CBF1000 => General Maintenance, Servicing, and Mechanical => Topic started by: NJD on 22 June, 2020, 10:44:15 PM

Title: Flapper valve modification, correct?
Post by: NJD on 22 June, 2020, 10:44:15 PM

So I've attempted the "valve flapper modification" after reading a few posts, and just wanted to check that I've done it correct (as simple a task as it is)? Put a screw into the pipe and covered it with tape to prevent it from rattling out, and some tape over the gold circle part on the inside of the air filter cover (not required, but just to prevent moisture etc).



I've attempted this modification because between 2,000-3,100 rpm at about 30 mph in second gear the throttle is very, very jerky; and often that's where I spent most of my time on the commute to and from work. I ride plenty of other roads at various speeds and gears, but a lot of the riding is inner city.

Its becoming increasingly annoying, and dangerous when I'm going down a road with a few bumps in and can't control a bike that seems to do its own thing. Very ON/OFF. If anything its actually slowing me down because there's little to no control.

I'm loosing the will to live because I've done everything in the almost one year that I've owned it beside valves (coolant, engine oil (twice), spark plugs, air filter, new chain, new tyres, lubricated throttle cable, cleaned all the brakes (many times over), lubricated both wheel axles etc). The only thing I haven't done is valves, but don't think they need looking at. It is high mileage at 57,000 but doesn't seem to be noisy. Reluctant to throw that kind of money for valve check at a bike I'm growing to hate.

Had an issue with starting on the sidestand warm or cold out of nowhere a few months after I got it that was overridden by sitting on it with the sidestand up and that seems to have vanished. Another quirk.

Went for a ride after doing the mod quickly and it seemed a little better but not a complete elimination. Will tell tomorrow as I was riding purposely to try and bring on the jerkiness.

I may book it into the shop to get the throttle lubricated and adjusted properly, and the chain (as simple as it is, just to be sure), before loosing my marbles all together and selling the bike when I can.

Literally just ON/OFF on a road with any slight bumps. Like riding a kangeroo. Pain in the arse.

edit: I should add this isn't all the time. Some days are fine, and its like another bike, but is a pain when the problems come back and make me want to put it into a hedge.
Title: Re: Flapper valve modification, correct?
Post by: alfau on 23 June, 2020, 12:33:06 AM
"Like riding a kangaroo." Whatever you do, 'Don't lose your rhythm'.

Fuel injector cleaner might stop the jerking, definitely worked for my bike. Takes a couple of tanks of fuel. Use it all the time.
For the Protocol Nazis. I am interested in the vacuum concept.

Title: Re: Flapper valve modification, correct?
Post by: NJD on 23 June, 2020, 11:02:16 PM
Just to expand for the person above.

Seems my issue is a common one, and is incredibly annoying given that my commute doesn't really go above 40 mph unless I take a detour to get some higher speed roads in for fun (which sometimes I do, but all the time wouldn't be practical). So in summary I have a lot of riding time to experience this issue.

Performing the "flapper valve modification" as per above did help, but isn't a total elimination. On the way to work, in perfect weather and most alert, I was able to roll off the throttle a little and find a sweet spot that basically eliminated the problem. Occurred slightly, but was manageable. The throttle felt lighter, perhaps meaning the bike was easier to pull along because there wasn't an in-house system (the flapper valve) fighting me for control.

On the way home, tired and just wanting it to work, it appeared a little more. Less tolerant of the jerkiness. Best one was entry onto a small roundabout and exit, has happened before mid corner banked over and made me think "this bike is going to kill me" way before I started this thread or started playing attention to the issue.

Problem with this issue is that you can't always control it. On tight windy roads filled with stones, or back lanes, there's no room to maneuver. Second gear at low revs is where I need to be for any possible hazards, road conditions etc. Which is what makes this dangerous, and on a bike with this much power having it turn the throttle ON/OFF on its own is a recipe for disaster.

In summary:

The problem is a "known problem spot" between 2,000-3,000 rpm. Plenty of threads on here to read how the flapper valve works, and why blocking it off prevents the bike from causing low down rev issues.
Removing all the slack out of the throttle cable seems to be recommended, so I'm going to try that next. Contrary to common sense, but will be interested to see how that works (you'd think you'd want to increase slack to make managing it easier). I'll take advice from those that have been here before and see where it gets me.

I think it varies from bike to bike, depending on how old it is and what has or hasn't been serviced/tried, but for me I'm able to pinpoint that in MY case the bike has been well serviced and that this is something on the bike glitching out at random intervals and is best "managed."

Won't be long before it gets flogged on if I can't solve it. Times too short to own s**t bikes.
Title: Re: Flapper valve modification, correct?
Post by: NJD on 24 June, 2020, 07:42:36 PM
Third and, hopefully, final update.

Popped down to my local bike shop to discuss the issue and he said at 57,000 miles it could be the throttle bodies. Quoting around 1000 to get them replaced (just your average garage, not even associated with Honda). Told me to get used to it, or ride around it; and in fairness if that was what it was %100 then I would given anyone with half a brain cell towards mechanical cost knows the words "throttle bodies" and "cheap" don't belong in the same sentence. I did a search on eBay and found used throttle bodies at an acceptable cost and banked the idea.

Having lubricated and adjusted the chain the jerkiness still remained.

Solution for me, for now: throttle adjustment.

Turned the engine on, loosened the locknut and adjusted the adjuster as many turns as it would towards the end of the thread (away from the handlebar) so that the throttle stayed open; and then turned it one complete turn (repeat) until I found on what turn it didn't stick open. Turning the handlebars on full lock to the right it stuck open for a couple of turns, and then finally I found the spot just before the throttle would stick on.

Important: if you are going to adjust the throttle yourself then make sure you rev the throttle, and let it snap shut on its own, with the bike on the centrestand and the bars at full lock to the left... in the middle (straight).. and full lock to the right to find the correct spot BEFORE going for a ride. I didn't do this ages ago when I fitted the heated grips and found myself at the side of the road with a red face.

And from there I managed a 60 mile ride on the hottest of days trouble free. I think I noticed a bit of to-and-fro once or twice, but nowhere near the level I had before.

So either I had the throttle adjusted with too much free play for the fuel injections like, or removing the throttle free play does mask the issue.

I remember buying the bike, replacing the grips and thinking the throttle free play was adjusted way too close; but now I think I was experienced the cold low down rev jerk caused by the flapper valve instead.

All's well that ends well.

Will update if anything dramatic occurs.


So low down jerkyness between 2,000-3,000 RPM when the engine is cold CAN BE caused by the flapper valve, and if it occurs when hot check things like chain adjustment and follow throttle adjustment as per above. Beyond that things to look at are all of your service items (spark plugs, air filter, coolant, engine oil, throttle lubrication etc).

Then you're onto more expensive things like sensors, throttle bodies, TPS etc (but I'd imagine you'd be getting fault codes for them).

Rusted earth points on the frame (under the tank) and on the ignition coils are other things I looked at during this.

Hope this helps if someone digs it up in the archives in the future.
Title: Re: Flapper valve modification, correct?
Post by: jm2 on 24 June, 2020, 11:42:48 PM
I don't think this has much to do with the air-box valve feed (unless faulty/worn).

At 57k you'll have bit of wear everywhere and, if you could, throttle body balancing would be a sound idea.  Far be it for me to mention the dreaded T word but defeating the throttle cable slack (which should be there) will have moved its position a little.  This may have moved the worn spot and your dead spot elsewhere (where it may be far less apparent).

Or your cables could just be knackered and warrant attention/replacement.
Title: Re: Flapper valve modification, correct?
Post by: NJD on 25 June, 2020, 12:45:35 AM
The flapper valve modification is something I should have done when I got the bike (under a year ago at 54k miles), but I didn't know about it at the time. I had low down jerkiness from cold that would last long enough into my commute for me to want to remove it, and I figured it was down to throttle adjustment.

I put new grips on, and when I did I don't think I did a good job at adjusting the throttle (perhaps carbed bikes I'd owned before are different, or perhaps I just did a bad job).

Today, with the flapper valve mod done and the throttle adjusted, I think I've finally re-set both to where they need to be to provide smooth running.

The cables were lubed several months ago (or a few thousound miles 54-57).

So based on where I'm at after today's pleasurable 60 mile ride I think I was experiencing a combination of low down from cold lumpiness combined with an ill-set throttle position.

If it reappears I'll know I have more serious issues, but I don't think there's anything majorly wrong with the bike beyond the normal service consumables.

At 100 miles of fuel for 9 litres return its certainly not showing signs of running badly.

Maybe now I can enjoy riding it, or you'll see a Honda in a hedge and more posts.  :008:
Title: Re: Flapper valve modification, correct?
Post by: Piper on 25 June, 2020, 04:23:24 PM
I did the flapper valve disconnect and took all the slack out of the throttle cables (except about 1 to 2mm as the method described in the manual but less slack of course) and it made a big difference to the jerking at the revs you describe. My problem was more between 2700 to 3000 rpm and it is still there a little but hardly noticeable. I did this about 20,000 miles ago and all still good. You mention the throttle bodies but I believe from reading this forum that its the throttle position sensor on the throttle bodies that can cause a problem of uneven running. Honda I understand only sell this as part of the throttle bodies but if you search this forum the sensor part (same as used on other vehicles) can be purchased quite cheaply online. 
Good luck. Pete.   
Title: Re: Flapper valve modification, correct?
Post by: NJD on 26 June, 2020, 10:47:21 PM
*Originally Posted by Piper [+]
Hi NJD...

Thanks for the response, nice to hear from someone direct who's suffered similar.

I waited to respond until I'd ridden again after my initial 60 mile pleasurable jaunt post adjusting the throttle position like you, and can report its as smooth as it was during that ride.

A lot smoother from cold for the first 1/4-1/2 of a mile leaving work (generally where it was most noticeable, and then of course are random intervals when engine warmed), which was nice. Went over some roads outside of the norm that were almost un-rideable before and while I could feel it at times a little bit the difference is way better. I think generally when I'm tired (ie: after work) it shows a little more because I'm not as focused, and therefore not as smooth. But honestly compared to before this is simply bliss.

There's a white dot beside the torx-head screw on the TPS so I'm not concerned about it having been messed with before, thankfully. The throttle body mention was what the guy at the shop had told me without putting a hand on the bike (listened to what I had to say). It may not even be that, but thank-you for the tip nonetheless.

I'll keep an eye on it, but initially it seems to have transformed the bike for the better.
Title: Re: Flapper valve modification, correct?
Post by: jm2 on 27 June, 2020, 01:24:51 PM
I wonder, now you've tweaked the tps and are happier with its running, how does it run with the air box valve reconnected and back in operation (as I suspect it is the tps all along).
Title: Re: Flapper valve modification, correct?
Post by: Piper on 29 June, 2020, 12:25:01 PM
Just re-read your posts and can't see the method of used to determine its new position when you adjusted the Throttle position sensor. Could you explain please just in case I get the same problem.
 Thanks Pete
Title: Re: Flapper valve modification, correct?
Post by: NJD on 29 June, 2020, 10:30:30 PM
I haven't adjusted the TPS, but rather the throttle itself using the adjuster / locknut on the cable coming of the R/H switch housing.

My remarks about the white dot on the TPS are to clarify that, as I understand it, they are factory placed markers; and that if they can't be seen then along the way in the bikes life its been messed with. It's advice I read on other posts (is there a white dot?).

Sorry if any confusion has inadvertently been caused.