CBX Carbs Argh!

Post Reply
User avatar
CopperCollar
ICOA Member
ICOA Member
Posts: 444
Joined: Mon Dec 20, 2010 3:32 pm
Location: Albuquerque, New Mexico, USA
Location: Albuquerque, New Mexico, USA

CBX Carbs Argh!

Post by CopperCollar »

A lot of us here prefer to do our own work, some for the joy of spinning a wrench, some to save a few bucks and some are just masochist. Regardless there is one thing we all like....really like and that is the sound of a CBX with properly set up carbs. Its just awesome.

It's been said here many times, as a novice you can expect to pull your first set of CBX carbs no less than three times . I think that's pretty true.

Several sets or more I have built yet I always learn with each build, for example:

I rebuilt this 80 engine. I also rebuilt the carbs and thought I did a great job. Well, on first start up it sounded like the friggin primary chain was going to come through the case. Nothing I did made it better, was it electrical, was it carbs or did I mess up the engine assembly. Troubleshooting revealed electrical and carbs; thankfully the engine assembly was rock solid.

Two of the three coils though ohm readings were in specs were nonetheless toast. Fortunately I had a three coils from a Honda F2 , this helped but no cigar. Next pulled out the infrared thermometer...very helpful. Headers two and three were cold, the other headers were all over the place and inconsistent. Thought balancing the carbs would help....didn't help one bit so I knew the carbs had to come out, I based this on header temps and only after I knew my electricals were okay.

My great job as I discovered was a disaster. I hadn't tightened down a carb cap, I had transposed the steel washer and o-ring on a fuel screw, had pinched the air cut off diaphragm...(How the hell did I do that)! Further investigation revealed the throttle plates were not closing properly and the slow jets were anything but #35 ( I hadn't gauged them; I took the stamp for granted), Slides were sticky in their respective caps and one bank......I think it was the left bank choke plates were not working even though they were coupled to the right bank, turns out the coil spring had detached itself.

My only excuse is I was in a hurry to get these on the bike for a show in Santa Fe that in the end I did not get to attend. I had just returned from Tennessee with a fresh mason jar of moonshine... quite yummy and I am sure that contributed.

SO Here is what I learned so others may benefit from.

First, Take your time and be methodical, be suspect of everything....everything! The pros have a system, I am sure of this and they follow it for each and every rebuild. Rebuilding CBX carbs is a mixture of science and arts; and don't drink moonshine...okay maybe beer but half a beer.

Now what have I learned with this latest adventure.

Some say it's okay to mix and match slides and caps. I think not. If you think about it these things have worn together and have established a wear pattern.
I keep them together as a set. This last set I received as a basket case so they were mix and match. Some of the slides just didn't work well no matter how I matched them so those sticky ones got the .....wait for it.....Ahgast....#0000 steel wool treatment with some Mequairs aluminum polish. Worked like a charm. I would recommend this only as a last resort but in this case it worked.

Slow Jets..... Just because they are stamped #35 does not mean they are #35. Others may have gone after them with a wire or drill bit insitu. Of 6 slow jets I had one gauge #35 (0.013inch) ...the other 5 were anywhere between .015 inch to .019 inch when I gauged them No wonder the bike idled and ran crappy.. Think about it, increasing the diameter of the hole will drastically change fuel flow for that cylinder and the carb balance was not compensating.

Throttle plates... Good Idea to always look at them to see if they are sealing when closed. Shine a light from the intake side and see how much gets around the plate, should be almost nothing. Maybe just a wee bit from were the linkage is, the carbs I did had massive leakage from every throttle plate and makes it very difficult to troubleshoot as the bike would hang at high RPMS.

Floats, get them all at 15.5 mm measured at the middle of the float, not the end of the float and be sure they are parallel. Sometimes one float will be higher than the other, it's simple fix to just tweak the float to bring it parallel with the other half. The CBX is sensitive to Float Timing and incorrect float height will affect your bike.

Fuel Screws, Take a look at the tip with a magnifying glass... nearly everyone on this set was corroded/pitted that I did not see with the naked eye, not sure if the pitting affect flow but I didn't chance it. I replaced them all. Not to pricey and the old proverb came to mind cheaper to do the job right than to have to do it over or something like that.

All those passages and bleeds. Be sure they are all clear and all flowing...especially those three little holes in front of the throttle plates. Mike Nixon's book details how to accomplish this. For any novice; get Mike Nixon's book.

Assembly; keep it clean. I like to use a piece of white cardboard; it looks clean and if you drop one of those itsy bitsy washers or O-rings it will be easy to see against the white background. Make sure each part seats properly with its counterpart and nothing requires force except for that pressed in pilot jet. Slides go up and down without sticking, I like to turn the carbs upside down and see if they fall with their own weight. Linkage should work smoothly.

Bench sync; some use wires under the throttle plate...these throttle plates are machined with an angled edge kinda like a knife edge to fit in the bore and seal properly, anything that dings the plate or scratches the bore changes the bleed air pattern and messes with airflow and thus mixture from those three little holes in the carb throat. Use the idle screw and set the # 4 carb plate to just expose a wee bit of the first hole then adjust the other throttle plates as close as you can to #4 using the synch screws. I have yet to master this but this last set I nailed it.

If you have a freshly built engine or one that has good compression and valves that are adjusted and seating properly you may not need to balance the carbs if you did a good bench synch, on the other hand if it's a tired engine you will probably have to balance the carbs with a vacuum gauge to get the primary chain/clutch rattle out.

Always, Always install an in line fuel filter. I rebuilt a set of carbs for a friend and installed them, I used a remote fuel source since he did not bring the tank with the bike . Balanced the carbs and this bike idled beautifully, good throttle snap just a great bike. He got the bike home and put the tank on and took a ride. The bike ran great but soon the idle was hanging. Brought the bike over and pulled the carbs, there was crap in the float bowls so we completely went through the carbs again, cleaned the fuel tank and installed a filter. Save yourself the headache.............install an inline filter.

Once I properly built the carbs and installed them I was rewarded with that awesome CBX sound, there was no primary rattle, no clutch rattle and the bike responded to the snap of the throttle returning to set idle without dawdling around at RPM . I threw vacuum gages on just to see what was going on and I don't think I will be changing anything. Finally I can have the whole beer.

This site is the best there is for searching I have found. Many weird things happen to the CBX especially carb related and someone has probably experienced it and posted the wierdness. I would recommend a through reading of the carb post before tackling CBX carbs your first time and of course Mike Nixon's book on the CBX carbs.

The CBX is an awesome bike and how they managed to make everything work boggles the mind, Carbs are a perfect example of the craftsmanship it took.

Hope this helps others taking on their first carb rebuild.

Mike
When given the choice between being right or being kind; choose kindness. W. Dyer

steve murdoch icoa #5322
ICOA Member
ICOA Member
Posts: 4069
Joined: Tue Mar 04, 2003 9:12 am
Location: St. Catharines, On. Canada
Location: St. Catharines, On. Canada

Re: CBX Carbs Argh!

Post by steve murdoch icoa #5322 »

An excellent post, Mike.
I have also had problems with mismatched caps and slides and choke springs being improperly set up.
Never thought to measure the slow jets but i will now.

Read varying opinions on in-line fuel filters. I use them but apparently some end up restricting fuel flow.
I did have a similar experience with a freshly cleaned/rebuilt set of GS1000 carbs that after many attempts would not operate properly.
Turned out the gas line from my remote tank was disintegrating on the inside and continually dirtying up the carbs.

Most of us don't get perfect the art of CBX carbs, we just get better.

User avatar
FalldownPhil
ICOA Member
ICOA Member
Posts: 929
Joined: Fri Feb 10, 2006 11:25 pm
Location: Marina Del Rey, CA. USA
Contact:

Re: CBX Carbs Argh!

Post by FalldownPhil »

Now that is a great post !!
Thank you Mike.
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

User avatar
herdygerdy
Power Poster
Power Poster
Posts: 266
Joined: Fri Nov 22, 2013 9:48 pm
Location: Sydney, Australia
Location: Sydney, Australia

Re: CBX Carbs Argh!

Post by herdygerdy »

Thank you for an excellent post Mike.

Your experience mirrors mine on so many levels, and your point noted about checking the size of the #35 idle jets. Given the age of these old gals and the "fine fettlin' folks" who may have been in there before with hammers and vice grips, best to assume nothing is correct until you have checked and confirmed it is so. So I think if/when I do another set, I'll be checking all jet sizes across the board. (As they say in the classics, "assumption is the mother of all stuff ups!"

Just finished yet another a set here in Sydney and the bike runs very sweetly indeed. Needles valves were gummed up solid!

And a big shout out to Randall for putting his very excellent kit together and to Mike Nixon for sharing his vast knowledge so willingly - taught me all I know : )

One more time saving tip I respectfully add is once you have the throttle cables on the carb end, but BEFORE you even think about fitting the carbs to the engine, do a test fit of the cables to the throttle tube on the handlebar end to make sure it all works as req'd. It is SO easy to get the throttle cables swapped over and you then have a throttle that opens by rolling the grip FORWARD. DAMHIK! And I even thought I had checked and confirmed I had it right. Doh!

Can't agree more to take your time, start fresh and be sure to stop when tiredness sets in. And no consumption of recreational substances (fluid or otherwise) during the process. Check, re-check and check again absolutely EVERYTHING. With CBX carbs there is simply no 'close enough'. It's either right - or it's wrong and you WILL end up doing it again.

IMHO, it's kinda like gentle "mechanical meditation". And the ice cold beer enjoyed only at the END of the gig makes it all worth while for sure.

Thanks again for a really great post.

Cheers...Tony

User avatar
CopperCollar
ICOA Member
ICOA Member
Posts: 444
Joined: Mon Dec 20, 2010 3:32 pm
Location: Albuquerque, New Mexico, USA
Location: Albuquerque, New Mexico, USA

Re: CBX Carbs Argh!

Post by CopperCollar »

Thanks Tony. Good point on throttle cables as I have done that in the past :laughing-rolling:

There is so much great stuff on this site! If one could devote the time and have the publishing skills I do believe a really great book could be done.

Sectioned much like the site but with only troubleshooting that others have done and posted. As it is now the search function works pretty good but just think of al the accumulated wisdom on this site!

Maybe Ian is up for another book? :laughing-rollingyellow:

Mike
When given the choice between being right or being kind; choose kindness. W. Dyer

User avatar
Mike Nixon
ICOA Member
ICOA Member
Posts: 375
Joined: Thu Aug 14, 2003 10:52 pm
Location: Prescott, AS
Location: Prescott, AZ
Contact:

Re: CBX Carbs Argh!

Post by Mike Nixon »

CopperCollar wrote:...really like and that is the sound of a CBX with properly set up carbs. Its just awesome.
Yeah, man!
CopperCollar wrote:Two of the three coils though ohm readings were in specs were nonetheless toast.
Yup! Take note all. Resistance tests of wire coils is poor troubleshooting practice.

http://www.motorcycleproject.com/text/95-50_rule.html

Artie
ICOA Member
ICOA Member
Posts: 171
Joined: Tue Oct 15, 2013 4:35 pm
Location: Medford Ma
Location: Medford Ma

Re: CBX Carbs Argh!

Post by Artie »

I've always been amazed at the perfect throttle response and idle of a stock CBX and not a flat spot anywhere high or low
another Honda masterpiece!
Mike Nixon rebuilt my carbs three years ago and after a on the bike sync initially they've still still perfect in over 9000 miles,had to pull them once though from clogged slow jet even with in line filter,oh well,now I use 1 oz of Techron for each gallon and let carbs run dry if I know I not going to ride it for 2 weeks or more
I run stock jetting with Kerker 6 into 2 flawless carburation
If this sounds like a plug for Mike ...I guess it is

User avatar
Mike Nixon
ICOA Member
ICOA Member
Posts: 375
Joined: Thu Aug 14, 2003 10:52 pm
Location: Prescott, AS
Location: Prescott, AZ
Contact:

Re: CBX Carbs Argh!

Post by Mike Nixon »

Thank you Artie!

Post Reply

Return to “CARBS: Cleaning, Rebuilding, Swaps, Aftermarket, Tuning, Syncing, and More”