Topic: Engine Missing While at Cruising Speed (1981 Honda CB650C)

[F16Viper68]

What service repair manual are you using??
 I think those are good compression #'s;was it a warm engine? & did you hold the throttle wide open w/ the choke butterflies wide open ?
Fresh plugs and a strong ride will give you a more accurate plug reading.
Did you adjust your cam chain? also check your spark advancer mechanism,it has centrifugal weights & springs and needs to return to base timing under a certain rpm, sometimes the weights jamb up a bit or get worn,or the springs need some tension; the pivot should be lubed w/ a thin coat of high temp lube.

I'm using the OEM service manual and Clymer's.  The engine was cold when I took those readings and yes I held the throttle wide open while cranking.  Yep, adjusted the cam chain and checked/lubed the advancer.  I lubed with WD-40 but I'm going to pull it apart again later and lube properly.

Thanks for all the suggestions.  Tomorrow I'm going to run it at night and see if I see any arching.  I have a set of wires from another CB650C I'm going to play around with.

I've been researching resistive sparkplug caps and wires.  This part is all new to me. 

Dave...

[RustyStuff]

Ok, one thing I never checked on this bike (stupid) is are all the spark plug wires setup correctly.  I discovered someone in the past had crossed up the #2 and #3 wire.  Interestingly enough it didn't make a whit of difference on how the bike idles, rides, or accelerates.    What in the world...

Also, today while riding (can't do this on my Wee Strom) I removed the #1 wire and noticed a big loss of power.  Same thing with #4. 

Later tonight I'm going to pull the plugs and see how they are doing. 

Dave...

Thats amazeing, on my bike if you pull one wire it wont hardly run!

[grcamna2]

What service repair manual are you using??
 I think those are good compression #'s;was it a warm engine? & did you hold the throttle wide open w/ the choke butterflies wide open ?
Fresh plugs and a strong ride will give you a more accurate plug reading.
Did you adjust your cam chain? also check your spark advancer mechanism,it has centrifugal weights & springs and needs to return to base timing under a certain rpm, sometimes the weights jamb up a bit or get worn,or the springs need some tension; the pivot should be lubed w/ a thin coat of high temp lube.

I'm using the OEM service manual and Clymer's.  The engine was cold when I took those readings and yes I held the throttle wide open while cranking.  Yep, adjusted the cam chain and checked/lubed the advancer.  I lubed with WD-40 but I'm going to pull it apart again later and lube properly.

Thanks for all the suggestions.  Tomorrow I'm going to run it at night and see if I see any arching.  I have a set of wires from another CB650C I'm going to play around with.

I've been researching resistive sparkplug caps and wires.  This part is all new to me. 

Dave...

It's hard to beat Original spec when it comes to those ign. H.T. leads.

[F16Viper68]

I have a new set of plugs (the ones in that pic are new too) that I'll drop in this weekend before I take it for a long ride.  That should at least give me a real indication of how my mixture is set.

It's now insured by Geico ($49 per year  ) and should have a plate tomorrow. 
Dave...

[grcamna2]

Dave,
    You've got excellent motivating forward progress...we're going to win on this one;you must be a very safe driver w/ 0 accidents because that's the best rate on insurance I've ever heard of,especially for a 650.

I would keep an eye on where you have your CB650 parked though...you wouldn't want it to go "missing" on you before you get the problems fixed .

[F16Viper68]

Dave,
    You've got excellent motivating forward progress...we're going to win on this one;you must be a very safe driver w/ 0 accidents because that's the best rate on insurance I've ever heard of,especially for a 650.

I would keep an eye on where you have your CB650 parked though...you wouldn't want it to go "missing" on you before you get the problems fixed .

That price is for liability only.  I just can't see spending the extra money for a bike that's "worth" $1,000.00 with a $500 deductible. 

I've been thinking about getting the rotors drilled so I can put on a disc lock.  I'd be more than annoyed if this thing turned up missing.  I love my V-Strom but if that thing disappeared I could replace it tomorrow.  Now the Russell All Day Long seat would be sorely missed.  That thing was custom made and took a long time to break in. 

My gut is telling me this is an ignition issue.  I'm going to swap out the plug and put the spare set of wires I have on it.  Still lost how you can swap the #2 and #3 wires and it makes no difference. 

Dave...

[grcamna2]

I believe that cyl's.# 2 & 3 fire at the same time. I'm just guessing about your problem of "rough running"?? in the low to midrange rpm's...do I have that right ?
I've found most of the times that carburetion seems to be the biggest problem;have you tried checking the carb float heights w/ a float level gauge ? most of the time those plastic floats are right on,but it never hurts to double check. It could be "stuttering" from having it a bit rich also;that ride will tell you a lot about your jetting w/ the plug color.Have you ever tried posting one of those youtube videos complete with sound ?
How are your carb slides? if they are the CV carbs...the carb slide chambers and pistons need to be real clean & operating very smoothly;clean all 4 real well and check for smooth operation and re-synchronize your carbs at operating temp w/ gauges if you have them...if all the other things haven't fixed the problem that is.

[F16Viper68]

I believe that cyl's.# 2 & 3 fire at the same time. I'm just guessing about your problem of "rough running"?? in the low to midrange rpm's...do I have that right ?
I've found most of the times that carburetion seems to be the biggest problem;have you tried checking the carb float heights w/ a float level gauge ? most of the time those plastic floats are right on,but it never hurts to double check. It could be "stuttering" from having it a bit rich also;that ride will tell you a lot about your jetting w/ the plug color.Have you ever tried posting one of those youtube videos complete with sound ?
How are your carb slides? if they are the CV carbs...the carb slide chambers need to be clean & operating very smoothly.

I didn't check the float heights since they can't be adjusted but when I pull the carbs to install the t-fittings I'll check them to ensure they are within spec.  I know they don't have fuel in them and slides are good.  I'll post up some video this weekend.  I spent took my time ensuring the carbs were clean and everything was working correctly. 

Works going to keep me away from that thing for a few day which honestly isn't a bad thing.  My checkbook will thank me.   

Dave...

[grcamna2]

It's good to get away from it for a while....and then go back with "fresh eyes".

[dave500]

those plugs are fouled,use 7s. and a few more revs?if you have a multi meter look for 5kohm through the plug caps,if they are as old as the bike they will be worth replacing anyway.

[w1sa]

I have a bike (cb900) that began doing that to plugs (just as in your photo)....I think it has the same ignition set-up as yours(and just as old)......Initially, I did the carbs (several times), valve clearance checks, plugs, caps and wires, timing, advance, pulse generator gaps, I expect all the regular tune-up stuff.   Progressed to a fresh battery...things seemed to improve for a bit before degrading to lower depths...then experimented with hotter plugs, leaner idle mixture settings....didn't really fix the problem............ until I upgraded the ignition.
So, (as many would say) you can spend a lot of time searching and hunting down running problems 'caused by the carbs' only to eventually find the main problem in the wiring, charging and/or ignition system.

If you have verified wiring, charging and battery as good, and there is nothing obvious  found in the ignition system, look for an opportunity to test/compare with ignition components (like coils, spark units, pulse generators) that are known to be good.

[grcamna2]

To go along with what wtsa says it helps to make sure all of your switch connections are clean and making good electrical contact all the way through the wires that run the entire ignition circuit;plus clean metal to metal "shiny" ground connections .

[F16Viper68]

I have a bike (cb900) that began doing that to plugs (just as in your photo)....I think it has the same ignition set-up as yours(and just as old)......Initially, I did the carbs (several times), valve clearance checks, plugs, caps and wires, timing, advance, pulse generator gaps, I expect all the regular tune-up stuff.   Progressed to a fresh battery...things seemed to improve for a bit before degrading to lower depths...then experimented with hotter plugs, leaner idle mixture settings....didn't really fix the problem............ until I upgraded the ignition.
So, (as many would say) you can spend a lot of time searching and hunting down running problems 'caused by the carbs' only to eventually find the main problem in the wiring, charging and/or ignition system.

If you have verified wiring, charging and battery as good, and there is nothing obvious  found in the ignition system, look for an opportunity to test/compare with ignition components (like coils, spark units, pulse generators) that are known to be good.

Can you tell me what you did to upgrade the ingition?  I've seen some threads about using GM auto parts on the CB's. 

Dave...

[F16Viper68]

To go along with what wtsa says it helps to make sure all of your switch connections are clean and making good electrical contact all the way through the wires that run the entire ignition circuit;plus clean metal to metal "shiny" ground connections .

That's something that will be addressed in a month of so when I take it apart for frame/engine painting.

Dave...

[w1sa]

I installed the 4 pin gm hei modules and I also chose the Dyna .5 ohm miniature series coils as replacements for the 30yr originals............... I went with the 1/2 ohm coils because they seemed the most successful/tested/orig spec item to suit the hei. I chose the Dyna because it was compact and fitted up to the original mounts/location (albeit at slightly red spacing, one drill hole)....................... apparently original spec coils can be used, but I'm not familiar.............the hei/coil combination I'm using works great with the original pulse generator/pick-ups which I didn't touch..........The average load on the electrical system (calc) is similar to the original oem set-up (these oem ignitions have a short dwell)......using oem spec plugs @ 1mm.......engine starts well, pulls strong right thru rev range, burns fuel well (consumption according to original  tests of the day) etc.........all subject to long term performance/reliability, of course, which I will continue to check...............well worth exploring as an option.   

[F16Viper68]

Before I took to the road for my first ride outside the neighborhood, I put in new plugs and installed a different set of wires (tested all at 5k ohms).  The bike did really well once it was warmed up.  It ran really smooth and pulled strong till the very end of the 30 mile trip. 

I was heading to home and I noticed at 55mph / 4k RPM the engine started to stumble.  If I cracked the throttle at all it nearly stalled. This is very weird because prior to this I had no issues getting the engine to pull up to 6k RPM while going through the gears.  I wasn't able to take the bike back out to see if this condition stayed.  I know it has plenty of gas because I hit the gas station at the beginning of the trip.  Unless it's getting 10 miles per gallon...

I did quickly pull the #1 and #4 plugs and they looked perfect.  If anything a little too white. 

Dave...

[dave500]

ignition module?

[F16Viper68]

ignition module?

At this point I'm not exacting sure what is going on but I'm going to take it for another ride today to see if I can duplicate the issue.  But I do think the GM HEI upgrade is in my future.

Dave...

[Hush]

My guess would be cracked carb isolators that are fine when cold but leak air into the system once they heat up and become flexible, this would explain your lean (white) plugs. A quick fix or test is to spray a coating over the isolators and see if the situation improves.
Also check the cable that goes to your choke, I owned an 82 CB650C and I experienced similar issues and found it was an incorrectly set choke cable that had "moved" after installation causing the choke butterflies to be slightly engaged and thus ruining any chance of correct tuning.

[F16Viper68]

Hush thanks for the advice.  I do know it's not the carb insulators because they are new.  I bought new insulators and bands to address leaks like you describe. 

Yeah, I took it for a ride today and it's like someone installed a rev limiter at 5k RPM.  I can easily get to redline if I'm just sitting still but under load it just sits there and stumbles at anything over 5k RPM's. 

The plugs are really white so I'm assuming I'm fighting a lean condition?  What causes a lean condition at speed?  Does the idle mixture come into play at higher RPM's?

Dave... 

[bender01]

Fuel line plugged or routed incorecctly? Have you had the petcock off the tank?

[F16Viper68]

Fuel line plugged or routed incorecctly? Have you had the petcock off the tank?

The fuel line is new and clear. The petcock is new. What do mean routed incorrectly?

[w1sa]

Fuel line plugged or routed incorecctly? Have you had the petcock off the tank?

The fuel line is new and clear. The petcock is new. What do mean routed incorrectly?

+1      ........also check fuel cap venting.... clear tube test of carb bowl fuel levels....., open drain test of fuel flow thru the carbs.

[Hush]

OK I have had this problem before on my 79 CB650Z, the auto advancer had rusted stuck closed and even at max revs the bike wouldn't accelerate it was like governed. Remove the electronic pick-ups on the right side of the motor and behind there you will find the mainly forgotten and negelcted auto advancer mechanism. Take it apart and clean/de rust it then lightly oil the small axles that the weights swing on.
I found I could actually get my old girl to wheel stand once I fixed this up.
If it's not this then I'm out of ideas.

[Spanner 1]

+1 on the tank vent. Nothing wrong except low/slow fuel delivery IMO..... Tank vent and/or fuel line routing. If ign. prob. would show-up before 30 mile run ! Carb settings all good but plugs white?... lack of fuel level in carb bowls..... usually the solution is more basic than imagined  ... that's been my exp. anyway with running probs.