Mikuni vs Hitachi carbs - needles

Before I start.
Did some xjbikes searching but for some reason the browser keeps locking up... That's my excuse.

The question is about the vacuum petcock and the results between mikuni and Hitachi if the needles decide not to seat.

The mikunis have overflow pipes so I figure you would end up with a driveway full of fuel if the tap was left on prime or you had a manual tap left on 'on'.

The Hitachis would leak fuel into the cylinders in the same circumstance and cause all sorts of issues, thin oil, vapour lock etc.

Or I'm just way off.

Please advise. Thanks.
PS: (having issues with tap vacuum plunger and have mikunis and have let it on prime so... That is the reason for this question)

 

And that's a good excuse, best one I've heard all week!

Not all Mikuni carbs do, and even with the ones that do have them, you can still end up with fuel in the crankcase or the airbox, since the overflow vent is above the floor level of the carb throat, where the main fuel jet/emulsion tube/needle are located. Now, it could be that when the engine is off (and the main jet needle is fully inserted into the emulsion tube and the main jet) that the flow of fuel up and past all those components is restricted quite a bit, and thus the overflow ports --- which are much less restrictive to fluid movement --- would be the recipients of any overfilled bowls. But I doubt that the main jet/needle/emulsion tube are actually fluid-tight, and some fuel is going to pour out of there, and where that fuel overflow goes (crankcase or air filter box) is dependent on the amount of overflow and the orientation of the bike (on centerstand or not, parked on a hill or not, etc.).

Early Hitachi carbs (the more-common HSC32 series) have bowl vents in the carb throat, about halfway "up", and facing the airbox. The HSC33 carbs do have bowl vent/overflow t-fittings between adjacent carbs, but again these arrangements are functionally just like the Mikuni carbs.

If I recall correctly, the later XJ900 carbs have an actual overflow nipple on the base of the carb body, and it may serve to capture fuel overflow before it gets to a level equivalent to the floor of the carb throat.......that seems to be ideal solution to a fuel overflow situation, if I am indeed correct in the assumption of their purpose.

 

Thanks for that Len.
Better fix it either way, just filled the tank up, damnit.
I'll send you an email for a kit.
Actually... What is your code for the 5G2 petcock kit?

 

fp129) We offer both standard and deluxe versions of the PETCOCK REBUILD KITS which contain all of the major parts needed to fully rebuild your factory petcock:

HCP124 Aftermarket PETCOCK STANDARD REBUILD KIT contains all the basic items you'll need to overhaul an original petcock: the selector lever o-ring and distribution valve, the HCP110 vacuum diaphram, and a petcock-to-tank mounting o-ring. Fits all XJ550, FJ600, all XJ650 (except Turbo models), and all 1981-83 XJ750 models. Also fits the following non-XJ models: 1980-82 SR250 Exciter, 1982-83 XS400 Maxim and Seca, 1982-83 XZ550 Vision, 1984-87 XV700 Virago, 1981-83 XV750 Virago, and 1982-83 XV920 Virago models. We strongly recommend the use of either the HCP663 spring shim washer or the HCP13145 replacement spring (not included) when rebuilding original petcocks. NOTE: petcock mounting screws, mounting screw washers, faceplate screws, and selector lever wave washer are NOT included in this kit and must be ordered separately if desired.

HCP6060 Aftermarket PETCOCK DELUXE REBUILD KIT contains almost everything you'll need to repair an original petcock: the HCP2282 deluxe diaphram repair kit with the plastic spacer plate; the selector lever o-ring, wave washer, and distribution valve; the petcock-to-tank mounting o-ring, two of the stainless faceplate screws, two petcock-to-tank mounting screws and their sealing washers, the fuel outlet plate gasket, and the in-tank filter. Fits all XJ550, all XJ650 (except Turbo models), and all 1981-83 XJ750 models. We strongly recommend the use of either the HCP663 spring shim washer or the HCP13145 replacement spring (not included) when rebuilding original petcocks. NOTE: the fuel outlet plate gasket that is included in this kit is not needed nor used on original FJ600 or XJ750 Maxim and Midnight Maxim petcocks. FJ600 and XJ750 Maxim and Midnight Maxim owners should also order the HCP1478 drain screw and the HCP7446 drain screw gasket, as those items are not included in this kit.


HCP13145 Aftermarket petcock vacuum diaphram RETURN SPRING. One of the many causes of a leaking petcock is a diaphram return spring that has weakened over time. These replacements are produced to a slightly longer specification than stock, resulting in approximately 10% greater spring pressure operating upon the vacuum diaphram disc (and thus upon the plunger sealing o-ring), thus helping to compensate for other worn original parts and helping to insure a leak-proof rebuild. Highly recommended when rebuilding any stock petcock. For use with all XJ550, 1984-85 FJ600, XJ650 (except Turbo), all 1981-83 XJ750 models, and all XS1100 Standard model petcocks.

 

Ordered Woot.
Thanks for the info Len.