Hey gang,

So I got one of Lancer's USED 38 mm Mikuni roundslide carbs... Need some help...

So I stuffed it in there with the jets he had in there, a 330 main and a 30 pilot.   Ran pretty okay from scratch, but it took a bit for it to idle down if I gave it some gas.  I fooled around with the pilot till it seemed return to idle correctly.  Rode it around some.  Seemed fine at low and midrange.  Stumbled real bad at WOT.  Dropped the main jet to a 320.  Fired it up and it ran fine, but didn't have a chance to test WOT.  

Now I can't get it to idle properly.  It just started doing it when I got back from somewhere and the bike was sitting for a couple of hours.

Symptoms:  Starts fine with choke, idles okay for a little bit with the choke off, then slowly idles down and stalls.  If I keep increasing the rpm by turning the idle screw in, the idle speed increases, but then it starts decreasing again.  Then fuel starts leaking out of the overflow tubes and I kill the bike.  I've tried going dwon to a 27.5 pilot, but it seemed very lean at all PMS screw settings and had the same result.  Now I've got the 30 in agian...

I keep checking the plug, too.  When I first pulled it out when it first started doing it, it was very fouled, but it wasn't a proper plug chop so you can't really tell anything about it.  The plug with the 30 in was a little fouled, but when I first started it up the throttle was stuck about half way open as the link under the carb had come out on install... killed the engine and adjusted it, so that doesn't tell me anything either.

Any help appreciated.

Pretty sure the floats are fine and that there is no dirt in the needle valve (fresh can of carb cleaner ).  I will check again, though.  The fuel only leaks when I fully seat the idle screw (or get a little close...)

Oh yeah, I'm at 4000 feet (1220 meters) above sea level.  Maybe I should drop the float a mm or two?

Getting good at pulling the carb out, but my hands are all dried out from gasoline!

Checked.

The float needle seems to seat all the way.  It is easy to move and there are no scraping type sounds.  I also blasted some more carb cleaner in there.

The floats float.  I filled the float bowl halfway with carb cleaner and they both floated.  However, as I type this, I realize that IF there is a leak, it could be at the top...

Also,  I measured the float height.  From the rib that the gasket sits on on the upper portion of the float to the float arm while the carb was up-side-down.  The top of the float arm reached 17 mm, as accoding to spec.

So, assuming the floats do not leak, what now?

Thanks,

V

My 38mm Amal Mk2 may have a similar issue but I'm not sure.  When I finish a ride, I can tap the ends of the vent tubes with my finger and get a small amount of gasoline on my fingers.  This seems to be less than a drop and I see no evidence of any dripping fuel, though it doesn't mean it may not happen in small amounts.  While it doesn't seem normal to me, I haven't tried tracking it down.  I've wondered if I might have to adjust the float because of the slight tilt of the bike since the carb isn't quite level.

If the float needle is stuck open, should it leak gas from the overflow at WOT?

I am calling in an order tomorrow and will put a new float needle valve on the list for you.  I really do not like stuff like this to go on when I have sent out a carb to some one.  
You said that the needle valve moved oK for  you, as it did for me when checking it over before sending it to you, but I am wondering if the spring in the valve assembly may be weak and not able to hold it closed when it is supposed to.  That is why I am ordering a new one for you, so we can at least eliminate the valve as a possible cause...if not solve the problem once for all.

So I yanked the carb this evening and came up with a good test for the float.  I filled the fuel line with carb cleaner and gently pushed the flaot arms up.  It definitely seated.  Fuel stopped flowing once the brass pin (the larger of the two moving pins, and not the one with the weird flower or gear like shape) stopped moving up.  When I lowered it, carb cleaner came out again.

Like I said, I just now tried this.  It seemed to close just as well before, but I'm not 100% sure.  I'm gonna go home now, reinstall the carb and see if it's any better.

Photo:


Sorry it's blurry... it was the best lit one...

Just checked.  A bit more gas on the ends of the overflow tubes.

When I masured the cloat height the otehr day, it was 17 mm, which is the lower end of spec.  It seems that it would seat all the way if I put it UP??? to 18 mm...