Topic: Marissa's 1972 CB500

[Marissa]

Oh thank goodness. I wasn't sure what to think, my boyfriends GS doesn't have an "off" for his fuel valve, and he also may have an accelerator pump (his is a 78 GS). So I was sitting here knowing he doesn't have to throttle his bike to start, assuming there must be an issue with mine since I have to. But then I realized his is later, and I remembered how cars needed throttle. So what a relief this is.


Here's what's going on now. The bike actually looks to be running lean now. Never thought I'd see this day.

To be honest, since I had to give it throttle to start, I assumed that was going to skew my idle readings so I took it around the block like 5 times, lol. It was really fun.

There was a point where I was able to get it in third gear, and even fourth, or so I believed, so I pondered if my clutch cable needed adjustment. I adjusted it and that seems to not have done anything, which is horrible lol. So at some point I will need to split the cases to figure out the issue, presumably. Although maybe I can drop the pan and find something visually wrong? Who knows.

Going to start it up tomorrow and let it idle a few times to see if the plugs change any bit. Then I guess I might go up a size from there.

[DaveBarbier]

A little late, but yes these old bikes need some throttle unless you have a fast idle cam on your carbs which you don’t.

I’m confused why you’d need to split the cases. Did it shift or not? Any grinding? Popping out of gear? Shift lever locking up?

[Scott S]

 That looks a little lean, but not bad. If your fuel has ethanol in it, it skews the spark plug readings a little bit.

 Do you have an IR temp gun? I like to shoot the headers, cylinders, etc., to get an idea of how hot the engine is running.

 Where did you end up on jetting and needle position?

[Marissa]

A little late, but yes these old bikes need some throttle unless you have a fast idle cam on your carbs which you don’t.

I’m confused why you’d need to split the cases. Did it shift or not? Any grinding? Popping out of gear? Shift lever locking up?

It’s not shifting into 3rd again. It’s not popping out of gear, there’s no grinding either, it’s just the shifter locking up if I had to guess. Or maybe forks aren’t right. I don’t really know.

[Marissa]

Okay. Got some more ride time in. Did at least 5 miles today. It's back to running rich again. It seems that the float valves were getting stuck again, at least somewhat. More fuel was in the drain lines, but it never started pouring out. It ended up getting difficult once it got hot and it stalled on me 3 times trying to get home. When I got home I found sediment in #1's line.

I also discovered today that I was not crazy and I do have all my gears. This seems to be dependent on heat -> viscosity. Today was the hottest I got the bike and sure enough I eventually got it into third, then so on and so forth. I confirmed by counting my downshifts.

I'm using OE Spec Honda 10W40. Is this something that could get better with ride time?

I don't have something to read temps unfortunately. I purged the carbs with an air hose in the drain tubes to "reset" the float valves and it seemed to actually work. So tonight I had to retune idle and it seems to be running lean again.

I guess I'll let it idle again tomorrow morning and see where that leads me. Here's some pictures from my adventures of stalling lol.

[RAFster122s]

I run 20w50 in my old bikes in hot weather. Does Honda's oil have enough zddp in it for our old bikes? That could contribute to shifting problems. Are your pods oiled too much? That can cause rich conditions.
Are your bowl gaskets OEM or aftermarket?  Just wondering if they are swelling and fouling the floats.  If you are still seeing sediment in your overflow lines or float bowls then this sediment will be likely cause of overflow and rich running when it blocks a float valve from closing when the carb bowl fills full.
My $0.02
David

[754]

 i would not blow compressed air into an assembled carb 

[DaveBarbier]

Yeah, I don’t know what’s going on with your sediment situation. Maybe your pods are disintegrating...? Maybe everything just isn’t as clean as it should be?

For the clutch thing that could be oil related. What do you mean Honda spec oil? What’s the brand? Honda oil? I really like Spectro oils. They’re in Brookfield, CT. 15 miles from me. I use the semi synthetic and shifting is super smooth and it’s cake to find neutral at a stop light after it’s nice and hot on a hot day.

[HondaMan]

If blowing up the drain lines into the bowls worked (and hopefully you have plastic floats? Otherwise the floats were damaged, likely), then you still have sediment troubles making the float valves stick open to cause the overflows and too-rich running. There must still be a little bit of it trapped in the lines, petcock, and the fuel tees in between the carbs. It don't take much, with these tiny float valves, to stick 'em open.

I used to remove the floats and needles (this is on 750 bikes, though, where the bowls are easy to remove while on the engine) and then turn on the petcock to drain straight into a (long narrow) pan until I was SURE it was all flushed out. On bikes from Missouri, in particular, in the 1970s this was a trouble before the 'final filter' gasoline pumps showed up at AMOCO and SUNOCO gas stations, as those guys ran their station's tanks to dry sometimes, picking up crud on the way. It was also legal there (in those days) to have above-ground gas tanks, and when those ran low they would tilt them toward the exit spigots, delivering the rust and crud directly to the cars...

[Marissa]

Yeah, I don’t know what’s going on with your sediment situation. Maybe your pods are disintegrating...? Maybe everything just isn’t as clean as it should be?

For the clutch thing that could be oil related. What do you mean Honda spec oil? What’s the brand? Honda oil? I really like Spectro oils. They’re in Brookfield, CT. 15 miles from me. I use the semi synthetic and shifting is super smooth and it’s cake to find neutral at a stop light after it’s nice and hot on a hot day.

Dave, I checked the pods and they sure don't look or feel to be disintegrating. For now, I took them off just to see if this changes things. The oil I use is apparently called Pro Honda GN4.

For the past few nights, I've been starting it and just letting it idle or at least try to idle. Recently, the bike will not start with choke fully closed. It seems to like it 3/4 open to start. It will hold at 1/2, and 1/4 pretty well. But the bike does not seem to like choke fully open. It won't hold idle once the choke is fully open, regardless of how long it's been warming up. It needs throttle, and once it's given throttle it rev hangs and pops really badly. I pulled plugs and they aren't wet, they still look a little rich though. I'd assume it's rev hanging because it's too rich, but if that was the case, why wouldn't it rev hang at 1/2 choke? at 3/4?



Here's how the drain tubes looked too. Only 3 had a drop of fuel in it this time. These results are really inconsistent for me to feel totally confident its the float valves.



I'm going tear down the carbs one more time before I throw in the towel on this and give it to a shop to look at. I also figured out that the reason I have some wobble is not because of a flat spot, but the shop I brought the rims and tires to didn't true them before mounting and balancing them. I don't have a truing stand, nor do I have the arm strength or desire to tear these down and try to fix it myself because I consider this a safety thing, so either way, the bike is going to need to go to a shop soon. I have no idea what a dismount and truing job would cost but it needs to be done. I found this out when I had my boyfriend take the bike for a spin and I saw the rear wheel wobble. Obviously, I put the wheels and spokes together, and I didn't true them because I knew I wanted the shop to balance them and set them up, so I'm really confident this is the issue.

[DaveBarbier]

Yeah, I don’t know what’s going on with your sediment situation. Maybe your pods are disintegrating...? Maybe everything just isn’t as clean as it should be?

For the clutch thing that could be oil related. What do you mean Honda spec oil? What’s the brand? Honda oil? I really like Spectro oils. They’re in Brookfield, CT. 15 miles from me. I use the semi synthetic and shifting is super smooth and it’s cake to find neutral at a stop light after it’s nice and hot on a hot day.

Dave, I checked the pods and they sure don't look or feel to be disintegrating. For now, I took them off just to see if this changes things. The oil I use is apparently called Pro Honda GN4.

For the past few nights, I've been starting it and just letting it idle or at least try to idle. Recently, the bike will not start with choke fully closed. It seems to like it 3/4 open to start. It will hold at 1/2, and 1/4 pretty well. But the bike does not seem to like choke fully open. It won't hold idle once the choke is fully open, regardless of how long it's been warming up. It needs throttle, and once it's given throttle it rev hangs and pops really badly. I pulled plugs and they aren't wet, they still look a little rich though. I'd assume it's rev hanging because it's too rich, but if that was the case, why wouldn't it rev hang at 1/2 choke? at 3/4?



Here's how the drain tubes looked too. Only 3 had a drop of fuel in it this time. These results are really inconsistent for me to feel totally confident its the float valves.



I'm going tear down the carbs one more time before I throw in the towel on this and give it to a shop to look at. I also figured out that the reason I have some wobble is not because of a flat spot, but the shop I brought the rims and tires to didn't true them before mounting and balancing them. I don't have a truing stand, nor do I have the arm strength or desire to tear these down and try to fix it myself because I consider this a safety thing, so either way, the bike is going to need to go to a shop soon. I have no idea what a dismount and truing job would cost but it needs to be done. I found this out when I had my boyfriend take the bike for a spin and I saw the rear wheel wobble. Obviously, I put the wheels and spokes together, and I didn't true them because I knew I wanted the shop to balance them and set them up, so I'm really confident this is the issue.

Ok, yeah the pod idea was just a shot in the dark. Didn’t think it was the cause but worth a check I guess.

If it won’t hold an idle with the choke not in use but it will with the choke applied (when you’re fully warmed up) then you’re probably lean. A hanging idle is a lean symptom. Check for air leaks?

And I didn’t know you also had a flat spot. Flat spot in acceleration/throttle? I don’t see how a flat spot could be caused by a rear wheel wobble but yeah that has to be taken care of. You can true your wheels by yourself. Keep the tire on, no need to break it down. And a truing stand? I use a rod, some v blocks and saw horses. Make anything that lets the wheel spin freely. Hell, true it while it’s still on the bike, just take the chain off and back off on the brake. Truing isn’t hard, watching some videos will give you pointers on which spokes to tighten. If you saw the rear wheel wobbling down the road then that’s a pretty big out of true issue. Make sure the wheel isn’t wobbling on the axle either.

As for the carbs, I don’t know what else to say other than make sure they’re clean. Are you certain the tank, petcock and lines are not holding debris? I’m not totally clear on your carb situation, unsure if the floats are leaking or if there is still debris in the float bowls. Have you done plug chops at idle with new plugs?

[Cb750 Racer]

Yeah, I don’t know what’s going on with your sediment situation. Maybe your pods are disintegrating...? Maybe everything just isn’t as clean as it should be?

For the clutch thing that could be oil related. What do you mean Honda spec oil? What’s the brand? Honda oil? I really like Spectro oils. They’re in Brookfield, CT. 15 miles from me. I use the semi synthetic and shifting is super smooth and it’s cake to find neutral at a stop light after it’s nice and hot on a hot day.

Dave, I checked the pods and they sure don't look or feel to be disintegrating. For now, I took them off just to see if this changes things. The oil I use is apparently called Pro Honda GN4.

For the past few nights, I've been starting it and just letting it idle or at least try to idle. Recently, the bike will not start with choke fully closed. It seems to like it 3/4 open to start. It will hold at 1/2, and 1/4 pretty well. But the bike does not seem to like choke fully open. It won't hold idle once the choke is fully open, regardless of how long it's been warming up. It needs throttle, and once it's given throttle it rev hangs and pops really badly. I pulled plugs and they aren't wet, they still look a little rich though. I'd assume it's rev hanging because it's too rich, but if that was the case, why wouldn't it rev hang at 1/2 choke? at 3/4?



Here's how the drain tubes looked too. Only 3 had a drop of fuel in it this time. These results are really inconsistent for me to feel totally confident its the float valves.



I'm going tear down the carbs one more time before I throw in the towel on this and give it to a shop to look at. I also figured out that the reason I have some wobble is not because of a flat spot, but the shop I brought the rims and tires to didn't true them before mounting and balancing them. I don't have a truing stand, nor do I have the arm strength or desire to tear these down and try to fix it myself because I consider this a safety thing, so either way, the bike is going to need to go to a shop soon. I have no idea what a dismount and truing job would cost but it needs to be done. I found this out when I had my boyfriend take the bike for a spin and I saw the rear wheel wobble. Obviously, I put the wheels and spokes together, and I didn't true them because I knew I wanted the shop to balance them and set them up, so I'm really confident this is the issue.

Did you ever adjust the air/idle mixture screws when you rejected the carbs? The jetting will change fuel all along the curve you'll have to adjust these screws to get the proper air/fuel idling and transitioning off of idle.

[Marissa]

I adjusted the idle air screws from stock location and turns all the way out to all the way in. This didn't solve it.

Turns out my problem was that the bolts for the slide elbows had started to back out due to the vibrations of the bike. I had bent the washers but I guess some of them weren't bent tight enough to grab the bolts. I found this by pressing on the spring loaded pieces and checking over every orifice on the carbs while it rev hanged. Sure enough it started to lower RPMs!



So I tightened up everything throttle related as best as I could. Throttle is super snappy now. Also tightened down the shifter on the spline a bit and secured the bolt with blue loctite and it's much better shifting into 3rd now.

Changed all the slows to 40s and that seems to have cured my popping issue totally. Also cleaned off the spark plugs and double checked gap. Found plug #2 was a little tight and I'm wondering if I accidentally altered gap when trying to put the plug in the hole.

Took the bike for another test ride Saturday and that was easily the smoothest and nicest ride yet... But it still ended in failure lol. Seems like all 4 carbs are overflowing slightly, and when the bike gets hot, it stalls out on me. Seems to stall after 8-15 minutes of ride time. Plug #4 honestly looked pretty good, the rest started to get pretty rich. I'm wondering if carb #1 is pouring the gas into the chamber instead of the overflow tube so the issue isn't so visible even though the plug is totally black.  The bike does not like throttle when it warms up after 10 minutes. I turned the choke on when it started to die down and didn't give it throttle to see if it was an issue of too lean/ too much air and this did nothing. And obviously giving it no throttle with it slowing down and it already upset isn't going to change it...



Plug #4



Vs. Plug #1 lol




One thing I'm becoming concerned about now is cylinder #1 seems to be running hotter than the rest of the cylinders. The other exhaust pipes are a nice brassy gold but #1 is purple and blue. The bike stalled on me Saturday and I pulled the pods off (I put them back on after I changed out the jets to 40 and that seemed to fix the popping issues) when I pulled the pod off for carb #1, I noticed all of this white smoke come out of the carb. I checked valve lash and it's perfectly in spec. I got the bike to start back up by putting my palm over the carb inlet and choking it of air completely then immediately pulling it off when gas got on my hand.



Could this be the ignition timing? But if so, wouldn't all the other cylinders also be consistent with the coloration of 1?

I'm wondering if maybe it's just SO rich that it's causing high EGTs (exhaust gas temps) for that reason and altering the color.

And now all the carbs have a least a little residual overflow.



I'm hoping to get the bike ready to bring to work on Oct. 5th for a car show we're having. The shop I was interested in bringing the bike to has yet to respond back to me so I may try this weekend to clean out the carbs myself again. Ugh. The end has to be close. These fuel filters are super fine there's no way new sediment is getting in there. So the sediment has to be from the fuel lines down to the carbs. There can't possibly be that much more that I'm missing. I'll take the lines off and blast air through them when I clean them next.

We are getting close. But reliability seems far, far away lol.

[jgger]

Very encouraging report, you ARE almost there. Clear tube those carbs one more time, I would bet you are still a touch high on the floats.

Use a pair of pliers on those washers so they fit tight to the bolt. If the washers only have 1 bolt hole then there should be a place to bend it down also or they won't hold because it will just rotate with the bolt.

Just a few more tweeks and you should be good to go.  BTW having been inside the motor you will always be second guessing yourself. I wish I had a nickle for every time I rebuilt my race bike on the starting line while waiting for the flag to drop. That was the longest 2 minutes in the world! Dead engine banner drop start for desert races. So you are doing fine👍😎

[RAFster122s]

Sooty plugs can be from poor spark. If idle is not sooting up your other plugs then the cylinder you are having trouble with could have a spark issue. If the float heights are good then I would pull the plug cap and test it for peace of mind. It should ohm out at 5k.  I think I would be tempted to change out the plugs to Denso from NGK with reports of plugs going bad quickly or out of the box. I forget HondaMan's recommendations for the Denso plug on the 550.

Glad you are making progress and were able to figure out one of your issues contributing factors.
Hang in there!
David


PS. A pipe that is bluing is a sign of a lean condition normally, not of too rich condition.

[DaveBarbier]

Bluing pipe could also be too rich if it’s reigniting in the header. That would make sense if the plug is black. But too rich or weak spark as David mentioned? Or fuel level raising because of grit or set too high.

Ignition timing is most likely not going to be the culprit.

Didn’t you replace all fuel lines with new?

You’re close! Everything you’re describing could be one issue.

[RAFster122s]

True, overly rich can be unburnt fuel in exhaust causing blueing. The bike will smell of unburnt fuel, hydrocarbons if it is that rich.

If sediment is causing floats to hang open it will have evidence of sediment in the float bowls.  Clear tube will answer your question about float level. Only adjust if it is not in spec. Adjusting floats is not a common maintenance item.
 Leaking floats can cause high levels as well.  Fuel will be in float if it is leaking. If you have metal floats they can often be soldered to fix, plastic floats have to be replaced if leaking.
Bent float pins can cause float to not move freely and hang leading to high fuel level that is intermittently sticking. So,check to feel how freely the float is moving on the pins. Sometimes a bend in the metal tab where the pin rides can cause it to get tighter in one area as it moves.
These are some of the little things that have contributed to float level problems.
Float needle sides should be smooth, no visible rough areas also. I would not expect to see a issue here...especially since the float needles are recent.

Overly rich fuel reigniting in header is going to have wet black plugs if pulled soon after shutdown, dry sooty plugs is often weak spark.

Just a few more thoughts...

You are very close to whipping the issue.
David

[HondaMan]

Do you have a timing (strobe) light? If so, check the ignition timing at idle to see if the timing is on the "F" and "LF" marks. If not, the engine will run irregularly and cause vacuum disruptions in the carbs: this can make the float bowls bubble and bounce, causing them to intermittently overfill. In the Fours where timing is perfect and carbs are otherwise fine, a leaking intake valve can cause the symptom of intermittent [apparent] carb overflow for short periods of time, usually when riding in city traffic.

But here, seeing the Dyna S ignition (I think?) in the picture above, makes me suspect the idle timing is not the same between the 1-4 and 2-3 side - just because of our experience with these units here in the last 10 years or so.

Aside from that: the overflow tubes of gas can also come from one or more of the slide lifter elbows being loose: this makes the slide hang during decel on one carb, but not the next, causing increased vacuum in the (normal) carb throat, which then causes the bowl to slightly overfill. A few iterations of this and the overflow tube pukes some fuel, then the cycle repeats.

All of this comes from the other cylinders pushing or pulling on the otherwise 'normal' cylinders when these engines are not evenly timed, or breathing equally, by way of them all running one crankshaft.

[RAFster122s]

Dang Mark!  Makes ya want to go to a single cylinder bike with that nightmare of perfect storm happening...

So, if the timing is fixed...then does most if not all these problems go away?  Hope so...

Could a bent shaft at the points plate and advancer introduce a bit of wobble and therefore inconsistency in timing from 1-4 and 2-3?
David

[Marissa]

Started tearing down the fuel system again. Didn't open up the carbs yet but I found some questionable stuff.

Starting with the gas tank, I was working to get that empty and I poured the gas into a plastic jug to inspect it for sediment. Found 3 bigger pieces of black stuff, assuming it's old rust from the tank that never made its way out.



Then, I pulled the petcock apart. There is epoxy in it. This threw me off quite a bit so I pulled the borescope out. The liner does not appear to be failing anywhere. There's no lifting, there's no bubbling, etc. The entire tank is still coated and looks fine. I'm wondering if this is from when I had to bolt the petcock back in and I got epoxy on the threads. It was a mess to reinstall and it seems perhaps that this is the reason for the epoxy. I don't know what else to think of it. The circles are where there's a bit of this stuff hanging out.







Luckily, I have the filters on the lines still. There is actually nothing on those filters that I can see. I plan on making a really small hose adapter for the shop vac to pull this stuff out.
We will see what else I find.

[Marissa]

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.

[Scott S]

 The green residue is probably from ethanol in the fuel.
 
 Did you vacuum sync the carbs? If so, it's not unusual for the slides to be slightly different.

 The emulsion tubes are held in place by the main jet and the main jet spring clips/holders. The fact that they fell out easily just means you have clean carbs and jets.

[CBJoe]

Is it the flash in the pic or is the #1 slide super corroded/pitted?


Sent from my iPhone using Tapatalk

[calj737]

Is it the flash in the pic or is the #1 slide super corroded/pitted?

For real! That looks unusable if it is that scarred.

[DaveBarbier]

That’s slide is strange. It should be nice and smooth like the others.

I also woulndt be concerned with the green on the inside of the main jet unless it’s restricting the hole. Looks to be just a film.