rich mixture

[jjinga]

I have recently purchase a 1971 Cub Loboy 154, it will fire and run rough with a very rich mixture. The carb is relatively new. It is a after market copy of the original IH. I disassembled and cleaned it , reassemble and get the same result. I have verified firing order, a fat spark, fuel is fresh. soot the plugs quickly. Any help or advice would be greatly appreciated.

 

[David G]

Have you adjusted the mixture?

 

[jjinga]

I have adjusted that but I am not sure how many turns out it should be.

 

[Janicholson]

Two things to check the first is if the air cleaner is clean and has 10-30 oil in the cup. Restricted air makes rich. Remove the rubber hose to see if no restriction makes a difference.
The second is the size of the main jets they must be as original. I do not think you will have a high speed mixture control, only Idle mixture. Lowering the float level in 1/16th inch increments will reduce high speed flow. Jim

 

[jjinga]

It has a paper filter(IH) and it not connected. One thing that I did notice was the tube screws inside the carb that ends at the mixture screw was not as large at top as at the other end and is wondering if that was possibly restricting air flow.

 

[jjinga]

I tried adjusting the float level and there didn't appear to make any difference. But I do appreciate the advice. I believe that someone has had the carb open before me. I do have the manuals on order. Is another carb going to be the answer or perhaps doing a kit first? thank you, Jimmy.

 

[BarnyardEngineering]

There is no adjustment to the mixture on those carburetors, both the idle and main jets are fixed. The adjustment screw is only an idle airbleed, and has very little effect at that.

Cleaning the carburetor will only make it worse because you are removing any restrictions to fuel flow. Gunk in the jets would slow down the fuel and lean it out.

Any fuel dripping from the carburetor when it's not running? That would indicate the float needle not seating, and could be the cause of your rough running.

Could be someone drilled out the main jet in a vain attempt to get more power.

 

[jjinga]

I checked the point on needle under a magnifying glass(old eyes lol) and it did not appear to be deformed. I will check the seat today. I don't have a gauge to determine the jet diameters. If I don't detect problem I will order a kit for the carb. Thanks for the reply. Jimmy

 

[jeffcat]

Hold on a second. You said someone may have been in there? Wonder if the main jet is just plain missing? Talk about a storm drain's worth of fuel! Incomplete carb rebuild?

 

[jjinga]

I have disassembled the carb, there does not appear to be any missing parts but another set of eyes will be here later today. I will post any info that may be helpful. Thanks Jimmy

 

[John M]

Have you verified the choke is opening?

 

[jjinga]

Manual choke and it is open, the engine runs a few secs. before shutting off itself. I have someone coming by this pm. I will take pictures of the disassemble carb showing all parts and post to see if some parts may be missing.

 

[BarnyardEngineering]

I'm talking about the FLOAT needle. You don't need a magnifying glass for that one and the shape of the tip is not very important, as the seal is farther down on the needle.

Plus, you would know that the float needle wasn't sealing by the wet spot on the ground and the steady drip from the carburetor.

That needle up on the neck of the carburetor is an airbleed for the idle. It really doesn't do anything. Whoever came up with the concept of airbleed mixture control was one smart cookie, because he made tons of money off something totally worthless.

 

[jjinga]

thanks for the reply. The only moving part is float and needle. Am I missing something I will dis assemble and try to post pics of carb and parts this pm also with the s/n and motor no along with them.

 

[Roger46]

Maybe it is like my Cub. Someone had drilled out the main jet thinking they would get more power out of it. It ran like you describe until I bought a new main jet. Easy to change as it screws in from the
outside of the carb. Roger

 

[jjinga]

(quoted from post at 17:51:51 04/08/16) Maybe it is like my Cub. Someone had drilled out the main jet thinking they would get more power out of it. It ran like you describe until I bought a new main jet. Easy to change as it screws in from the
outside of the carb. Roger

I just ordered a kit to replace needle and seat and main jet. will post an update after they are installed. thanks everyone for your replies. Jimmy

 

[jjinga]

(quoted from post at 22:52:40 04/08/16)

(quoted from post at 17:51:51 04/08/16) Maybe it is like my Cub. Someone had drilled out the main jet thinking they would get more power out of it. It ran like you describe until I bought a new main jet. Easy to change as it screws in from the
outside of the carb. Roger

I just ordered a kit to replace needle and seat and main jet. will post an update after they are installed. thanks everyone for your replies. Jimmy

Update, after receiving the service manual, reading about the carb operation, I was able to get the eng. running. It seems the AF needs to be hooked to the carb to get proper operation. It still needs to be tweaked and a few other minor issues and the loboy will be operational. Thanks to all who replied. This is the way we all learn how to work through issues. Thank you very much. Jimmy