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Carb Jet ?

8832 Views 18 Replies 5 Participants Last post by  Alfalfa
(New to wrenching forgive my ignorance.) well I took the carb apart again and the slow jet (#38 but manual says should be #80) looks like it is clogged half way down. I tried running some wire through it to clear it up but that stuff is stuck in there good. So then I filed a nail down to fit inside the jet and still the damn thing won't go through. Also it looks like there is some kind of brass plug where there should be a hole in the pilot jet here is a pick. Should I just buy a new slow jet and pilot jet? Also the carb kit on ebay has the #38 listed as opposed to the #80 as recommended in shop manual. How much of a difference would this kind of thing make.


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Alfalfa said:
well i took it apart again and the slow jet (#38 but manual says should be #80) looks like it is clogged half way down. I tried running some wire through it to clear it up but that stuff is stuck in there good. So then I filed a nail down to fit inside the jet and still the damn thing won't go through. Also it looks like there is some kind of brass plug where there should be a hole in the pilot jet here is a pick. Should I just buy a new slow jet and pilot jet?
The Honda CB500T manual is wrong in this case - slow and pilot jets range from 35 to 40, 38 being the most commonly seen.
Main jet anywhere from 140 to 150.
There is no jet in the carb that's 80 size.

What is identified as a "pilot" jet actually is a plug, there is no hole in it, at least from the top (or end that hangs down in the float bowl, with the number stamped on it) - that's why you can't seem to clear it out. The pencil points to it in the photo.

The photos are actually of a 450 carb, but they're the same as 500T, except for the goofy "air cut valve".

The "slow" jet lies underneath this, screwed in the little tube or cavity (arrow #1).
It receives its fuel from a tiny passage that is connected to the main jet cavity (arrow #2).
It's a bit difficult to see from the photo, but if you pull it apart you can see the little passageway.
Arrow #3 points to a little brass sealing ball, pressed into the opening that was used to drill out the little passageway.

Does this help???
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very much so! thank you. One more question. Should the hole in the slow jet run the same diameter all the way through the needle. Mine seems to get very narrow in the middle and I can't figure out if this is normal or if it should look just like the main jet only smaller. Like i said I tried getting whatever it is in there out. At this point i'm thinkin maybe it's supposed to be there?


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In your last picture the hole is a little smallish looking. It will be tiny though. There should be holes on the sides as well that need cleaned too. Soak that thing in some good cleaner for a while then try to re-clean. I use a wire bristle pulled from a wire brush to poke around a little. It won't do any damage to your jets and still manages to clean them pretty well. Don't jam anything in there though. You can confirm its clean by blowing through it with cleaner and it should spray out the bottom hole and the side holes.

If your tank has ANYTHING in it (rust, etc..) then this problem will come back to haunt you. Make sure tank is clean and you may want to run an inline fuel filter as well..

My two cents...

GB :mrgreen:
Everything CLEAN! Twice!! but alas still cannot close choke all the way. hmph. When i close the choke all the way it sputters then dies OR it idles but when i roll on it only revs reluctantly then sputters and dies. Can someone post a photo looking down the needle of their slow jet? Is this a carb setting issue. Would engine timing play a factor? I have so much to learn...
If it will idle but starve out when you roll on the throttle, then it would'nt hurt to have a look at the timing and specifically the advance mechanism. Check petcock condition as well. Fuel filter yet??

petcock flows freely, have had inline filters since I got it. Gonna clean the tank out one day, plenty of rust. The filters seem to be catching all the rust. Also ordered a timing light the other day so I can take care of that. Will keep yall posted.
Its quite normal for bike to die when you close choke, it runs too rich.
You need to check the arrows and open it.
Did you clean carb bodies as well? there is a drilling between main jet and pilot jet (its how pilot gets fuel.)
You have probably destroyed pilot and possible main jets by poking at them with a filed down nail.
That picture of main jet looks like a 150+, it may have been drilled out by a previous owner?
Pilot jet hole is real small, a #38 is only about 16 thousandths of an inch diameter, #35 about 13 thou (not exact numbers but close enough for reference) Use copper wire if you have to, never use steel it will mess up jets.
Its a learning experience, time to get some new parts.
I agree with PJ on this....Never use steel... I use two fine strands from 16 or 18ga copper wiring twisted together into a "drill" depending on jet size.....
Normally I avoid poking anything down in a jet, the brass can damage pretty easily.
When I feel I have to, I use a piece of old guitar string, which I always have in abundance, and can be very thin.

As Steve has pointed out before, jet sizes refer to the orifice diameter in mm - meaning a 130 is 1.3 mm, 38 would be 0.38 mm, etc.
That's a pretty small opening.

All that really matters on a jet is the orifice size - I think the slow jet may be bigger-to-smaller to provide sort of a reservoir - since it's not fed directly from the float chamber, but has a couple of right angles to go through, it may be a necessary design feature.
Just guessing about that, but ol' Man Honda generally knew what he was doing.

I have a couple of spare 450 carbs around, if you decide you want to replace the slow jets.

If it will only run with the choke partly applied (not sure what you mean by on/off) then it's a lean condition. Could be caused by plugged jets, too small jets, sticky slides, a variety of reasons.
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I was kind of confused on what he meant by closed/open on the choke as well.

I've used steel bristles pulled from stainless steel brushes (the small 8" wooden kind) for years with no problems. The bristles are actually smaller than any holes in any 450 jets. You just have to have sense about you when poking them around. IE not jamming them into holes they don't fit in. Just use TLC when cleaning any brass jets.

Obviously this procedure is not liked here though, so use your own judgement.

GB :mrgreen:
so lets clarify for an ignorant new guy (that'd be me) when the choke lever is turned in the direction of the arrow, then this is applying the choke and thereby cutting off some of the air supply and making the mixture more rich correct?
Look inside the "throat" of the carb. The end that air goes into. Then work the choke linkage. When the choke butterfly (round metal plate) closes and blocks off the air, then that's the choke being closed. By choking it, I mean closing the butterfly. When it's closed, it will richen the mixture.

I aint talking bout chicken... :p

GB :mrgreen:
I'm pretty sure CB450 has a slider choke with a spring loaded flap valve.
When you lift lever the slider lowers, (airbox side of carb)
Its a real choke mechanism, many are enricheners, although thats generally Mikuni carbs.
So am I wrong by thinking that this style of choke is called a butterfly choke? It's connected by a strip of metal between the two carbs, and operates a "flap" or butterfly. There's no knob to pull, just a lever that is either up or down, with the "flaps" being opened or closed(choked).

Slider choke??? What's that? Is that the pull knob variety, like on my Mikuni 34mm's???

GB :mrgreen: :?: :?:
GB -

Yeah, it's a flapper type of choke.
Properly installed, when the lever is straight up and down, there is NO choke action.
When the lever is turned to the horizontal position, that's full choke.
There is a little spring loaded window-thingy in the choke flapper, so that at least some air gets through, even at full choke.

Open/Closed, potato/potahto, whatever. I prefer full choke/no choke.
uh oh... I hope nobody else was planning on winning the homer award... So the bike ran really great when the lever was all the way down (no choke). Maybe a bit rich cause the plugs were allways fouled up. But it ran pretty well. Now that I have been messing with it... Oi!
Yeah, I'd say that puts you in the running for the January Homer.
Unless you don't want it, of course.
we'll see if anyone can top me i still got another 12 days
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