Topic: Ever heard of needles and jets going bad?

[raymond10078]

Another forum user has been told (by his mechanic) that he needs four new needle jet sets.

While the bike is a "A" model, I was hoping that non-A owners could share if this seems reasonable.  My first impression was to wave the BS flag.  Bike is a 750A with about 8,000 miles.

If it turns out to be true (parts needed), I've tried to find these parts (trying to help), to no avail so far.  If somebody knows of a source for these rare "A" model parts, any leads would be appreciated.  I've advised the owner to start looking for other carb sets, too.

[Gordon]

It's rare for jets and needles to need replacing.  They're brass, so they don't really corrode.  The needles can become tapered in the middle due to wear from rubbing the inside of the jet, but it takes a lot more than 8,000 miles to do that. 

[madmtnmotors]

Yeah, hard to imagine. I've been following the other thread as well and my carbs (78' 750K) are pushing 60,000 miles with the original main jet needles and seats. Runs like a top. I think he needs a new mechanic.

[Bob Wessner]

I agree with everyone else, seems unlikely. If nothing else, have him ask the mechanic 'specifically' what conditions he is seeing that suggests these all need replacing.

[vames]

Could it be that the mechanic's nomenclature is terribly off and he's actually referring to the float valves (which are seldom but sometimes refered to as needle valves). What symptom is he claiming that new needles/jets will fix? Is he saying that replacing them will fix how the bike is running or that it will stop fuel from leaking out the overflows? Could be the difference between whether he's simply a moron or whether he's a uncouth moron.

[TwoTired]

Could be the difference between whether he's simply a moron or whether he's a uncouth moron.

Now that's funny..

 

[Duke McDukiedook]

Or not a moron (but wrong) and just wants to unburden your surplus of greenbacks.
Unless the needles are bent, they do not wear out all that often.
 

[DavePhipps]

 Lpease correct me if I'm wrong on this guys, but from what I know of other carbs, needle jets are the emulsion tubes. Those are the tubes with holes in them that are below the jets.
Wear can happen with these if the brass is very soft. It's a known issue with another bike I own.
If this is what the guy is talking about, just remove the tubes and inspect them. If the tube has an oval shape it will need replaced.
Symptom of bad emulsion tube/needle jet: If the carbs are perfectly clean and setup per factory spec with stock airclener and the bike runs rich at closed to 3/4 throttle position.

[madmtnmotors]

Could it be that the mechanic's nomenclature is terribly off and he's actually referring to the float valves (which are seldom but sometimes refered to as needle valves).

In the other thread the main jet needles and seats are called out by part number, which does indeed match the part number for the main jet needles and seats. Now whether the mechanic gave him that part number, or whether the member looked it up from the description the mechanic gave, is not clear. Of course it has been difficult to get clear and accurate information from "fuwad84" since he is having trouble holding back his frustration (THAT part I understand completely):

http://forums.sohc4.net/index.php?topic=93138.msg1087254#msg1087254

[DavePhipps]

Just in case

http://www.z1enterprises.com/products01/Carb-Rebuild-Kit-CB750A-1976-78.aspx

[dave500]

ive never seen worn honda kiehin needles,ive seen aluminium mikuni/suzuki ones worn flat as a matchstick on one side though.

[mrbreeze]

Lpease correct me if I'm wrong on this guys, but from what I know of other carbs, needle jets are the emulsion tubes. Those are the tubes with holes in them that are below the jets.
Wear can happen with these if the brass is very soft. It's a known issue with another bike I own.
If this is what the guy is talking about, just remove the tubes and inspect them. If the tube has an oval shape it will need replaced.
Symptom of bad emulsion tube/needle jet: If the carbs are perfectly clean and setup per factory spec with stock airclener and the bike runs rich at closed to 3/4 throttle position.

The emulsion tubes are below the needle jet. The needle jet is pressed into the carb body. The jet needle goes through needle jet and they do indeed wear over time. I'm not sure how long it takes to kill them or what the symptoms might be when they are bad.The emulsion tubes screw into the carb body under the needle jets. The main jets screw into the bottom of the emulsion tube. This area is where the tip of the jet needle lives. A coupla years ago ...the needles & jets were still available through Honda. I cant remember exactly how much they were but I'm gonna go from memory and say $ 50-100 for 4 sets.

[Gordon]

When discussing wear aspects, lets keep in mind we're talking about a bike with 8,000 miles on it. 

[DavePhipps]

Never rule out the PO factor. Especially a PO with a drill.
I'm not saying that happened but I don't rule out anything.
BTW my Mikunis on my FZR have ovaled emulsion tubes, and need replaced.
That and the factory pro website are where I'm getting my info on needle jet/emulsion tube symptoms.

[Deltarider]

In over 130.000 kms still no signs of wear nor on jets nor on needles. Doesn't surprise me at all as the total flow of gaz is divided over four carbs.

[Duanob]

Could be the other side: crud and what not on the needles from sitting for a long time. Mileage has nothing to do with it but crud can make your needles to not seat properly making the bike usually run on the rich side.

A good cleaning of the needles with 0000 steel wool will fix that right up. Of course after everything else has been cleaned.

[phil71]

needle jet? Maybe they just meant needle and seat? I could see putting 4 new ones in on a bike that sat too long with fuel in the bowls.

[fuwad84]

I want to thank everyone who has helped out so far with this issue I'm having. So back when I bought the bike it was running super rich, with gas leaking out of the vacuum hole on top of the carb float bowl, got so bad that it actually stained the starter cover. The thing always wreaked of gas to when ever it ran and even a for a little bit after. Yanked all four spark plugs out and they're all covered in soot. Not knowing much about multiple synchronized carburetor systems vs single carb engines which I am mostly used to.

I decided that it's best to have a shop look at them and determine whats best. I'm told they need to be rebuild and that it won't be cheap. I think about it for a little bit, put together some extra cash and pull the trigger on it. I get it back a few days later and it runs great...at first. Slowly little by little it begins to bog down. What I did notice immediately was that the fuel mileage on it was still the same, about 25 MPG. I call back about it and hear from the mechanic that it most likely needs to Needle Set and Jet (Honda part number 16012-393-014), rebuild kits I've found so far don't include these. If you look in the image I uploaded it's part number 3.

Honestly, I think it's a little fishy as well.  Right now I'm sticking with this guy because I've already paid him and he's agreed to fix this problem till it's solved, but I'm still on the hook for parts. He doesn't seem like a bad guy, his shop is very old, very well known and gets lots of business despite being in the middle of no-where so I have reason to believe that I'm not being just dicked around and I may infact have a relatively rare problem.....or not.

What do you guys think my next move should be?

[mrbreeze]

I'm not reading back to who said it but we are NOT talking about the needle and the seat!!!!!!! I bought 4 rebuild kits 4 or 5 years ago. K&L kits from Dennis Kirk. Supposed to be a way better kit than some of the crap you buy on Ebay.... (Keyster comes to mind big time!!!)............Anyhow.....the kits were $20 each +/- .....under $100. They did include the needle/jet pair in their kit although there was much dicussion here as to the difference in needle taper on the aftermarket needles. I remember most people went with stock Honda for those parts and used the aftermarket kits mainly for gaskets, seals, float needles & seats (wut you were confused with!!!)............If ya wanna run stock carbs..............DON'T buy stuff like Keyster (you will get it IN the Keyster!!!). Don't use the supplied needles/jets from any of the kits.........go OEM........my opinion  ....good luck & happy trails with whatever ya use.

[ofreen]

8000 miles is a little soon for any significant wear on the needle jet sets.  But they do wear out after awhile.  Here is a thread I did 3 years ago on the topic -

http://forums.sohc4.net/index.php?topic=41542.0

[crazypj]

It's rare for jets and needles to need replacing.  They're brass, so they don't really corrode.  The needles can become tapered in the middle due to wear from rubbing the inside of the jet, but it takes a lot more than 8,000 miles to do that. 

I've seen complete carbs worn out at 12,000 miles (on Yamaha  )
 The needle can develop wear ridge if bike is left at idle for extended periods, the pulsing makes needle 'vibrate' against needle jet.

In over 130.000 kms still no signs of wear nor on jets nor on needles. Doesn't surprise me at all as the total flow of gaz is divided over four carbs.

 Same thing happens when bike is used for commuting and is kept at pretty constant throttle.
 I've seen Kawasaki's where tip of needle has broken off (must be a Mikuni thing?  )
It isn't the flow of gas, it's the vibration of needle against needle jet

 Any half decent mechanic will show you where the wear is although you sometimes need magnifier to see 'pear' shaped needle jet hole
 How many hours has he charged?
 I wouldn't even consider doing a set of 4 for less than 4 hrs labor and have spend 9+hrs on a CB750 SOHC  set of carbs (the bike was a runner and 'looked' clean  )
 I probably spent at least 6~7 hrs on my Katana carbs, but they were pretty 'gummy' after standing 16months.
You really NEED to use a 10x jewelers loupe to check for corrosion inside drillings in jets and carb body, just because air blows through jet it doesn't mean it's clean (which is why it's cheaper to replace jets in a shop, less than the cost of labor)

[ofreen]

I've seen complete carbs worn out at 12,000 miles (on Yamaha)
 

True enough.  I've seen carbs where the slides rattle in their bores like peas in a gourd.  Fortunately, the Keihins on the 750s are a lot more durable. 

[somesuch]

ive never seen worn honda kiehin needles,ive seen aluminium mikuni/suzuki ones worn flat as a matchstick on one side though.

Exact same experience here.

[david 750f]

I have definitely seen worn needles on a CB750. Needles can rattle around, there not held in place like a main or slow jet..

[Gordon]

Nobody is saying the needle won't wear.  My point is that any significant or even measurable wear is extremely unlikely after only 8,000 miles.  The bike is barely even broken in at that point.