Topic: 657A and 7A carbs on the same motor repair kit

[Choppr]

Hi, I need to replace the floats on my K1 and figured I might as well get the whole repair kit in case I need other parts. While looking for the right kit, I noticed on my bike that I have three 657A carbs and one 7A (it's a home built '71 chopper).  Looking at various posts in the forum, apparently they are just about the same, what I am not clear on is the Main Jet numbers (110 vs 120) and JN (Jet Needle?) numbers (4 vs 3).  I would rather not buy two separate kits, do these Main and JN differences matter?  I am not the one that first put the carbs on, so I don't know the exact parts in the carbs, but the bike has always run fine.  This here is the carbs specs list that I found in this forum multiple times that I got the numbers from (http://www.hondachopper.com/garage/carb_specs/carb_specs.html).  Thanks for any and all input!

[Gurp]

I'm sure it was running decent before but for less headaches in the future may be worth it to swap the one body you have oddball out for a matching one.

I'm sure someone on the forum has a set parting out.

Sent from my LE2127 using Tapatalk

[CycleRanger]

The carb bodies, 7A, 657A & B are all identical.
It's perfectly fine to mix & match the carb bodies.
Only the jets and needle setup differed from the factory depending on the year.

Check what's in your carbs now and verify they are all the same. (jets and needle setting.)
If the bike is running fine as it is there shouldn't be any reason to change any of the jets or needles.
In fact, it's better to keep the genuine Keihin components whenever possible as none of the aftermarket kits are made to the same tolerances.

Oh, and howdy and welcome! 

[newday777]

Hi, I need to replace the floats on my K1 and figured I might as well get the whole repair kit in case I need other parts. While looking for the right kit, I noticed on my bike that I have three 657A carbs and one 7A (it's a home built '71 chopper).  Looking at various posts in the forum, apparently they are just about the same, what I am not clear on is the Main Jet numbers (110 vs 120) and JN (Jet Needle?) numbers (4 vs 3).  I would rather not buy two separate kits, do these Main and JN differences matter?  I am not the one that first put the carbs on, so I don't know the exact parts in the carbs, but the bike has always run fine.  This here is the carbs specs list that I found in this forum multiple times that I got the numbers from (http://www.hondachopper.com/garage/carb_specs/carb_specs.html).  Thanks for any and all input!

Welcome aboard the forum Choppr.
How long have you had this chopper? Do you have much experience in working on the 750s?

Do your carbs have the brass floats still and are they leaking? (Shake each float and hear gas in them?) Is that why you want/need to replace them? If so, you can use the newer style plastic floats. But verify that you have leaking floats first. If you are adept at soldering you can solder any leaks in the brass floats to reuse them.

Or is it that you have overflowing carbs out the drain tubes? That can be bad float valves needing replacement (only buy from Honda, not aftermarket kits!). Or the brass overflow tubes in the bowls can be cracked and need to be sealed.

As CycleRanger said the bodies are the same. And don't buy aftermarket brass! They don't make them to the same precise specs. Use only Keihin brass parts. Clean the Keihin brass parts and reuse them.
You can use aftermarket bowl gaskets, but most likely the bowl gasket is fine to reuse unless yours is torn.

You want to use the same jet and needle size in all 4 of your carb bodies so it will run properly.

[Choppr]

Am trying to reply to individual comments but can't figure out how, so here's reply to the comments so far:

- The bike has always run fine with the mixed carbs
- Have had the bike for about 23 years, bought it from a friend that originally built it and had it for a couple of decades
- Have done all he work it has needed myself (Magento, Stator, Points and such) but don't have hands on experience with the carbs except for adjusting the floats a few times over the years
- It's leaking heavy from the top of bowls, is due to floats is the general consensus from other 750 owners I talked with at a gathering recently, and also original assembler.  Is not leaking from drain tubes.
- The floats are not brass, are the black closed cell type (think that's the name for them), and they are at least 25+ years old

Regarding: "You want to use the same jet and needle size in all 4 of your carb bodies so it will run properly." It does run fine, it's just leaking gas when I turn on the petcock.  Since I have already messed with the floats a few times over the years I figure it's time to replace them.

Regarding:  "The carb bodies, 7A, 657A & B are all identical.  Only the jets and needle setup differed from the factory depending on the year."  So, since the carbs are for 69 through 76 motors, and if I do need to replace the needles or other parts for some reason (hope not to), I would have to buy two different kits per the chart in my original post?  I can't have a Main 120 and JN 3 for a 675A carb, or vice versa Main 110 and JN 4 in 7A carb?

Or am I missing something, are the Main and JN numbers just adjustment settings numbers and not part sizing numbers, are the parts identical for the two different carbs if I buy a kit?   That was really my main question.





 

[CycleRanger]

Am trying to reply to individual comments but can't figure out how, so here's reply to the comments so far:

- The bike has always run fine with the mixed carbs
- Have had the bike for about 23 years, bought it from a friend that originally built it and had it for a couple of decades
- Have done all he work it has needed myself (Magento, Stator, Points and such) but don't have hands on experience with the carbs except for adjusting the floats a few times over the years
- It's leaking heavy from the top of bowls, is due to floats is the general consensus from other 750 owners I talked with at a gathering recently, and also original assembler.  Is not leaking from drain tubes.
- The floats are not brass, are the black closed cell type (think that's the name for them), and they are at least 25+ years old

Regarding: "You want to use the same jet and needle size in all 4 of your carb bodies so it will run properly." It does run fine, it's just leaking gas when I turn on the petcock.  Since I have already messed with the floats a few times over the years I figure it's time to replace them.

Regarding:  "The carb bodies, 7A, 657A & B are all identical.  Only the jets and needle setup differed from the factory depending on the year."  So, since the carbs are for 69 through 76 motors, and if I do need to replace the needles or other parts for some reason (hope not to), I would have to buy two different kits per the chart in my original post?  I can't have a Main 120 and JN 3 for a 675A carb, or vice versa Main 110 and JN 4 in 7A carb?

Or am I missing something, are the Main and JN numbers just adjustment settings numbers and not part sizing numbers, are the parts identical for the two different carbs if I buy a kit?   That was really my main question.

Presumably whoever swapped in the different carb body rebuilt all four and installed the same parts (jet size) in all four carbs.
If your carbs are leaking it could just be the needle valves getting stuck or tips are worn. (Or just cleaned of accumulated crud.)
It is possible the floats need replaced but I'd look at the needle valves first. Heck, the carbs may only need a good cleaning, some new o-rings, and new bowl gaskets.

Since the carbs have been rebuilt at least once there's really no telling what size the current jets are.
You should pull the carbs before you order kits. You need to know what jets are currently installed so you can order the kits with the correct (matching your current setup) jet size. You would order the same kit for all four carbs.
However it's unlikely that you need to replace any of the jets unless they're damaged or hopelessly clogged but since you indicate that the bike is/was running well they probably are not.
So, pull the carbs and see what's inside now. Verify the jet sizes, see if they are original Keihin, or aftermarket and check their condition and report back. 
Don't order new floats until you verify they are the problem. The plastic floats in my 750's are going on 50 years old now and are still fine.

It may turn out that all you need is four of these kits. PN 16010-300-305

[Choppr]

Good info, thanks!  So if it turns out that I do need to replace the jet(s), how do I verify jet sizes, is it by a number stamp or do I measure them or ...?  And how do I verify they are Keihin ones, are they stamped?  I've never had trouble with the carbs besides the few times float adjustment so I am not familiar with the insides as I should be by now (I know the rest of the engine pretty well   P.S.  Thanks for the gaskets kit link!

[CycleRanger]

Good info, thanks!  So if it turns out that I do need to replace the jet(s), how do I verify jet sizes, is it by a number stamp or do I measure them or ...?  And how do I verify they are Keihin ones, are they stamped?  I've never had trouble with the carbs besides the few times float adjustment so I am not familiar with the insides as I should be by now (I know the rest of the engine pretty well   P.S.  Thanks for the gaskets kit link!

The jets will be stamped with the size and a "K". (If they're Keihin)
https://www.jetsrus.com/FAQs/FAQ_genuine_vs_our_oem_equivalent_jets.html

Carbs may seem intimidating but they're really pretty simple. You've indicated you're handy with tools so I don't think you'll have any trouble.
The worst part is just getting them on and off.   
Grab a PDF of the shop manual and the parts list from the site linked in my sig if you don't have one.

[Choppr]

Great, now I now what to look for on the part(s)!  I do have the Haynes workshop manual for the bike, and also in PDF form on computer, so I am good there.  The bike is a chopper, I have good clearance go get to the carbs, have never had to take them off but looking at it looks pretty straight forward, let me know if there is anything to be aware of, thanks again!

[CycleRanger]

Very nice! Always ready for Halloween! 

With those pods it's unlikely the carbs still have the stock sized jets.

[HondaMan]

If you have overflowing carb bowls, chances are good that the tabs on the floats that push the float valves shut have become dimpled slightly: this makes them stick open until the bike hits a significant bump to shake them closed. Look closely at the tabs for markings from the float valves, and use a small jeweler's file to smooth them back out again. I see this in about 50% of these carbs I rebuild for folks. It causes intermittent bowl overflow issues, more so on hot days.

To echo the other smart guys above: DON'T change the brass parts like the needles and jets, and the current crop of aftermarket plastic floats DON'T WORK. Plastic floats never wear out, but might need to be cleaned from time to time: I haven't done mine in at least 12 years, but they needed it back then.

[Gurp]

I just gotta say great looking chop!
Did you build it?

Sent from my LE2127 using Tapatalk

[Choppr]

I wasn't going for the Halloween look, but guess it turned out that way   A friend of mine originally built it a few decades ago, and when I bought it from him 23 years ago I wound up changing a lot on it. Mechanically I left it the same but changed the paint, gas tank, mirrors, footpegs, grips and various other mostly non mechanical parts (besides stator and magneto that gave out).

Based on all the input so far, it appears I've been overthinking this, the bowls sometimes leak a lot and then next time they don't, which has been frustrating since it's not a steady issue. And sometimes just a couple leak, other times all four of them.  I'm going to take off the carbs assembly and look at the parts on the bench and give them a good cleaning and inspect the needles and floats and clear any blockages ....and then take it from there.  I probably won't get to it for a while, riding season is just about over, am not in a rush, but will post an update when I do it.  Thanks for all the input so far from all, very much appreciated, let me know if there is any other thoughts or things I should consider!

[newday777]

The other leak point is the orings on the fuel Tees between the carbs 1-2, 3-4. They are 7.8mm(ID) x 1.9mm
#45 on the fiche

[Choppr]

Thanks!

[HondaMan]

A tip from my own use: I always put an ounce or two of oil in the gas. This helps the engine since there's no lead in the gas anymore, and it helps the carbs if they are on the edge of 'crusty'. It also helps when it gets parked for a week that turns into the all-winter park with no further preparation: the carbs will be much happier next Spring and the top rings of the pistons won't stick.

[Choppr]

This actually brings up a question:  When I know I won't be riding the bike for a few weeks or months, I turn off the petcock and let the engine run until the float bowls are empty and the engine stops due to lack of fuel.  Reason I do that, so the gasoline does not sit in the carbs system and get gummed up.  In that regard, that has always worked fine, but now I wonder if there is a downside to have the carb system dry for an extended period of time, O-rings and gaskets dry out ....?  This is a whole new discussion, but your comment made me think of it 

[Kaze]

Off-topic, but are those orange vanity bits that clip-on to the sides of the motor strictly cosmetic? I've seen them only once before and they were chrome.

[Choppr]

Yes, they are mainly cosmetic, but they do protect the engine cooling fins if something were to bump into them ... in theory anyway  .  They are really hard to find these days, and they are supposed to be Chrome, wish I had bought them a couple of decades ago when they were still available.  After lots of searching, I found a seller finally that makes them, but they are just steel, not very good looking, is why I painted them.  Thought about painting them Chrome, but Chrome paint usually doesn't turn out that well, so I figured why not Orange to make them stand out a bit from the engine and match the frame and graphics.

[newday777]

This actually brings up a question:  When I know I won't be riding the bike for a few weeks or months, I turn off the petcock and let the engine run until the float bowls are empty and the engine stops due to lack of fuel.  Reason I do that, so the gasoline does not sit in the carbs system and get gummed up.  In that regard, that has always worked fine, but now I wonder if there is a downside to have the carb system dry for an extended period of time, O-rings and gaskets dry out ....?  This is a whole new discussion, but your comment made me think of it 

Honda recommended to turn off the petcock each time you shut the bike down to prevent any possibility of overflow from leaks, a wise choice. I've seen gas filling the carbs, draining into the cylinders and getting by the rings into the oil(when that happens you need to change the oil to get rid of the deleted oil).
As to running the gas out of the carbs, I do it each shut down to prevent leaks out of the overflow tubes.
And I also drain the carbs for winter storage, then fill the carbs with Marvel Mystery Oil so things don't dry out in the carbs, then just drain the MMO out in the spring, fresh gas and it's good to go.
The tank, I drain it of gas, then put in a qt of denatured alcohol, rotate all around and shake the tank to capture any water that might be in the tank, dump that out through the lid, wipe out the excess that doesn't come out of the lid with a clean rag as best I can. Then pour in 5-6 oz of 2 stroke oil and rotate the tank to coat the tank to preserve it. Come spring I drain the oil out and put in fresh gas. It works well every time.
And as Mark said, during riding season adding an oz or 2 of oil every tank is good to prevent rust, lubes the carbs and engine parts.

[newday777]

Off-topic, but are those orange vanity bits that clip-on to the sides of the motor strictly cosmetic? I've seen them only once before and they were chrome.

They actually bolt on the motor to secure them.
I bought an 836 motor that had been in a chopper that had them on it, and yes they came chrome back in the 70s. These ones have peeling chrome now.

[CycleRanger]

This actually brings up a question:  When I know I won't be riding the bike for a few weeks or months, I turn off the petcock and let the engine run until the float bowls are empty and the engine stops due to lack of fuel.  Reason I do that, so the gasoline does not sit in the carbs system and get gummed up.  In that regard, that has always worked fine, but now I wonder if there is a downside to have the carb system dry for an extended period of time, O-rings and gaskets dry out ....?  This is a whole new discussion, but your comment made me think of it 

Honda recommended to turn off the petcock each time you shut the bike down to prevent any possibility of overflow from leaks, a wise choice. I've seen gas filling the carbs, draining into the cylinders and getting by the rings into the oil(when that happens you need to change the oil to get rid of the contaminated oil).
As to running the gas out of the carbs, I do it each shut down to prevent leaks out of the overflow tubes.
And I also drain the carbs for winter storage, then fill the carbs with Marvel Mystery Oil so things don't dry out in the carbs, then just drain the MMO out in the spring, fresh gas and it's good to go.
The tank, I drain it of gas, then put in a qt of denatured alcohol, rotate all around and shake the tank to capture any water that might be in the tank, dump that out through the lid, wipe out the excess that doesn't come out of the lid with a clean rag as best I can. Then pour in 5-6 oz of 2 stroke oil and rotate the tank to coat the tank to preserve it. Come spring I drain the oil out and put in fresh gas. It works well every time.
And as Mark said, during riding season adding an oz or 2 of oil every tank is good to prevent rust, lubes the carbs and engine parts.

Speaking of the petcock, it would be good to check to make sure it's not leaking when closed.
If it's never been rebuilt it may be time. Replacement parts are still available from Honda.

[jonda500]

I only ever turn of the fuel tap when I want to remove the tank or if I am fixing a leaking needle & seat in one of the carbs. Since the eighties I have always done this - I want to know if my carbs are leaking!! But also ever since harisuluv restored my carbs with the incorrect rubber type of fuel tee o-rings, if I turn off the fuel and then end up not riding the bike for a couple of weeks they will dry out and fuel will piss out all over the crankcase when I turn the fuel back on.
If for some reason I can't ride the bike for an extended period, I will for each carb: turn off the fuel tap, undo the drain screw, drain the bowl into a little container, tip it back into the tank (-skim off any floating crud first and discard the last few drops if contaminated)  and turn the tap back on to refill the bowl.
John