1981 CB650c Won't Start

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Maldenite
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1981 CB650c Won't Start

Postby Maldenite » Wed Jun 06, 2018 11:03 pm

Hey everyone. First-time poster, but I've been lurking on here for the past couple weeks and I am looking for some advice.
I just picked up a 1981 CB650c for $800 about 3 weeks ago from this older lady who said the bike had belonged to her husband that high-tailed it out of the province and wasn't coming back.

Anyways, she told me that the tank was off the bike, but it did start (it did not infact) and that the bike had had a lot of work done to it over the winter (cleaned carbs, new gaskets and seals) and my buddy who knew the lady vouched for her on it, so me being completely inexperienced with motorcycles, decided to buy it figuring it would be no problem to get it started. (just connect the tank and go, right?)

Oh did I mention this is my first bike?

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This will be a long post.....

So I brought it home and opened the tank and it was completely covered in rust, so I did some googling on how to remove it and picked up a couple jugs of Evaporust and dumped it into the tank with a bunch of bolts and let it soak for a week while I flipped/rotated and shook it daily. The end result was great.
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The tank is still soaking in fresh evaporust to make sure I get it all, and so it doesn't happen again while I decide if I want to try using a tank sealer.
So, my first question I'm looking for advice on is: Should I use a tank sealer?
I've done a lot of reading and watched tons of videos of different products to seal a gas tank and I've come down to two options, POR-15 or Caswell.
So if anyone has tried either of these products, I'd like to know how it turned out? Did it fail after a while? Or am I better off to not seal it all all?

Either way, while my tank was out of commission, I made an auxiliary fuel tank to test the bike.
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I couldn't get it to start.

So I replaced the spark plugs, the old ones had lots of carbon build up and one didn't have good continuity.

It still didn't start.

I hit it with two short sprays of quick start through where the air filter sits and I got it to run for maybe 10 seconds with the throttle wide open before it died out. I tried this a few times until I killed the battery. (which I have also replaced with a new one a few days after, I figured it couldn't hurt)

So after having no luck getting it started I tested the compression on the cylinders to see if that could be the problem.
The results came back as:

#1 - 90 PSI
#2 - 90 PSI
#3 - 60 PSI
#4 - 75 PSI

So I did some more googling, and I attained 3 different shop manuals for CB650's and decided I might as well try to set the valve clearance and see if that helps. After triple checking all of them and was satisfied with the results I put the cover back on and did another compression test.
The new results were:

#1 - 90 PSI
#2 - 90 PSI
#3 - 65 PSI
#4 - 90 PSI

So I figure something is probably wrong with cylinder 3? Maybe a leak? (the spark plug is also a pain to get to without the EXACT socket...)
Either way. I figure this thing should still fire up with these readings, right? I picked up a new set of piston rings if I end up having to take the engine apart anyway. (I'll probably overhaul it in the winter regardless)

So now my next step was to examine the carbs...
So I drained and removed them from the bike with the help of my roommate and opened up the first float bowl expecting to see freshly cleaned carbs, like the lady had said.
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It was grimy as hell!

So I went through all 4 carbs and cleaned tons of build up and rust from them.
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The gasket from the accelerator pump needle split in two as soon as I removed it.
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After cleaning them all I assessed what needed to be replaced.
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I've ordered 4 carb rebuild kits, 4 floats and new parts for the accelerator pump, which I'm currently waiting to receive.
So once the new parts arrive, I'll be removing the carbs again and overhaul them. Hopefully it solves the problem.

Now the other thing I noticed is the starter doesn't always catch to crank the engine, I removed it and it looked like it had just been replaced.
I stuck my finger in the hole and it didn't feel stripped either.
I tried turning the engine by hand and it seems like the starter catches when it sits in a "sweet spot", otherwise it seems pretty random when it turns, or not.

I know that's a lot of information for one post, but I think I covered everything up to now.

Any advice or suggestions would be greatly appreciated!
Thanks!
Last edited by Maldenite on Wed Jun 06, 2018 11:03 pm, edited 1 time in total.
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Folsoml
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Re: 1981 CB650c Won't Start

Postby Folsoml » Thu Jun 07, 2018 8:34 pm

Have you checked out the carb cleaning manual here in the General Discussion forum? The carbs wont be exactly like your's, but the techniques are basically the same.

Drop about a tablespoon of oil in each cylinder through the spark plug hole. If the compression improves, your problem it most likely the rings. If it does not, you probably need to redo the valves.
Have a problem with your CB650? Have a technical question? Click here!


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Maldenite
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Re: 1981 CB650c Won't Start

Postby Maldenite » Fri Jun 08, 2018 11:21 am

Folsoml wrote:Have you checked out the carb cleaning manual here in the General Discussion forum? The carbs wont be exactly like your's, but the techniques are basically the same.

Drop about a tablespoon of oil in each cylinder through the spark plug hole. If the compression improves, your problem it most likely the rings. If it does not, you probably need to redo the valves.


Yeah, I've been through the carb cleaning manual, lots of good info in there.
And I'll try putting the oil in the cylinders and see what happens.

Thanks man!
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cb650
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Re: 1981 CB650c Won't Start

Postby cb650 » Fri Jun 08, 2018 1:48 pm

nice looking. But I'm biased as one of mine is just like that. If you have the auto fuel shut off still on the carbs ditch it.
Sounds like your starter clutch is going out too. Couple threads on it here.
Did you clean the tank out?!?!?!?!

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Re: 1981 CB650c Won't Start

Postby Maldenite » Sun Jun 17, 2018 6:43 pm

UPDATE
So my carb rebuild kits came in and I've been through them and replaced what was in need of repair.
I noticed that 2 of my floats are sitting kind of flat and had no springiness to them when you apply pressure.

The good one on the left, the floppy one on the right
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I didn't figure it would be a big problem so I closed them up and put them back on the bike.
So the good news is I got the bike to start!

But once the bike was sitting idle for a bit it started revving up to 4k-5k rpm pretty randomly on its own.
https://youtu.be/53mj-EHV2xA

There was also fuel coming out of the overflow tube on the bottom of the bike.
Any ideas what could be causing these two issues? Is it because of the floppy floats?


Thanks!
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Folsoml
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Re: 1981 CB650c Won't Start

Postby Folsoml » Sun Jun 17, 2018 6:50 pm

Did your kits include new float needles? If not, check the ones on the "floppy" floats and make sure the spring in the needle is springy. Also, try tapping on the float bowls with a screwdriver handle or something similar. Often this is all it takes to make them seat and stop leaking.

The high revving sounds like an air leak in your insulators. When the engine is idling, spray brake cleaner (not carb cleaner) on each insulator (one at a time). Any change in the idle is an indicator of a leak.
Have a problem with your CB650? Have a technical question? Click here!


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Riche
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Re: 1981 CB650c Won't Start

Postby Riche » Wed Jun 20, 2018 5:47 am

1.Compression test should be done with the carbs held open (full throttle) or better off the bike altogether.
2.Bend the tabs on the floats to get them all sitting at the correct height. The fuel is flowing out of the over flow because the floats are not at the right height.

Glad your making progress..

Rich

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Maldenite
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Re: 1981 CB650c Won't Start

Postby Maldenite » Sat Jun 23, 2018 11:30 am

Riche wrote:1.Compression test should be done with the carbs held open (full throttle) or better off the bike altogether.
2.Bend the tabs on the floats to get them all sitting at the correct height. The fuel is flowing out of the over flow because the floats are not at the right height.

Glad your making progress..

Rich


I'm not so much worried about the compression test anymore since I got the bike to start, but it's good knowledge to have, thank you!

I'm not sure what you mean by "bend the tabs", but I'm assuming you mean this?
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It also seems like the needle sits at 2 different heights in their housing.
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https://youtu.be/TpbWCK0atfw
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Re: 1981 CB650c Won't Start

Postby Maldenite » Sat Jun 23, 2018 11:34 am

Folsoml wrote:Did your kits include new float needles? If not, check the ones on the "floppy" floats and make sure the spring in the needle is springy. Also, try tapping on the float bowls with a screwdriver handle or something similar. Often this is all it takes to make them seat and stop leaking.

The high revving sounds like an air leak in your insulators. When the engine is idling, spray brake cleaner (not carb cleaner) on each insulator (one at a time). Any change in the idle is an indicator of a leak.


I did replace the float needles with the rebuild. The spring on the top of it seemed pretty springy on all of the new needles.
But it looks like the needles are sitting at 2 different heights in the housing they sit in, could that be an issue?

By "check the insulators" do you mean the carb boots that go to the engine? or the air box side?
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Maldenite
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Re: 1981 CB650c Won't Start

Postby Maldenite » Sat Jun 23, 2018 11:37 am

ALSO

I'm looking for info if anyone can tell me if I'd need to replace my starter clutch for sure (before I get any deeper into this thing, I'd rather not if I don't have to)

So I took a video of what's happening when I try to start the bike.
https://youtu.be/ythm_mnn74A
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Folsoml
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Re: 1981 CB650c Won't Start

Postby Folsoml » Mon Jun 25, 2018 7:05 am

Don't worry about bending any tabs. Your issue is definitely with those float needles. Also, the plastic floats you have are not adjustable. If you put the float needles side by side, are they the same size? If not, what is down in the needle seat that is keeping them from going all the way in?

Spray the brake cleaner (again, not carb cleaner as it will eat away rubber parts) on the insulators that go between the carbs and the cylinder head.

Your starter issue is almost certainly the starter clutch.
Have a problem with your CB650? Have a technical question? Click here!


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Maldenite
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1981 CB650c Won't Start

Postby Maldenite » Fri Jun 29, 2018 9:12 pm

Folsoml wrote:Don't worry about bending any tabs. Your issue is definitely with those float needles. Also, the plastic floats you have are not adjustable. If you put the float needles side by side, are they the same size? If not, what is down in the needle seat that is keeping them from going all the way in?

Spray the brake cleaner (again, not carb cleaner as it will eat away rubber parts) on the insulators that go between the carbs and the cylinder head.

Your starter issue is almost certainly the starter clutch.



So you’re saying my floppy float is the one that’s seated correctly? Because the needle sits lower?
The needles are all also the same size.
Is there supposed to be an O ring inside the seat?
And Is the seat removable? I tried to pull it out gently when I had cleaned them the first time and couldn’t.

I’ll also try spraying the break cleaner on the insulators once I fix the carb problem, I just don’t want to leak anymore fuel first.

I priced out the starter clutch parts and it will cost me $150 - $240 depending on how bad some of the more expensive parts are damaged. I won’t really know until I open her up.

Not sure if I should take care of the starter clutch problem or the carb problem first though, they both seem equally important.
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Re: 1981 CB650c Won't Start

Postby Folsoml » Sat Jun 30, 2018 9:12 am

Since the bike won't run correctly as long as either problem exists, they are both equally important.

The seats are not removable, and there should not be an o-ring or anything else in them. When you clean them, they should shine like new pennies. I use cotton swabs and a product called Nevr-dull. Nevr-dull is a metal polish you can get at Walmart.
Have a problem with your CB650? Have a technical question? Click here!


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