RPM ISSUES UPDATE

If it's broken or just needs tweaked

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Cresty
Posts: 8
Joined: Fri Aug 10, 2018 4:52 pm

RPM ISSUES UPDATE

Postby Cresty » Fri May 03, 2019 6:06 pm

As I posted a couple of weeks ago, I was having rpm issues with my 81 CB650C. Any RPM over 4700 the engine would start to miss and cutout until the rpm is reduced. Any rpm below that the engine operated find, at idle or hard acceleration up to 4700 rpm. Thanks to the members who suggested area of problems I could explore. Today I removed the engine air filter, which was an K and N brand and all my rpm issues went away. The filter came on the bike that had been setting for many years. As I went through the engine I cleaned and inspected that filter and thought it would be serviceable. So my problem was due an air volume problem at high rpm. I was wondering if any other members are able to use this filter on their bikes? It's expensive and used in a lot of applications.

wely
Posts: 5
Joined: Wed Mar 23, 2016 7:45 pm

Re: RPM ISSUES UPDATE

Postby wely » Tue May 07, 2019 6:04 am

You can wash them and re-oil and reuse but test again to see if the curb is dialled right for these filters, it seems it’s if if run ok without them.


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Volker_P
Posts: 5365
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: RPM ISSUES UPDATE

Postby Volker_P » Thu May 09, 2019 1:09 am

Thanks for the Feedback. :)
1981CB650C should have the VB/CV carbs so it is interesting to hear that K&N make the bike cut off even below 5000rpm.
Do I understand correctly that it runs fine without any air filter?
Or do you run the stock air filter now?

BTW, it would have been more useful to just continue the initial thread so it is easier to track for someone else later. :wink:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

Cresty
Posts: 8
Joined: Fri Aug 10, 2018 4:52 pm

Re: RPM ISSUES UPDATE

Postby Cresty » Thu May 09, 2019 4:25 pm

Yes the bike runs fine now without the K & N filter. I have a paper filter on order and will install it when received. The engine was running way rich at rpm above 4700 rpm and I noted that my miles to gallon has increased quite a bit. Hope the filter was my problem and we will see when I install the new filter. I don't know if the K & N filter was every produced for the CB650C or whether some one was trying to use it. Like said before it is expensive and used in serval applications.

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Volker_P
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Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: RPM ISSUES UPDATE

Postby Volker_P » Fri May 10, 2019 12:43 am

It is not really recommended to run without an air filter.
Moreover as K&N are typically reported to be less restrictive than stock air filters be not too surprised if it is the same again or even worse with the paper filter you just ordered.
In this case check your choke flaps position and main jets.
What's your mpg now?
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

Cresty
Posts: 8
Joined: Fri Aug 10, 2018 4:52 pm

Re: RPM ISSUES UPDATE

Postby Cresty » Wed May 15, 2019 3:56 pm

Installed the paper engine air filter and took the bike out for a ride. The engine ran great and performance was prefect. The K & N filter will not work in this bike for some reason. Air flow to the engine was my problem, problem solved. Thanks for all the comments and suggestions.
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