Help! My Cub is only running so-so now!

[WayneW]

It's been running like a top for a while. Didn't start it for about a month or so. Now the power is a little on the weak side and in order ro keep it running smoothly I have to have the choke out about 1/4 of the way. Tried playing with the idle adjustment screw......but nothing.

-as always, thanks for any help.

 

[ronjhall]

Wayne

The fuel tank or the glass fuel may have dirt in them. Remove the glass bowl make sure you have a good fuel flow when the valve is turned on. Try removing the fuel line from the carburetor. Turn on the fuel valve. You should get a good flow of gas. If you have good fuel flow, check the float inside the carburetor. It may be stuck in the up position. You may want to clean the whole carburetor while its off the engine,
One last item you may have water in the gas?

 

[Gatorboy]

I'm thinking water in the fuel as well. Do you have a water separator that you can open up and see if water runs out?

 

[Ledgemere Farm]

get some lead substitute too if you haven't already. My Farmall ran bad until I started addind a little.

 

[Soundguy]

Choke enriches the mixture, and provides extra manifold vacume. That tells you where you need to look based on these following ideas:

An enriched mixture allows a weaker spark to fire a plug.

Check your wires, pointsm rotor and cap. Pull a wire and see how your spark looks.. should be snappy and blue.. not red yellow or straw colored. Should be able to jump 3/16 of in inch. I fthe points are coroded, either dress with an ignition file.. or for a quick test.. use a piece of brown paper grocery sack pulled thru the contacts a few times.. works great on all but the most burnt points. Check your plugs too. A fouled plug is hard to fire.. especiall wet ones. Here's how to read insulator colors on a spark plug. Sooty black is rich.. oily black is fouled from ring blowby / oil consumption, white/ash is lean.. tan is correct mix. wet is gas or coolant fouled.

An enriched mixture will also help offset a vacume leak.. which leans the mixture. It is doubtfull that setting for a month has made you develop a vacume leak.. but it is possible. Throttle shaft packing is felt and may have 'died'. Easy to check for a leak by spraying a whif of ether or even unlit propane from a plumbers troch around the carb and manifold immediatly after starting the tractor. ( BE CAREFULL !!!) If the engine changes sound/rpm when you do this.. you have a vacume leak.

Choke increases manifold vacume to the fuel and air system. This will help pull air thru a clogged air breather, or fuel thru a clogged fuel bowl screen.. or thru a partially clogged mainjet.

Good luck.. those ideas should get you pointed in the right direction.

As a last resort.. if none of those do it, and you still lack power.. check the centrifugal advance weights in the distribuitor.

Soundguy

 

[Gunfighter]

In addition to all of the above, there's one more place to check.
The L fitting at the carb inlet has a screen on the side that
screws into the carb... Don't know if all Cubs have this but
my 1949 did an it clog on more then one occasion...

RJK Sr (Richard)
West Michigan...

 

[WayneW]

Ok, checked the simple stuff. The screen in the carb is clean, so is the fuel filter. Float in carb, well it floats. Have a pretty good spark on all plugs. When I get a little free time, I'll pull the plugs and give them a look over. Will also try adding some lead substitite like Greenrules suggested. See if that helps.

Though I also noticed on the, I believe it's the governer (shaft in front of the engine that goes to the carb), where it attaches to the carb, the lever is a little loose. I thought of tightening it, but have no idea where it should be. Does anyone know what I'm talking about here? I'll be **** if I can explain it better. Though it may be why because this is not a solid connection, I have poor throttle response. (sometimes I increase the throttle, and if works ok, other times, no response)

 

[Gunfighter]

Your hand throttle lever doesn't control the throttle plate in carb
directly. The throttle lever attaches to the governor and it's the
governor that controls the position of the throttle plate in the carb.
If I remember correctly it does feel loose dependent on throttle
lever setting....

Have you check compression an ignition timing???

RJK Sr. (Richard)
West Michigan...

 

[Soundguy]

I havn't looked at the exact gov settings in the shop manual.. but on other tractors, the gov teeds to not be under tension.. and not have any slack either.

Lead substitute won't do much for you unless you don't have hardened valve seats.

Flyweights in the ignition advance may be stuck as well..

Soundguy

 

[DeereIHRebel]

Flyweights in ignition advance?? Cubs don't have timing advance.