Jet cover plates

So I've aquired an XJ750J. Upon inspection the carbs do not have the jet cover plates under the top cover. I found a set on Ebay for $10 which I now have in my possession. The screws are an issue as I don't have them and neither did the seller. The manual shows that they may be 'special'. do I really need to install these plates? What are the ramifications?

 

the plates were not installed on all carbs from the factory. you do not need them.

 

You can live without those covers.
On Carbs without Covers, ... Insure that the Air Jets are the right size and CORRECTLY PLACED.

:::: Position Illustrated <> 750 Shown ::::

 

does anyone know the advantages of having them? they had to serve a purpose. otherwise Hitachi wouldnt of botherd making thread and stamping the plates. right? my carbs have them and i left em in there because in my mind they are needed to control airflow. perhaps it forces it into the jets more efficiently? less area to try and pull the air down through them? perhaps allowing better throttle response? idk im taking a random guess here. anyone know what there actual purpose is? Chacal? fitz? rick?

 

Your guess is as good as mine.

I know a Bike runs great without them.

 

Could have something to do with emmision control maybe ?

 

hmm. maybe they do the opposite of what im thinking . maybe a form of restrictor plate? maybe ill take mine out. lol

 

They could be there to break-up any resonating pulse that might be in the air-chamber that is affected by the slider-piston. The shrouded jets would "see" cleaner air.

Could be a case of over-engineering.

 

Hey, thanks to all on this. I won't bother putting them in. I just didn't want to be in the, "Oh, that's why it won't run!" situation. Or worse somehow blow it up and always wonder if that was why.

 

Somebody needs to write a letter and find out what their original function was lol

 

I have them on my 650 Carbs. Only thing I can think is when they designed them it was a for a broad spectrum of different models of XJ and they are used to restrict air making the carbs run richer on the smaller CC bikes and didn't need them in the larger CC bikes due to larger stock jets.

Just a stab in the dark.

 

How about to keep the jets' airflow from directly acting on the diaphragms?

I always assumed they were a "baffle" of sorts to keep that from happening.

Just a SWAG though.

 

hmm. they suck correct? you may be onto something here fitz.

 

Atmosphere is always present in that cavity.
The Vacuum occurs within the Diaphragm, Carb Cover and Inside the Piston area when pressure is lowered within the Diaphragm Assembly as the Intake Air rushes across the Drilled Hole at the bottom of the Piston.

The Cavity must have Positive Atmosphere Pressure in order for the Diaphragm to collapse and for Fuel to be Siphoned from AIR entering the Air Jets.

::: I have theorized that the Atmosphere Cavity where those AIR Jets are located experiences a NEGATIVE PRESSURE variant when PODS are installed. Because rapid Intake Air Flow --> across the Atmosphere VENT "Bean-shaped" orifice at the top of the Intake Horn <-- lowers Pressure within the Atmosphere Cavity:
a) Robbing AIR Jets from an adequate supply of Atmosphere to get drawn into the Main and Pilot AIR Jets. Impeding siphoning.
b) Negating the Collapse of the Diaphragm because the Pressure is LOWER in the Atmosphere Cavity than it is within the VACUUM Chamber causing the Piston to Fail to RISE sufficiently to enrich the Mixture. :::

 

Riiigghhtt. So, that being said, are those plates indeed there to prevent all of that sucking/blowing/whatever from acting directly (and therefore unevenly) on the diaphragm? They are certainly baffles; why would an engineer "baffle" airflow, be it positive or negative? To spread out the flow, so it doesn't create an effective bulge in one area of the diaphragm?

Could be...

That's my theory anyway. Wanna discuss the "suck pipe" on the bottom of the NA market 550 Seca airboxes? Why the shape of the 550 clutch cover (in the area of the breather "maze") changed twice over the life of the 550/600 without the part number changing?

"Band aids?" Why???

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