Topic: 72 CB500 Restomod - *Update* Sold!

[Scramps]

Put the old rusty 4 into 2s that were on the bike when I bought it back on, since they’re at least intact and comparable to what I want to end up with. Did another plug chop. It idled a lot better with this exhaust, and didn’t smoke anywhere near as much, but it doesn’t look like #3 was burning at all



I think I’ve probably had enough carbon monoxide for one day, so we’ll try to do something else tomorrow.

Oh yeah, I keep forgetting to show you guys my cool shirt that I found at Old Navy, believe it or not

Did I mention it’s super hot out here tonight? Anyway, happy trails

Edit: wrong department store attribution for the shirt, whoops!

[Gurp]

Was 3 wet when you pulled it?

[Scramps]

yeah, I think #3 is flooding

[Gurp]

Check fire. If its got heat it's def flooding. PO had my carbs all out of whack when i got it. Mine cb500 carbs are sitting on a 74 550 atm

[Scramps]

[Scramps]

I made some nice rudimentary sheet metal side covers, inspired by Born Motor Co. I'm gonna have them painted to match the tank and headlight bucket. Looking back at the pictures of my progress so far, I'm sticking with yellow. A yellow-orange with a white strip and pinstripe along the bottom.



Whoosh!

[Scramps]

Nope, scratch the side covers, not happening.

[Scramps]

I got the bike running well enough to brave a short jaunt around my front yard last night, which was exciting, first time the bike has moved around under its own power since god knows when.

Clutch doesn’t release until the lever is almost all the way out, but that seems to be a common thread with these.

#3 is still flooding. Read some threads from people who had similar issues. I need to borrow my friend’s timing light and get a GOOD battery, since the one I’ve been forcing to work should have been recycled 2 years ago.

Either way though, exciting times! Got to actually RIDE the thing!

Til next time,
Keep on Sohc-ing

[Gurp]

Throw some coka a cola and a asprin in the old case might get more life out of it. Beennthere done that a few times.

[Scramps]

Finally got my hands on a compression tester, and after some fully open choke, fully open throttle testing, I was able to confirm all four cylinders are close to 150psi cold. I didn’t have time to do a warmed up test last night, but I’m reasonably satisfied that I do have at least decent compression.

[Scramps]

Tested a couple more hypotheses this evening. Verified that my crummy old exhaust isn’t clogged up, so that’s good news. Also did some stroboscopic timing, which is what is recommended for the Pamco. Got it firing just right, but #3 still doesn’t want to do right.

I decided that I was finally ready to take the bike down the road and back, either way.

There’s a gas station about 2 miles from my house, I rode down to it and came back.

The bike seemed like it was running decently enough. I didn’t really call on it, but it seemed maybe a little underpowered. Shifts great! Front suspension is pretty soft, bounced me around a good bit. Brakes work just fine. Most critically though, nothing fell off. So that’s a win in my book.

Pulled back into the garage, #3 exhaust pipe is cool enough to wrap my hand around it.

I think I’m going to have to pull the head back off and get it checked out by someone who knows what they’re doing.

Confession time:
I didn’t lap my valves during my engine rebuild. I just cleaned all the carbon deposits out, verified that the ports looked serviceable, cleaned the thing up and slapped it back on there. I didn’t have access to a valve spring tool that would fit, or else I would have pulled it all apart and really cleaned it all up and replaced the valve stem seals. I still have new ones on my workbench.

But anyway,


Good night everybody

[seanbarney41]

If you have 150psi compression there is no problem with the valves

[RAFster122s]

Before you go pulling the head you should adjust the valves if you haven't done so by the book and then your compression test will tell you if you have #3 as a problem. You need three things to have combustion:   compression , fuel and spark.
Compression test can tell you if you have compression , naturally with 150 psi compression, you are good because they are all even.

Then you will check for spark pulling the plug wire and putting another new plug on the lead and hold it to the cylinder or a bare metal area while cranking...you should see the spark at the plug and as it jumps to the frame or a bolt on the motor. Lower light will let you see this easier than a bright sunny afternoon...

Then there is fuel. If after running if it doesn,'t have a wet plug with gas  then you have a carb problem... Because it should be drawing fuel even if it is not firing.

It feels down on power because it is running on 3 cylinders rather than four!
Otherwise you would not be able to touch pipe 3 without a burn...unless you were very fast and light with the touch.

FWIW, YMMV
David

[Scramps]

Not sure what else I can do in regards to the carbs. I pulled them again when I started trying to diagnose this issue. I read a thread from last year about a dead #3 cylinder that ended up being a loose jet in the bowl, so I wanted to make doubly sure that wasn't my problem first. While I had them off, I pulled all the bowls, checked all the jets, float heights were all level (22mm), no clogged passages, no debris, no stuck float valves, etc. I went back out a little earlier to confirm that there is gas in the bowl for #3, and there is.

As for the valve timing, I checked it Monday evening. Using the old shop manual as reference, everything checked out.

Cal mentioned a while back that a weak battery would cause weak spark. The battery being the only variable I can't rule out, I'm inclined to think (read: hope) that that's the problem.

I'll have to wait until I'm not quite so strapped and purchase a good one.

[RAFster122s]

Got a set of booster cables and car battery? Have you charged you MC battery? The car battery can be used in parallel with you MC battery (car not on) and if your MC starts firing on all four you could have a battery issue.

The coil should be showing inconsistent behavior where #2 and #3 are intermittently firing either #2 or 3. That apparently is not the case. I don't think you would consistently be seeing #3 misfiring or not firing and #2 always firing if the coil was bad as it would depend upon which began firing for the decay in voltage to only affect one cylinder and always the same. But, I guess it could. Swapping your coils and seeing if the problem switches to cylinder #1 or 4 then you have a coil problem.

With the compression you have you certainly should not see a lack of fuel in cylinder #3. So,if after running you do not find a wet plug on #3 then it is baffling how you can have fuel level in the bowl consistent with the other 3 fuel bowls and not have a wet plug as cylinder vacuum is going to be drawing fuel into the cylinder.

Is my logic on this deduction flawed? If others think so, please say so...
I would like to learn as I am sure Scramps would.as well.

[calj737]

If the battery were the issue, then more than just #3 would be weak. If the coil were the problem, then 2/3 would be problematic. Same for condenser and points. That leaves carb since compression is good.

If you pull #3 plug, what does it look like? Wet and clean? No spark. Dry and sooty, weak spark. Wet and sooty, too much fuel.

I have never liked setting floats by measure,ent, instead am wholly in favor of Clear Tube method. When you run the motor, #3 will get hot from the spark alone, just not sizzling if the fuel isn’t combusting.

So dig through those answers, and we can point you in the direction of the problem.

I suspect the emulsion tube in #3 is badly clogged, or the fuel level is too low...

[flatlander]

Oh yeah, I keep forgetting to show you guys my cool shirt that I found at Old Navy, believe it or not

LOL look what i wear today. bought this a few years ago, apparently then the routes were not scenic yet.

[Scramps]

That’s pretty cool, I like that super simple sketch style stuff. Did that shirt come from old navy also?

Historically, when I’ve pulled the plugs, #3 has been wet and clean. I’ve gotten this result with a couple of different plugs. It is not outside the realm of possibility that the 2 that I’ve tried were both dead, so that will be another easy one to check.

As for the clear tube fuel level method, I’ve seen some pictures of people doing it, but never really dug into how it’s done. Do you just pull your bowl drain plugs and jam the tube in there? Or do you need to get some special adapters?

[calj737]

Historically, when I’ve pulled the plugs, #3 has been wet and clean. I’ve gotten this result with a couple of different plugs. Swap the plug with #4. Repeat the test. What happens? Same? Swap condensers from 1/4 to 2/3. Same result? Time to look at the plug cap boot and wire on your coil...

As for the clear tube fuel level method, I’ve seen some pictures of people doing it, but never really dug into how it’s done. Do you just pull your bowl drain plugs and jam the tube in there? Or do you need to get some special adapters?

You can grab a plastic vacuum plug from the auto parts store, 3/16 works. Thread it into the bowl in place of the drain bolt. Slip the tubing over it. Get 4 of them, and 4 lengths and you can do all carbs simultaneously. 

[Scramps]

On the left, #1, on the right, #2



On the left, #4, and on the right, #3.



I believe I have found the cause of my problem

[Scramps]

Looking at the float needle valve, there does not appear to be anything impeding its movement. Air can flow pretty easily through the fuel line, through the t-splitter, and into the bowl. Seems like if the thing were sticking, it would stick in the open position.

Am I missing something?

[Robbo]

I would swap the float and float needle  between 3 to 4 and see if the problem moves to 4 or stays in 3.

You will narrow it down further.


Sent from my iPhone using Tapatalk

[flatlander]

That’s pretty cool, I like that super simple sketch style stuff. Did that shirt come from old navy also?

i bought it a few years ago, memory fades... could have been old navy.

[calj737]

All of your fuel levels are a bit low. Goal is 3-4 mm below bowl seam.

Remove the drain screw all together on 3, does any fuel come out? If not, look at the fuel inlet T between 3&4. Something is not correctly plumbed.

[Scramps]

When I removed the drain plug to put the vacuum plug in, some fuel did come out of #3, but not as much as the others.

Air can pass through no problem without the float and needle in place, but once you put them back, air cannot pass through, in the upside down position