1981 CB650 #1 Cylinder not firing

If it's broken or just needs tweaked

Moderators: Volker_P, tidd650

Kidonaclassicbike
Posts: 16
Joined: Wed Mar 30, 2016 7:51 am

Re: 1981 CB650 #1 Cylinder not firing

Postby Kidonaclassicbike » Wed Apr 27, 2016 8:22 am

Thanks for the replies !

The main problem is not confidence in my wrenching abilities but more of a space and time issue. I have a windy patio with a lot of dust flying around and a job that often leaves me out of town for a day or two, so its hard to start working on something that I might not finish. I cant leave tools / parts around. If I start a job I have to finish it in an hour or two and put everything back together and pack my tools.

Weekends are my best bet, but spring has not arrived in Canada fully yet, so its still too chilly to stay outside for hours.

I will read up on my manual and try to open the carb. What should I look for in there ? What could cause a too rich condition ? Do you think I can rotate some adjustment screws to try and lean out the mixture ?

Arghhh I wish I had more time to thinker around with this bike.

Kidonaclassicbike
Posts: 16
Joined: Wed Mar 30, 2016 7:51 am

Re: 1981 CB650 #1 Cylinder not firing

Postby Kidonaclassicbike » Tue May 31, 2016 5:29 pm

Hello,

So the guys at the shop started looking at the bike yesterday.

They told me 130 120 120 130 for compression on warm engine, WOT and carbs ON the bike

I went through all the threads involving compression and I am still a little confused. Will having the CV carbs on the bike while testing show 30-40 PSI lower compression readings ?

I gave them the go ahead to look at spark next.

They said spark is very weak on all 4 but almost non existent on #1 and #3

Bike has an year old battery that has been recharged before the test, new CDI spark igniters and a working charging system (going by measurements on the battery terminal)

So the shop and I agreed on replacing the very old (they seem original) spark plug caps and the few years old spark plugs. Putting new gas in the bike. See how it runs.

So are those compression numbers OK ? There is WHITE smoke and water coming out of #3 and #4 for a couple of minutes after starting the bike, but not even a hint of gray, black or blue smoke.

Could the weak spark be cause by the Gaps of the Pulse Generator ? Should I tell them to adjust it ?

If the bike is not running well after spark is good whats next ? Carbs or check the valves ?

Thanks !

User avatar
Folsoml
Posts: 1634
Joined: Sat Apr 07, 2012 9:02 pm
Location: North Florida

Re: 1981 CB650 #1 Cylinder not firing

Postby Folsoml » Wed Jun 01, 2016 5:40 am

Sometimes on these old bikes you lose a lot of voltage just through the wiring harness--causing weak spark. There is a direct coil modification that runs the power to the coils straight from the battery.

What you need is some 12 or 14 gauge wire, an inline 10 amp fuse, and a 12 volt automotive relay (weatherproof). Run a wire from the positive post of the battery (do not connect to battery yet), through the 10 amp fuse, to the number 30/51 terminal on the 12 volt relay. Disconnect the black and white wire from the coils, and run a wire from the 87 terminal on the relay to the place on the coils where the black and white wire would have connected. Take the black and white wire that you took off the coils and connect it to the 86 terminal on the relay. Run a wire from the 85 terminal to a good solid ground. Once everything is hooked up, connect the wire to the positive post of the battery. What happens now is that instead of the weakened voltage coming through the black and white wire being used to fire the coils, it is used to flip the switch inside the relay. Once the switch is flipped, good strong voltage coming straight from the battery is used to fire the coils.

Image
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

Kidonaclassicbike
Posts: 16
Joined: Wed Mar 30, 2016 7:51 am

Re: 1981 CB650 #1 Cylinder not firing

Postby Kidonaclassicbike » Wed Jun 01, 2016 9:00 am

That is a great idea and it is easy to implement.

I am hoping that when I get the call today from the shop it will be something like "We changed the caps / plugs and the bike runs perfect", but if it doesn't
I will do this mod for sure.

I keep reading about compression and the most of the guys seem to think that close readings between cylinders means that the engine is doing OK, but I will do the 2 day Seafoam soak when I get the bike back to see if I can increase those compression readings. I am reluctant to pay for or do a ring, cylinder job so I will do what I can to bring that compression back up if it is indeed low. I have been reading a few threads in which guys have gone from 90-100 psi to 160-170 after a few Seafoam soaks on old motorcycle engines, so there is hope :)

Someone has experience testing the compression with the CV carbs ON and then OFF ? I am still curious to know if there is a big difference between WOT carbs ON and carbs OFF.

Thank you.

User avatar
Folsoml
Posts: 1634
Joined: Sat Apr 07, 2012 9:02 pm
Location: North Florida

Re: 1981 CB650 #1 Cylinder not firing

Postby Folsoml » Wed Jun 01, 2016 12:47 pm

The bike should run fine with those compression readings.
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

jcasey007
Posts: 225
Joined: Sun Jan 13, 2013 3:38 pm
Location: Stratford Upon Avon - UK

Re: 1981 CB650 #1 Cylinder not firing

Postby jcasey007 » Wed Jun 01, 2016 4:29 pm

wont using a relay introduce a change in ignition timing as there will be a millisecond delay in closing the contacts.......or is this a test for checking the standard wiring to the coils only?

User avatar
Folsoml
Posts: 1634
Joined: Sat Apr 07, 2012 9:02 pm
Location: North Florida

Re: 1981 CB650 #1 Cylinder not firing

Postby Folsoml » Thu Jun 02, 2016 5:08 am

I've run it on several different CB750C and CB900C Hondas with no issues with timing. Never actually done it on a CB650, but I can't see where it would be different.
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

Kidonaclassicbike
Posts: 16
Joined: Wed Mar 30, 2016 7:51 am

Re: 1981 CB650 #1 Cylinder not firing

Postby Kidonaclassicbike » Wed Jun 08, 2016 8:08 pm

Got the bike back from the shop. It has new Plugs and Caps. Starts faster than i can let go of the button. It doesnt need much choke if at all. I have to hold 1/8 throttle for a minute to be able to leave it idle on its own.

Ran somewhat good but it did not want to go over 5000 rpm. I did the washer trick on the filter and now it revs to the sky, but it has no where near the power i have seen on those bikes in youtube or in the forums. I am at 5.5k rpm in 5th gear going 60mph. :|

Is the lack of power because of the low compression or the bad tune ?

#1 is still colder than the rest, but now the bike for sure idles on 4. Its smooth.

I am pretty sure that the carbs where cleaned and made to work with that hole in the air box, so now the bike is running way too rich. I am going to take it to a friend of a friend who owns a couple of old hondas including a 650c. I hope he can tune the carbs, but I am still worried about the compression.

What needs to be done to increase compression ?

New rings and a hone or bore ?

Thanks for the answers. I really really appreciate your time.

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1981 CB650 #1 Cylinder not firing

Postby Volker_P » Thu Jun 09, 2016 4:02 am

So how does your #1 plug look like?
Rather wet or dry?
And moreover how does it look like compared to the #4 plug?

Typically about 65mph top speed can be reached with only two cylinders working properly.

How clean is your tank? You may release some fuel in pertcock reserve position into a clean jar to find out.
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

User avatar
Folsoml
Posts: 1634
Joined: Sat Apr 07, 2012 9:02 pm
Location: North Florida

Re: 1981 CB650 #1 Cylinder not firing

Postby Folsoml » Thu Jun 09, 2016 5:22 am

Kidonaclassicbike wrote:What needs to be done to increase compression ?

New rings and a hone or bore ?

Thanks for the answers. I really really appreciate your time.


Make your valves are adjusted properly. You also may need to pull the head to lap the valves.
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1981 CB650 #1 Cylinder not firing

Postby Volker_P » Fri Jun 10, 2016 1:26 am

Kidonaclassicbike wrote:They told me 130 120 120 130 for compression on warm engine, WOT and carbs ON the bike

All four are more or less equal. That's fine.

Kidonaclassicbike wrote:Will having the CV carbs on the bike while testing show 30-40 PSI lower compression readings ?

Compression tests are done at open throttle. For CV carbs, one would have to lift the pistons manually, too. Without that, readings will be lower. :wink:

For me your engine seems all right from the compression side. It should run somehow at quite close to full nominal power if everything else (ignition, carbs) would be fine.
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

Kidonaclassicbike
Posts: 16
Joined: Wed Mar 30, 2016 7:51 am

Re: 1981 CB650 #1 Cylinder not firing

Postby Kidonaclassicbike » Fri Jun 17, 2016 9:00 am

Had a friend clean the carbs out and adjust them by the book. That got all 4 cylinders running strong. The Bike still does not rev up when the Air Box cover is on there. Buddy says its running lean with the cover off, so I ordered 125 jets to replace the 120.

It idles at 1500 when warm now. That is a bit high, should i worry ?
I noticed buddy did not put the Black plastic screw on the bottom which adjusts the idle, so I cant even adjust it.

I rode it through downtown yesterday sitting in some traffic. It did not seem to be bothered by sitting in traffic.

Kidonaclassicbike
Posts: 16
Joined: Wed Mar 30, 2016 7:51 am

Re: 1981 CB650 #1 Cylinder not firing

Postby Kidonaclassicbike » Mon Jun 20, 2016 6:27 am

I am blind. The black adjustment screw is there. I adjusted the Idle and its all good now.

Bike runs like a champ. I am riding it around almost every day now no hiccups. I am curious to see if it runs even better with the new jets.

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1981 CB650 #1 Cylinder not firing

Postby Volker_P » Tue Jun 21, 2016 2:29 am

Good to hear you solved it. :)
The CB650 typically runs on the lean side, so probably no urgent need for the 125 jets. Depends however on altitude etc., so finally a question how your plugs look like. A bit of white is still all right.
I would expect you mpg will reduce a bit with the 125's.
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


Return to “Technical Discussion”

Who is online

Users browsing this forum: No registered users and 36 guests