Topic: Difference in parts from a carb rebuild kit from 4into1 vs existing parts

[gmoss]

Just a warning that I got a CB500K carb rebuild kit from 4into1 and the air mixture screw had the pinhole in a different location as well as the pilot jets being a different size. Pilot jet size probably doesn’t matter if I understand carb function correctly but the air mixture screw difference is probably a Bad Thing….

[Flyin900]

General consensus is while the rubber parts maybe OK in the cheap Chinese junk kits, all brass from them should be avoided. They are never close to the original quality and specs of the OEM Keihin parts. If you use the fuel needles from these kits then make sure you reset the float levels, as they are always a different height than stock OEM Keihin parts.
Reuse your original brass parts after a good and thorough cleaning is best practice. 

[gmoss]

Yeah well, I guess I've learned that the hard way.

IS there a good source for OEM Keihin parts from this era?

[PeWe]

Pilot jet 4-1 sells for CB750 K6 carbs is crap. Learned the hard way.
The thinner part with holes going in was a little bit too wide. I thought it was the threads that were tight when mounting them as jets usually are when new. 2 of them snapped inside.

I had to remove carbs and drill the brass debris out of the carbs. I drilled all 4 to ensure equal holes. Used 2 mm drill.

Stock Keihin went in.

I have bought many aftermarket jets to my Mikuni carbs that work fine.
Main jets for VM29 and TMR from UK, unbranded.

Pilot jets to TMR marked EBC on bags also a UK seller.
Pilot jets to VM29 from Germany also really fine.

Main jets to CB750 K6 carbs, Keihin. They can be found for OK price on eBay. I think UK seller too.

Chinese/Taiwan  rubber in engine crap too. It cost to replace rubber inside when it cost gaskets to tear down, new oil, all work. Done that too.
Carb inlet rubbers can make damage WHEN crack, not if.
I'm sure thats for all bikes.

[pjlogue]

Try here:  https://www.jetsrus.com/a_jet_kit_street/a_jet_kits_street_selection.htm#honda

-P.

[Flyin900]

Watch "Jetsrus" as I bought a supposed OEM Keihin jet from him and it was aftermarket even though his listing specified it was a genuine Keihin part.

It may have been a mistake in picking/shipping; so it wasn’t worth the trouble to return it.

Do you not have the OEM Keihin parts from these carbs to clean up? Honda may have them still available yet if so prepare to open your wallet wide.

[TwoTired]

Those pilot jets are to be avoided  As there is an obvious design change to the emulsion tube as well as the length of the jet reaching into the carb bowl.
New is good, new with a design change means you are now quality assurance testing the engineering of those changed parts.

I'd rather just clean the original undamaged design that's proven well for 45 years and reuse it.

But, its your time and effort to gain experience.

Cheers,

[gmoss]

Those pilot jets are to be avoided  As there is an obvious design change to the emulsion tube as well as the length of the jet reaching into the carb bowl.
New is good, new with a design change means you are now quality assurance testing the engineering of those changed parts.

I'd rather just clean the original undamaged design that's proven well for 45 years and reuse it.

But, its your time and effort to gain experience.

Cheers,

Time, effort, and don't forget the money. Kind of bummed about it.

[Flyin900]

Do you not have the OEM Keihin parts from these carbs to clean up? Honda may have them still available yet if so prepare to open your wallet wide.
[/quote]

Reuse the original Keihin parts, or source a used set if you can’t find proper replacements. Someone on here may have a set or a complete used carb rack.

[dave500]

soak old brass parts in vinegar,long as you want,they come out nice rose gold!use 0000 steel wool after and a good soap clean,keyster jets etc are just rubbish,even the jet hole will be wrong,for example i had a #100 main jet keyster that a new 1mm drill bit wouldnt pass through it,tried it on a genuine jet and it was like a precision bush,those cheap jets can go either way,also had a deformed #$%*ed up keyster slow jet here,they can suck my sweaty balls,look close at the one on the left.

[dave500]

lotta repro ignition carb and ignition parts are rubbish truely,over the years ive been on this forum the number of guys pulling carbs over and again and the repeated points adjustments and failed carb syncing etc?these bikes were never like that new,these were easily serviced and tuned bikes in the day with simple tools,add the modern thing of using pod air filters and #$%* just boils!if youve got good solid genuine un corroded brass clean and use it full stop!

[Scott S]

 Those short pilot jets will cause problems.  They aren't long enough to stay properly submerged in the fuel.

[PeWe]

Those pilot jets are to be avoided  As there is an obvious design change to the emulsion tube as well as the length of the jet reaching into the carb bowl.
New is good, new with a design change means you are now quality assurance testing the engineering of those changed parts.

I'd rather just clean the original undamaged design that's proven well for 45 years and reuse it.

But, its your time and effort to gain experience.

Cheers,

Fully agree.
The old jets work fine unless size change. My K6 carbs needles had no visible wear after 100.000 km, the other jets good too. Float needle fine too.

My bad experience was testing a step  larger pilot.

TwoTired, Long time no see you here. Your experience and posts loaded with good facts are very useful!

[gmoss]

Those short pilot jets will cause problems.  They aren't long enough to stay properly submerged in the fuel.

The short ones were what was on the bike when I got it! The long ones are the new ones. I looked for but couldn't find a photo of what the stock brass might look like for the CB500 / 627b carbs.

When I got the bike the symptoms were: couldn't idle below ~2k (well, not for long, at least), and if I opened the throttle for a bit and then closed it or coasted to a stop it would die. I *think* this could be explained by the pilot jets not getting any gas, then? I'm also not sure about the air mixture screws -- which ones are closer to original dimensions, the shiny new one or the blackened current one? With the shiny new one, the pinhole is about 2-3 full turns back from where the old one had it, so there's no way an adjustment would be remotely similar.

[HondaMan]

I just had to 'rebuild' a set of CB550 carbs that had those parts in it. Nothing worked except the rubber parts. It took a month to find enough OEM parts to put them back into running condition. The kit's pilot jets also stripped the pilot jet hole, wrong threads by 0.5mm pitch.

[gmoss]

Found some Keihin original pilot jets for this exact carb on David Silver. Fingers crossed they work.

[HondaMan]

Found some Keihin original pilot jets for this exact carb on David Silver. Fingers crossed they work.

You can also get them at JetsRus.

[Redline it]

this is kind of a touchy subject for the 4into1 operators standing by to correct any customer complaints. not too far off the subject, i bought 4 of the float level jet and needled assembly's and out of the 4 in any combination the needles wouldn't even restrict let alone stop a pressure from going through. they're kind of easy to see if they'd leak by putting the jet in your mouth, either way, needle on the outside or inside and while pushing air through it, apply pressure to the needle by your tongue  or finger and if it completely stops the air without having to press hard or get it wet, then it's good, even if by getting it wet, is what it takes then still you're in the ballpark. just don't inhale the needle. so these jets all failed bad. i called and let em know about their product. i was talking to one of the owners or managers of the warehouse. and i wasn't being sarcastic i said i have some experience with these jets just to let him know before bs'n me about it. and i told him about the testing methods i was using (trust me it works,) and the next thing he said was "we sell thousands of these jets world wide and we have never gotten a single complaint," at that point i realized why they might be young and never heard of quality control, from who they purchase parts from or in their warehouse in san fran, and then he said the only way to ensure that they will not leak is to mount them on the carb, and install the carbs on the bike, and see if they work or not. that's a true story. i felt bad for sending them back at the same time i should've got a trophy for the being the first one ever to have a problem. i used to buy parts from them. gotta be careful baggin on them, they get bent  out of shape, even if you are the first one ever... i sent a message recently about bumping up the quality of the seat material, using the same 3d printer or design their seat guy was using would be awesome and i'd pay higher price for that. the message was blocked.  but think about it, they've got the line on it, they could do a lot better by changing minor things. seats last me 2 years, they simply start splitting, i'd put a 4into1 sticker on my bike if it lasted 3.

[dave500]

sounds like they got their heads up their arse?thousands sold and no complaints = people cant be bothered?or dont know any different?all these sellers want to be cool and often go on about "old school"etc,fair enough but how often on this forum is there posts on rejetting for pods for a start,using these new jets and ill guess theres all ways gonna be one jet in four are wrong?there goes ya tune up!points are the same,combine the two and mr Honda is turning in his grave.it #$%*s me off these sellers that dont actually do any restorations or get these bikes going again themselves yet brag on about the quality of the #$%* they sell?rant over.

also,if your having trouble with idle and off idle response try solid air screws,the drilled ones will only let you enrichen so far even when fully closed they pass air,if you have spares solder them solid,youll have better full control over the idle circuit that way.

[jgt750]

Those short pilot jets will cause problems.  They aren't long enough to stay properly submerged in the fuel.

The short ones were what was on the bike when I got it! The long ones are the new ones. I looked for but couldn't find a photo of what the stock brass might look like for the CB500 / 627b carbs.

When I got the bike the symptoms were: couldn't idle below ~2k (well, not for long, at least), and if I opened the throttle for a bit and then closed it or coasted to a stop it would die. I *think* this could be explained by the pilot jets not getting any gas, then? I'm also not sure about the air mixture screws -- which ones are closer to original dimensions, the shiny new one or the blackened current one? With the shiny new one, the pinhole is about 2-3 full turns back from where the old one had it, so there's no way an adjustment would be remotely similar.

I bought Canadian kits before and the needles made my 76 run like crap. Put stock back in and all was great again. Did my 74 yesterday with all Honda needles/seats and gaskets.

[Bankerdanny]

I have this conversation with new folks at the CB750 and 750F pages on Facebook all the time. Everyone thinks their carbs need 'rebuilding' when they just need fresh gaskets and a good cleaning.

[PeWe]

Here the bad non Keihin pilot jets.
One broken one not.
Brass residues in carb can be seen in the hole to the left.

I had to drill the hole clean, 2 carbs. Really important to not drill too deep, only remove the broken jet

[gmoss]

I have this conversation with new folks at the CB750 and 750F pages on Facebook all the time. Everyone thinks their carbs need 'rebuilding' when they just need fresh gaskets and a good cleaning.

Lots of compelling arguments on many forums and websites stating all sorts of different things. Hard for a newb who just wants to have some fun wrenching to make a discerning decision -- just have to learn the hard way. Which is part of the fun, so whatever. If I wanted an out of the box perfect ride I'd have bought a brand new SV650.

Anyway as stated the pilot jets in the carb as I bought the bike were definitely not original, too small, didn't reach the gas in the bowl. I believe someone put #40 slow jets for the CB twins into my 500K2, which are 7mm shorter than the CB Four jets (compare[1] and [2]). Definitely needed new gaskets. Everything else I kept the originals and am cleaning them now while I wait for the corret Keihin slow jets to arrive.

[1] https://www.jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99124-286_slow.html
[2] https://www.jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99124-076_slow.html

[gmoss]

Finally got the Keihin slow jets in the mail. Turns out they're identical to the ones in the 4-into-1 rebuild kit. Photo in next post.

The float valves and seats, however, were different sizes, and the replacement float valves close at a much lower level of fuel. This renders the 22mm manual height of the float inaccurate, and, I HOPE explains the lack of fuel going into the cylinder.

Also, a question -- does the orientation of the main jet matter? Interior restriction is asymmetrical -- the way I got the bike, the restriction was pointing down (with the carbs installed on the bike), and the size mark was inside the carb. In the replacement kit, the o-ring was oriented such that the restriction was up into the carb, and the "100" size was visible from the float bowl. Which is correct? (Photo in next post).

It started raining as soon as I got the carb re-assembled so nothing confirmed yet. Fingers crossed.

[gmoss]

Pics from above

[ekpent]

 Me personally and as I have seen on 750's I would mount the jets so the size stamp is visible when mounted.

[gmoss]

Thanks ekpent. That means the 4into1 kit had it right, and the PO or whoever did the carbs last didn't. That makes sense given the 7mm shorter CB500T slow jets that were also on the bike.

[PeWe]

Be careful with the pilot jet. Measure the thin part with a caliper. Mine that looked the same were a little bit thicker so they broke in carbs and I had to drill the remaining crap out of the carbs.

This to test 42.5 in CB750 carbs.
My old stock 40 went back in.

[Deltarider]

Main jets need the conical hole in top position and the seal in its top ring, so the shiny one has it right, the other one has it wrong.