Engine issue - need opinion


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Skyguy
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Engine issue - need opinion

Post by Skyguy »

I posted this issue previous and was incorrect in stating that the issue was cleared up. I guess I really didn't test it throughly after I posted it was fixed...Dang! Same issue

So my 1980 engine in my CBX has been giving me the fits. It starts and idles perfect, no issues. It's when it revs above 3500-4000 RPM it balks and stutters. It will rev above that but it's rough at best. It's not the mystery Honda Pulser as they are gone with the installed Dyna-s ignition.

- Compression is average to good across the board, (158 to 171)

-Ignition is timed at 10 degrees BTDC exactly and the advancer works.

-Plug wires are brand new.

-All spark plugs can jump a 5 mm gap with a plug tester.

-All spark plugs are new and gapped correctly.

-All coils register at 3 OHMs plus.

For now I am ruling out the ignition system and compression.

-The carbs have Been carefully cleaned, (twice) according to Mike Nixons directions.

-The pilot systems and jets and passageways all spay fine when aerosol applied. *these carbs were totally rebuilt by Mike about 4 years ago.

-The leak down test reveled only # 4 with a slight "Hiss" (borderline green & yellow Band) from the exhaust. About 25% loss. The others were all about 10-15% loss.* Could this almost failed leak down on one cylinder cause this issue?

-The carb boots appear to have no cracks and seal good.

-The gas cap vent is a non-consideration as I use a suspended Auxiliary Fuel Tank gravity gas tank.

-The air cleaner boots appear to be good with no cracks, (Doubt either boots with cracks would cause it to run this bad.)

-The exhaust is a pipe master exhaust and is in near perfect shape, no clogs.


I'm thinking carbs....Again. I tried the "Tee-shirt test" on the intakes and it was inconclusive. Although I cleaned all the jets and made sure the jet passageways were clear, I can't help but thinking with the complexity of these carbs that it's time to roll the dice on a full up carb job.

Video of issue:

https://www.youtube.com/watch?v=GR0TQqk ... e=youtu.be

What would you do?

Thanks in advance, Again!


Sky

CBX-tras
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Re: Engine issue - need opinion

Post by CBX-tras »

Airbox or pods?

In the video, it sounded like a dead miss to me.

daves79x
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Re: Engine issue - need opinion

Post by daves79x »

You have ruled out the component most likely to be your problem - The Dyna ignition. Sounds like you might be dropping a pulse unit as the bike warms up and revs up. It has happened to several of the Dyna units. If you have the stock components, I'd put them back in and see what you have. A bit of trouble, but not much compared to what you've been doing.

Dave

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Re: Engine issue - need opinion

Post by Skyguy »

CBX-tras wrote:
Wed Jan 06, 2021 8:22 am
Airbox or pods?

In the video, it sounded like a dead miss to me.
Pods.

CBX-tras
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Re: Engine issue - need opinion

Post by CBX-tras »

Skyguy wrote:
Thu Jan 07, 2021 11:36 am
CBX-tras wrote:
Wed Jan 06, 2021 8:22 am
Airbox or pods?

In the video, it sounded like a dead miss to me.
Pods.
Using pods dramatically alters the vacuum signal necessary for proper CV carburetor function. Not to say that it can't be tuned out with slide needle shimming and changing jets but, that can be a crap-shoot.

Even using a K&N filter can do this.

Chances are, if you re-install the airbox and a paper filter, your problem will go away.

daves79x
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Re: Engine issue - need opinion

Post by daves79x »

OK - you said in your opening post that the 'air cleaner boots appear to have no cracks and seal good'. That obviously implies you are running the stock airbox. Thanks JR for ferreting out that you indeed are NOT running the airbox, but are using pods. As JR said, until the carbs are jetted correctly for those pods, the bike will never run close to right.

You said Mike Nixon rebuilt the carbs. Did he know you were running pods when he did the rebuild? If not, then you aren't jetted nearly rich enough. You said it was an '80 engine - are the carbs '80 also (VB62) or '79 (VB60)? or maybe '81-'82 (VB64)? I can get you close on pod jetting for any of those, so can JR or Mike.

But as JR also said, the bike will never run as smoothly and cleanly with pods as it will with the stock airbox.

Dave

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