Topic: New press-in jets don't go in as far as old. Is that ok?

[Mercutiojb]

I just bought new press-in pilot jets for my 77F from Sirius.  I've read in a few posts that they may just be slightly larger where they actually meet the carb bodies.  This does seem to be the case for me.  I've noticed that both the new and old have a sort of 'tapered stair step' where they enter the carbs.

The trouble is, the new ones don't go in quite as far as the originals.  They seem to fit as intended (as far as I can tell), but they're roughly 1mm or so lower than the originals. (lower, as in further into the float bowl).

My question is, is that ok?  Seems ok in all other respects... haven't tested on the bike yet, though.

[flybox1]

if they are in snug, i think you'll be ok. 
The change in length may or may not need to be tuned for as they sit deeper in the fuel.  You'll just have to ride and see.

btw...what made you decide you needed new jets?

[Mercutiojb]

I suppose it was laziness, or perhaps a guarantee that they would be clean.  I didn't want to have to pull the carbs 3 time due to the press-in jets, and I was going to have to pull them anyway to really clean them. I figured, why not?  The money seemed worth it to avoid headaches, and I had to buy new mains anyway. I figured I might as well buy both.  Especially with these press in jets, they seem to be pretty rare. I figured I'd start from 'new' new and (hopefully) not have to worry about it for a long time to come.

I'm also trying to get my bike as close to stock running condition as I can before I start changing things.  I have no experience with these CB's other than my own, so I'd never know if my bike were way-off-spec after modifications. I figure I'll get it running well, and well tuned, before I make any major changes. At least then I'll have a solid baseline?

[flybox1]

I see.  well, i hope kept your originals. 
they really do clean up easily. as long as the holes are clear, and they aren't bent, they are usable.

your baseline for 'stock' is now skewed by 1mm 

[Mercutiojb]

I did! I'm already learning to keep everything related to these old bikes!

[Mercutiojb]

Also, what would that 1mm change, exactly? What type of changes would need to be made to compensate for it?

[flybox1]

it can change your a/f mixture.
you'd need to do a plug chop to see if an a/f mix screw adjustments are needed.

[raymond10078]

IMO - your issue won't change fuel delivery at all.

Based on my understanding of carbs, fuel delivery is changed by:

• fuel orifice size; and/or
• the different in the height of the fuel and discharge point of that fuel.

I assume that we are talking about the slow jet here.  The outlet into the carb hasn't changed.  The fuel level hasn't changed.  So I don't understand - what is causing the change . . . ?

Provided that the top of the slow jet is the same size, and the top bottoms out (or tops out, I suppose) where the internal drilling changes sizes, I don't see a problem here.

[lucky]

You are lucky. The push in jets from Sirius can vary by .002 thousandths. Larger or smaller. If they are smaller you can put a wrap of teflon tape around the end to make them tight. I have only gotten one set of ones that were small out of 6 sets.

The ones that you have are tight. Sometimes you can just take a brass block or brass punch and GENTLY tap them all the way in. Just a couple taps.
You could lightly sand them with same #400 black carborundom paper before pushing them in.
ALWAY push them in by hand. If they go in crooked the bottom end can get bent.
Be careful to make sure they get started into the hole straight.

[Mercutiojb]

Are you saying I should attempt to get them all the way in?  I don't think they'll go past the current point without either some serious sanding, or some serious pounding.

The ones that you have are tight. Sometimes you can just take a brass block or brass punch and GENTLY tap them all the way in. Just a couple taps.
You could lightly sand them with same #400 black carborundom paper before pushing them in.
ALWAY push them in by hand. If they go in crooked the bottom end can get bent.
Be careful to make sure they get started into the hole straight.

[Irukandji]

if you feell they bottomed out and they all look the same,(1mm wont kill it) you dont need to go hitting on them. go on with your rebuild and tune to what you have

[lucky]

Are you saying I should attempt to get them all the way in?  I don't think they'll go past the current point without either some serious sanding, or some serious pounding.

The ones that you have are tight. Sometimes you can just take a brass block or brass punch and GENTLY tap them all the way in. Just a couple taps.
You could lightly sand them with same #400 black carborundom paper before pushing them in.
ALWAY push them in by hand. If they go in crooked the bottom end can get bent.
Be careful to make sure they get started into the hole straight.

NO SERIOUS POUNDING!!!

I have installed more than 6 sets and they often need to be tapped to get them all the way in. Most of them need to be tapped in.

Just make sure you start them by hand. Make sure they are straight.
A couple light taps with a brass block or brass punch and a very small jewelers hammer. Thats all. You can always sand them a tiny bit by hand.

It is all about the feel and I cannot give that to you on the internet.

[lucky]

Are you saying I should attempt to get them all the way in?  I don't think they'll go past the current point without either some serious sanding, or some serious pounding.

The ones that you have are tight. Sometimes you can just take a brass block or brass punch and GENTLY tap them all the way in. Just a couple taps.
You could lightly sand them with same #400 black carborundom paper before pushing them in.
ALWAY push them in by hand. If they go in crooked the bottom end can get bent.
Be careful to make sure they get started into the hole straight.

Then why write into this forum??? In your heart you know they should go down to the shoulder don't you, but you are just afraid because you have no experience.
That is why you wrote in.

Just lightly tap them. DO NOT POUND!!!

You should have put a little drop of WD40 on them too. Aluminum and brass are "sticky" metals, they need lube.

[Mercutiojb]

Why? For exactly the reason you claim.  Because I DON'T know.  Because maybe 100 other users have had this problem, and know that it works just fine.  Or doesn't. Or that another product is better. 

"What I know in my heart" is of no concern.  My heart knows nothing. That's why I ask.

Then why write into this forum???

[raymond10078]

Let's not make this harder than it really is.

Compare the lengths of the old and new jets - from shoulder to the end.  The old ones will "show you" about how much can/should be inserted.  If your still unsure, find a drill bit (or other) that corresponds to the thickness of the end of the new jet, then use it to find out how deep the drilling is.

Between the two, you should be able to figure this out.

[Frostyboy]

You haven't mentioned if you've had the emulsion tubes out of those carbs. Are we talking about a 550 here?
Just be sure the emulsion tubes are fitted the right way up. I think it would be more than a mm though. The emulsion tube should protrude into the throat of the carb. The top of the tube is smaller od than the bottom.

[Mercutiojb]

Yup, emulsion tubes are out and have been cleaned.  It's a 77 CB750F

[lucky]

Maybe if we could see a photo it would help.

I have tapped many of them in the last little bit with no problem.