X4 special air box tube issue

[Steven Rempel]

I have a x4 special, engine has new seal and a leak down test was done all good. it has 140 psi on both mag and PTO sides. I rebuilt and cleaned the Bendix carb and set as per the service manual specs. new spark plugs gaped to 20 thousand's, it has E start with new battery. New ish drive belt and clutches where both disassemble and cleaned. sled has 1010 miles. she seems to all ways want a shot of prime to get going, unless she is good and hot and is restarted with in a few min. a 20 min sit and it will need a shot of prime to get going again.

the issues are I am having a problem that with the air box on with the air tube it will not hold an idle. But if you remove the tube and just use the air box it will hold a idle but need a ever so small throttle bump once a min. If you set the idle screw to open the throttle any more then its current setting it will rev higher but then the clutch starts to engage. and less then it will fall flat on its face. If you lean out or rich in the idle air/fuel screw it will rev engage the clutch or fall flat. and I have tried every combo of the two to get it to hold a idle with the air tube on.

Currently I have a idle set and it will hold it own for the most part but still needs a small bump every so often to keep it running. about 2300 rpm. the clutch is engaging about 3000 or 3200, but tack can not be trusted as it bonces around. If at this time after the engine is warmed up and you put the air tube back on it almost dies instantly. if at this point you pull the throttle there is no help and seems to die even faster. I have check for blockages and it is clean and clear.

what would be causing this.

note. I took it for a 1 hour hard run last night with no air tube and she runs fine with no issues other then a bit rich, but still just getting the frist tank of 50:1 through. but the sound is deafeningly loud and annoying.

[Steven Rempel]

I was thinking today that I have not looked ate the fuel pump since I rebuilt it two years ago. Is it possible that this might be a weak fuel pump????????

I am going to replace the fuel filter and check the tank pick up check valve, it was new at the same time as the fuel pump rebuild.