Jump to content

VFR Slow to rev and bad low end response


Recommended Posts

The VFR800 has a lot of mechanically actuated things supplemented by electrical sensors.  I recently had to grapple with power hesitation, followed by sudden acceleration, then later engine dying on me.  It also was slow to rev and didn't want to rev above 7k.  I thought it was all mechanical but it turns out it was my Start/Stop Switch had gone bad.  But not until I had replaced quite a few things related to fueling.  

 

Sometimes air cooling and carburetors are so much easier to diagnose!

Link to comment
Share on other sites

  • Member Contributer
15 hours ago, Urbanengineer said:

Huh! I wondered about that. Thought it was another symptom of my mechanic skills failing to check the VTEC unit or something... turns out the ECU tells it when it's okay to open up VTEC vales when building temp. Thanks for the knowledge.

 

I'll test the flapper tomorrow by putting the bike in gear. These bikes have a lot of stuff that could go wrong. Technology, folks! 

 

I appreciate your replies Terry.

If you want to test the flapper at a standstill you can just pull the neutral switch wire off the post on the right side of the motor, that way when the gearbox is in neutral the ECU will think it is in gear and allow the above/below 5500 rpm flapper operation. 

 

All machines are a set of individual systems that interact; you just need to understand the logic of what is meant to be happening when attempting to diagnose a fault, and that is where forums like this come in handy. I've certainly picked up plenty of info over the years.

Link to comment
Share on other sites

So, slow rev down issue seems to be fixed, as I had a cracks in many 5/8” vacuum hoses. I replaced 7’ worth of hoses today between the MAP lines, the exhaust splitter lines, the “FPR” lines, and the vacuum chamber / flapper hoses. 

 

Now im getting some exhaust gases through cylinder 3 😿cylinder. It has to be the valve adjustment because it’s only when I get on it when the bike is cold. One more check I suppose 👀

Link to comment
Share on other sites

  • Member Contributer

When combustion returns through intake ports, it's valve adjustment, or out of time cams.

If it's valve adjustment it normally only happens when engine is hot (unless it's really out), as expansion of valve stem and cam shaft closes the gap and stops valve from fully closing.

Make sure your cam timing is correct.

 

Link to comment
Share on other sites

  • Member Contributer
1 hour ago, Urbanengineer said:

Interesting. I'll pull the cover and provide pictures on Tuesday. It would *be nice* if it ran perfectly before I put it back together. Thanks for the direct reply. 

 

If it was timing might cylinder 1 also have an issue?

Cylinders 1 and 3 use the same cams, so if the timing is out it will affect both. If the valve clearance is off it can affect just one. There should be some easy to see lines scribed on the cam sprockets that will align with the cam cover face when the crank is aligned properly to a timing mark. These are from my VTR but the principle is the same. 

IMG_1341.JPG

Link to comment
Share on other sites

Yep. For the rear cylinder it’s RE on the front cam and RI for the rear cam. Those lines line up with the head and it’s supposed to be good. I thought I checjed it but maybe I was wrong 😕. I’ll check again (im getting good at this process).

 

as for this adjustment it is not affecting the VTEC valves so it must be the regular two valves on that cylinder. Ill check those again.

Link to comment
Share on other sites

  • Member Contributer
11 hours ago, Urbanengineer said:

Yep. For the rear cylinder it’s RE on the front cam and RI for the rear cam. Those lines line up with the head and it’s supposed to be good. I thought I checjed it but maybe I was wrong 😕. I’ll check again (im getting good at this process).

 

as for this adjustment it is not affecting the VTEC valves so it must be the regular two valves on that cylinder. Ill check those again.

 

Never done a valve check. But.. For the rear cylinders 1 & 3, wouldn't the cams be RE exhaust at the Rear and RI intake at the Front.?

Link to comment
Share on other sites

Yeah lol I wrote it while in a meeting at work. Checked today and it's accurate. Whatever it was that was causing that exhaust thing is gone, bike runs very well now. IDK... Sometimes bikes need a good beating to get back into operating condition I guess.

Link to comment
Share on other sites

  • Member Contributer
3 hours ago, Urbanengineer said:

Still need to test the flapper valve but it seemed to be not operating from earlier testing. Will pull the neutral switch tomorrow and go from there.

 

Hardly worth worrying about IMO. As long as all the Vaccum hoses attached to the system aren't leaking. No wonder Honda got rid of the whole system on the 2017 8 gen.

Glad your bike is running well at last.

 

Link to comment
Share on other sites

Carb sync tool on order now for delivery Thursday. Wouldn’t it be funny if the carb/TB sync was worlds off?

 

It would make me feel silly, that’s for sure. Would explain the slow revving. I have an old Honda that needs some diagnostic work so it made sense to finally buy a set of these carb sync tools. $75 after tax. 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy.