Topic: Marissa's 1972 CB500

[Cb750 Racer]

Okay, good news. The epoxy bits do appear to be entirely from installing the fuel valve. Found a big piece of it, also not pictured is a piece with thread imprints on it. Whew!



Going through all the carbs all over again and I found one of my main jets has this weird green powder residue on the inside. A result of contaminated fuel or something? I pondered brass corrosion but that would seem odd too.



Inspected and found that slide #1 was set slightly more open than the rest of the carbs. Perhaps this was doing something.





After taking the mains out and turning the carbs over on the bench, my emulsion tubes started coming loose. That's a problem, isn't it?



Thinking about trying 98 mains with the 40 slows and stock needle height when this is all buttoned up.

If you zoom in on the first pic you can see that slide #1 is extremely pitted. That's not the flash, definitely replace that even if that's not your problem with the throttle hanging.That's gonna be a problem in the future with that slide. Replace any others as bad and check if the corresponding area where the slide sits is worn out on the carb body because that pitting has had to cause some damage.

[SF]

It’s not that nice hard anodized colour either somethings reacted with the anodizing.


Sent from my iPhone using Tapatalk

[Marissa]

Thanks for the info guys. I'll be ordering other slides soon. All 4 were actually like that, and the only reason there is a clean one now is because I swapped that slide out since the screws for the needles were stripped.

While we are admiring how messed up these carb internals are, any chance anyone could tell me if this wobble for the main jet is normal? I have this fear that these are so corroded that gas is actually slipping past them.

[Scott S]

 The O-ring is supposed to seal it there. You may have the wrong size O-ring on the main jet.

[Marissa]

The O-ring is supposed to seal it there. You may have the wrong size O-ring on the main jet.

Is it possible to have the wrong size o ring seal come already installed on the Keihin brand main jets? I wouldn’t think they would do that.

[rosewood]

Marissa can you remove the main jet and post a close up picture of the inner surface where the o-ring is intended to be seated?

This has been raised before and most people seem to think if the sealing surface inside that post still looks clean then it should be fine regardless of the corrosion/oxidation that is visible.

Is that a new mainjet and o-ring? if it is older the O-ring may have worn/flattened and need replacing...

I feel your pain....have been chasing similar issues myself..

[Marissa]

Marissa can you remove the main jet and post a close up picture of the inner surface where the o-ring is intended to be seated?

This has been raised before and most people seem to think if the sealing surface inside that post still looks clean then it should be fine regardless of the corrosion/oxidation that is visible.

Is that a new mainjet and o-ring? if it is older the O-ring may have worn/flattened and need replacing...

I feel your pain....have been chasing similar issues myself..

Sorry to hear you are facing similar issues. Let me know if you figure out yours!

Here's a picture of the insides. They look maybe okay to me? The jets are all new btw. Either way, for the price of buying slides individually on eBay vs. ordering a whole new carb rack, I opted to get a new set of carbs instead.

I'll tear down the "new" carbs, ultrasonic them, swap all my good pieces over, and slap them on and see where that gets me. Either way, the season is pretty much going to be over by the time I complete this, which sucks. But I'm hoping this is a step in the right direction and may eliminate guessing games.









Just got a truing stand in the mail, and a motorcycle jack should be here today as well. I will be attempting to true my wheels in the next few weeks.

[calj737]

If it were me, I would make sure the interior of those jet holders are much cleaner and more shiny. Remove as much corrosion as possible.

[rosewood]

I'm no expert but it looks like the corrosion has gone up to and past the sealing surface of the o-ring..maybe ream/hone/clean with something and then try a thicker o-ring?

I think you are on the right track with replacing them for a better set though.

I pieced mine together from two sets which were both corroded, maybe not as bad as yours..I then came across a third set which was cleaner so have opted to use them...

I've had a float valve issues and rich running so far...but I need to get a new set of float valves before I go any further.

Have you thoroughly gone through your ignition system including advancer? check timing on both sets of points with a timing light at idle and advance? make sure your advance is not kicking in too early with weakened springs...   

Marissa can you remove the main jet and post a close up picture of the inner surface where the o-ring is intended to be seated?

This has been raised before and most people seem to think if the sealing surface inside that post still looks clean then it should be fine regardless of the corrosion/oxidation that is visible.

Is that a new mainjet and o-ring? if it is older the O-ring may have worn/flattened and need replacing...

I feel your pain....have been chasing similar issues myself..

Sorry to hear you are facing similar issues. Let me know if you figure out yours!

Here's a picture of the insides. They look maybe okay to me? The jets are all new btw. Either way, for the price of buying slides individually on eBay vs. ordering a whole new carb rack, I opted to get a new set of carbs instead.

I'll tear down the "new" carbs, ultrasonic them, swap all my good pieces over, and slap them on and see where that gets me. Either way, the season is pretty much going to be over by the time I complete this, which sucks. But I'm hoping this is a step in the right direction and may eliminate guessing games.

[754]

 I would wet the oring before pushing jet in, and see if they wiggle... or turn easily....I will go watch your video.
 if they are  loose they may leak past them.

 Another thing I am seeing.. (might just be my eyes)
 Your slides seem to have a little burr or bulge at the middle of the cutout edge. this can happen if you use a screwdriver  to unstick a seized set of carbs or maybe very rough trying to use a rod to synchronize on the bench.
 Anyway if there is a deformation, it may alter the slide cutaway at idle, and if its a raised burr, may be scratching away at the hole in the carb, that the slide moves up and down in. If it wore a groove,  it would not be good.

[Marissa]

Update!

Dave Barbier and my boyfriend came over a few weeks ago, the three of us worked together one Saturday to completely rebuild the "new" carbs I got and see what that would do. A few hours later, we go around to getting the bike ready to fire up and low behold, my Shorai battery was deader than dead. Funnily enough, I found out a week later I purchased it exactly a year ago. I have been charging it with a trickle charger, guess it didn't like that. Also oozing out some goo from the charging port. So after a wasted night, I purchased a new Shorai and a Shorai charger.



Today I finally had time to put the new battery in and start it up. Took a little bit but once it took it was sort of promising. I played around with ignition timing a bit and I got it pretty good; only thing is it's overflowing into the drain tubes.

So it instantly dies with throttle. Super rich, of course. Next time I have time these carbs will be coming off, floats will be tested on the bench with the clear tube method, and hopefully this is the only thing stopping it. On the bright side, at least all of the cylinders are showing very similar results.

#4, reflection from being wet with gas



#3



#2



#1



A few of the other goodies I got to make the bike nicer over the winter.

[RAFster122s]

Congrats on the promising progress.  I hope you are able to get it dialed in to get it on the street for a while before you have to put it away for winter.

[Marissa]

No progress yet, busy with school and work.

I’ve been thinking about the bike in my free time and I think it might be a good move to change out the ignition system for a more common and known to be reliable system just to rule out my lack of confidence in this ignition and the timing that it tells me it wants.

I like Charlie’s system, but it seems like most use Dyna. Is it only worthwhile to get the Dyna 2000 system or is the more simplistic and cost effective Dyna S perfectly acceptable and reliable?

[MauiK3]

The stock points system is very reliable. If you wanted to go one step further you could install Hondaman's transistorized unit so the points become just the trigger and not the load bearing switch. The points system along with stock coils put less electrical load on the alternator too. It's one of those "if it ain't broke" things.

[Mark1976]

+1
Hondaman,
Best  ignition  investment I ever made.

[RAFster122s]

The stock points system is very reliable. If you wanted to go one step further you could install Hondaman's transistorized unit so the points become just the trigger and not the load bearing switch. The points system along with stock coils put less electrical load on the alternator too. It's one of those "if it ain't broke" things.

One should not that when you put a new set of TEC points in with HondaMan's electronic ignition box it will be the Last set of points you buy as long as you have HondaMan's ignition installed. Can't beat that with a stick!  Seriously, better starting feels like the ignition timing (After you take a loop or so off the advancer springs... measuring the rpm that the advance reaches full advance until it is at the recommended values for each of the SOHC4 bikes.) And, it provides better cold starts, improved  idling in transitions to full advance and beyond.  The bike gives the impression that it is smoother and stronger going up through the gears, it feels different from a stock points, feeling better of course...
I am shocked how cheap it is...given the benefits it provides it is worth every penny! Today it is a great value when considering the cost of simple things for a bike , much less a quality electronic box like this and it's function.

My $0.05 worth.
David

[DaveBarbier]

Yeah I’d say go with points. The Dyna S is nice but it’s more expensive and points are super reliable. You won’t get any reduction in horsepower at all. It’ll be as smooth and happy as any electronic ignition.

I haven’t used Hondaman’s box but 100% of people here recommend it. Never heard anything bad about it.

[Marissa]

Alright, new OEM points plate assembly ordered from DSS.

Progress has been little to none. I've had no time thanks to work and school. Quitting my job to focus on finishing up my final year in school and doing a little part time gig to keep some money coming in. Hopefully will have more time for the bike as well.

Started using the Astro pneumatic threadserts. Satisfying stuff. I will find more opportunities to use it I'm sure.



Definitely something not right with these carbs. Bike has been sitting for a month now and there's wet gas seen by the butterfly. These floats will be the death of me.



Since it's already so cold out, I decided to make a blueprint for the electronics tray. I used a free program called Sketchup. I now have a fully scaled template for when I'm ready to assemble.









That's all for now.

[DaveBarbier]

I have no idea what’s going on with your carbs. They were by no means pristine examples of keihin carbs but they were clean and seemed like they’d function properly.

As for the points plate and rivet threads, awesome! Will you be using this CAD thing as just a template to make one from metal or 3D printing anything?

[Marissa]

Unfortunately I don't know anyone that can 3D print that large, so I'll be making it out of 5052 aluminum.

[Marissa]

Got the points system in today. After an hour of trying to set the timing, I figured out I set the points cam in 180 off. Whoops. Fixed that and finally setting the ignition timing was a breeze.

Now I can 100% confirm my issues are purely carburetor. These carbs are now rev hanging too like my other set was. Frustrating and tiring.

I guess I will be rebuilding these over the course of the next few weeks.

Does anyone on here rebuild these? I'd consider shipping these to someone who truly knows these if its a solid price vs. dealing with whatever local Harley shops would do.

Here's a vid:

[jgger]

I'm going to go out on a limb here and that sounds like a cable or linkage issue to me. Trying to not sound insulting here, but are you positive that everything is closing down when the throttle is closed? But once again I could be full of crap, and I didn't stay at a Holiday Inn last night either. Haha.

[HondaMan]

This is a common symptom when a couple of things are present.
One is: too-soft springs in the spark advancer (this will make it REAL sensitive to anything else that is wrong).
Another is: the tiny O-rings on the mainjets are too old and have turned to plastic now (thanks in part to ethanol), so they leak fuel past them, unmetered fuel.

One thing that may get you running long enough to figure out if the carbs are the culprit or the spark advancer is: retard the spark timing to almost "T" on both sets of points, by turning the whole points plate CCW a little. Then when it starts it will be retarded in timing, making it less sensitive to the spark advancer portion of this issue. If it still wants to jump up and idle at 3500 RPM (like it sounds) then the mainjet O-rings are likely at fault. Given your dark sparkplugs (or were those from the other carbs?), this seems likely.

The biggest issue we are seeing right now in rebuild kits for these carbs is: too-big O-rings in the non-Honda kits. This prevents the jets and the float valves from being assembled properly, even to the point of breaking parts. They are supposed to be 1.2mm in cross-section, but the kits supply 1.5 or 1.6mm instead, causing the trouble. This is the #1 reason why it seems so hard to rebuild the CB500/550/400fcarbs these days!

The carb 'rebuild' consists of (besides cleaning) replacing the O-rings on the mainjets, float bowl drain screws, and the fuel feed tubes, and sometimes the float bowl O-ring that seals it all up. It's pretty simple, especially for someone with fingers as nimble as yours! It's just hard to get the right O-rings. I have tried before (and may try again) to have a local seal shop import a bag full of these tiny ones: if I can get them, I'll let everyone here know about it.

[Cb750 Racer]

Got the points system in today. After an hour of trying to set the timing, I figured out I set the points cam in 180 off. Whoops. Fixed that and finally setting the ignition timing was a breeze.

Now I can 100% confirm my issues are purely carburetor. These carbs are now rev hanging too like my other set was. Frustrating and tiring.

I guess I will be rebuilding these over the course of the next few weeks.

Does anyone on here rebuild these? I'd consider shipping these to someone who truly knows these if its a solid price vs. dealing with whatever local Harley shops would do.

Here's a vid:

How far are you from CCSU? I could stop by and take a look after class one day if your up for it. The bikes been at 95% for too long IMO

[jgger]

Honda man have you tried these guys?
https://www.theoringstore.com/