Topic: Advice Needed: Hesitation/Bucking on 73CB500 (no idea where to begin)

[etout00]

Hi All,

I completed a full tear down and rebuild of a bone stock 73 CB500 that was in fairly great shape to begin with (not a basket case restore by any means).

I took the bike down to the bare frame and did full nut/bolt rebuild/restore. After putting it all back together, I took it out for its first ride, after about 35 miles the bike began to hesitate/buck/sputter at about 40 mph and then completely shut down. Luckily I was right by my house so I just walked home and installed a new set of plugs thinking the bike had fouled the plugs. The plugs looked fine, so I attempted to start the bike and was successful, however it bucked/hesitated the whole ride home.

I assumed it must be a fuel starvation issue or a venting issue with the fuel cap. So I took the fuel cap off and verified that it was venting properly (soaked in Metal Rescue just to be safe). I next moved onto the carbs as those were the only thing on the bike I did not take apart during the restoration as the bike was running good prior to the cosmetic restoration.

None the less, I pulled the carbs and performed a full rebuild this time. All the jets/seats/floats are genuine Keihin and the carbs were in nearly immaculate condition inside. I pulled the jets and seats to be sure and cleaned them manually and reinstalled. The carbs were bench synced before being put back on the bike.

After installing the carbs today, the bike started up and idled correctly and a used a Morgan Carbtune Pro to sync all the carbs.

Upon the first test ride today the bike is doing the SAME thing as before the carb rebuild/clean....bucking/hesitating while driving, all gears, all RPMS above an idle.

I honestly don't know where to begin.

Here is what was replaced during the full bike rebuild/restore that is related to Fuel/Ignition:

- New Magna 5 ohm Coils/Caps and Plug wires (http://4into1.com/magna-5-ohm-coils-and-caps-honda-cb350f-400f-500k-550/)
- New NGK D7EA spark plugs (verified gaps)
- New Honda OEM petcock (original had a slow drip)
- New Honda OEM Air filter (completely stock air box set up)
- Brand new Repo 4into4 OEM-Style Exhaust (From CMS)
- All New Genuine Honda Carb gaskets
- Clean genuine Keihin jets Slow#40/Main#100(Stock set up)
- Verified and set floats to correct height
- TEC Ignition Points plate looks to be brand new (was installed when I bought the bike)

I have verified the plug gaps, cam chain tension, valve clearance, verified fuel is flowing thru the petcock.

The bike idles fine, but hesitates/sputters/bucks under any form of load.

I have replaced/verified just about every nut/bolt and part on the bike. What would cause the bike to suddenly hesitate/sputter/buck after 35 miles on a test run and no change in condition after a full carb rebuild and Carbtune sync?

Is this a timing issue, a fuel starvation issue, carburetor issue, ignition issue?

[TwoTired]

Check the center electrode insulator for a black carbon deposit coating.  This will make spark intermittent.

Is your choke detent working and keeping the choke off while riding?

Could you have an intermittent connection in your ignition circuit?

Check the point condensers.  Aged condensers can fail.

Do the spark plug deposits look the same as all the other cylinders?

Cheers,

[BomberMann650]

I'll hedge my bets on a dying condenser.

[etout00]

Thank a for the replies. Would an ignition problem (dying condensor) cause the bike to idle ok and start up fine, but buck/hesitate/stall under any load?

I was planning on changing to a DynaS ignition. I'd be more apt to order one today if Tosca chance these problems are ignition related and not fuel related?

[BomberMann650]

Many here run Pamco ignitions.  The dyna's have been trouble.

The cost compared to a couple OEM condensers is comparable.

[etout00]

Many here run Pamco ignitions.  The dyna's have been trouble.

The cost compared to a couple OEM condensers is comparable.

I'm not sold on any brand in particular, whichever has the best reviews, if Pamco is it, I'm good with that brand.

If this issue truly is a points/condenser issue, I'd rather just replace the whole thing for electronic.

Im new to points ignitiond, so i may be asking obvious things (aplogies in advance). Does my symptoms sounds like a condenser issue though? I assumed it was fuel related, fuel starvation, carb related?

[etout00]

Check the center electrode insulator for a black carbon deposit coating.  This will make spark intermittent.

Is your choke detent working and keeping the choke off while riding?

Could you have an intermittent connection in your ignition circuit?

Check the point condensers.  Aged condensers can fail.

Do the spark plug deposits look the same as all the other cylinders?

Cheers,

When I rebuilt the carbs I verified the choke detent is working and even across all 4 carbs.

All 4 plugs looked like they were running proper, slightly tan electrode,  not sooty after that 35 mile run.

How can I verify if my condensers are faulty? I ask as the plate/condensers appear to be recently changed by the PO. I have no way to verify this, but the plate and internals look new, which is why I didn't bother replacing the ignition when I was rebuilding the bike.

[TwoTired]

The condensers are part of the capacitor family.  Therefore, you can test using a capacitance checker.
Capacitance checkers aren't in everyone's arsenal of tools.  So, the most common troubleshooting procedure is by substitution.

If the capacitors are weak, then so is your spark.  Spark demands are higher when the engine is under load.  And idling would be pretty low engine load.
It is possible that the symptoms you describe can be attributed to condensers. 
I think it odd that they would both go equally bad at the same time.  But, it's possible.

Condensers can be had for $9.  But, if you rather pay ten times that for electronic, it's your call.
All my SOHC4's still use the points system that the factory included with the bike.  I've no complaints about it.

Another thing you should check is a visual check of the, wires and caps when running in the dark.  If you find arcing in the dark, essentially spark energy leaks, you've found a problem that electronic ignition modules won't cure.  Insulation cracks will allow arcing.

I had symptoms you describe on my 74 Cb550.  Sure enough the wire insulation where it joined the coil was cracked.  Idled nice.  Sputtering power when driving.
Nice light show in the darkened garage.


Cheers,

[etout00]

The coils, plugs, caps and wires are all brand new. When I installed the coils I used dielectric grease in the coil sockets...its a long shot, but could that be causing a weak spark under load? I feel like I grasping at ideas here.

I have no issue installing a new electronic ignition and/or new condenser/points. I'm hoping there is some way I can verify this is the issue before I place the order though.

Also, if my static timing was off would this cause the bike to hesitate/buck under load even if it idles ok?

Here are some pics of my points plate. Anything blatenly wrong? (Entire plate/condensers appears to be new, Diatchi condensers by the way--installed by PO):

[etout00]

Video of points plate running....clearly I'm missing something, 1-4 arching, 2-3 not arching. In video, slight misfire at 10 sec:

Revving motor:

Is the arching caused by a poor ground? Frame was powder coated and wire harness is grounded in factory spots...i did not remove the powder coat on frame grounding points.

[evinrude7]

Video of points plate running....clearly I'm missing something, 1-4 arching, 2-3 not arching. In video, slight misfire at 10 sec:

Revving motor:

Is the arching caused by a poor ground? Frame was powder coated and wire harness is grounded in factory spots...i did not remove the powder coat on frame grounding points.

that's a starting point.  clean where the ground contact is. 

[etout00]

Video of points plate running....clearly I'm missing something, 1-4 arching, 2-3 not arching. In video, slight misfire at 10 sec:

Revving motor:

Is the arching caused by a poor ground? Frame was powder coated and wire harness is grounded in factory spots...i did not remove the powder coat on frame grounding points.

that's a starting point.  clean where the ground contact is.

I just sanded down the powder coat on the frame ground, applied dielectric grease and restarted motor.....arching at points still.

So what could be the cause of the arching? Bad condensors?

[TwoTired]

So what could be the cause of the arching? Bad condensors?

Yes.  Didn't I mention bad condensers, earlier?

These can go bad simply sitting on the shelf for 40 years.


I'm done...


Cheers,

[evinrude7]

...also, you need to very carefully inspect the ground wire at the ignition plate to insure it is not shorting out.

+1

[BomberMann650]

So what could be the cause of the arching? Bad condensors?

Yes.  Didn't I mention bad condensers, earlier?
These can go bad simply sitting on the shelf for 40 years.
I'm done...
Cheers,

Those are Daichi condensers.
Nor is the TEC logo on the plate.

Both are known troublemakers.

Go for the PAMCO if you want.

[etout00]

So what could be the cause of the arching? Bad condensors?

Yes.  Didn't I mention bad condensers, earlier?
These can go bad simply sitting on the shelf for 40 years.
I'm done...
Cheers,

Those are Daichi condensers.
Nor is the TEC logo on the plate.

Both are known troublemakers.

Go for the PAMCO if you want.

I agree, I misstated that the plate was TEC, it's been replaced at some point. I read up on several old posts aboit issues with Diachi condensers being terrible quality.

I'm placing an order for an electronic ignition setup...hopegully that'll fix my issue. I'll revise the thread once installed.

Appreciate all the advice

[Deltarider]

1. Verify correct installation,

I read up on several old posts aboit issues with Diachi condensers being terrible quality.

Yes, but bear in mind that most 'complainers' are repeating what has been repeated by others that have repeated... etc. Why not just swap condenser 1+4 and see what is does. Easy and cheap. I know others that don't have a problem with Daiichi points whatsoever.

[BomberMann650]

You're lucky delta.  I had a daichi go tits up in 1000miles after install.

[TwoTired]

Diachi appears to have poor quality control.  Which explains the variation in user experience.  The users have to do (and pay for) the quality control inspection, and absorb the cost of failed or out of spec components when encountered.  It's an accountants dream.  Sell your manufacturing problems to the end user.

Lots of products like that these days as the average consumer does not know how to recognize quality and generally won't pay anything extra for it.

It's an electrical part.  Warranty, if offered, is void when power is applied to it.  Can't prove you didn't over stress it?  No refund, No exchange.  Next customer!

[etout00]

I believe I can consider this issue corrected. New electronic ignition installed today, bike runs/idles great now...hesitation/bucking/stalling gone. It was bad points/condensers afterall...thanks for all the suggestions.

[Deltarider]

 

It was bad points/condensers afterall...

All four?!

[etout00]

It was bad points/condensers afterall...

All four?!

At least 2 points and one condenser.

[TwoTired]

I'm with delta. You only proved something on the point plate was bad.  You could have replaced the whole motorcycle and made the same conclusion.

You might have replaced just one condenser for ten bucks and been riding happily.
Since you went the shotgun approach, you'll never know.

Oh well, it's your money.  Or at least it was...

Cheers,

[etout00]

Whether it was one point, 2 points,a condenser, , both condensers, ect ....I was planning on converting to electric ignition either way, this issue just made my decision very easy.

I'm simply not interested in dealing with points/condensers; much props to those who do and enjoy it though.

[Stev-o]

Good to hear you got it sorted.   Do you do the paintwork on this bike?