Topic: CB750 aftermarket pilot jet different to OEM #40

[Ace]

Hi all, I'm cleaning out a set of carbys from a K2 and the bloke purchased an aftermarket rebuild kit for them. Parts are all there apart from the fuel t joint O-rings. I've just noticed that the pilot jets in the kit are different length, have 2 holes less, have smaller holes in the tube and are positioned different. Both are #40 with the aftermarket still having the Keihin logo on it (from Taiwan). Pics below.  Now do I throw these as I may have issues with idle setting rich/leaner? Jets are different in so many ways.  Cheers.

[bjbuchanan]

If your float heights are a little off then it will matter more. Most of us "in the know" use the stock Honda idle jets. They reach deeper and as long as you don't hog them out they are 40 jets too.

The other nice thing is the hole spacing and sizes, the rebuild kits never match up. Conventional use of these kits now is to use all your good brass stuff and use just the gaskets as you need them. Needle and seat are replaced regardless usually

[lucky]

I would use the stock jets unless you think the OEM jets have been altered.

Very Important....If you drill out a jet PLEASE file the number off of the jet .
It could save some hair pulling by another mechanic.

[Ace]

I would use the stock jets unless you think the OEM jets have been altered.

Very Important....If you drill out a jet PLEASE file the number off of the jet .
It could save some hair pulling by another mechanic.

The hole up the guts is the same size on both hence still being #40 I guess. The holes you can see on the tube are smaller and less of them.  That's my concern.  The OEM pilot jets I pulled out someone had drilled one of them larger.

[lucky]

I would use the stock jets unless you think the OEM jets have been altered.

Very Important....If you drill out a jet PLEASE file the number off of the jet .
It could save some hair pulling by another mechanic.

The hole up the guts is the same size on both hence still being #40 I guess. The holes you can see on the tube are smaller and less of them.  That's my concern.  The OEM pilot jets I pulled out someone had drilled one of them larger.

Unclear. Do you mean the hole that goes through the center?

If so I would use the new jets from the kit. I am sure they will be fine.

[Scott S]

 Those aftermarket pilot jets gave me FITS on a CB500. Re-use the stock jets unless they're damaged.

[Ace]

I would use the stock jets unless you think the OEM jets have been altered.

Very Important....If you drill out a jet PLEASE file the number off of the jet .
It could save some hair pulling by another mechanic.

The hole up the guts is the same size on both hence still being #40 I guess. The holes you can see on the tube are smaller and less of them.  That's my concern.  The OEM pilot jets I pulled out someone had drilled one of them larger.

Unclear. Do you mean the hole that goes through the center?

If so I would use the new jets from the kit. I am sure they will be fine.

The hole that is inside the jet (up the guts), not the ones you can see in the pics.

[Scott S]

 The length is what gave me tuning problems. I had a hanging idle because the jets were not deep enough into the fuel. Simply switching to stock jets solved the problem.

[lucky]

The length is what gave me tuning problems. I had a hanging idle because the jets were not deep enough into the fuel. Simply switching to stock jets solved the problem.

Great time saving information.
I would go one step further then.


write or call that company that sold the "rebuild"kit, and tell them that you want the right jets or that you may have to tell 20,000 members of this website that their company is selling parts kits that have the incorrect parts. How about that?

Show them that photo of the two jets side by side also.

[Hastenbrucke]

Agree Ace ......new HONDA Jets # 40 on their way ......I have to say YAMIYA for parts are so helpful and reliable. They post straight away.