Clunk-die theory

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Twitchy
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Clunk-die theory

Post by Twitchy »

Looking for some feedback or input from all the VTR knowledge gained over the last 19 years!

The Problem;
I have what some call the 'clunk-die'. Idling nicely at the lights, a mechanical clunk, idle drops instantly and if the idle was too low, the bike cuts out (dies). Many people say to bump the idle up to 1500 to cure the problem. At the moment my bike idles at 1500+ rpm. I also have an issue with the idle slowly decreasing and when it gets to about 1200, I increase the revs by throttle and hold it until the traffic lights change. Sometimes I get the ‘clunk-die’ and sometimes it ‘clunks’, severely drops rpms (to 900 or lower) but does not die. One day last week it did the ‘clunk’ just as I was moving off on the green traffic light, and yes, it died. I was in front of a line of cars and it was a tad embarrassing! The ‘clunk-die’ thing is now the only reason why I am nervous about filtering/splitting the traffic, because I cannot reply on the bike not playing silly buggers and holding up cars & trucks.

The Rectifications;
Drooping idle – suggestions of vacuum lines deteriorating, petcock diaphragm failure, tank vent lines blocked have been listened to and while not done yet, petcock arrived this week, sourced some proper silicone vac lines and crimp style clamps to ensure zero vacuum leakage, and tank vent lines will be blown out with compressed air.
Clunk-die – read on SH forum about spraying silicone lube on the friction part of the cv slide (worse if anything), bumped idle to above 1500rpm – still get ‘clunk’ but if above about 1300 does not ‘die’.

The Clunk;
One day I was doing a carb balance, and had the tank up to get to the carb balance screw. Idling away, I happened to have my hand on the rear of the airbox lid when it did the ‘clunk’. Wow! It was like someone whacked a hammer with medium force from inside the airbox lid, rather startled me! I will guess it was the rear carb that made the ‘clunk’. Anyway, having a good think about it over the last month or so and I have some ideas I would like to throw around.

The Theory;
When reinstalling the cv slides (the long ones) to the carby, I always check the operation of the slide before proceeding any further. I also use my thumbs and do both slides together to make sure they are closing at the same rate/time. The only thing under the airbox that can make a mechanical clunk has to be the slides, and if you open them up and let them close by spring pressure they do shut reasonably hard. So I can imagine if there was a vacuum differential across the diaphragm with more vacuum on inlet tract side, aided by spring pressure, the slides will get pulled shut very rapidly, making a considerable clunk on seating. My theory (or question) is this; with the 270 degree ignition of the Honda V Twin, is it possible that randomly (or not randomly but regular and well spaced) there is a discrepancy between the ignition and non factory jetting, and it causes excess vacuum on the back side of the diaphragm drawing it open, which would bring in the fuel of the needle range fuel into the rear cylinder, flooding it, and then through the next cycle or part cycle the higher vacuum transfers back to the inlet tract, sucking the diaphragm back shut again with force, not enough air to equalise the fuel/air mix leaving the rear cylinder flooded at idle, and that is too much for only 2 cylinders to cope with, killing the engine. If this happened on a v4, would the other 3 unflooded pistons be enough to keep it rotating until the fuel in the flooded cylinder burnt off? Whereas only 1 other cylinder on the v twin is not enough.

Talking to a mate about it on the weekend, and only describing the symptoms, the first thing he asked was if I could advance the timing. That then got me thinking on revisiting the advance rotor conundrum – to get or not to get (can get 2 degree rotors off ebay).

I hope I have explained well enough as it sounds in my head! I welcome any feedback, suggestions (criticism?!) that may help me (and others) understand this unwanted phenomenon.
06 VTR1000F; bits by Jack Flash, Erik Marquez & Jamie Daugherty. SP/954 front and SP2 rear in the works.
Build thread; http://vtr1000.org/phpBB3/viewtopic.php?f=41&t=36638
StuartWags
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Re: Clunk-die theory

Post by StuartWags »

farting back through the carb.... ??? possibly a bit lean on idle.
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lloydie
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Re: Clunk-die theory

Post by lloydie »

I always but it down to flooding and when the "wasted spark" fired it sent a blow back into the air box .

Tho I can't remember it doing it when I ran a +4' advancer .
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sirch345
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Re: Clunk-die theory

Post by sirch345 »

Your case seems extreme to what most who experience this problem suffer, so I hope you manage to solve or reduce the problem soon.
When I've discussed this before with people in the know, it seems that it could be the engine is gassing up at tick over, which in turn causes it to stall as you accelerate away.

The strange thing is, apparently not all Firestorm's/Superhawk's have this problem, so may be it is to do with fueling.

Good luck with getting to the bottom of it, do keep us posted,

Chris.
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alanfjones1411
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Re: Clunk-die theory

Post by alanfjones1411 »

Seems like a fueling problem problem and when tick over slows down you are getting the normal vtr carb farts.
SO WHEN DOES THIS OLD ENOUGH TO KNOW BETTER KICK IN
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lloydie
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Re: Clunk-die theory

Post by lloydie »

It could be why the Aprilia rsv runs two plugs per cylinder !
Maybe it's not burning enough fuel at low rpm and the excess builds up till it burps it out into the air box .
Could try a hotter or colder plug ,can't remember which way to go with them to get a better burn .
It also could be due to fuel it self with not being of the best quality .
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bazza696
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Re: Clunk-die theory

Post by bazza696 »

On the advancer, I spoke to Mr Ditchfield a while back about this, he stated that his racing VTR's were retarded by 2º at low RPM and advanced by 4º I think after 6 or 7000 rpm, so he suggested that a good compromise due to not running the bike at full chat all the time would be the 2º advancer, also you wouldn't have the problem of running the bike as hot as with the 4º advancer.
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popkat
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Re: Clunk-die theory

Post by popkat »

Could be a valve not seating, check valve clearances
or cam Timing out

Has it always done it, think about when it started happening worse.



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sirch345
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Re: Clunk-die theory

Post by sirch345 »

lloydie wrote:It could be why the Aprilia rsv runs two plugs per cylinder !
Maybe it's not burning enough fuel at low rpm and the excess builds up till it burps it out into the air box .
Could try a hotter or colder plug ,can't remember which way to go with them to get a better burn .
It also could be due to fuel it self with not being of the best quality .
That's what I was getting at.

Interesting about Aprilia RSV running two spark plugs per cylinder.
popkat wrote:Could be a valve not seating, check valve clearances
or cam Timing out
Good call that :thumbup:

Chris.
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Twitchy
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Re: Clunk-die theory

Post by Twitchy »

popkat wrote:Could be a valve not seating, check valve clearances
or cam Timing out

Has it always done it, think about when it started happening worse.
Checked valve clearances when installing Kreiger ccts less than 1000 km ago. However, the rear cct is weeping oil down the thread so need to recify that and can check the clearances while I'm in there - that will be a winter job though as its prime riding time Down Under right now!
bazza696 wrote:On the advancer, I spoke to Mr Ditchfield a while back about this, he stated that his racing VTR's were retarded by 2º at low RPM and advanced by 4º I think after 6 or 7000 rpm, so he suggested that a good compromise due to not running the bike at full chat all the time would be the 2º advancer, also you wouldn't have the problem of running the bike as hot as with the 4º advancer.
I have seen the 2 degree advancer on ebay, might pull the trigger on that then.
lloydie wrote:It could be why the Aprilia rsv runs two plugs per cylinder !
Maybe it's not burning enough fuel at low rpm and the excess builds up till it burps it out into the air box .
Could try a hotter or colder plug ,can't remember which way to go with them to get a better burn .
It also could be due to fuel it self with not being of the best quality .
I interpret that as I am too rich at idle. Mmmm....

Snippets from NGK Canada website;
Air/fuel mixtures;
- Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability
- Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage

Advancing ignition timing;
- Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C

Misfires;
- A spark plug is said to have misfired when enough voltage has not been delivered to light off all fuel present in the combustion chamber at the proper moment of the power stroke (a few degrees before top dead centre)
- A spark plug can deliver a weak spark (or no spark at all) for a variety of reasons...defective coil, too much compression with incorrect plug gap, dry fouled or wet fouled spark plugs, insufficient ignition timing, etc.

Heat Range Explanation;
http://www.ngk.com.au/spark-plugs/techn ... xplanation

I am currently running DPR9EIX-9 plugs. So with those above snippets in mind, checking plug colour possibly being a plug issue rather than a fueling/jetting issue. Kinda hammers home the importance of killing the engine immediately at xxxx rpm when doing a plug chop rather than idling to a stop! All Interesting. Advancing ignition timing is interesting considering bazza696 comments from Roger Ditchfield, and I can see why so many have have noticeable improvements with the advancer.

So my conclusions are;
- install the 2 degree ignition advancer to increase plug tip temp to allegedly ignite more fuel at idle
- try a DPR8EIX-9 plug (1 step lower in the heat range = 1 step 'hotter' plug)
- lean out fuel screws a tiny bit

Thanks guys, I have learnt a little bit more about this very 'characteristic' machine :Beer1:
06 VTR1000F; bits by Jack Flash, Erik Marquez & Jamie Daugherty. SP/954 front and SP2 rear in the works.
Build thread; http://vtr1000.org/phpBB3/viewtopic.php?f=41&t=36638
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Twitchy
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Re: Clunk-die theory

Post by Twitchy »

Update; replaced petcock, replaced rubber hose from petcock to tee piece with new good clamps, blew out both breather lines up the pipe and down the hose. Now the drooping idle is worse and so is the clunk die problem.

As mentioned earlier, fuelling could be a part of the problem, and I reckon my bike is a bit flat above 5k. Combined with Factory Pro telling everyone to pick the right mains before mucking around with needles or screws, I think I need to pop some standard plugs in it and go do a plug chop at about 6000rpm to see whats going on.
06 VTR1000F; bits by Jack Flash, Erik Marquez & Jamie Daugherty. SP/954 front and SP2 rear in the works.
Build thread; http://vtr1000.org/phpBB3/viewtopic.php?f=41&t=36638
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VTRDark
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Re: Clunk-die theory

Post by VTRDark »

Reversion is what you want to look up and this I believe is partly the reason why I think Honda installed what we call the restrictors in the later models along with the PAIR. Unspent fuel getting forced back up the intake.
http://www.hotrod.com/how-to/engine/ctr ... reversion/

It could be any number of things but Popkat is on the right path. Start with you timing and valve clearances first, then move onto carb tuning. It could be simply related to bad fuelling / mixture. I had a similar issue with mine when I first got it. Adjusted the TPS, tweeked the fuel screws, done a carb balance and all was good. Also check that you carbs are seated correctly and there are no leaks, including the exhaust system.

An advancer may or may not help. More info on ignition timing in the following thread.
http://www.vtr1000.org/phpBB3/viewtopic ... 31&t=33343
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8541Hawk
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Re: Clunk-die theory

Post by 8541Hawk »

To add a little to this discussion. First the firing order is actually 270-450 and that long "coasting" bit is what can cause issues.

As for the ignition advancers, first they are only for use on the first generation VTR, if you have a fuel gauge then the advancer isn't going to work for you as the ECU has a different curve.
Second, the dyno has shown that if you do run one, the only one worth installing of the 3 options (they had 2,4 & 6 degree units at first) was the 4 degree unit. The rest were not worth the trouble.

Another question that hasn't been asked is how many miles are on the engine. Again as someone who lived through the whole clunk-die thing when it first happened. The main cure was to finish breaking in the engine.
Once that was done the issue went away, If you have issues after that then it sounds like you are too rich on the bottom end (or everywhere)

The whole dying at idle, like the dying when pulling in the clutch at higher RPMs and trying to coast are things that go away once everything is well broken in....or around 10K miles or so. :beer:
Loud pipes don't save lives, knowing how to ride your bike will save your life.
KarimSC36
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Re: Clunk-die theory

Post by KarimSC36 »

Hey guys,

My name is Karim and I'm a fellow VTR1000F enthusiast that lives in Melbourne, Australia! I currently own an '03 VTR1000F (purchased 3 months ago) and guess what? I have this exact problem!

I think I may have diagnosed my issue, however. Hear me out and tell me what you think

Here's how it began:

Last month i heard a massive clunk and this was followed by my Sh*tStorm dying. At first I thought that a valve hadn't seated properly and that was the end of my short experience as a Honda rider. However, the bike restarted and rode fine for the next week with no issues.

A week or so later, I serviced my bike myself as I normally do with past bikes and used Motul 10W40 fully synthetic oil. Shortly after the service, I began hearing a strange sound coming from my clutch when in neutral. I don't recall hearing it before the change but nevertheless it didn't affect my bike....then the clunk came and off my bike went.

Last weekend I took my bike on a 700km journey to the Great Alpine Road which involved some hard riding including 100km on gravel. A few hours after returning home I couldn't believe how many times it made a massive noise in the airbox and died. The following day it was unbelievable. I counted 20 times that it clunked and 10 of those were enough for it to stall the bike. I felt like it must have been something that I did during that ride or the previous owner never told me. After hours of research, I understood that its a common issue with the firestorms so I took the bike apart, balanced and cleaned the carbs, checked my TPS sensor and also removed both spark plugs for inspection.

Upon inspection of the spark plugs, I noticed the rear plug was fouled with carbon deposits while the front looked pretty standard for a bike with 35k km. Anyway, concluding that everything was operating correctly, I put the bike back together and turned it on. Once again, a massive clunk and it stalled shortly after.

As you can imagine I was backtracking my every single kilometer on the bike to pin point the time I noticed it and it got worse. It didn't make sense th

What I can conclude is that after the 700km ride, I did remove the baffles on my staintune exhaust. I believe this may have further altered the fuel air ratio and caused this issue to worsen. It's also possible that the previous owner never 're-tuned' the VTR after installing the aftermarket exhausts. It sounds extremely basic, but it's very possible that this could be a potential reason

I don't really know how to adjust the air fuel mixture but tomorrow I'm going to re-install the baffles and it should make a difference. If it doesn't then I'm totally out of options.

I'd be interested in knowing what everyone thinks. Sorry for the essay guys
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VTRDark
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Re: Clunk-die theory

Post by VTRDark »

Welcome to the forum Karim.
I don't really know how to adjust the air fuel mixture but tomorrow I'm going to re-install the baffles and it should make a difference. If it doesn't then I'm totally out of options.
It's no easy task on the VTR but see the following thread
viewtopic.php?f=31&t=14214#p238528
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