Topic: Carb rebuild questions... *She runs!*

[iron_worker]

So I took the plunge and am tearing into my carbs.

Stats for my bike:
-1974 CB750 K4
-Stock Airbox with stock type element
-Stock 4 into 4 (rusted out ... but a new one on the way)
-Very recent tune up
-Plugs that I pulled showed an almost perfect light tan brown color on all plugs
-Cold starts are *very* rough ... seems to run on 2 or 3 cylinders for a while
-When warm it runs pretty well .... still a slight low RPM hesitation


So far this is what I've accomplished:

-Complete teardown of airbox and carb rack assembly
-Fixed a crack in the airbox, applied linseed oil, soaking airbox rubbers in linseed oil/thinner in an attempt to soften them
-Teardown/clean/rebuild of #1 and #2 carbs

Then I got to #3 carb and of course stripped out one of the small phillips screws in the top of the slide. Arg! I'm soaking it in cleaner over night again and hopefully it will come out ... any tips for that?

Some other things I noticed:

-I had at least 2 plugged idle jets (haven't checked #4 yet)
-1 choke plate was not "sync'ed" with the other 3

These were definitely contributing factors to my cold start issue and low RPM hesitation I'm sure.

Things I'm not so sure about:

-Floats are all set to about 21-22mm from the raised lip around the float bowl (as I understand it ~26mm is the factory float height).
-My rebuild kit came with 110 mains and 40 pilot jets but there were 105/40s in the carbs.

My question: Do you think I should set the the float level back to the recommended 26mm (effectively leaning the bike out over the entire range) and change to the new 110 mains? OR should I stick with the 105s that were in there despite the fact that I chewed them up a bit trying to get them out of the emulsion tubes.

Lookin forward to your responses.

Thanks,

IW

[Johnie]

My 74 had cold starting issues when I first got it. I did the usual...new plugs, new plug caps, timing, points, condensors, valve adjustment, carbs and sync. What a huge difference. You did not need to remove the jets from the emulsion tubes to clean them. Put the floats back to OEM 26mm for sure. Be sure the tank is clean of rust and crapola or you will be tearing those carbs down again. There is also a good link on this board under the FAQ area for carbs. Here is a link to the 750 specs which may help you out.
http://www.hondachopper.com/garage/carb_specs/carb_specs.html

[iron_worker]

I didn't need to remove the jets from the emulsion tubes but I had it in my head that I wanted to use all the new parts from the carb rebuilt kits. (Made sense at the time?)

I think I will go ahead and try the 110 mains with floats set to 26mm. If I have to I can change main jets on the bike.

Looks like if the 105 mains are truly stock then I have the 657B or 086A carbs ... which according to that the jet needle should be on the 4th from the top. My jet needles were set at 3rd from the top (middle). Apparently someone has been d!ckin with my carbs before. Suprise surprise. ha

I think I should be good as far as crap in the tank. The tank was lined a while ago but I also run an inline filter on each fuel line.

Thanks for the advice. I'm looking forward to getting it all sync'ed up and running like it should for the first time in a looonnnggg time.

IW

[lucky]

So I took the plunge and am tearing into my carbs.

Stats for my bike:
-1974 CB750 K4
-Stock Airbox with stock type element
-Stock 4 into 4 (rusted out ... but a new one on the way)
-Very recent tune up
-Plugs that I pulled showed an almost perfect light tan brown color on all plugs
-Cold starts are *very* rough ... seems to run on 2 or 3 cylinders for a while
-When warm it runs pretty well .... still a slight low RPM hesitation


So far this is what I've accomplished:

-Complete teardown of airbox and carb rack assembly
-Fixed a crack in the airbox, applied linseed oil, soaking airbox rubbers in linseed oil/thinner in an attempt to soften them
-Teardown/clean/rebuild of #1 and #2 carbs

Then I got to #3 carb and of course stripped out one of the small phillips screws in the top of the slide. Arg! I'm soaking it in cleaner over night again and hopefully it will come out ... any tips for that?

Some other things I noticed:

-I had at least 2 plugged idle jets (haven't checked #4 yet)
-1 choke plate was not "sync'ed" with the other 3

These were definitely contributing factors to my cold start issue and low RPM hesitation I'm sure.

Things I'm not so sure about:

-Floats are all set to about 21-22mm from the raised lip around the float bowl (as I understand it ~26mm is the factory float height).
-My rebuild kit came with 110 mains and 40 pilot jets but there were 105/40s in the carbs.

My question: Do you think I should set the the float level back to the recommended 26mm (effectively leaning the bike out over the entire range) and change to the new 110 mains? OR should I stick with the 105s that were in there despite the fact that I chewed them up a bit trying to get them out of the emulsion tubes.

Lookin forward to your responses.

Thanks,

IW

Better stay with those #110mm mains with those exhausts.

The screw in the slide is a big problem.
It takes a #2 phillips if you do not want to strip more of them.
Maybe needle nose pliers?
Next step is a die grinder or Dremel tool to get down in there and grind the head off. What a night mare.
 Always use the correct size screwdriver bit.

SET THE FLOAT LEVEL like the book tells you. END of story.

Let us know if you get that screw out.

[iron_worker]

Well I have a kit that I hope has a #2 philips in it. The screw driver I was using worked fine for the first 2 carbs but the 3rd one is givin me trouble. I'm going to give it a shot of PB Blaster after work and see if I can work it loose tonight. Maybe try a punch on the back side of it to try and break the rust loose if I can find a way to support it so as not to mar the sides/bend the needle.

My last resort I think I will attempt to drill out the screw head and use pliers.

I think I may have some philips head screws that I may replace them all with.

Thanks Lucky.

IW

[iron_worker]

Ok well here is an update if anyone is interested.

I got the needle retainer screw out! A proper #2 Philips is a must! I was using a #1 prior to that. I also support the slide on the edge of my desk so that the needle was out of harms way and gave the backside of the screw a good whack with a punch and hammer. I find (in other situations) this sometimes helps to break up the rust/gunk in the threads. I reassembled them all with allen head cap screws.

I checked the number on the carbs and they are 657B style carbs ... so according to the link posted above they should be:

-105 main
-40 pilot
-4th needle clip position (I assume this is from the top?)
-1 turn out idle mixture screw
-26mm float height

What they were when I found them:
-105main
-40 pilot (2 clogged)
-3rd needle clip position
-1-1.25 turns out
-21mm float height

What I have them set at for now:
-110main
-40 pilot
-3rd needle clip position
-1 turn out
-26mm float height

I'm waffling between setting them up as 657A (110,40,4,1) or 657B carbs (105,40,4,1). I think what I have will definitely run but if I can set up it up perfect the first time then all the better.

What do you all think?

I also just found out that my new 4 into 4 stock type exhaust should be shipping today from the Netherlands. Probably will be several weeks before it's here though I imagine.

IW

[Johnie]

The worst that can happen in the 3rd position is you may want to try the 4th position later. Put it where you want it and give it a try. The 2nd time is a lot easier if you need to change the clip. Since mine is 100% stock I went with what Honda calls for and there was no need to go back in the carbs. She runs and idles great. Let us know how you come out.

[lucky]

Well I have a kit that I hope has a #2 philips in it. The screw driver I was using worked fine for the first 2 carbs but the 3rd one is givin me trouble. I'm going to give it a shot of PB Blaster after work and see if I can work it loose tonight. Maybe try a punch on the back side of it to try and break the rust loose if I can find a way to support it so as not to mar the sides/bend the needle.

My last resort I think I will attempt to drill out the screw head and use pliers.

I think I may have some philips head screws that I may replace them all with.

Thanks Lucky.

IW

I would not punch it from the back side. Asking for trouble.
If you punch it from the back side it could spread out and be even more of a problem.
I would keep the same metric screws.

What I have them set at for now:
-110main
-40 pilot
Keep the needle the same position for now.
-1 turn out
-26mm float height


I would keep the needle clips in the same position for now.

[iron_worker]

Yes perhaps punching the slide from the back side was not such a good idea but I was pretty careful and no harm done so far as I can tell.

The midrange throttle response was always good on my bike before while the low end had a bog and the upper end felt a bit flat (proper timing and points gapped helped that).

What I was stumbling on was that I want to keep the solid midrange so I was going to put the needle clip back where it was (#3 position... 1 position leaner than factory recommendations). However now that I found out the floats were way out of wack (21mm ... instead of 26mm factory height) I wasn't sure if that was effectively compensating for my leaner needle clip position with a richer float height (reduced height for fuel to be drawn up into the carbs = more flow ... I think).

I'm probably way over thinking it and I should just try it. I'll probably have to tear into them again regardless of what I choose. lol

Thanks for the help guys. I am going to try and bench sync them tonight and hopefully get the carbs and airbox put back on this weekend ... and my new chain and sprockets!

IW

[iron_worker]

I got the carbs reasonably bench sync'ed last night. I decided to stick with how it was set up for now. Seems like probably a pretty good chance I'll have to tear em down one more time anyway. Hopefully I can get it on and going this weekend... that is if I can find a masterlink for my chain locally... arg.

IW

[chewbacca5000]

Yes perhaps punching the slide from the back side was not such a good idea but I was pretty careful and no harm done so far as I can tell.

The midrange throttle response was always good on my bike before while the low end had a bog and the upper end felt a bit flat (proper timing and points gapped helped that).

What I was stumbling on was that I want to keep the solid midrange so I was going to put the needle clip back where it was (#3 position... 1 position leaner than factory recommendations). However now that I found out the floats were way out of wack (21mm ... instead of 26mm factory height) I wasn't sure if that was effectively compensating for my leaner needle clip position with a richer float height (reduced height for fuel to be drawn up into the carbs = more flow ... I think).

I'm probably way over thinking it and I should just try it. I'll probably have to tear into them again regardless of what I choose. lol

Thanks for the help guys. I am going to try and bench sync them tonight and hopefully get the carbs and airbox put back on this weekend ... and my new chain and sprockets!

IW

From reading these threads I am starting to think float height is a huge factor in hard starting and over all performance.  With the float height adjusted to factor spec you should see a big difference.  One tip if you get overflows don't blame it on the high immediately just take the bowl off and put it back on.  Sometimes those floats hang up.

[iron_worker]

Yeah I've done the old "whack the bowl with the big end of a screwdriver" trick before with some success before. lol

IW

[lucky]

Let us know what happens Ironworker.

[iron_worker]

Found a master link locally that I think should work. I have my professional practice exam tomorrow morning (eeek!) but then I'd like to put in a few hours on the bike. Weather looks like it should cooperate too so that is nice... that's a big factor in Canada. ha

IW

[iron_worker]

*Weekend Update*

Note: If you don't want to read a huge pointless story then just skip to the verdict in the last paragraph or 2.

Well I did battle with my bike pretty much all of Saturday afternoon and most of when I had light in the evening. The reassembly did *not* go without a hitch.... pretty much every part fought me in some way. ha

So the way I left it I had the old chain off and and the new sprockets on (but no chain). I decided to try out the master link I found locally just on the chain off of the bike to see if it would fit (since it was a different brand than the chain). The plate didn't seem to want to slip on the other side but I thought it was the o-rings jamming it up so obviously I got frustrated and tried to force it. Well I got it stuck on the chain and then couldn't get it off! Well after some hammering and cussing I got it off in one piece. So I tried just assembling the link itself without the chain in between... the plate still wouldn't fit! The holes were too small for the pins?! WTF Well anyway, some careful work with a dremel cured that ...but that really should not be necessary. Strange.

So get the chain on the bike and the master link in (after putting the clip on backwards once of course). Then I started to reassemble the rear brake arm and the little swing arm that holds the drum brake. For the life of me I couldn't get the brake lever onto the splined shaft far enough to get the pinch bolt through. I fiddled for quite some time before I just made myself take the wheel completely off again and start over. I pushed the splined shaft through from the inside of the drum plate and all was well. Reassembled the back end and adjusted the brake (works better now ... I locked it up by accident on the test ride lol).

On to the carbs!

I start putting the rubber boots back on the head and getting the clamps in place etc. I start to wrestle the carbs into place but no matter how hard I push I can NOT get them to push into place. I tried turning them at different angles to get them to line up better. Struggle struggle struggle. No go. Finally, I pull one of the boots off and try pushing it onto the carb by itself ... OH! I had the 1 and 4 cylinder boots backwards. Get them flipped around and the carbs pop right in. Great.

Now I notice that one of my choke mechanism arms is loose ... the locknut is not staying locked so I decide to try some nylock nuts on there to hold it. Run up to the 3rd floor apartment ... yes I live in an apartment and have to drag down my tools every time I want to work on bike (outside). Get that one choke mechanism fixed and decide I should probably put lock nuts on the rest of them ... on the 2nd one I managed to strip the thread on the arm....and further mangle it in desperate attempts to save it. Finally I get smart and take the carbs off, clean up my tools and push my bike back into it's spot. Time to give up for a bit ...

While pushing my bike back I notice something is rubbing ... chain is rubbing on the chain guard. ARG! I am about ready to freak out at this point. What else could wrong? So I spend a few minutes adjusting (bending) it and head up to my condo, defeated.

I get to tinkering on my carbs and my solution to the stripped threads is to cut off the stripped portion with a dremel to try and save the rest ... It doesn't leave much thread but it works! I put a nylock nut on it backwards to lock it in place and good to go.

Supper time!

After supper I drag all my tools back outside for another go. Frustration levels much lower for now ...

I throw the carbs on again (this time they go on easily with the boots facing the right way lol). Get the air box in. Ok, this is looking good. Go to hook up the throttle cables ... hmmm what the heck?! How does this work? Study it for a while. Fawk. I have the throttle cable bracket on backwards ... didn't pay enough attention when I tore the carb rack down for cleaning. Out comes the air box again, out come the carbs, quickly flip the bracket, carbs back in, airbox back in....

CRACK! I re-broke my airbox where it was cracked before. I had fixed it with JB weld but it didn't hold. Damn it! Oh well, now I know why it was cracked in the first place. ha (The snorkel is cracked from jamming it between the carbs and the frame.)  I ain't taking it out again at this point so I just leave it. It's not really hurting anything.

Hook up the throttle cables ... have some issues with getting them to line up right and have to do some "adjusting" to the bracket. I realize that my throttle could have been binding before and may have been causing it to seem pretty dogish. Sheesh.

Fuel lines hooked up. Vent lines in place. Everything is looking good. Tank back on, battery is in. Everything is in!

Now I nervously turn the fuel on and let it sit while I clean up my tools. Check back ... no leaks out the overflow. Woohoo!

Turn the key on ... neutral light is on. Good ....  Choke on.... Double check fuel... Good... Hit the button and...

VROOM! ... and it dies ... oops. Had the idle adjuster set all way out. Fire it up again and hold the throttle while I adjust the idle. It idles beautifully!

I took it for some sweet victory laps in my parking lot (I'm sure the neighbours loved that!). Bogs a bit at low RPM when it's stone cold but I think that's normal for carb'ed bikes.

Clean up my tools and out for an official test ride:

It runs great! Pulls nicely all the way to redline. Still a bit of popping on decel so I could be a bit lean yet... but I think my new exhaust (which I think will be more restrictive) should fatten up the mixture a bit. I will do some plug chops to confirm mixture when I get the new exhaust on but I think it's pretty close.

I still haven't even sync'ed it yet! And of course the rain on Sunday did away with that hope but oh well. I'm very happy.

IW

[iron_worker]

After doing some more reading today I have found that since I still have some popping on decel and some bogging at low rpms (below 2500 ... but way better than it was!) I am going to move my needle clip down to the 4th notch (now in the 3rd notch ... from the top).

I should be able to rip into those carbs at a blistering pace. ha

IW

[Johnie]

Correct...you should be able to do it in less than an hour now.

[iron_worker]

Is it possible to take the carbs out with the airbox still in? Good idea?

I also need to get a new gasket for my air box, new "velocity stack" rubbers cause my are hard as hell, and the proper wing nut bolts that hold the bottom of the airbox on because mine are flat heads for some stupid reason. I am also considering switching up the K&N stock type filter as I've heard it's a good mod that usually doesn't require re-jetting.

IW

[Johnie]

You will not be able to get the carbs out with the air box attached. Not enough room to slide them back to remove. The air box rubbers as well as the air box gasket are still available as I bought them recently. Have heard mixed reviews on the K&N. I stick with the OEM and always get the performance Honda has designed these motors for. I think I bought those Wing nuts from Honda a few years ago. Check with your dealer or put an ad in the wanted section of the board. Someone might have them for you.

[iron_worker]

Bikebandit.com has all of the above if I am willing to pay $40 shipping ...

IW

[Tews19]

Ehhhh I dnt like bike bandit.

[bjatwood]

Sounds like you are making progress AND bonding with that bike. Once you get all thru it, the thrill of riding it and talking about it with people that stop gawk at it, and then tell you "I had one just like it back-in-the-day" will bring you many smiles to the miles.
Got some pics of this bike anywhere to show us?

[lucky]

*Weekend Update*

Note: If you don't want to read a huge pointless story then just skip to the verdict in the last paragraph or 2.

Well I did battle with my bike pretty much all of Saturday afternoon and most of when I had light in the evening. The reassembly did *not* go without a hitch.... pretty much every part fought me in some way. ha

So the way I left it I had the old chain off and and the new sprockets on (but no chain). I decided to try out the master link I found locally just on the chain off of the bike to see if it would fit (since it was a different brand than the chain). The plate didn't seem to want to slip on the other side but I thought it was the o-rings jamming it up so obviously I got frustrated and tried to force it. Well I got it stuck on the chain and then couldn't get it off! Well after some hammering and cussing I got it off in one piece. So I tried just assembling the link itself without the chain in between... the plate still wouldn't fit! The holes were too small for the pins?! WTF Well anyway, some careful work with a dremel cured that ...but that really should not be necessary. Strange.

So get the chain on the bike and the master link in (after putting the clip on backwards once of course). Then I started to reassemble the rear brake arm and the little swing arm that holds the drum brake. For the life of me I couldn't get the brake lever onto the splined shaft far enough to get the pinch bolt through. I fiddled for quite some time before I just made myself take the wheel completely off again and start over. I pushed the splined shaft through from the inside of the drum plate and all was well. Reassembled the back end and adjusted the brake (works better now ... I locked it up by accident on the test ride lol).

On to the carbs!

I start putting the rubber boots back on the head and getting the clamps in place etc. I start to wrestle the carbs into place but no matter how hard I push I can NOT get them to push into place. I tried turning them at different angles to get them to line up better. Struggle struggle struggle. No go. Finally, I pull one of the boots off and try pushing it onto the carb by itself ... OH! I had the 1 and 4 cylinder boots backwards. Get them flipped around and the carbs pop right in. Great.

Now I notice that one of my choke mechanism arms is loose ... the locknut is not staying locked so I decide to try some nylock nuts on there to hold it. Run up to the 3rd floor apartment ... yes I live in an apartment and have to drag down my tools every time I want to work on bike (outside). Get that one choke mechanism fixed and decide I should probably put lock nuts on the rest of them ... on the 2nd one I managed to strip the thread on the arm....and further mangle it in desperate attempts to save it. Finally I get smart and take the carbs off, clean up my tools and push my bike back into it's spot. Time to give up for a bit ...

While pushing my bike back I notice something is rubbing ... chain is rubbing on the chain guard. ARG! I am about ready to freak out at this point. What else could wrong? So I spend a few minutes adjusting (bending) it and head up to my condo, defeated.

I get to tinkering on my carbs and my solution to the stripped threads is to cut off the stripped portion with a dremel to try and save the rest ... It doesn't leave much thread but it works! I put a nylock nut on it backwards to lock it in place and good to go.

Supper time!

After supper I drag all my tools back outside for another go. Frustration levels much lower for now ...

I throw the carbs on again (this time they go on easily with the boots facing the right way lol). Get the air box in. Ok, this is looking good. Go to hook up the throttle cables ... hmmm what the heck?! How does this work? Study it for a while. Fawk. I have the throttle cable bracket on backwards ... didn't pay enough attention when I tore the carb rack down for cleaning. Out comes the air box again, out come the carbs, quickly flip the bracket, carbs back in, airbox back in....

CRACK! I re-broke my airbox where it was cracked before. I had fixed it with JB weld but it didn't hold. Damn it! Oh well, now I know why it was cracked in the first place. ha (The snorkel is cracked from jamming it between the carbs and the frame.)  I ain't taking it out again at this point so I just leave it. It's not really hurting anything.

Hook up the throttle cables ... have some issues with getting them to line up right and have to do some "adjusting" to the bracket. I realize that my throttle could have been binding before and may have been causing it to seem pretty dogish. Sheesh.

Fuel lines hooked up. Vent lines in place. Everything is looking good. Tank back on, battery is in. Everything is in!

Now I nervously turn the fuel on and let it sit while I clean up my tools. Check back ... no leaks out the overflow. Woohoo!

Turn the key on ... neutral light is on. Good ....  Choke on.... Double check fuel... Good... Hit the button and...

VROOM! ... and it dies ... oops. Had the idle adjuster set all way out. Fire it up again and hold the throttle while I adjust the idle. It idles beautifully!

I took it for some sweet victory laps in my parking lot (I'm sure the neighbours loved that!). Bogs a bit at low RPM when it's stone cold but I think that's normal for carb'ed bikes.

Clean up my tools and out for an official test ride:

It runs great! Pulls nicely all the way to redline. Still a bit of popping on decel so I could be a bit lean yet... but I think my new exhaust (which I think will be more restrictive) should fatten up the mixture a bit. I will do some plug chops to confirm mixture when I get the new exhaust on but I think it's pretty close.

I still haven't even sync'ed it yet! And of course the rain on Sunday did away with that hope but oh well. I'm very happy.

IW

Popping on decelration is too rich. Remember you are using a #40mm idle jet.

[lucky]

Yeah where is the pics???

Got to take time to smell the Castrol fumes.

[Johnie]

Pics...we love pics...