Ran yesterday...Wont run today

[Don Distel]

Try a different carb .

[Rob Voska]

On gas it sounds just rich. Put ANOTHER new plug in it. Lower the arm or screw in the needles. Test start it but don't drive it. I don't like running less than 1/2 turn but to test run it on a stand it it will be OK even if it's shut off (but it probably won't run). If screwing in the needles makes it run OK take the carb apart and lower the arm .015 and then back the screws out. The carb will pump a little less fuel so the needles will need to be open. At least that's what I would try.

Then do what Don said.....get another carb!

PS It ain't a lawn mower.....don't think your going to start it and it will sit an idle for a minute.....if it does it will be to lean when your on the track.

[steveohara]

Set the low speed needle ( the one closest to the engine ) at 1.25 turns and the high speed needle ( the one furthest from the engine ) at 1/2 turn. Turn the idle adjusting screw out until it does not touch the throttle lever and then screw it back in till it just touches, then one more full turn.

To check the pop off pressure you need a pop off guage that you can get at your local kart shop of borrow one from a karting buddy. Hook it to the fuel inlet and pump up the carb to see if it hold pressure... go to about 5 psi first and see if it will stay put. If the carb won't hold 5 psi it either has a bad gasket somewhere or the fulcrum arm is set too high. If the fulcrum arm is too high the leakage from the pressure test will bubble out through the brass dump tube and other fuel orifices in the bore of the carb. You can dunk the carb in a bucket of water to see where the leaks are. If the carb will hold the 5 psi it means the arm is set at the right height and there are no bad gaskets so move on to check the pop off pressure by pumping the carb up until it loses the seal and the needle on the guage drops back to a lower reading. Note the highest pressure point you see on the guage.... that is the "pop off" pressure and it should be no less than 15 lbs. Many kart pop off guages only go to 16lbs so you may find the you peg the guage..... if you do that is fine and you are in good shape on the pop off pressure.
Before running the motor again you may want to make sure it does not have excess fuel accumulated in the case as it will cause the type of problem you describe. To assure the case does not have a bunch of fuel standing at the bottom, remove your spark plug and your fuel line. Plug the spark plug cap with a non conductive material or tape over the end with some good tape.... you need to be sure it cannot arc to the engine. With the throttle held wide open and the fuel line and plug removed, spin your motor over with your starter for at least 15 seconds as fast as your starter will turn it. You might want to stuff a rag in where the spark plug goes to absorbe the excess fuel that blows out so you don't make a mess of the motor. Once you have the motor cleaned out, clean the plug with brake cleaner, acetone or some other strong oil cutting, fast drying chemical and re install the plug. Hook up the fuel line and safety wire the connection to the carb.
Fire it up and fine tune as needed to get the engine to idle clean and have crisp throttle response without blubbering or starving.... blubbering means it is too rich and you need to screw the low speed needle in to clean it out. Starving.... that kind of waaaa, waaaa sound when you crack the throttle means you are too lean and you'll need to open the low speed jet and possibly the high speed as well. Once you have found a setting that gives you decent throttle response, adjust the idle screw to fine tune the idle to a speed a bit higher than you would expect a chain saw or two stroke dirt bike to idle.
When you drive the kart and have the engine at full throttle for more than a couple seconds, if the engine does not blubber or 4 cycle as some folks describe it, back off the throttle and open the high speed needle quarter turn and try full throttle operation again. You want to find the setting where the motor will run clean way up to high rpm and then just break in to a 4 cycle or blubber state at the peak rpm.
Good luck!
Steve O'Hara

[Eric Haynie]

okay...
I pressure tested the carb...It is blowing air out of the brass tube at the front of the carb bore, it is also leaking out the hole at the back of the diaphram plate.
1---is the brass tube the (main fuel discharge check valve)?
2---if so is it supposed to be hollow?
Eric

[Eric Haynie]

took carb apart again...bent arm down (it is at .020 below carb body) still blowing air through both the same holes. water also entered the inside of the carb

[steveohara]

OK.... we are getting somewhere. If air finds its way out through the hole in the bottom of the middle plate it means there is a leak in the diaphragm and it must be replaced. The metering diaphragm must seal air out and fuel in for the carb to work properly and consistently. The next problem is the dump tube... the brass dump tube is the main fuel delivery path to the venturi and air can only flow out through the dump tube if the inlet needle fails to seal. Usually, a leaking inlet needle is due to the arm height being too high but you adjusted the arm to below flush so that should not be the problem. Sometimes the arms get tweaked and causes the needle to tilt and it messes up the seal. You want to be sure the fork on the end of the fulcrum arm has both tangs in the same plane and the fork tangs should be perpendicular to the needle when it is in the closed position. You should also look closely at the area of the needle where the tangs touch the needls to assure there is no wear. If the needle is worn, the arm will not settle in the same place each time.
For gas, the arm should be flush with the body of the carb and the inlet needle should be able to hold pressure up to no less than 15 psi steady without leaking or "poping off".
Does your carb have the rubber tipped inlet needle? Some folks changed to solid metal or nylon and those just don't seal well most of the time. If it is a rubber tipped needle, inspect it carefully to assure there are no dings, cuts, grooves etc. It is a first priority to get the inlet needle to seal and pop off at the right pressure. From there, it is just a matter of making sure the plates are clean and flat ans you have a good metering diaphragm and pumper in the carb. You bought the correct new version of the duck bill so you should have no problems in that area.
One last thing to check..... make sure you have the gasket and flapper gasket in the correct sequence under the circuit plate. The flapper goes immediately below the metal circuit plate, then the gasket or gaskets. There are several thicknesses of circuit plate gaskets out there and you can run one or more as long as they add up to at least .040" thick and do not exceed .060" thick.
Last bit of advice.... if you use a metering diaphragm with the metal plate in the center held on by a rivet you must run it with the extra gasket to provide enough space under the first plate. Without the extra gasket, the rivit will bottom against the fulcrum arm and the plate above and hold the arm open just enough to leak.
Good luck.... if you get the carb set up right it will idle clean, have good throttle response and run well through the full range of rpm without lean spots. The Mac carbs are much maligned.... mostly due to careless mechanics that screw them up.
Regards,
Steve O'Hara

[Eric Haynie]

my needlle is rubber tipped...looks pretty good..I will check out the folcrum arm.
my diaphram has the metal plate....what extra gasket are you talking about?

[Eric Haynie]

I need to find out who I can get a needle,diapham,and new arm would be nice, mine is showing wear on one of the tongs
on the gaskets for the plate on the carb body... is it.040 w/the plate or just the gaskets.
Thanks
Eric

[Rob Voska]

Certified Parts Corporation - http://www.certifiedpartscorp.com/, 800-356-0777. Brand new Margay / Fox plastic tanks, and other Kart parts

Comet Kart Sales kart parts, mac gaskets. 317-462-3413 http://www.cometkartsales


Listed under parts and resourses on the front page.........everyone please take a minute to look.

[Eric Haynie]

I could not find anything at certified.
Comet does not have diaphrams