Carb advice

Sun Oct 03, 2010 12:33 pm

I really hate to bother you guys but this carb is driving me to drink. I've taken the carb off 3 times and cleaned it with carb cleaner and compressed air. I use the choke to start and it starts right up push the choke off runs fine.Before I go further the idle screw is turned in against it's seat, It will idle and run full throttle and any where in between but you have to play with the choke or feather the throttle to get it to increase in speed.Now if I open the idle screw 1/2 turn or a full turn the only way it will run is with the choke on 3/4 of the way and i get smoke from the exhaust from over rich mixture.Tractor purrs like a kitten with idle screw turned in against seat and does not smoke at all but will not accelerate with out choking or feathering. The ignition system seems ok with a nice spark and I've checked timing. Any ideas ??

Re: Carb advice

Sun Oct 03, 2010 12:54 pm

Sounds like it's still plugged. When I clean them, I take a piece of stranded automotive wire and cut a piece about 3" long then pull a single strand out of the bunch. I use this to clean out all the holes and jets.

I also have a jewlrey ultrasonic cleaner for the really tough ones.

Re: Carb advice

Sun Oct 03, 2010 1:26 pm

I used a torch tip cleaner tool .

Re: Carb advice

Sun Oct 03, 2010 8:35 pm

Never use a tip cleaner. They are made of very hard steel and will enlarge the hole you are trying to clean. Always use a strand of copper wire. Telephone inside wire is just the right size. There is still a piece of dirt in there somewhere. The idle mixture screw also controls transition from low to high speed. Starting point is usually one and a half turns out. Is this a zenith or I/H carb?

Re: Carb advice

Mon Oct 04, 2010 4:18 am

It's a IH carb.

Re: Carb advice

Mon Oct 04, 2010 6:54 am


I ain't no expert, but I am learning. Cleaning the carb itself may not be the solution. You might actually have it clean but as soon as you introduce fuel to the carb it gets plugged again. Not likely but a possibility. Suggest that you clean the whole fuel circuit starting at the fuel tank ensuring that the tank is clean and there is no rust/dirt/crud/other contaminants present in the tank. The the fuel sediment bowl should be cleaned, make sure the gasket seals properly and that the sediment screen is present and in good condition. Next ensure the fuel line is clear of obstructions/buildup/crud and that the carb inlet screen is present and clean. Then continue on into the carb. Make sure that all the passage ways are clean - use an aerosol carb cleaner to provide the pressure needed or even canned air - do not use your compressor - way too much pressure. The needle and cage area needs (item #9 below) to be looked at closely - ensure that there is no dirt/crud/flakes of varnish in the cage area. Remove the main metering jet (item #28 below) - clean both orifices - the large lateral orifice and the much smaller longitudinal orifice. As Cecil suggested never ever use torch cleaning tips as they will damage the jet. Use on a single strand of indoor twisted pair aka telephone wire. It is the right diameter to enter the longitudinal orifice and clean without scratching or distorting the orifice. Ensure the float moves freely and is set correctly and that the float is not full of fuel from some sort of breach. Make sure that the mating surfaces are both flat and that the gasket seals properly. These are all steps required to properly clean the carb. See the following for assistance if needed:



  1. How To Install A Fuel Tank Strainer
  2. How To Install an In-Line Filter in 5/16" Steel Gas Line
  3. How To Upgrade A Cub Fuel System
  4. How To Straighten IH Updraft Carburetor Tops

Cub-154 Lo-Boy Owner's Manual

Lurker Carl's Cub Carb Fixes

Also, you mentioned that the idle screw (item # 22) is pretty well tightened down. Again as Cecil said it needs to be set somewhere between 1 and 1-1/2 turns out. Then you adjust the idle set screw at the throttle lever (item #2 above) until the rpm is somewhere between 400 and 600 rpm. You can do that by ear or by using something similar to a Stewart-Warner 757-W Hand Tachometers

Image Image

After all of this and the problem persists the next step would be to see if the governor is functioning properly as well. The "Tractor purrs like a kitten with idle screw turned in against seat and does not smoke at all but will not accelerate with out choking or feathering." kinda hints that the governor may also be involved. Hope this helps some.

Re: Carb advice

Mon Oct 04, 2010 7:17 am

There are many areas to clean on a carb. Assuming you have good flow to the carb, no leaking gaskets, it does sound like it is still plugged somewhere in the carb itself. Carb cleaner and compresses air is a good place to start. Don't use compressed air with the carb assembled but apart there should be no risk (assuming you do not have a 3000 psi scuba compressor). However, there may still be corrosion which is what the cleaning wire is for. Don't forget the discharge nozzle, the holes on the sides and a much larger cleaning wire for the center of the tube. Some discharge tubes are open on both sides but some are closed on one end. That is where corrosion can hide. Make sure the center is clean since it it functions both as the accelerator and as the mid to high speed circuit. Run a wire to the bottom of the carb body where the discharge nozzle screws in to clean the accelerator well. In the bottom 1/2 of the carb is a hole that the idle tube goes into, that hole should connect into the accelerator well. Next to that hole is a much smaller hole that is the high speed air bleed, it should connect also to the accelerator well. Also check the two slits downstream from the throttle plate, they should be open into the area around the idle adjust screw. There may be an inlet screen so check it also.

I had on that acted similar but turned out the timing was way off, may be worth checking also.

Re: Carb advice

Mon Oct 04, 2010 2:05 pm

Thanks Guts alot of good info here. The governor seems to be working ok the timing is right on the money I had the lines and tank off and cleaned them . So I'll take the carb back off and take it apart again. I always turn the regulator on the compressor down when I'm cleaning carbs. So it will be a couple of days before I tackle it again but will keep you posted Thanks again :D

Re: Carb advice

Wed Oct 06, 2010 5:08 am

Sorry guys, I said guts in last post the t is too close to the y any way took carb off again sat down with it again completely disassembled and cleaned and blew out still doing same thing. I've check timing and spark all good but i'm going to change points and condenser and spark plugs.I've rebuilt probably 100's of carbs since my hotrod days and never felt this dumbfounded so I've convinced my self that the carb is ok so if you hear of a guy in new york and shooting his tractor it's me. Starting to understand why I can't sell it for $500.00.

Re: Carb advice

Wed Oct 06, 2010 5:23 am

Still don't see that you poked it out with a piece of wire. Especially the high speed jet. Some times just blowing it out isn't enough.

Re: Carb advice

Wed Oct 06, 2010 7:45 am

I did poke it out with a piece of wire. :D

Re: Carb advice

Fri Oct 08, 2010 9:25 pm


I had been through this kind of problem a little while ago with Ellie and her newly redone carb. I cleaned the jet religiously, the float was indeed perfectly set (Cecil did it so there was no doubt), carb body was straight, all required parts were where they were supposed to be. It was a head scratcher for sure.... I almost :big give up: gave up.

I found the problem when after conferring with Cecil that he suggested I re-check the needle and cage again as that was the last likely spot for a blockage. I told him I had done that a couple times and found nothing, but he insisted that I take a really close look. It took a lot of intent inspection of the condition of the needle and cage ..... :oops: but when I took the cage out and held it up to the light from the window I could just make out a bit of cloudiness in the cage. Seems a flake of varnish was causing the problems. The flake was not noticeable when I looked at the cage previously under the light from my fluorescent fixtures.

Now I am not saying that this is the problem, but it might bear looking into. The least likely sometimes can be the actual source :oops: it was for me.

Re: Carb advice

Sat Oct 09, 2010 4:35 am

Thanks Rudi,Sometime in the next couple days I'll check it out,Just am real busy at the moment.Thanks again