HITACHI IDLE MIXTURE SCREWS NOW AVAILABLE

REPRODUCTION HITACHI IDLE MIXTURE SCREWS NOW IN STOCK!



ims83) Aftermarket replacement IDLE MIXTURE SCREWS (sometimes referred to as pilot screws, or pilot mixture screws, or "those stripped out things in that hole up front"), for all Hitachi HSC-32 and -33 series carbs as used on XJ650 (except Turbo), all XJ750 Maxim and Seca models, and XJ700 non-X (air-cooled) carbs. Correct reproduction screws are available in the original styles to exactly replace damaged, stripped, or missing originals.

The original screws were available in three versions:

a) Alloy steel, with coarse-pitch threads, used on 1980-81 XJ650 Maxim and Midnight Maxim model carbs. The best description I can give for "coarse" threads is that the threads are sized much like you would see on a standard screw (like the carb bowl drain screws, etc.).....the threads are rather "wide apart". This is in contrast to..........

b) Alloy steel, with ultra-fine-pitch threads, used on 1982-up XJ650 models with Hitachi carbs, all XJ750 Maxim and Seca models, and possibly on early model XJ700 non-X Hitachi HSC33 series carbs. Ultra-fine thread pitch looks like screw threads used on some kind of jeweler's or watchmaker's incredibly-closely-spaced threads.

c) Brass, with ultra-fine-pitch threads, used only in XJ700 non-X Hitachi HSC33 series carbs.


Note that the determination of which style screw YOUR carbs have can vary from what MODEL AND YEAR bike you have, as someone may have switched a carb body, an entire rack of carbs, or due to original mass-production and supplier differences and timing of production.

ALL ORIGINAL HITACHI IDLE MIXTURE SCREWS ARE IDENTICAL AS TO FUNCTION AND DIFFER ONLY BY THEIR THREAD PITCH (coarse versus ultra-fine) AND THE MATERIAL THEY WERE MADE OF (alloy steel versus brass). Owners of carbs with the ultra fine-pitch threaded screws CANNOT use coarse-thread pitch screws, and vice-versa.

However, owners of carbs with the (much more common) ultra-fine pitch threaded bores and screws can use either the steel or brass screws interchangeably----although we recommend sticking with one or the other in a full rack of carbs.

Why did Hitachi change from using coarse thread (1980-81) to fine-threaded screws? Who knows, but it probably has something to do with the fineness of the adjustability needed for these precision mixture screws.....a fine-threaded screw offers a much more precise level of fine-tuning adjustability than a coarse-threaded screw does ("coarse-pitch" screws move the screw further along it's bore for each given amount of turning, so a 1/4-revolution turn of a coarse-pitch screw will move that screw FURTHER up or down in its bore than the same 1/4-revolution turn will move a fine-pitched screw).

Thus the standard advice of using the 2.5-to-3 turns out (from bottoming) as a "starting point" for the idle mixture screw setting is really based on the use of the fine-pitched screws; the earlier coarse-pitch screws would need to be initially set at about 1.5-to-2 turns out as an initial starting point.

More questions from the audience: Why did Hitachi change from using steel screws (most 1980-83 model carbs) to brass screws (1985-86 models)? Who know, but it was either a cost saving measure (brass is not normally cheaper than steel, but it is much easier to machine precisely), or, given how these screws are known for seizing up in their bores, perhaps it was to provide a material that was not as susceptible to seizure (such as brass).

Either way, since you will be using some anti-seize fluid when installing your new screw (or even when re-using your old screws during a rebuild), this is not really an issue any more. Right? RIGHT? I mean, you WILL use anti-seize, won't you?

These idle mixture screws are exact reproductions of the originals, with the original straight-blade screw head, and are available in either the coarse-pitch in a Type 304 stainless steel material (instead of the original alloy steel), or in the fine pitch versions----and the fine pitch versions are available in either a Type 304 stainless steel material (instead of the original alloy steel) or screw-grade Brass.


HCP8392 Aftermarket Hitachi IDLE MIXTURE SCREW, coarse threads, for all Hitachi HSC32 carbs with coarse threads in the idle mixture bore holes, type 304 stainless steel material. Normally found on 1980-81 XJ650 models, but that may vary, so check your original screws or carb bore threads before ordering. Each:
$ coming soon!

HCP8392SET4 Aftermarket Hitachi IDLE MIXTURE SCREW, coarse threads, type 304 stainless steel, set of 4:
$ coming soon!

HCP8392KIT Aftermarket Hitachi IDLE MIXTURE SCREW SET, coarse threads, complete with one each of an HCP8392 stainless steel mixture screw, an HCP895 O-ring, the HCP6573 tension Spring, and the HCP896 spring seat Washer. Does one carb:
$ coming soon!

HCP8392KIT4 Aftermarket Hitachi IDLE MIXTURE SCREW SETS, coarse threads, type 304 stainless steel, set of 4 does one entire rack of carbs:
$ coming soon!




HCP8393 Aftermarket Hitachi IDLE MIXTURE SCREW, ultra-fine threads, for all Hitachi HSC-32 and -33 series carbs with fine threads in the idle mixture bore holes, type 304 stainless steel material. Normally found on 1982-84 XJ650 models and all XJ750 models, but that may vary, so check your original screws or carb bore threads before ordering. Each:
$ 14.95

HCP8393SET4 Aftermarket Hitachi IDLE MIXTURE SCREW, ultra-fine threads, type 304 stainless steel, set of 4:
$ 54.95

HCP8393KIT Aftermarket Hitachi IDLE MIXTURE SCREW SET, ultra-fine threads, complete with one each of an HCP8393 stainless steel mixture screw, an HCP895 O-ring, the HCP6573 tension Spring, and the HCP896 spring seat Washer. Does one carb:
$ 19.95

HCP8393KIT4 Aftermarket Hitachi IDLE MIXTURE SCREW SETS, ultra-fine threads, type 304 stainless steel, set of 4 does one entire rack of carbs:
$ 69.95




HCP8394 Aftermarket Hitachi IDLE MIXTURE SCREW, ultra-fine threads, for all Hitachi HSC-32 and -33 series carbs with fine threads in the idle mixture bore holes, brass material. Normally found on 1985-86 XJ700 non-X (air-cooled) models, but that may vary, so check your original screws or carb bore threads before ordering. Each:
$ coming soon!

HCP8394SET4 Aftermarket Hitachi IDLE MIXTURE SCREW, ultra-fine threads, brass, set of 4:
$ coming soon!

HCP8394KIT Aftermarket Hitachi IDLE MIXTURE SCREW SET, ultra-fine threads, complete with one each of an HCP8394 brass mixture screw, an HCP895 O-ring, the HCP6573 tension Spring, and the HCP896 spring seat Washer. Does one carb:
$ coming soon!

HCP8394KIT4 Aftermarket Hitachi IDLE MIXTURE SCREW SETS, ultra-fine threads, brass, set of 4 does one entire rack of carbs:
$ coming soon!





HCP254 Idle Mixture Screw Removal/Adjuster Tool, fits all Hitachi models and all Mikuni idle mixture screws.
$ 17.95

 

1993 xj750. are Carbs HSC 32 or 33 ? someone lost the idle mixture screws. they were brass fine thread and not sure where to get replacements ? or buy another set of carbs or buy a different brand or what the mm size is ? can anyone help ? AL.

 

Alu, send us an e-mail or a PM (private message service on this website) and I'll get you all the ordering/payment info, etc.