 or 350 isn't carbureted. L03 or L05 if memory serves.

 

[Russell Stephan]

I have a feeling your main one most certainly does burp and fart through town. Literally.

Referencing the dozens of street and dirt bikes that have passed through my garage over the decades. A quiet street-legal dirt bike is worth its weight in gold since the machines are already looked upon unfavorably by others in the forest-going public.

 

[jherbicide]

And no doubt, I've visited a few since my vehicles don't fart and burp through town.

And they won’t, unless they’re short straight piped or grossly out of tune. This phenomenon only happens with short and low restriction exhaust, and on high rpm throttle closures. None of this applies to most cars and even stock type motorcycles. But it does apply to OPE…