Topic: preferred method for removing carbs w/stock airbox?

[gmoss]

Rebuilt my carbs over the past few days, found that three of my four slow jets were quite clogged so no wonder it died below 2.5k rpm. I think I must have messed up the float height because now it won't start, throttle and choke make no difference. Plenty of spark and there's fuel in the bowls.

So I need to take the carbs back off I guess.

Which I've discovered is a massive pain in the ass. The best method I've figured out so far is:

1) loosen the clips on the tubes running forward from the carb to the head
2) loosen the clips on the air box adapter tubes, from the carbs back to the plenum/air cleaner/whatever you want to call it, ugly rubber thing, I'm going to call it a plenum, I don't care if that's not technically correct, that's not the point.
3) (this is the step I hate) pull the air box adapter tubes/rubber "velocity stacks"/whatever INTO the plenum by reaching inside it from the air filter hole. This part blows.
4) now there's finally enough room to pull the carbs off and out.

I tried so many things. I tried removing the entire airbox and battery holder assembly to make room for the plenum to be removed without removing the rubber "velocity stacks". I tried removing the rubber attachments from the head itself (awful, awful).

Now I also need new rubber "velocity stack" tubes, because I tore two of them in the process. I superglued them back shut for now but obviously that's not a permanent solution.

Honestly it's all enough to make a guy ignore all the advice and just get pods or a breadbox. If I wanted a bike that was a PITA to work on and also ran perfectly, I'd get a brand new SV650.

What am I missing? Should I be removing the metal intake manifold from the head itself? What's the correct order of operations here??

[bryanj]

Nope, just fresh rubber and care, it is the worst job to do

[goodtryer]

I completely agree with your assessment. Carb install & removal is a huge hassle on these bikes and unfortunately is necessary all too frequently in my experience.

At the risk of being accused of heresy, here's an idea that makes it somewhat easier: replace the threaded studs that hold the intake runners to the head with bolts.

https://youtu.be/E5E0NASixo4 (Courtesy of Mike Nixon at motorcycleproject.com)

I recently did this on my 550 and it made the process noticeably easier; not great, just better. It's still a PITA. It comes with risks, primarily the threat of stripping threads in holes in the head. But wrestling the carbs off has risks, too, and frankly I decided it was worth it.


One more thing, another way to get a little extra wiggle room is to remove the 2 bolts that hold the airbox to the frame. That lets the airbox shift back an extra millimeter or 2.

[ekpent]

 On the CB550's and CB500 I've done in the past I was left shaking my head as to why the glorious engineers at Honda could not have designed the set-up with maybe an extra 1/2 inch or so of play room to make the job easier on the mechanic and the parts.

[bryanj]

If you want the absolute easiest way remove front engine monts and top rear then koosen footrest bolt and let engine povot

[jonda500]

Whenever I have to wrestle the carbs I always strongly consider cutting the diagonal frame tube out of the way and installing a 750 frame kit so that the diagonal frame tube could be removed every time I need to pull the carbs out allowing the plenum chamber thingy to be removed first!
John

[gmoss]

At the risk of being accused of heresy, here's an idea that makes it somewhat easier: replace the threaded studs that hold the intake runners to the head with bolts.

https://youtu.be/E5E0NASixo4 (Courtesy of Mike Nixon at motorcycleproject.com)

oh interesting, this guy removes the bolts at the head. I can try that I guess.

If you want the absolute easiest way remove front engine monts and top rear then koosen footrest bolt and let engine povot

this seems like using a cannon to kill a cockroach.

Whenever I have to wrestle the carbs I always strongly consider cutting the diagonal frame tube out of the way and installing a 750 frame kit so that the diagonal frame tube could be removed every time I need to pull the carbs out allowing the plenum chamber thingy to be removed first!
John

what does it say that "cutting up your frame" is the *more* reasonable solution than "aftermarket air filters". I guess we *really* can't have a flat spot in the mid throttle range on a 50 year old bike, eh? ok I think I don't want to open that can of worms...

[bryanj]

You tried killing a damn cockroach!

[Honda_CB_Rider]

Just remove the battery box and loosen the electrics. On a 550f supersport it is than. You can remove the air box via the battery channel, easy!!

Cheers

[wildtapholer]

Am I missing something here, what is the actual bike we are talking about. I have a 1977 CB400f and had a carb problem with overflowing in order to test each time I had to put the carbs back on the bike reconnect everything then fire it up  only to find a leak again. After 6 times I got to the point where I could remove and refit the carbs in an hour.

[gmoss]

Sorry, 73 CB500.

I'm sure I could remove them in about 10-15 minutes now (will find out this weekend) but it's highly unpleasant, especially removing the rubber connectors from the back of the carbs with my hand inside the air cleaner.

@goodtryer posted about removing the manifold bolts from the head itself but I'm worried I don't know about the state of the gaskets in there, and while I plan on having the top end rebuilt anyway due to a head gasket leak, I don't want to deal with that quite yet -- the goal for now is just to get the bike idling and moving.

[bryanj]

Not gaskets but O rings and same as tappet cap

[gmoss]

Not gaskets but O rings and same as tappet cap

perfect, that's good to know, i'll add a set to my next order!

[wildtapholer]

I'm guessing at this, but I use this web sight   https://www.cmsnl.com/honda-cb500k2-four-1973-usa_model461/partslist/                                                                                                                                              as a reference to find out if any parts missing and I can work out from it how most things come apart from the exploded view.

[05c50]

The whole job is  much easier with soft, pliable air box connectors (velocity stacks).

.......Paul

[jonda500]

The whole job is  much easier with soft, pliable air box connectors (velocity stacks).

.......Paul

Yes soft new air cleaner side rubber boots are much easier to drag the carbs past - I remove the hose clamps first or they get bent up in the process. With my original over 40 years old hard boots that were permanently glued into the air chamber the job was a right P.I.T.A.! Undoing the filter assembly from the frame gives you a valuable few extra mm's of room as Goodtryer said.
John

[gmoss]

Not quite the same as o rings in the tappet cap…. Or are these just so old they’ve pancaked?

[RAFster122s]

They turn into flat plastic when old and no long resemble an Orings. Also, tend to leak or won't reseal if you try to reuse them once removed.
They are the same size as the tappet cover o-rings...

[Kevnz]

You probably already know that the carbs are going to come off several more times. Once you have them off, remove the manifold and then press the carbs back onto the manifold; it's much easier on the bench or ground pressing downward than pulling forward on the bike, especially if the rubbers are old and hard. ( wish I was made of rubber, I'm old and soft ) Then you refit the carbs onto the bike with 2 nuts, connect the tank and fuel lines and check for leaks etc and if the carbs need to come off again, just 2 nuts to undo. When you finally sort out your issue you can reassemble properly. I have found that a nearly foolproof way of stopping the carbs leaking out the overflow ( assuming you have done all the other stuff like cleaning the needle assy and setting float height etc) is to check that the needle valve falls straight out of the seat when slowly inverted. (with seat removed from carb body) If it sticks, even slightly, polish the seat and the needle with liquid metal polish and a cotton bud until it just flops straight out as soon as you invert. I think the bore of the seat gets a fine buildup of grot which can cause the needle to bind ever so slightly. I've just gone through this process with my 500, carbs off 5 or 6 times, and only this has had any effect. No leaks now, leaving overnight, if all good in the morning and garage not awash with petrol, I will refit the whole caboodle.

[TwoTired]

Anybody remember the trick of treating hard rubber with wintergreen oil to soften them?

When I did this last, it also slightly enlarged the rubber bits.  So, you don't leave them soaking too long.  But, slightly larger carb couplers make carb install easier.  And, the rubber then gradually shrinks over time.  Curing itself of seal issues.  Soft rubber also keeps them from cracking when deflection is needed.

Something to consider…

Cheers,

[gmoss]

( wish I was made of rubber, I'm old and soft )
...
Then you refit the carbs onto the bike with 2 nuts, connect the tank and fuel lines and check for leaks etc and if the carbs need to come off again, just 2 nuts to undo.
...
I think the bore of the seat gets a fine buildup of grot which can cause the needle to bind ever so slightly.

1) TMI man!
2) I think I need to replace the manifold studs with bolts for this to work, but if I have to take them off one more time that'll be worth it.
3) That's a great tip about the valves sitting cleanly in the seats, thanks!

Anybody remember the trick of treating hard rubber with wintergreen oil to soften them?

Already went and bought new rubber bits for both end of the carbs. Makes re-attaching the carbs (without removing the manifold) *possible* now, where it was damn near impossible before, though still quite unpleasant.

[dave500]

carbs for re build only have to come off once on 500s/550s!if you do a proper clean thats done,the bowls can be removed on the bike,use allen head screws on the float bowls,all the jets etc can done done on the bike,first thing be 100% sure the ignition is truely squared away,so many carbs come off over and again and people chase their tail thinking the problem is the carbs,be sure ignition is solid first.

[gmoss]

first thing be 100% sure the ignition is truely squared away,so many carbs come off over and again and people chase their tail thinking the problem is the carbs,be sure ignition is solid first.

#$%*in tell me about it. I got the bike starting and idling (!!!) and then I went to swap out the coils because the ones on the bike were original, but it has a Dyna S ignition. Turns out the wiring harness is all original, too -- if you look at it wrong the pin connectors disintegrate. Long story short, I can only turn the bike over now if I disconnect the key ignition and short the pins with a screwdriver... and now also it will only turn over and not start because I guess I jostled the connectors on the wires from the Dyna S to the coils (they route right behind the goddamn airbox) and now *those* aren't connecting.

So now the question is, do I a) chase gremlins and swap out part by part, b) figure it all needs replacing and look for all-new OEM harnesses and connectors everywhere, or c) say #$%* it and just go m-unit?

Leaving tomorrow for ~10 days of camping in Wyoming and Montana so I'll have some time to meditate on my priorities and goals here.