Honda Motorcycles - FireBlades.org banner

1 - 18 of 18 Posts

·
Registered
Joined
·
78 Posts
Discussion Starter #1
Folks, I’m creating this as a ‘searchable’ solution to a problem I’ve recently had in the hope that it might benefit some other frustrated amateur (or maybe professional) mechanic....
Please let me know if you think it should reside somewhere else or in a different form.....eg. is there an easily found archive of common problems and solutions somewhere on this site or on the net?
The key of course is to make it easily found by a searcher.

The problem
In this case I’m referring specifically to Honda CBR900RR 929 & 954 but this may be relevant to other bikes. It has certainly been documented as a problem by a number of people so I believe worthy of record.
Engine starting as normal and ticking over for a few seconds at around 2,000 rpm before a steady climb to alarmingly high revs (ie 4,000 plus rpm) on stone cold start. This is clearly undesirable with any engine and certainly not working as designed. Normal cold start should be in the range of 1,500 to 3,000 rpm dropping to between 1,000 and 1,500 once normal operating temperature is reached. In my experience this drop began at an indicated 36C on the gauge.

How it works
Because one of the key factors in the cold start process is coolant temperature affected, I would guess that in steamy Asia (where I’ve rarely ever used a manual choke) it would be different from in dear ol’ Blighty where we use some full choke all year round. The system will of course start from different temperatures.
On this fuel injected bike the traditional manual choke system is replaced with an automated system.
In its cooled state the ‘choke’ is always set to ‘On’. Coolant is fed around the wax element body and as the coolant temperature increases with engine heat a wax pellet expands and extends a rod which progressively moves forward. This rod is connected to an assembly which controls the starter valves. These piston like devices are in the top of the throttle bodies and dictate how much air is passed for both tickover & cold start (the throttle butterflys are fully closed when the throttle is at rest and therefore contribute no air at all).

The solution
On description of these symptoms the most common cause is stated to be the wax pellet being at fault. This could be the case and would indeed cause similar over revving if it failed to expand and close down the air by-pass tracts once warm.
My wax pellet was working as designed though... It can be tested by removing it from its body and standing it in cold water in an old pan. Put it on the heat and as it warms the steel pin will extend by about 5mm.
Problems with fuelling could also be caused by air ingress from a damaged pipe or other component. There are also a number of sensors feeding information back to the ECU which are relevant. I believe they were all working as designed on my bike though.
What appeared to be the problem on my bike was very simple (with the benefit of hindsight...).
All 4 starter valves are controlled together by the wax element rod. Number 1 starter valve is different in design from the other 3 and is factory set/non adjustable. My manual stated that the controlling rod must not be adjusted!!! Numbers 2, 3 and 4 only should be synchronised to match number 1 for smooth running.
If however the overall setting is too wide for any reason, the tickover will be normal until the MAP sensor receives information that more fuel is required – this takes a few seconds. Once it instructs the ECU to add more fuel to the mixture a cycle begins causing the revs to escalate. When the coolant reaches operating temperature the starter valves are pushed forward, closing the by-pass air down to the point dictated by the manual tickover control and all is again well.
Increasing the extension via the nuts on the controlling rod and causing the cold start position of the starter valves to be further forward at all times cured the problem on my bike at a stroke.

It now starts, ticks over at 2,000 rpm and drops to a steady 1,100 when fully warm.
Thanks to all those on Fireblades.org who contributed to this solution.
 

·
Registered
Joined
·
3,890 Posts
Has anyone else done this? My bike likes to idle high when cold, sometimes up around 4000 rpm. This looks like a good solution to me.

(disclaimer - yes I know this is an older post, but it's relevant).
 

·
Super Moderator
Joined
·
32,034 Posts
Has anyone else done this? My bike likes to idle high when cold, sometimes up around 4000 rpm. This looks like a good solution to me.

(disclaimer - yes I know this is an older post, but it's relevant).

Adjusted the starter valves you mean?
Yes, adjusting them would be the way to lower the cold idle speed.
 

·
Super Moderator
Joined
·
32,034 Posts
Not the starter valves, the rod that comes from the wax unit.

Yes, the rod that actuates the starter valves. You probably could adjust each starter valve seperately to get the same result though I guess.
 

·
Registered
Joined
·
3,890 Posts
I don't have a vacuum gauge, so I'm hoping that way will work on all of them at once, instead of guessing and getting them out of sync.
 

·
Super Moderator
Joined
·
32,034 Posts
I don't have a vacuum gauge, so I'm hoping that way will work on all of them at once, instead of guessing and getting them out of sync.

As long as they're reasonably close to synchronised already you should be fine just adjusting the actuator rod. If you still have problems though perhaps one starter valve is way out. It's common on carbed bikes when you can't get the idle down that one of the throttle plates is holding the others open.
 

·
Registered
Joined
·
3,890 Posts
Mine's the 929, so FI. Just went out to lift up the tank, and the ONE allen key I need to undo the rear bolt is the one that's missing out of the set. Dammit !!
 

·
Super Moderator
Joined
·
32,034 Posts
Mine's the 929, so FI. Just went out to lift up the tank, and the ONE allen key I need to undo the rear bolt is the one that's missing out of the set. Dammit !!

Yes, I know :)
Carbs don't have starter valves.
 

·
Registered
Joined
·
3,890 Posts
Just to confirm the first post - I loosened off the screw at the top of the wax unit where it connects up at the throttle bodies, and the idle is now a gentle 2000rpm when cold, not the 4-5k it used to be. :)
 

·
Super Moderator
Joined
·
32,034 Posts
Just to confirm the first post - I loosened off the screw at the top of the wax unit where it connects up at the throttle bodies, and the idle is now a gentle 2000rpm when cold, not the 4-5k it used to be. :)

Great result :)
 

·
Registered
Joined
·
69 Posts
I have posted on this subject with my bike but mine doesnt do it all the time.....maybe 60% of the time.....shall I change my starter valve settings? The reason Im asking is ...what happens to the normal tickover speed if I adjust for the abnormal high 4000-5000rpm start?
 

·
Registered
Joined
·
3,890 Posts
That can be adjusted with the idle adjuster behind the fairing (it pulls on the same area as the wax unit). The starter valves should just be sync'd to the number 1 cylinder though (which is fixed).
 

·
Registered
Joined
·
69 Posts
cheers sky91.......I will try that as soon as I can get out to work on the bike......I am wondering how to sync the throttle bodies with the tank in the way.....I can only lift it a few inches cos of the short petrol hoses????
 

·
Super Moderator
Joined
·
32,034 Posts
I have posted on this subject with my bike but mine doesnt do it all the time.....maybe 60% of the time.....shall I change my starter valve settings? The reason Im asking is ...what happens to the normal tickover speed if I adjust for the abnormal high 4000-5000rpm start?

If you're talking about an F2 it doesn't have starter valves or throttle bodies. It has carburetors with choke circuits.
 

·
Registered
Joined
·
69 Posts
its my 929 Im talking about this time bladeracer mate.....I have done the sync on the f2's carbies many a time but this has me stumped...I cant even see underneath the tank on the 929 cos the hoses are so short!!!
 

·
Registered
Joined
·
1 Posts
Hi there all, sorry to be a pain. My bike is also doing the same
Do you guys have any pictures as to what you did to correct this problem.
 
1 - 18 of 18 Posts
Top