4000rpm bog

Salman_z8
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4000rpm bog

Post by Salman_z8 »

New to me cbx1000 79’
Had sat for a few months before i got it, in very good condition.
The PO had it sitting without the airbox, but carbs were on and intake venturi’s sealed with tape.

Tank was like new inside.
A new battery and fresh gas, and it fired up and idled perfect once warm.

Airbox was put on, but i didnt have a filter or lid yet.

A little test run, bike ran good off the start, and would bog around 4k first gear. Ran through the gears, all seemed good.
I chalked it up to no filter and lid being present.

Fast forward, all the missing pieces on, bike runs better but still gets stuck at 4k, almost like a rev limiter.
My first thought was ignition, but since all ignition problems are usually carb problems, i am suspecting clogged jets ?

So before i yank those bad boys off, can someone else chime in if i am on the right path. But in my experience if it was an ignitor issue, the cylinder would either be dead, or die as it would fail ( temp or whatever ) not fail at a certain load, correct ?

Have a tiny oil leak, but thats irrelevant at this point.
The rest of the bike is actually too good for what i had expected.
One day, i’ll have em all finished.

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

Might add, i have a fair bit if carb experience, just dont want to be tilting the engine and fighting the carb manifolds unnecessarily.
Thanks
One day, i’ll have em all finished.

tevan
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Re: 4000rpm bog

Post by tevan »

I would check your advancer. Make sure it operates smoothly. Simple check.

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bobcat
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Re: 4000rpm bog

Post by bobcat »

If adding the filter and air box lid made it better, it sounds like a lean mixture condition.
Is the filter a paper or other aftermarket ? If the bog (or stumble?) begins at 4000 rpm
it's not likely to be the slow (pilot) jets which would be the first to be clogged from sitting
too long.

Also, do you know what the PO had done to the carbs, if anything ? New tank ?
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

No history on the carbs, but the bike starts, and idles perfectly.
Accelerator pump works the way it should.
It sounds exactly like it hit the rev limiter.

Air filter is oem, and with new oem foam from louis.
One day, i’ll have em all finished.

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

The slides, if i remember correctly, all seemed to fall at the same rate once lifted.
I have always had pilots clog, while the main being bigger is almost never an issue on conventional carbs.
One day, i’ll have em all finished.

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

tevan wrote:
Thu Jul 14, 2022 6:09 am
I would check your advancer. Make sure it operates smoothly. Simple check.
Will do that
One day, i’ll have em all finished.

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

Tank is original, repainted in some yellow. But pristine inside
One day, i’ll have em all finished.

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NobleHops
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Re: 4000rpm bog

Post by NobleHops »

Here’s a little tutorial on servicing the advancer.

https://www.facebook.com/media/set/?set ... 039&type=3
Nils Menten
Tucson, Arizona, USA '80 CBX, sort-of restored :-)

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

NobleHops wrote:
Thu Jul 14, 2022 11:19 pm
Here’s a little tutorial on servicing the advancer.

https://www.facebook.com/media/set/?set ... 039&type=3
Thanks alot
One day, i’ll have em all finished.

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

Salman_z8 wrote:
Thu Jul 14, 2022 2:02 pm
tevan wrote:
Thu Jul 14, 2022 6:09 am
I would check your advancer. Make sure it operates smoothly. Simple check.
Will do that
Advancer is nice, clean and smooth.
One day, i’ll have em all finished.

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bobcat
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Re: 4000rpm bog

Post by bobcat »

This is a long shot but remove a float bowl and check to see if the primary and secondary
main jets have been installed backwards, switched by error. I've seen it before and it would
run exactly as you describe. Check the plugs first. If the jets are switched the plugs will be black
or very dark.
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

bobcat wrote:
Fri Jul 15, 2022 9:26 pm
This is a long shot but remove a float bowl and check to see if the primary and secondary
main jets have been installed backwards, switched by error. I've seen it before and it would
run exactly as you describe. Check the plugs first. If the jets are switched the plugs will be black
or very dark.
So i guess the carbs will be coming off then ?
Is there enough room to get a bowl off while mounted ? Doesnt seem like it.

I will pull em next week, if there is anything else, please feel free. I hate tilting the motor
One day, i’ll have em all finished.

Salman_z8
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Re: 4000rpm bog

Post by Salman_z8 »

bobcat wrote:
Fri Jul 15, 2022 9:26 pm
This is a long shot but remove a float bowl and check to see if the primary and secondary
main jets have been installed backwards, switched by error. I've seen it before and it would
run exactly as you describe. Check the plugs first. If the jets are switched the plugs will be black
or very dark.
So i guess the carbs will be coming off then ?
Is there enough room to get a bowl off while mounted ? Doesnt seem like it.

I will pull em next week, if there is anything else, please feel free. I hate tilting the motor
One day, i’ll have em all finished.

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bobcat
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Re: 4000rpm bog

Post by bobcat »

Check the plugs first ! You should be able to get no.6 off without too much trouble.
If you don't know the history of the carbs, there's all kinds of possibilities.

Edmonton, nearly 2200 ft. elevation, I doubt that it needs much, if any re-jetting.
Last edited by bobcat on Thu Jul 21, 2022 9:06 am, edited 1 time in total.
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

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