Author Topic: Carb top seals? (Read 10462 times)

BillyC · « **on:** September 24, 2013, 03:59:22 PM »

I am rebuilding a set of 74ish CB750K carbs (657A) for a customer. I'm anal about it and have finally got them just about perfect except... for lack of a better term the tops have a seal that the slide shaft runs thru. I'll try and post a pic below, forgive my newbness to this site. Anyone have a source or recommendations on a fix for these disintegrated seals. I just ordered some oilite sleeve bearings that should fit well enough to make a real difference but it sure would be nice to get the real deal seals. TIA.
Billy C

added pics

spazz1984 · « **Reply #1 on:** September 24, 2013, 06:12:40 PM »

Well I just went to ronnies.com microfiche to look it up and its a disconnect part sorry some times tho you can for it on eBay

Sent from my SPH-L710 using Tapatalk 2

bjbuchanan · « **Reply #2 on:** September 24, 2013, 06:59:50 PM »

I don't know of a good source but I do know that regular old rebuild kit top seals suck. The cutouts don't usually line up, most reuse them because they are serviceable

brandEn · « **Reply #3 on:** September 24, 2013, 07:27:25 PM »

subscribed.
If you figure it out I wanna know!

CycleRanger · « **Reply #4 on:** September 24, 2013, 07:47:24 PM »

Yeah, they were never available as a separate part, only as part of the now-discontinued "carb top set".

I had to mix & match from a several sets of carbs to get a set of tops with usable seals.

Looks like an item Yamiya should reproduce!

iron_worker · « **Reply #5 on:** September 24, 2013, 07:57:43 PM »

I also could use a seal for that spot. One of mine is missing. However, between the fairly tight fit of the slide to the carb body and the fit between the bushing and the slide rod that there shouldn't be much of a problem in terms of vacuum leaks. However, it would be nice to have something there as a wiper to keep dirt and grit out.

IW

BillyC · « **Reply #6 on:** September 24, 2013, 10:17:29 PM »

I've got fellow biker enthusiast/Engineer out in Cali looking at it. If I do come up with something suitable I will surely post it here.

I'm quite good on the Honda V4 carbs and took this set on as a favor knowing better. But, I've gotten thru the learning curve now and just this one part is kicking my butt. The top has a full rubber gasket under it so I gotta believe vacuum was a concern for the design engineers 40 yrs ago. Then again that gasket does cut off the vacuum from the choke section too. I do agree that very little vacuum should be able to leak past the brass bushing/lift rod and it probably is not a big deal. I am more concerned with water getting in there while riding or parked in weather. I just can't bring myself to send these carbs back not right.

I was absolutely amazed to find the throttle lift forks rubber boots still available both from Honda and aftermarket.

oldschoolcarbs · « **Reply #7 on:** September 25, 2013, 09:27:40 AM »

We're toying with rolling out some obscure soft parts for various carb models. Most of my attention is focused on dust seals for the CBX carbs but the wipers you're referring to are on the radar as well. Those and the dust seals for the 550 throttle/synch compensators.

Everyone who builds carbs as a commercial enterprise knows that they're unobtranium. I have a carefully guarded hoard that I've scavenged but it would take a lot to pry one from my fingers. Perhaps harisulove (sp.?) has some.

My local guy, who manufactures parts for motorcycles, says that he can make them for literally pennies apiece. The catch is that the process of reverse engineering, mold-making on the CNC, and prototyping/testing will cost 2 grand. Up front. Yikes!

I've wheedled him down because my son is CNC certified and he can whip up what we refer to as a "print" (machine language for the mold cutting process), but only a little.

So the nut, as far as SOHC are concerned, is that there would need to be a robust market for them or you'd wait for years to recoup. That is unless about 150 guys prepaid, say, 30 bucks per set of carbs... Not bloody likely. Especially because in the vast majority of instances you can safely remove the old ones, once you know the trick that is.

CBX? Yes it looks like we're going there but probably not for the SOHC.

OSC
http://www.oldschoolcarbs.com

BillyC · « **Reply #8 on:** September 25, 2013, 10:41:52 AM »

If you have the CAD drawings you can go to a variety of Chinese seal manufacturers and have them made a lot cheaper out of any rubber compound you desire but for a 40 yr old SOHC there just isn't any ROI there. Gotta find an off the shelf solution.

Harsh · « **Reply #9 on:** September 25, 2013, 11:04:07 AM »

Have you checked S.C.I.?

http://www.siriusconinc.com/index.php

BillyC · « **Reply #10 on:** September 25, 2013, 11:45:26 AM »

Quote from: Harsh on September 25, 2013, 11:04:07 AM

Have you checked S.C.I.?

Thanks, yes, already tried them. No joy. Good resource for when I do the odd one off carb rack like this one. Gotta watch out for mis-sized jets and jet needles but otherwise quality stuff. I have a dealer acct with them.

lucky · « **Reply #11 on:** September 25, 2013, 04:13:49 PM »

Quote from: iron_worker on September 24, 2013, 07:57:43 PM

I also could use a seal for that spot. One of mine is missing. However, between the fairly tight fit of the slide to the carb body and the fit between the bushing and the slide rod that there shouldn't be much of a problem in terms of vacuum leaks. However, it would be nice to have something there as a wiper to keep dirt and grit out.

IW

IF the seal is too tight it could make a sluggish slow throttle response.

CycleRanger · « **Reply #12 on:** September 25, 2013, 04:29:11 PM »

I had the thought of finding an o-ring that had the inner diameter of the rod and the proper out diameter & thickness to fit down in that groove in the top.

You'd have to measure the rod and gap and look for something close to those dimensions.
Or measure an intact original seal.

But as Lucky warns, if it's too tight it might impede throttle response.
(A dab of silicone grease and a new return spring might be enough to counter any friction however..)

oldschoolcarbs · « **Reply #13 on:** September 25, 2013, 05:16:04 PM »

Quote from: CycleRanger on September 25, 2013, 04:29:11 PM

I had the thought of finding an o-ring that had the inner diameter of the rod and the proper out diameter & thickness to fit down in that groove in the top.

You'd have to measure the rod and gap and look for something close to those dimensions.
Or measure an intact original seal.

But as Lucky warns, if it's too tight it might impede throttle response.
(A dab of silicone grease and a new return spring might be enough to counter any friction however..)

The oring is easy and it just happens that one of the sizes I stock fits the bill perfectly. The problem there is if you get any water on them at all, it'll tend to actually pool there and be drawn down the rod instead of being directed away as the wipers are designed to do.

Perhaps I'll snap a photo of a rather elegant solution we thought up. Looks darn near perfect and is only a small cheat. But like I said I have a stash so it's only in case of a last resort.

The one thing we do make and which has turned out to be very useful are those teensy aluminum spacers that go inside the SOHC CB750 lifters to keep them from breaking under screw-torque. (You builders will know what I'm talking about.) It seems like on about half the sets we take in, somebody in the past took---or tried to take--- the lifters apart and the spacers fell out sight unseen.

Oh, and the chinese guys only want to make very small parts in 100,000 lots. As for quality control I can only say one thing: Are you kidding? I deal direct with Japan and they want even more to tool up for the CBX parts than my local guy!

OSC
http://www.oldschoolcarbs.com

brandEn · « **Reply #14 on:** September 25, 2013, 05:26:12 PM »

You got a pic of those spacers by chance?

BillyC · « **Reply #15 on:** September 25, 2013, 05:59:42 PM »

Quote from: CycleRanger on September 25, 2013, 04:29:11 PM

I had the thought of finding an o-ring that had the inner diameter of the rod and the proper out diameter & thickness to fit down in that groove in the top.

The retainer groove is wide but short. An o-ring being round won't fill a rectangular area.

An oil seal would fit the bill very well I suspect but I've not found one that fits (too small). The oil seal types are wide ranging but a thin profile lip would seal the area with minimal drag. I'll continue my search but so far no joy. I think I mentioned using a grommet that had light drag? X 4 it added up and the return from WOT to idle was agonizingly slow.

My local seal supply guy tells me most commercial seals are in fact produced in China, what isn't nowadays? The rubber stock is mostly still Japanese. The US just can't beat the labor and regulatory costs they offer. So don't be so quick to bash Chinese quality, we're not talking WalMart here. Many of the companies there are registered to meet or beat ISO and other industry standards. Makita tools are made there now. Commercial airliner parts, auto parts that US manufacturers use etc. I'm old enough to remember the then deserved term Jap Crap. They got better. I'll put the average Jap car up against anything the US makes today and the Chinese are learning fast. Give them 10 yrs and we'll be driving Chinese made cars here. And in 20 yrs they'll likely be very competitive with anything we make. Hell, the computer you are using to make your post with was likely made in China, is it crap?

oldschoolcarbs · « **Reply #16 on:** September 26, 2013, 11:51:18 AM »

Quote from: brandEn on September 25, 2013, 05:26:12 PM

You got a pic of those spacers by chance?

Tried but I don't seem able to upload photos. Or maybe it'll come through with I hit the post button.

oldschoolcarbs · « **Reply #17 on:** September 26, 2013, 11:59:03 AM »

Okay so that's weird. Why don't photos appear in the preview pane? Let's see if this one comes through. A set of sandcast SOHC carbs, nickel plated.

brandEn · « **Reply #18 on:** September 26, 2013, 12:23:29 PM »

Pictures work for me. Thanks for posting. Not sure I recognize where they go.

oldschoolcarbs · « **Reply #19 on:** September 27, 2013, 08:46:59 AM »

This is so aggravating. With no image in the preview pane you can't tell whether you're shooting a blank or not.

In any case, they prevent over-tightening of the lifter clamp screws.

brandEn · « **Reply #20 on:** September 27, 2013, 09:27:18 AM »

Perfect picture. Thanks. Clears things up for me!

Gamma · « **Reply #21 on:** February 18, 2017, 09:31:14 AM »

I know it's an old thread, but I just rebuilt a set of standard carbs and needed those top seals for the slide rods. I used these grommets that popped in a treat, not sure if they'll be ok in use, but they do look like they'll do the trick

PeWe · « **Reply #22 on:** February 18, 2017, 12:11:07 PM »

Gamma, your carbs look better than they looked as new from Honda!

Tim2005 · « **Reply #23 on:** February 18, 2017, 12:16:33 PM »

That sounds promising- keep us posted on how well they work. Where did you buy them from?

drumstyx · « **Reply #24 on:** February 18, 2017, 01:35:37 PM »

Quote from: lucky on September 25, 2013, 04:13:49 PM

Quote from: iron_worker on September 24, 2013, 07:57:43 PM
I also could use a seal for that spot. One of mine is missing. However, between the fairly tight fit of the slide to the carb body and the fit between the bushing and the slide rod that there shouldn't be much of a problem in terms of vacuum leaks. However, it would be nice to have something there as a wiper to keep dirt and grit out.

IW

IF the seal is too tight it could make a sluggish slow throttle response.

Wouldn't it just make it harder to open the throttle? These slides are directly actuated, so x amount of movement in the throttle = x amount of movement of the slide, regardless of how tight it is. Maybe a sluggish return though.

News:

Author Topic: Carb top seals? (Read 10462 times)