Topic: Carbs CB750

[DaveInTexas]

I removed them last night to look at the leaky T fitting between two of them.  I hope new Orings will fix that problem. 
Now that I have them off I was thinking I will clean them up and look them over, not really interested in a full bore overhaul as I believe they are in pretty good shape and previous owner sent new needles, seats and floats which I am putting in.
Still haven't found the definitive float setting anywhere for these fiber floats and don't have the special tool.  Not too keen on Clymer's idea of checking fluid level with soldered brass tubing, clear hose etc.
so if anyone has that, please post.

I was going to soak them in mineral spirits, plastic brush and rag, then spray with carb cleaner safe for rubber, blast with air hose.  Check settings of throttle valve, choke when open.  Synch with vac gauges (does that manometer thing really work?).

Would you pull the jets or just blow them out?  What about that wire trick I hear about to clean the jets?

Boy the manual terminology could do with help; "needle jet" and "jet needle" in the same sentence!
 

[Raul CB750K1]

It seems that you have lots of questions with your new project, but may I suggest you buy/download first a shop manual and search in the old threads? Most of what you need to know has been asked before and there is plenty of information about it. Then, if still in doubt, you can ask what is not clear.


Raul

[mcpuffett]

hi dave , you need to check out bob wessners web site he is the carb guru round here   mick.

[DaveInTexas]

It seems that you have lots of questions with your new project, but may I suggest you buy/download first a shop manual and search in the old threads? Most of what you need to know has been asked before and there is plenty of information about it. Then, if still in doubt, you can ask what is not clear.
Raul

Actually, Raul I gave quite a bit of thought before I posted and
a) neither Clymers nor the Shop Manual (I have both) say much about any of the questions I am asking and in any case I am interested in what the people here have to say regardless of what is in these older books.  Nothing like modern info from people actually doing this stuff today!
b) the whole issue of searching for past topics has never really worked for me.  Search engines turn up a lot of irrelevant stuff when you put in a simple word string and I find I never really get my questions answered that way.  No offense but I have always felt like the reply 'go away until you have read past answers' (I've seen it in many other boards, you are not the only one) is not really a positive or helpful contribution.  This is purportedly an active SOHC Tech forum.  If the reply to every question is, "we've covered that already, please stifle your questions" then I don't think the forum will ever fulfill its presumed goal of current helpful advice to all who come for assistance.
I hope you can see I am not slamming you with this thought; I am simply encouraging those who are uninterested in certain old topics to pass them by, and leave them to people who want to participate.

[mcpuffett]

hi dave , if you have your carbs of you may as well give them a good clean inside and out, i believe a lot of the guys in the states use yamaha carb dip to soak their carb bodies in,here in the uk i personally use a aerosol carb cleaner and compressed air , i would take the jets out etc and give everything a good blast out , then re sync with vacuum gauges,  mick.   

[Bob Wessner]

I removed them last night to look at the leaky T fitting between two of them.  I hope new Orings will fix that problem.  
Now that I have them off I was thinking I will clean them up and look them over, not really interested in a full bore overhaul as I believe they are in pretty good shape and previous owner sent new needles, seats and floats which I am putting in.
Still haven't found the definitive float setting anywhere for these fiber floats and don't have the special tool.  Not too keen on Clymer's idea of checking fluid level with soldered brass tubing, clear hose etc.
so if anyone has that, please post.

I was going to soak them in mineral spirits, plastic brush and rag, then spray with carb cleaner safe for rubber, blast with air hose.  Check settings of throttle valve, choke when open.  Synch with vac gauges (does that manometer thing really work?).

Would you pull the jets or just blow them out?  What about that wire trick I hear about to clean the jets?

Boy the manual terminology could do with help; "needle jet" and "jet needle" in the same sentence!

Dave, I thought the '70 still had the brass floats? Might be wrong though. I know I had a time getting the float height nailed down on my bike, which has the brass floats. The recommended height, I was told was 26mm. Definitely did not work, carbs leaked through overflows. I then went to 28mm at least and it was much better. I did do a sight check, but it was much less involved than soldering anything. I took some clear plastic tubing that was a snug fit in the bowl drains (take a bowl with you to the hardware store) then taper around the end slightly with a razor blade and put a couple of wraps of Teflon plumber's tape around it. Screw that end into the bowl drain hole and then tape the other end up against the side of the bowl. Repeat on all the carbs, then turn on the petcock. This way you can see all four at the same time. You needn't be concerned about fuel compatibility with the tubing or Teflon, you're only using it briefly.

[eldar]

You should post a pic of your carbs or the model numbers. I did not think the 70 carbs had fiber floats either.

[Lumbee]

...after rereading your post Dave you seem to imply that the carbs run good the way they are.  If thats the case  I don't know that I'd screw aroudn with a good thing.  The old carbs can be finiky beasts.  If you want to learn more about your carbs, buy a set off Ebay, and overhaul them, but I wouldn't tear into the ones you have if they are running good.

[Raul CB750K1]

It seems that you have lots of questions with your new project, but may I suggest you buy/download first a shop manual and search in the old threads? Most of what you need to know has been asked before and there is plenty of information about it. Then, if still in doubt, you can ask what is not clear.
Raul

Actually, Raul I gave quite a bit of thought before I posted and
a) neither Clymers nor the Shop Manual (I have both) say much about any of the questions I am asking and in any case I am interested in what the people here have to say regardless of what is in these older books.  Nothing like modern info from people actually doing this stuff today!
b) the whole issue of searching for past topics has never really worked for me.  Search engines turn up a lot of irrelevant stuff when you put in a simple word string and I find I never really get my questions answered that way.  No offense but I have always felt like the reply 'go away until you have read past answers' (I've seen it in many other boards, you are not the only one) is not really a positive or helpful contribution.  This is purportedly an active SOHC Tech forum.  If the reply to every question is, "we've covered that already, please stifle your questions" then I don't think the forum will ever fulfill its presumed goal of current helpful advice to all who come for assistance.
I hope you can see I am not slamming you with this thought; I am simply encouraging those who are uninterested in certain old topics to pass them by, and leave them to people who want to participate.

No offence taken whatsoever. Actually, I've just re-read your original post and you are perfectly right. My apologies.

Raul

[TwoTired]

previous owner sent new needles, seats and floats which I am putting in.

If you are talking about the float needles (not slide needles), your option to change.  Personally, I have a hard time changing parts known to work and I can't find anything wrong, with parts that are unknown, even if new.

Would you pull the jets or just blow them out?  What about that wire trick I hear about to clean the jets?

The jets are screw in aren't they? I like to see light pass through them.  And, I've had no success doing that while still installed.
Besides that, there are emulsion tubes hidden behind them.  They have tiny holes to clear, too.  Also, if any gunk is found in jets or emulsion tubes, the passageways behind them probably need cleaning.
I don't like wire to clean jets unless they are hopeless.  Cleaning techniques begin with low aggression and escalate as needed.  If pressurized carb cleaner won't do it, then I'll poke nylon or boars bristle in there.  Copper wire is the most agressive I use to safely clean a jet orifice.  Clip the end of the wire with a dykes so it has a flattened taper, and you can use it like a drill to excavate crud.  Use carb cleaner as a drill lube.  Copper is still softer than the jet material, so orifice mods should be minimized.  Whatever you try to push through the orifice, make sure it is a smaller diameter than the orifice itself.  #40 jet is 0.40mm (0.0157 inch)

Cheers,

[upperlake04]

Clip the end of the wire with a dyke

  I personally am not aquainted with one of these.    The online dictionary doesn't shed any light on what this means either. Is this an American thing?
  BTW TT,  thanks for your tireless posting that have helped  many of us, although I admit I don't understand much of the electrical info.

[TwoTired]

Actually, I forgot the "s".  They are called dykes, or diagonal cutting pliers.  (google search-  Dykes tools)

The Flush cutter variety leaves a nice long chisel point on one side of the wire cut.

You're welcome.  And, thanks for the feedback.
I remember back when just a small bit of information would have saved me time, money, and the machine I was working on.

I'm going on the theory that the world will be a better place with a few less frustrated Honda wrenchers.  You never know, I may just be out in that part of the world someday.  Sometimes, helpfulness is contagious.

Cheers,

[Dusthawk]

Clip the end of the wire with a dyke

  I personally am not aquainted with one of these. The online dictionary doesn't shed any light on what this means either. Is this an American thing?
 BTW TT, thanks for your tireless posting that have helped many of us, although I admit I don't understand much of the electrical info.

I really have to agree with Upperlake on this one, TwoTired, You are an invaluable asset to this group and, along with a few others, make this entire conglomeration of owners, riders, bikers, enthusiasts, etc. such a great place to gain knowledge and wisdom. There are any number of times I myself have found help in one of your old posts or have asked directly.

Thank you for being here and being so giving of your time, energy, and wisdom.

Jeff.

[dusterdude]

I removed them last night to look at the leaky T fitting between two of them.  I hope new Orings will fix that problem.  
Now that I have them off I was thinking I will clean them up and look them over, not really interested in a full bore overhaul as I believe they are in pretty good shape and previous owner sent new needles, seats and floats which I am putting in.
Still haven't found the definitive float setting anywhere for these fiber floats and don't have the special tool.  Not too keen on Clymer's idea of checking fluid level with soldered brass tubing, clear hose etc.
so if anyone has that, please post.

I was going to soak them in mineral spirits, plastic brush and rag, then spray with carb cleaner safe for rubber, blast with air hose.  Check settings of throttle valve, choke when open.  Synch with vac gauges (does that manometer thing really work?).

Would you pull the jets or just blow them out?  What about that wire trick I hear about to clean the jets?

Boy the manual terminology could do with help; "needle jet" and "jet needle" in the same sentence!

Dave, I thought the '70 still had the brass floats? Might be wrong though. I know I had a time getting the float height nailed down on my bike, which has the brass floats. The recommended height, I was told was 26mm. Definitely did not work, carbs leaked through overflows. I then went to 28mm at least and it was much better. I did do a sight check, but it was much less involved than soldering anything. I took some clear plastic tubing that was a snug fit in the bowl drains (take a bowl with you to the hardware store) then taper around the end slightly with a razor blade and put a couple of wraps of Teflon plumber's tape around it. Screw that end into the bowl drain hole and then tape the other end up against the side of the bowl. Repeat on all the carbs, then turn on the petcock. This way you can see all four at the same time. You needn't be concerned about fuel compatibility with the tubing or Teflon, you're only using it briefly.

bob,the 70 did have brass floats,however i have plastic floats from god knows what kind of carbs in mine.

[DaveInTexas]

I believe I have the original carbs as they are the one-cable type.  I am removing the old brass floats.  They are well bent-up and suspected of leaking.   I was sent some 'plastic' (I am told they are in fact 'fiber') floats, with new needle and seats & washer from the previous owner and it was suggested to install them.  They seem to fit just fine, and the bike ran with two in place.

I really like that idea of jamming the tubing with teflon into the float, that I can do; much easier.
Has anyone done the home-made manometer thing?

Here is my plan:
I believe I will clean the carbs well with mineral spirits (paint thinner) , remove and 'progressively' clean the two jets (I hope they are threaded) with; first bristle then maybe soft wire if necessary.
Carb cleaner seems to do very little on this residue - I believe it will require mechanical cleaning (stiff fibre brush, rag) plus solvents, airgun.   
Then set the float level to  ~28 mm down from the mating surface. (right?)  I will make sure all the chokes open fullly.  I will make sure the throttle valves are all set to the same height.  I will preserve the current throttle stop and air screw settings for now.
I will then install and confirm they are working still. 
Then I will investigate tuning!

Last note: 
I too extend a huge gratitude to all who share their time and knowledge on SOHC4 tech forums.  You folks have a terrific attitude, and have saved many of us mewling newbies great aggravation and expense. 



PS Dykes or Dikes:
http://en.wikipedia.org/wiki/Diagonal_pliers

[DaveInTexas]

hi dave , you need to check out bob wessners web site he is the carb guru round here   mick.

Mick, can you confirm this is the location:
http://home.att.net/~bobwessner/wsb/html/view.cgi-html2.html--SiteID-756666.html
Thanks, Dave

[mcpuffett]

hi dave , thats it  you will find bob's site very informative , i know i did ,   mick.

[scunny]

I'm glad the dyke turned out to be diagonal cutters, here in NZ a dyke is a "lady" with butch tendencies

[TwoTired]

According to google, dykes are waaaaayy more popular than many tools.





 

[upperlake04]

Thanks for the clarification guys. I knew TT is a mechanical wizard and extremely articulate,  but I couldn't quite get a mental image of the procedure... 

[DaveInTexas]

Carbs, guys - carbs! 
never mind images of twin, bi-girls!

[techy5025]

Whatever else you do to the carbs, I would recommend you go with the composite
floats...even if you keep the original four pull carbs.  I traced most of my early carb
problems to leaky brass floats.

Jim

[Heirborn]

I too read Bob's article/post about the brass floats. 26mm was not right for mine either. I went to 30mm. I synced the carbs and then had a high idle issue. I pulled the carbs this week to check out one of the idle rod adjustment screws, shoved everthing back on as far as I could, put new hose clamps on the insulator closest to the engine intake, shoved the airbox back on, made sure everything was tight,  synced, and messed with it for a while until I was comfortable with everthing, buttoned it back up. Set my idle screws out 2 1/2 turns as I was having a rich problem at low speeds. Took it out this morning and everything seems to be good.....we shall see. By the way I have the inexpensive Motion Pro or Pro Motion (what ever it is) and like it...very easy to use.