poor performance

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oferbr
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Joined: Sun Dec 25, 2016 10:13 am

poor performance

Postby oferbr » Mon Jun 17, 2019 4:36 am

I bought 1982 cb650 last year not running and since then I am trying to get it to good running condition with some successes . got it to run but it is running poorly. it doesn't have power as I expected and at 5th gear it goes up to 50 MPH at 4000 RPM so cruising at 60 MPH is not fun and very lowed.

So far i done this things:
1. New air filter.
2. overhauled the carbs. Cleaned them changed all O rings, changed the jets to 35# and 120#, changed acceleration pomp. didnt do yet pilot screw tune up and I did only bench synchronization.
3. new plugs
4. I did dynamic ignition timing
5. I did valve clearance tune up.
6 Compression is 105 on all cylinders.
7. New battery.
8. cleaned the gas tank

What did I miss?
Thanks
Ofer
Last edited by oferbr on Tue Jun 18, 2019 2:01 am, edited 2 times in total.

Mr_Crow
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Joined: Wed Jun 12, 2019 10:16 am

Re: poor performance

Postby Mr_Crow » Mon Jun 17, 2019 1:56 pm

Top gear should be much faster than that I would think. I don't know too much about motorcycles just yet but I do cycle a lot. Has the gear ratio between the chains ever been changed?

bendiesel3
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Joined: Tue Jun 04, 2019 7:08 am

Re: poor performance

Postby bendiesel3 » Mon Jun 17, 2019 10:06 pm

Coil packs?


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Volker_P
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Re: poor performance

Postby Volker_P » Tue Jun 18, 2019 12:52 am

First check out if all four header pipes get equally hot.
Plug cables from left coil go to cylinders 1+4, from right coil to 2+3. :wink:
50mph at 4000rpm at 5th gear sounds reasonable. The CB650 lives from revs rather than torque. Also full oil pressure is available only from above ~3000rpm on, so avoid riding at load below.
If you still want to lower the revs a bit: a 17 front sprocket will still work with the sprocket cover and the chain length. Was fine for me that way. :)
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

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GeorgeSweety
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Location: UK.

Re: poor performance

Postby GeorgeSweety » Tue Jun 18, 2019 2:28 pm

Have you checked and cleaned your timing advance unit? located behind your pulse generator on the right hand side of your engine as you sit on the bike. The bob weights can stick so that your timing will not advance with engine speed.

oferbr
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Joined: Sun Dec 25, 2016 10:13 am

Re: poor performance

Postby oferbr » Tue Jun 18, 2019 4:16 pm

Mr_Crow wrote:Top gear should be much faster than that I would think. I don't know too much about motorcycles just yet but I do cycle a lot. Has the gear ratio between the chains ever been changed?


front sprocket 17 teeth. rear sprocket 39 teeth

oferbr
Posts: 11
Joined: Sun Dec 25, 2016 10:13 am

Re: poor performance

Postby oferbr » Tue Jun 18, 2019 4:20 pm

GeorgeSweety wrote:Have you checked and cleaned your timing advance unit? located behind your pulse generator on the right hand side of your engine as you sit on the bike. The bob weights can stick so that your timing will not advance with engine speed.


I did a dynamic test with a light gun. the advance timing is good. I checked the at 2750 rpm.

oferbr
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Joined: Sun Dec 25, 2016 10:13 am

Re: poor performance

Postby oferbr » Tue Jun 18, 2019 4:24 pm

Volker_P wrote:First check out if all four header pipes get equally hot.
Plug cables from left coil go to cylinders 1+4, from right coil to 2+3. :wink:
50mph at 4000rpm at 5th gear sounds reasonable. The CB650 lives from revs rather than torque. Also full oil pressure is available only from above ~3000rpm on, so avoid riding at load below.
If you still want to lower the revs a bit: a 17 front sprocket will still work with the sprocket cover and the chain length. Was fine for me that way. :)


All 4 header pipes get equally hot.
coil set up is ok left go to 1+4 and right go to 2+3.
front sprocket is 17 and rear is 39

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Volker_P
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Re: poor performance

Postby Volker_P » Wed Jun 19, 2019 12:37 am

So far things sound unsuspicious to me.
Do you have any issues like backfire, hesitations at the throttle or something like that?
Or does it run more or less fine and smooth but just lacks top end power?

What is your current topspeed and what is your mpg?
Do you live at somewhat higher altitude above sea level?
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

oferbr
Posts: 11
Joined: Sun Dec 25, 2016 10:13 am

Re: poor performance

Postby oferbr » Wed Jun 19, 2019 5:50 am

Volker_P wrote:So far things sound unsuspicious to me.
Do you have any issues like backfire, hesitations at the throttle or something like that?
Or does it run more or less fine and smooth but just lacks top end power?

What is your current topspeed and what is your mpg?
Do you live at somewhat higher altitude above sea level?


No backfire, yes some hesitations at the throttle. it runs ok but it is very lode and there is a lack of power.
Top speed 55 MPH did not measure the MPG (mile per gallon).
I live at 400 meter above see level. warm weather

oferbr
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Re: poor performance

Postby oferbr » Sun Jun 23, 2019 3:57 pm

I found that there is no GASKET on my air filter - part #17217-426-300.
Could this be the problem?
anyone now were can I get this part? (it is missing in any site that I go to)

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GeorgeSweety
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Location: UK.

Re: poor performance

Postby GeorgeSweety » Mon Jun 24, 2019 9:22 am

oferbr wrote:I found that there is no GASKET on my air filter - part #17217-426-300.
Could this be the problem?
anyone now were can I get this part? (it is missing in any site that I go to)

If it is missing then it "could" be a problem, mine was also missing but I cut one out of a thick rubber type sheet and stuck it in place with strong double sided tape. I would suggest that you try to make something to fit, at least to see if it helps your problem.

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Volker_P
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Location: southern Germany

Re: poor performance

Postby Volker_P » Tue Jun 25, 2019 12:53 am

A CB650 could make 55mph on two cylinders. So something is really wrong here.

As you should have the CV carbs, I doubt that it is the missing air filter seal alone but it should provide already a step to the right direction.
For the air filter seal I found that one or two rubber rings from preserves glasses would do the job, too. :wink:

How do your plugs look like? All four equal?
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues


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