Hey everyone!
I have a 1980 CB650 custom that I rebuilt 5 years ago, and I’m having an oil burning issue. I dubbed the bike Ol’ Smokey a while ago, but I’ve been doing my best to keep the smoke in where it should be.
Recently I redid the top end (with the help of my Dad), since I had low compression on #1 cylinder (60psi). Here’s the list of what was done:
Cylinders honed and new piston rings gapped and installed.
Cleaned head bolts and head bolt threads (with a tap and die)
New top end gaskets, o-rings, exhaust gaskets, etc. The only gaskets that we’re reused we’re the valve cover gaskets (there are 3 on this bike)
Reassembly went smooth with the exception of one head bolt (front middle) that started to pull threads, and 2 bolts in the head cover. We didn’t fully strip them, but we couldn’t torque them fully.
New spark plugs, wires checked, and timing reset.
Checked the carbs, and they were pretty clean... no clogged jets or passages I could find, blew carb cleaner and air through everything I could find. We installed aftermarket needles, and raised their position 1 notch (the bike would bog when you opened the throttle, and that drastically improved it.
Synced the carbs, and set the idle mixture screws at 2.5 turns out. (it runs and idles best at this setting)
No oil leaks that I’ve seen since the rebuild, plugs look great (all tan in color), and did a compression test (115, 110, 105, 115)
Modifications:
K&N single filter in the stock airbox, and a 4 into 1 Mac exhaust. Main jets are 95 (stock in the carbs, and these are the PD carbs, stock idle jets)
Problem:
The bike is still burning oil. Less than it was before, but I’ve burned about 3/4 L of oil in 500km. Bike accelerates and drives better than it ever has. But when I let off the throttle from high RPM, I get quite a bit of smoke coming out of the exhaust. From what I can tell, this is the only time I’m getting smoke from the exhaust.
I know this is a loooong post, but I’ve tried everything I can think of. I’d like to figure out what the next step is... any suggestions would be greatly appreciated!!
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Old Smokey is still smokin!
- GeorgeSweety
- Posts: 462
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- Location: UK.
Re: Old Smokey is still smokin!
Hi flatlander, you don't mention anything about your valves, did you re-seat them and change the valve stem seals? When they go bad oil gets past them into the combustion chamber.
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Re: Old Smokey is still smokin!
GeorgeSweety wrote:Hi flatlander, you don't mention anything about your valves, did you re-seat them and change the valve stem seals? When they go bad oil gets past them into the combustion chamber.
I lapped the valves and replaced the valve seals... I thought that might have been the problem 2 years ago, but she was still smokin...
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- GeorgeSweety
- Posts: 462
- Joined: Tue Aug 08, 2017 11:47 am
- Location: UK.
Re: Old Smokey is still smokin!
Ok, you never mentioned the valves so I thought I'd ask. When you say burning oil I presume you mean "using oil"? When you rebuilt the top end did you fill the oil gallery on top of the cylinder head? This holds a fair bit of oil and if it wasn't filled by you could account for some of your oil disappearing as it would eventually fill up. You say the plugs look great so it doesn't sound like any oil is getting where it shouldn't be. Is the exhaust the same one that you had when the bike was smoking badly? It may just be burning off any crap that was left in the exhaust from before you did the top end rebuild, keep an eye on it and see if it improves.
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- Joined: Fri May 05, 2017 9:08 pm
Re: Old Smokey is still smokin!
I realize I forgot to mention the valves... I was trying to be thorough, and totally whiffed on it! Haha...
When I say the bike is still burning oil, it both because the bike is using oil (level is down from where it was), and I’m getting some smoke out of the exhaust (only on deceleration from high RPM)...
I’ve been given a few suggestions (rings or valve guides)... so I’ll have to watch and make a plan to re-open the engine sometime!
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When I say the bike is still burning oil, it both because the bike is using oil (level is down from where it was), and I’m getting some smoke out of the exhaust (only on deceleration from high RPM)...
I’ve been given a few suggestions (rings or valve guides)... so I’ll have to watch and make a plan to re-open the engine sometime!
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Re: Old Smokey is still smokin!
If you have piston rings "gapped" this sounds to me like you use oversize rings with standard pistons after cutting them to fit your honed bore?
Note that the gap increases when you hone worn cylinders to get rid of the grooves but you still use the standard pistons.
In such case new rings might provide nice compression for some time but high rpm oil consumption will rise again soon.
How many miles?
Note that the gap increases when you hone worn cylinders to get rid of the grooves but you still use the standard pistons.
In such case new rings might provide nice compression for some time but high rpm oil consumption will rise again soon.
How many miles?
Cosky's great (free) online manual: http://cosky0.tripod.com
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
forum links to common technical issues
If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum
- canadianpatriot
- Posts: 10
- Joined: Sat Jan 28, 2017 6:24 pm
Re: Old Smokey is still smokin!
We installed aftermarket needles, and raised their position 1 notch (the bike would bog when you opened the throttle, and that drastically improved it.
HI, I have a question for you based on the above statement. I have the same carbs (PD 50) and want to change needle positions as well, I just am unsure how this is done in these carbs?!? (Bike bogs and has no power on 1/4 throttle onward.)
I have read they are pressed in needles however, I dare not pull from the "bowl" end without reassurance I am doing it properly? Any suggestions based on your experience.
Thanks!
HI, I have a question for you based on the above statement. I have the same carbs (PD 50) and want to change needle positions as well, I just am unsure how this is done in these carbs?!? (Bike bogs and has no power on 1/4 throttle onward.)
I have read they are pressed in needles however, I dare not pull from the "bowl" end without reassurance I am doing it properly? Any suggestions based on your experience.
Thanks!
1980 Honda CB650C
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- Posts: 36
- Joined: Fri May 05, 2017 9:08 pm
Re: Old Smokey is still smokin!
canadianpatriot wrote:We installed aftermarket needles, and raised their position 1 notch (the bike would bog when you opened the throttle, and that drastically improved it.
HI, I have a question for you based on the above statement. I have the same carbs (PD 50) and want to change needle positions as well, I just am unsure how this is done in these carbs?!? (Bike bogs and has no power on 1/4 throttle onward.)
I have read they are pressed in needles however, I dare not pull from the "bowl" end without reassurance I am doing it properly? Any suggestions based on your experience.
Thanks!
I think you’re referring to the needle seat that is pressed into the body of the carb. I didn’t remove those. The needles are removed from the top of the carbs (they’re screwed into the slide) so the slide has to be undone from the linkage. We used the aftermarket needles because they had the 5 clip positions. If you have the stock needles, I believe they can be shimmed with a small washer.
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- canadianpatriot
- Posts: 10
- Joined: Sat Jan 28, 2017 6:24 pm
Re: Old Smokey is still smokin!
I was afraid of that! OK, I'll get to work.
Thanks for the quick reply!
Thanks for the quick reply!
1980 Honda CB650C
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- Posts: 36
- Joined: Fri May 05, 2017 9:08 pm
Re: Old Smokey is still smokin!
Old Smokey out for a ride yesterday… running like a champ. Less smoke now (using 15w40 oil)…
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Re: Old Smokey is still smokin!
nice pic - she's a fine expression of the 650
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