Rare carbs

These carbs are fitted to a '85 xj 750, they have 4 spigots not seen on any other carbs, is anyone running these, be nice to get some feedback.

 

Perhaps its a fuel overflow valve? Does each Carb have one? I'm sure someone else will know for sure

 

A Blind Plug belongs there.
That's a point where the Passage's are drilled.

I'd guess it was an attempt to provide Auxiliary Air to the Pilot or Enrichment Circuit.

If there is a Port drilled from inside the Diaphragm Bowl that meets that Opening at a Right Angle, ... It might be an Atmosphere Vent.

 

1985 should make it an RL model .. Hitachi hsc33-11? these may help
http://xjbikes.com/Forums/viewtopic/t=3 ... ation.html

http://xjbikes.com/Forums/viewtopic/p=288734.html

 

My 2 XJ750RL's have the hoses on the Carbies
The 750RL supplement to the 900 manual show the hoses in the carby information but says nothing about them.
I have the supplement as a PDF if you want it.

 

i just picked up an 85 xj700 maxim.... and i have the same thing on those carbs. there's drain hoses off of all of them.... dunno what's up with that....

 

If you plug those you get an impossibly rich condition, the hoses must be exactly 10" long & they lean out the mixture as the revs increase.

 

I rummaged thru all my Carb Bins and couldn't find a one that has a hose fitting there.

I looked at a Hitachi sites.
Couldn't find it listed.

Checked the 750RL Site.
No specific information.
The 750RL Carbs View shows the Hose w/o a P/N.

 

They are HSC33s. very rare & I might add a PITA.

 

I think "atmospheric vent" is a good possibility based on the behavior you're describing.

 

You're probably right, Fitz, but is there a 'special' way to sync the swines.

 

You may need to block-off those vents when synching?

 

Reading up on atmospheric vents, they would appear to have the opposite effect, because the AVs force the float down & produce a richer mixture, whereas the more air these suck the leaner it becomes.

 

Could it be that those are for the Calif. version that would have the canister behind the right side cover?

Dave Fox

 

Hi Wiz,

My 84 750RL has those same pipes (1 on each carb) with Hitachi carbs.
I have just rebuilt the carbs with all parts from Len (isn't he great!) including throttle shaft seals & float needles & seats.
I have done a bench sync & re-fitted them & it runs ok-ish.
I am up to doing a running sync (but I have no YICS tool), so I'm interested to see what other info you get on this one.

Cheers,

Tim

 

+1 Len is simply the best, rock on XJ4EVER.

 

Cut the Botttom Hem off a Cotton T-shirt.
::: Mostly Cotton :::
Then, ... cut the Bottom around the waist making a continuous ribbon of T-shirt one-half inch wide.

When you get a 20-foot ribbon of T-shirt, ... wind it into a Ball and soak it with Marvel Mystery Oil.
Wring-out the excess MMO.

Open the YICS Passage.
With a Rod or Dowel, ... Unwind the T-shirt and STUFF it into the YICS Passage.
Pack it tightly :::: (From BOTH Ends)

Once the Passage is stuffed full ...
Apply the End Caps and Go-about Vacuum Syncing.

Before you begin ...
BENCH Sync the Throttle Plates with an Ultra-thin Medium.

::: 3X5 Card Strips -- Business Card Strips -- Resume' Paper Strips -- 35mm Negative Strips :::

 

So.... here's my question, can i swap these out on my 86? same hitachi 33's, but with the plug instead of the vent?

 

Write=down all the Jet Sizes.

If they'll bolt-up, ... give 'em a shot.
Try to find-out what those upper Hose connections are actually for.

You might get lucky and run like a champ.
Or, maybe you'll need to tune and tinker.

Good Luck.

 

1986 versions of the HSC33's used on the XJ700 air-cooled engines do NOT have those brass vac ports..........only the 1985 versions have them.

 

Len, is there something mechanically different with the 85 and 86 engines that would necessitate the difference?

 

Not that I'm aware of...........I think we've only had one or two sets of the 86 carbs, they're quite rare.

 

So would it be anything to do with item 11 the bypass hole??

 

No.- 11
Bypass Hole.

The Bypass Hole is supposed to be Covered by the Throttle Plate Edge when the Throttles are Closed and the Engine IDLING in Pilot Mixtures, alone.

When the Throttles are Opened, ... Vacuum evacuates the Fuel ABOVE the Pilot FUEL Jet into the Intake Stream ... Enriching the In-rushing Air just ahead of the Main Jet Supplied Fuel ... preventing hesitation.

The Size of the Hole and the Size of the Pilot Jet regulate the Air~Fuel Ratio.

The Pilot Mixture Screw is a AIR Regulating Mechanism.
When the Supply of AIR is INCREASED by Turning the Mixture Screw OUT, ... the Quantity of FUEL --> Siphoned <-- up from the Pilot Fuel Jet is INCREASED.

 

A micro fich I have shows it as "29R-14148-00 Pipe
XJ750RL 44X motor

 

So..what was the result of your findings in regard to synching / tuning th HSC 33 carbs. And what else is crow riding these days?

 

The vent hoses connected to mine appear to be longer than what is on the photo from Wiz.
They all go from the vent spiggot to over the top of the airbox along with the 2 overflow tubes (that's what I thought they were).
Mine are 12-14 inches long.

Cheers,

Tim

 

whoops!

deleted..........

 

How did this go from Rare Carbs to Brakes?

Very confusing to me.

To others, I would expect, ... too!