[Blaze]

Hi folks,
I've got a three weeks trip in few month so i need to transform my sleeping for too long tengai on a rallyraidproof bike.
I will put some picture and text of my work but for now i've got a little problem with it (this is the reason why it sleep for some year on my garage).
Let me explain, a few years ago, after a 300km trip (sorry impérial users), i stop at a friend house and at the time to start my bike something went wrong. As i press the start the engine wont go, so i press again, and again but this time i Keep pressing it and after 30sec or so, i heard a VERY loud bang that scared all people around (and myself as i didnt understood at first that this thing was my bad), even my friend came out his house...
I've Never been the wisest of the band so i tried starting it again and first press, first sec start, everything fine.
Since, its always the same procédure to start it, 30sec press, big bang and Real start only after...
As i was wondering what's wrong, i've changed the KACR spring as it was cheap (i was a student at this time) and hoping it would do the job but of course it didn't make the cut.
From this time the bike is sleeping so i need to figure it out before spending some cash on it.

Does this speak to someone?

 

[pdwestman]

I feel the need to suggest that you need to invest in a proper service manual for your bike.

The USA (english) service manual is part # 99924-1113-02.
Could the original OEM Kawasaki service manual be acquired thru French dealerships?

Read the LINK in this link and then watch the videos, "Care And Feeding Of The CVK40"

Do you have the tools to properly measure the engines Cold Cranking Compression? Did you measure & record the valve tappet clearances when you replaced the KACR spring?

 

[Blaze]

Thanks mate, i've got an E.T.A.I. one that is not the best one i recon..
to ad some context, i've bought this bike just after passing my license and my only preocupation was to ride it
i got it for 300€ because it wasn't running, so i cleaned the carb and a jet was cloged. i put it back on after looking at the level of floater and it run perfectly. i've rode it couple month before this banging story.
thanks for the link, i'll rebuld the carb (perhaps klx needle or 22cents mod, but after)
i'll check compression and valve clearance as soon as i can, effectively this is the first step before any other. that said once it's started, the engine run great, top speed about 170km/h on the speedo.
if i succesfuly get it starting at first try without waking up all the neighbourhood, i wiil do the doo and more mods to it.
this tengai is stock, about 40k km, all fairing are repaired (poorly but i wonder if i can do better) i'll put some pics in few comments

i'm preety aware that my problem had to do with the top end engine, after resolving this problem i plan to clean al port and see cylinder and piston condition too

 

[Blaze]

I forgot to ask, did this happened to someone before ? Did you have a theorie on the causes of this detonation ?

 

[pdwestman]

A partially fouled spark plug could cause the sharp report thru the exhaust system. I've heard it/seen it more than a few times on different engines over the years.

This is easily over-looked by long distance mechanics, because we usually install a new spark plug after performing a proper cold start compression test which we need to do to Confirm the engine is mechanically sound enough to justify further work.

 

[Pig and the Pendulum]

@pdwestman if my bike was running fine a few months ago (even though I let it sit, procrastinating), any reason a 20k mile '04 would need a compression test? The only issues I had as a daily rider was slight power surging in higher gear around 60-70mph which I heard was common on stock KLRs. I don't know much about compression testing nor what it entails except that I think I did it to a 4cyl 'yota like...10-15 years ago. I lost my garage a bit after, so never got to continue my auto-fantasies.

 

[Blaze]

So, today i've got some time to start working on it.

First, the plug, oily but it still spark. I'll change it anyway


New Gazoline, new batterie, and it's running
Great but i'm still worried by the bang as i don't know if it can happen again.. can you please explain me how a dirty plug can cause the detonation? For my understanding 🧐

I've also performed a compression test (i will check valves clearances tomorow for a cold engine accuracy)
Open throttle with KACR normaly in place i'm aboutit 80PSI

With KACR disabled it goes up to 160PSI, it's not that bad but not great either ( i was not expecting Good results)

I dunno, part of me want to put out the head, check piston and bore, clean the head, put news vittons and gasket. The other want not to risk damaging some working condition stuff..

But first, valves clearances and (probably) new shim

 

[pdwestman]

Blaze, Adjust the valve clearance to the upper end of specs & re-check CCC with an active KACR. 100 to 125psi with an active KACR is great. 160 psi with a DE-Activated KACR is very acceptable IMO.

Pig and the Pen, EVERY engine of questionable starting or running issues needs a Cold Cranking Compression test to confirm the engine is NOT worn beyond serviceable limits.

Takes a mere 2 to 3 minutes of total time, per cylinder, unless frame parts cause access issues on some bikes (if the bike is already undressed & you have the proper tools) .

 

[Blaze]

So, i've make the valves clearance test, intakes one are not so bad, exhaust one are way too low...
A is for admission french word for intake, g is for left d for right. P for pastille french of shim

Accordingly to some calculator, i could take my exhaust shim to replace the intake one, and i need two 2.4mm for the exhaust one.
2.60 for intake is a bit too high, i probably loose some torque but it could do the job or i need 2.55 one?

I will do a new ccc with new shim on it. Thanks Pdwestman, i'll fell lonely without you ^^ 160 Psi is ok for me too, i was not as entertenaid (entertaid? Sorry) by 80psi as it on the low spec limit
I still believe that is not directly about the big bang on my bike... but new shim are just necessary.

Subsidiary question, i've a 4.6ah li-ion battery and a mosfet regulator laying around, as my acid one (14ah) is not in great shape, can i swap it or it's not gonna make the cut?

 

[pdwestman]

The shim calculation looks fine.

I don't now enough about lithium batteries to make a suggestion. If an application chart suggests that size for 650 class single cylinder motorcycles, it should work fine. Those batteries are potent little buggers.

 

[Blaze]

This week-end i've put on new shims, and made a new compression test. With KACR on i've made it to 105 psi,

Better, but without KACR i'm still at 160psi.
Now i've got a weird thing, after bolting up the engine, i started it, and after a minute running, the engine was hot and the beginning of the exhaust was cherry red... dis i make something wrong ?

 

[pdwestman]

Your engines KACR is working "exactly" as it is supposed to, to make life easier for the light weight starter, starter gears, sprag clutch and battery. It should start great in any tempuratures which I would care to ride in with 105 psi of CCC, if everything else is correct.

Was the cold start enrichener still pulled fully on and running 1500-1800 rpm when you spotted the Glowing exhaust head pipe? I'll call that Normal.
Unless the cylinder head is from a Gen 2 model and has an open exhaust Air Injection System hole near the spark plug, which needs plugged.

Did you measure the engine warmth? Was the cooling system full? The KLR engine is One Giant Radiator, it really can't get very warm in 1 minute or even 5 minutes if it has a normal operating oem cooling system.