Hitachi 4H700 Carb Pilot Air Screw Setting

I am rebuilding a set of Hitachi Model 4H700 carburetors for a 82 Yamaha XJ650RJ. I have two questions. History of the bike, I have not seen this motorcycle run, I got it free, with a broken primary chain guide section jamming the shift drum. Bike had been sitting over ten years, I found a large amount of varnish in the float bowls.

1) The number of turns open for the Pilot Air Screw? I found the only pilot air screw that I messed with to be open 4 1/2 turns. From past experience with Bing and other carbs I find this to be excessively open, normally on other carbs 1 to 1 1/2 open. I do not know what the PO has done to the carburetors. I have a Genuine Yamaha Service Manual that states that the Pilot Air Screws are factory set and not to be messed with. I want to make sure all air and fuel passages are open.

2) Is there a good source for parts for the Hitachi carbs? I have rebuild many Bing CV carb and have found that the Hitachi diaphragm to be stiffer then I would like to see in a Bing. All the parts sources I have found do not list many parts for Hitachi carbs.

 

Those are more commonly known as HSC32 carburetors. Len (Chacal) has most parts for them that are available. Normal starting point for pilot screws is more like 2 1/2 turns out.

A JIS #2 screwdriver is really nice to have when working on these.

 

I now understand the reason that Pilot Air Screws where open the 4 turns from seated. The threads on the screws are of a very fine pitch. One turn does not move the needle very far. Other carbs I have worked on have a much coarser pitch.

 

Yes they are of a fine pitch. Even so 2 1/2 turns out from a soft seat is the recommended baseline. Most of us end up with them at around 2 3/4 turns out once the fuel/air ratio is dialed in. Your plugs should show signs of the mixture being quite rich. If they don't, then you should suspect a vacuum leak, or some other condition that would have leaned the pilot mixture (not having the stock airbox for example).

The Hitachi diaphrams are generally stiffer, but not having yours in-hand I can't tell you if yours are overly stiff or not.

I suggest that you peruse The Information Overload Hour, and InThe Church Of Clean if you have not done so already.

The primary chain guide section will need to be addressed, as the entire chain guide has likely failed. Most of the XJ series engines (yours included) utilize a fixed guide for the alternator chain (there is no true primary chain in the shaft driven bikes). When that guide fails it allows too much slack in the chain, and then that chain then will damage either the alternator chain oil nozzle, or the engine case, and sometimes both.
You can choose run the engine without replacing the guide, but the longer you leave it go the more damage is done, and the more expensive the repair becomes. This is also the perfect opportunity to rebuild the starter clutch since the cases have to be split to do either job.

 

Thanks
I have not seen this bike run. I got the bike for free after the bike had sat indoor for 10 years after the broken chain guides had jammed the shift drum. The PO had been quoted over a grand for repair and abandoned the bike.

I have split the cases and have replaced the chain guide. The chain had not touched the oil nozzle.
The spark plugs did show signs of having ran rich.