Carb Frustration

[pfrederi 20,323]

Last year I cleaned up a a C-160-8 complete engine overhaul .010 over/under new valves /guides. I had purchased a used #30 Kohler carb.  It had been worked on as the throttle linkage the ball is on had been welded.  I went ahead cleaned it put a bushing on the throttle shaft, and it ran like cr**p.  Have now had at least 3 extended soaks in Berrymans, two trips through the ultrasonic cleaner and it runs fine over 2000 rpm but I cannot get it to idle.  The idle mixture seems to have very little effect ,it will run for 10-15 seconds then start to slow down sometimes she catches and speeds up and will run again for 10 seconds but then dies again. I bought a Chinese carb ...(hey sometimes they work )...this one didn't, still wouldn't idle well and top end was not as smooth.  Began to wonder if I had screwed up something in the overhaul.  Double checked timing with Timing light ...spot on.    Out of frustration I fired up a C-160-8 project tractor (or resale) She runs really well  so I took her carb and put it in my rebuild .  Now she runs great!!! However I want to get a carb on the project tractor.. as expected the Chinese card ran really rough at idle and high speed.  So now I am back to looking at the the #30 carb I had cleaned up.  I have not removed the idle passage freeze plug.  I have rehabilitated many carbs and have never had to do that....Is there a source for just the replacement plug (or can i get something from McMaster). Also looking closer there is some play on the lower end of the throttle shaft.  Would air leakage there affect the idle???

[ebinmaine 78,380]

1 minute ago, pfrederi said:

I have not removed the idle passage freeze plug.  I have rehabilitated many carbs and have never had to do that....Is there a source for just the replacement plug (or can i get something from McMaster).

 

PM me your address. I'll send you one. They're very hard to find because they're aluminum. McMaster does not sell them.

 

1 minute ago, pfrederi said:

Also looking closer there is some play on the lower end of the throttle shaft.  Would air leakage there affect the idle???

Definitely.

[WHX?? 56,178]

2 minutes ago, pfrederi said:

I have not removed the idle passage freeze plug

I never have either but that's almost gotta be the problem. Bet ya Big Unit @ebinmaine has. 

[pfrederi 20,323]

5 minutes ago, ebinmaine said:

 

PM me your address. I'll send you one. They're very hard to find because they're aluminum. McMaster does not sell them.

 

Definitely.

 

 

Thank you   PM sent.  I guess it is worth a try on the idle passage but may be the loose lower end is the cause...

[ebinmaine 78,380]

12 minutes ago, WHX?? said:

I never have either but that's almost gotta be the problem. Bet ya Big Unit @ebinmaine has. 

 

 

I've rebuilt 15 or 20 carbs over the years. I've only had a couple that I have been forced to get into that galley. Can get pretty gunky in there. But it's definitely not normal and it's very easily cleaned, most of the time.

 

 

7 minutes ago, pfrederi said:

 

 

Thank you   PM sent.  I guess it is worth a try on the idle passage but may be the loose lower end is the cause...

 

 

I would definitely try the extra cleaning first. I have a couple of well worn number 30 carburetors here that still run and drive okay even though they are pretty Loosey Goosey.

[WHX?? 56,178]

46 minutes ago, pfrederi said:

loose lower end is the cause...

Can those be re-bushed? I never give that area a thought. 

[ebinmaine 78,380]

33 minutes ago, WHX?? said:

Can those be re-bushed? I never give that area a thought. 

 

Probably, but....

Not with the tooling I have. It would take a precise drill press and holding vise to go down through the top bore, or find the ability to line it up and drill up through the bottom.

 

At that point you have to weigh whether it's worth taking the time.  

[953 nut 65,371]

1 hour ago, pfrederi said:

the loose lower end is the cause..

1. That would be my .   A down and dirty test would be to cover the bottom with grease to see if air in-leakage at the bottom is causing the problem. 

[Handy Don 16,307]

1 hour ago, ebinmaine said:

Quote

Also looking closer there is some play on the lower end of the throttle shaft.  Would air leakage there affect the idle???

Definitely.

Does the lower shaft penetrate the carb body or is it in a “pocket”? Penetration: can leak air. Pocket: cannot leak air. 😉

I do believe most are pockets for two reasons: 1) so that the base of the shaft is supported, which keeps the plate centered in the throat, and 2) no leaking air!

[Bill D 2,781]

Can you get the brass center jet out?  I did that on one and found a spider nest in it.  Had to clean it manually.  Solvent wouldn't dissolve spider silk.

[ebinmaine 78,380]

2 hours ago, Handy Don said:

Pocket: cannot leak air.

 

 

By strict definition that's correct but the reality is that the lower shaft being loose allows the upper shaft to flex even more and the butterfly can wander around in the main bore.

You're not getting an air leak from the bottom in that case but you're getting erratic operation because the butterfly is just Clowning Around half the time.

[pfrederi 20,323]

Got the plug out no dirt in there.... I guess the worn lower shaft pocket is a culprit.  In addition to the butterfly wiggling around air can be sucked around the shaft sitting in the enlarged pocket.  

 

 

[ebinmaine 78,380]

3 minutes ago, pfrederi said:

Got the plug out no dirt in there.

 

Just for kicks take a can of brake clean and spray back & forth through those galleys.  See where they go and clarify cleanliness.  

[pfrederi 20,323]

Just ran thin stainless wire through all the ports and tunnels nothing came out all were clear

[sqrlgtr 2,630]

Only other thing I can think of that has not been mentioned is maybe a bent main or idle mixture screw the needle end???? I bent one once and it never would adjust right but robbed one off another and it worked IDK if I just got lucky or they all will swap around....

[pfrederi 20,323]

8 minutes ago, sqrlgtr said:

Only other thing I can think of that has not been mentioned is maybe a bent main or idle mixture screw the needle end???? I bent one once and it never would adjust right but robbed one off another and it worked IDK if I just got lucky or they all will swap around....

They looked ok but I have some others to try... good idea

[wallfish 19,759]

Just taking a stab as I know Paul is an experienced engine guy.

Main jet needle holes and clean them with a piece of copper wire. ( I use copper wire in all the holes and passages because it's a soft mater that won't scratch or gouge anything)

Spray into the holes as that needle is actually a tube so spray should come out the top holes too.

The pointed tip should be smooth.

You could try just changing the jet needle from carb to carb and that may tell you if there's a difference or if there's an issue there. 

[ebinmaine 78,380]

The plug mentioned above is a 3/8" aluminum welch plug. 

 

My source is 

 

Mike's Carburetor & Injector Parts

Chehalis, WA 

 

PM me for more information.  

 

I'll be ordering another bag so if anyone else needs one - lemme know.  

 

 

 

[squonk 46,177]

The loose lower shaft shouldn't effect mixture as it's after the idle needle unless it's moving enough to make the top shaft still leak. It will cause erratic operation as the throttle blade will not sit still in the bore.

 

[squonk 46,177]

10 minutes ago, ebinmaine said:

The plug mentioned above is a 3/8" aluminum welch plug. 

 

My source is 

 

Mike's Carburetor & Injector Parts

Chehalis, WA 

 

PM me for more information.  

 

I'll be ordering another bag so if anyone else needs one - lemme know.  

 

 

 

I could use a couple Eric

[ebinmaine 78,380]

15 minutes ago, squonk said:

I could use a couple Eric

 

You got it.  

Do I have your address? 

[sqrlgtr 2,630]

Eric, I could use a couple my self. Let me know and I will help you purchase them.

[ebinmaine 78,380]

Just now, sqrlgtr said:

Eric, I could use a couple my self. Let me know and I will help you purchase them.

 

PM me your address