Do Kohler Magnum carbs have an intermediate jet?

[RED-Z06 2,567]

My m12 has a bog just off idle, idles perfect, runs otherwise perfect, the plug looks good...but if i crack the throttle it just acts like its wanting fuel...now, if i opens enough to get into the main jet it takes off.

 

Carb has been cleaned and built but i did not remove the Welch plug because it usually ends badly

[pfrederi 18,654]

Many Magnums seemed to come with Walbro Fixed Main jet carbs..Is that what you have?  They can have issues  so far as I know there is no intermediate jet.

[RED-Z06 2,567]

Thinking out loud...carbs usually have a port just forward of the throttle butterfly that is primarily used on tip-in, just as the idle circuit loses vacuum but the venturi at the main jet doesn't have enough vacuum, the little intermediate port lets a little fuel in to bridge that gap.  But I know kohler had issues with commands dealing with a bad off idle bog that required an actual accelerator pump to be added...so, not sure if this was just a problem with magnums or if they maybe updated the carb at some point

[RED-Z06 2,567]

1 minute ago, pfrederi said:

Many Magnums seemed to come with Walbro Fixed Main jet carbs..Is that what you have?  They can have issues  so far as I know there is no intermediate jet.

Its the adjustable main and idle/pllot jet model.  I dont see a brand on it like carter

[ebinmaine 72,595]

14 minutes ago, RED-Z06 said:

if i opens enough to get into the main jet it takes off

Lemme just say...

 

I WOULD want it fixed if it were mine. 

 

But....

Technically...

As long as it DOES get past the stumble every time it doesn't matter. 

Because...

An air cooled engine shouldn't ever be 

16 minutes ago, RED-Z06 said:

just off idle

 

Unless it's about to be shut off. 

 

 

[pfrederi 18,654]

Looked at you video would say you have a carter/Kohler adjustable main jet.   Looks like the ones on K series main screw on top.....   Walbro adjustable  the main was at an angle on the side.

[RED-Z06 2,567]

12 minutes ago, ebinmaine said:

Lemme just say...

 

I WOULD want it fixed if it were mine. 

 

But....

Technically...

As long as it DOES get past the stumble every time it doesn't matter. 

Because...

An air cooled engine shouldn't ever be 

 

Unless it's about to be shut off. 

 

 

But thats the thing, it doesn't always get past the stumble, if say im done pushing dirt and catch 3rd to putt around back to the shop and im down near idle and i bump it up...may take off..may cut off, if i increase the main jet fuel flow, the bog is barely noticeable but its way too fat up top 

[ebinmaine 72,595]

35 minutes ago, RED-Z06 said:

But thats the thing, it doesn't always get past the stumble, if say im done pushing dirt and catch 3rd to putt around back to the shop and im down near idle and i bump it up...may take off..may cut off, if i increase the main jet fuel flow, the bog is barely noticeable but its way too fat up top 

 

Maybe try the @formariz laquer thinner soak?

 

[Jeff-C175 7,206]

@RED-Z06  What RPM you have the idle set at?  From what I've seen most ppl have the idle set too low.

 

 

https://www.smallenginesuppliers.com/html/engine-specs/kohler/Kohler_Carburetor_Reference_Manual_TP-2377-E.pdf

 

[ebinmaine 72,595]

2 minutes ago, Jeff-C175 said:

@RED-Z06  What RPM you have the idle set at?  From what I've seen most ppl have the idle set too low.

 

 

https://www.smallenginesuppliers.com/html/engine-specs/kohler/Kohler_Carburetor_Reference_Manual_TP-2377-E.pdf

 

Actually now that you mention it my  1974 C160 isn't happy below about 1350 RPM.  

[RED-Z06 2,567]

10 minutes ago, Jeff-C175 said:

@RED-Z06  What RPM you have the idle set at?  From what I've seen most ppl have the idle set too low.

 

 

https://www.smallenginesuppliers.com/html/engine-specs/kohler/Kohler_Carburetor_Reference_Manual_TP-2377-E.pdf

 

Per my tach 1350...but ill go check to be sure

[RED-Z06 2,567]

Here is a video.  Warmed up about a minute before filming...as you see, idle is rock solid and its smooth up top, i even added fuel hi and low, just doesn't like to come off idle

 

 

[oldlineman 1,537]

Just thinking out loud would low fuel pressure or a low float cause that? Bob

[RED-Z06 2,567]

19 minutes ago, oldlineman said:

Just thinking out loud would low fuel pressure or a low float cause that? Bob

That would normally show up as starvation under demand, I set the float level then went back and went just above level, hoping to see some improvement but no change, i left it where it was the 2nd time.

[Handy Don 14,054]

That idle doesn't sound even close to 1350 RPM to me--well under 1000 is more like it.

Still, I'd suspect a partial blockage of the main jet or clogging in one of the pressure balancing air passages in the carb body. Either way, serious cleaning--ultrasonic tank, if you have access to one.

[ebinmaine 72,595]

4 hours ago, RED-Z06 said:

Carb has been cleaned and built but i did not remove the Welch plug

 

I don't normally remove those either. 

I do use a ~ minimum ~ of a full can of brake clean to spray through all the galleys back and forth several times. If you can clearly see which port(s) are connected to the welch plug get some cleaner flowing through there in BOTH directions for a bit. 

 

 

[Handy Don 14,054]

Welch plugs are intimidating at first but the shape of the chamber behind them makes it tough to scour them clean without removing the plug--spraying in both directions can work but can also just move dirt back and forth. All the good rebuild kits come with a plug for that reason. Watch a YT or two to see how to set a new one back in there. 

[AMC RULES 37,196]

 

[RED-Z06 2,567]

2 hours ago, Handy Don said:

That idle doesn't sound even close to 1350 RPM to me--well under 1000 is more like it.

Still, I'd suspect a partial blockage of the main jet or clogging in one of the pressure balancing air passages in the carb body. Either way, serious cleaning--ultrasonic tank, if you have access to one.

Unfortunately the flash refracted off moisture on the lens of the tach but it said 1360, and 3570 flat out.

 

The carb was disassembled, spent 2hrs at 180*F in my ultrasonic, then 2 more hours the following day, then blasted with 150psi and carb cleaner, and a new kit put in.

 

Im probably going to have to pop the welch plug off, i just hate doing that.

[kpinnc 14,629]

I know some folks hate the china copy carbs, but situations like this are why I keep a couple on hand. They are good backups, and work fine in the short term for troubleshooting. If you swap the whole carb and the trouble goes away, the tractor isn't down while you properly rebuild it. 

 

I can't help but wonder if you don't have a weak fuel pump or the fuel system is sucking air. Walbro carbs on the other hand, don't allow much adjustment to play with. If it has only one brass adjustment on it, it's a Walbro. Do yourself a favor if that is the case and find a Carter or Kohler carb with the high and low adjustable jets.

 

 

Edited January 9, 2022 by kpinnc

[RED-Z06 2,567]

24 minutes ago, kpinnc said:

I know some folks hate the china copy carbs, but situations like this are why I keep a couple on hand. They are good backups, and work fine in the short term for troubleshooting. If you swap the whole carb and the trouble goes away, the tractor isn't down while you properly rebuild it. 

 

I can't help but wonder if you don't have a weak fuel pump or the fuel system is sucking air. Walbro carbs on the other hand, don't allow much adjustment to play with. If it has only one brass adjustment on it, it's a Walbro. Do yourself a favor if that is the case and find a Carter or Kohler carb with the high and low adjustable jets.

 

 

This one appears to be a Kohler/Carter #26 post Kohler buyout, has both needles.  The fuel tank grommet, valve, all the lines, and filter are a couple weeks old, the pump shoots gas out pretty good, a good 10" geyser.  I ran it wide open 20 minutes, ran great...just that off idle hesitation.

[Maxwell-8 4,367]

1 hour ago, RED-Z06 said:

.just that off idle hesitation.

Air fuel at idle is incorrect.

You should find the point were the engine runs the fastest on idle by the air-fuel ratio on idle adjustment. 

Then bring down or up the rpm with the idle speed screw to 1200rpm.

[formariz 12,041]

Is it possible that you have the wrong carburetor for that engine? Not drawing enough will create that very symptom, hesitation or worse when moving into high throttle. The M12 requires a #26 carburetor which has a 1.07" throttle  bore and a ".812" venturi. They may all look alike outside but are not the same internally.

[RED-Z06 2,567]

9 hours ago, Maxwell-8 said:

Air fuel at idle is incorrect.

You should find the point were the engine runs the fastest on idle by the air-fuel ratio on idle adjustment. 

Then bring down or up the rpm with the idle speed screw to 1200rpm.

Oh im aware...thats why my C100 is perfect.  This one will not do that, if i set the idle to 1200/1250 using the normal method it absolutely will not come off idle.

 

Im going to replace the pump, carb...im tired of screwing with it..something isnt right, and traditional cleaning isnt helping.

[RED-Z06 2,567]

51 minutes ago, formariz said:

Is it possible that you have the wrong carburetor for that engine? Not drawing enough will create that very symptom, hesitation or worse when moving into high throttle. The M12 requires a #26 carburetor which has a 1.07" throttle  bore and a ".812" venturi. They may all look alike outside but are not the same internally.

No markings inside but has part number 47-053-62 on it which is correct for an m10/m12