Bing Carb On '72 Wr250

I've finally got round to finishing my WR and have managed to get it to run, albeit badly.

I had the engine rebuilt with new crank, piston, RH case. Ignition is good and new coil.

Carb has been stripped and ultrasonic cleaned and i can see light through all holes i should be able to see light through, before i buy new jets, needles etc is there anything i can try-

The bike starts if i 'prime' with petrol directly into cylinder or a small amount into carb mouth, the bike runs ok about 1/4 throttle and more, especially if blip the throttle. below that it just dies and it's difficult to catch it with the throttle to keep it running. When i cuts i have to prime it again to get it to start so I'm guessing the pilot jet is the issue as it's a lean cut.

There is no filter on it and it runs much better if i cover half the carb mouth so i assume its running lean with no filter fitted.

The slider isn't badly worn and brass parts seem ok to the eye.

Fitted jets are 35 Pilot, 2.85 needle jet, and 170 main jet. all standard apart from main which book says should be 195.

The needle has 3 positions. i have it on the bottom richest position.

1/36m06 is cast into the body so i assume it's a 36mm.

Any suggestions would be greatly appreciated.

It does sound like it is lean and could possibly be an air leak. When the motor was rebuilt one of the last things the engine builder should have done was a leak down test. If a leak down test was not done then it is a crap shoot as to whether the motor is sealed good or not. Why was the RH side motor case replaced, was it badly corroded? Makes me wonder what the LH side looked like. Also check the float height. The fuel level in the float bowl may be to low. Double check the idle circuits in the carb are 100% clear.

Marty

Thanks for the reply Marty, The case had been welded up inside, it was a mess. I got a pair of used cases and the builder used the two best cases.
I'm not sure if a leak test was done but he is a reputable builder so i would assume yes.
I took the carb apart again today to check and there was some fine powder in the bowl that had got past the gauze in the fuel tap.
I stripped it down, put it in the ultrasonic cleaner for a while, checked all holes etc and re-assembled with the float level slightly higher. I cleaned the fuel tank out and fitted an inline fuel filter.
I fitted the air filter but this made no difference so removed it.
If I cover half the carb up it seems to run ok, not perfect but acceptable. If the idle circuits were blocked would it even run like that?
Maybe i'll order new jets then i can eliminate that side of it.

I will also suggest a pressure/ leak down test just to verify all is good . I do have a question for you , does the primer button on the carb work ? You stated that you have to prime with fuel using other methods . The primer when pushed down presses on the float to allow extra fuel into the float bowl . If it doesn’t , that may be an indication that your float level is set too low . You also stated that the brass jets appear to be ok . While they might be ok the needle jet is a wear item on bing cards and chould be replaced if you can . This is the brass jet the needle that is attatched to the slide goes thru . 50 year old carb used for unknown amount of years with the needle sliding and moving thru it . Just a suggestion .

I'm an idiot!!
I stripped the carb apart again, ultrasonic cleaned it again, checked all parts against the parts diagram before I put them back then noticed that atomiser had been fitted 180 degrees the wrong way round. I had been re assembling the carb how i found it, stupidly not checking this was right.
Now with the atomiser the correct way round and tested the bike ran like a dream. Still not the easiest to start but once running it idled and revved without issue.

The atomiser is part 2 in this diagram and has a cut out which should face the engine. I had it facing the mouth of the Carb

Rob, I am glad it was something simple. Much easier to fix rather than chase air leaks!

Marty

Thanks Marty, me too.
Still may have to split the cases though as got gearbox trouble now. Will post a new thread though.

Rob, did you sort this out? I have the identical bike and having the same issue. Thanks

What will cause this is an air leak at the intake manifold to cylinder transition or at the carb to intake transition. The pilot circuit is super sensitive to the lack of vacuum. The intake manifold on these old Huskys can warp at the screw-flanges on either side causing a bow in the center of the manifold on the bottom that results in an air leak even with new gaskets. The second place these bikes are famous for air leaks is at the carb to manifold transition. Husky didn't engineer any sort of sealing mechanism at this location, its just the aluminum carb clamped to the aluminum intake spigot. Over time vibration and continuous removal and re-installation of the carb loosens the fit between the two and creates an air leak thats enough to disrupt the idle.

Solution is to remove the carb and the exhaust then plug the manifolds with something like an expandable plumbing plug and apply 5 to 6 lbs air pressure through the spark plug hole or through one of the plugs if they're set up for that. Check for leaks using a spray bottle of dish soap and water. While you're at it check the base gasket, and the head to cylinder transition too. Also, check the carb to manifold spigot clearance by seeing if you can wiggle the carb when its on the manifold while not tightened. There shouldn't be any wiggling, wiggling isn't allowed on Huskys.