Intermittent warm restart fail

[Beaker99]

Hi all,

I have a Kawasaki J300 I picked up about a year or so ago which had been left sitting for 18months before I got it. I did a full service etc and got it running well but it’s got an intermittent issue where it will fails to restart sometimes if it’s been running and warmed up to operating temperature then turned off for a few mins. I happens most often if I ride it down to the shops to pick something up. On a cold start it fires up almost immediately every time. But if I drive to the shop, park up for a few mins and then return, it will often simply turn over and not even try to fire up. It’s like there is no spark. It’s turning over normally but there’s not even a hint of ignition. I usually have to turn the key off, wait 20 seconds then try again and if I do that a couple of times it suddenly fires up as normal.

Does that sound ECU related? Could it be something else?

I do have a second J300 so I’m thinking about swapping the ECU’s over to see if that fixes the problem, but I’m really dreading having to strip down two bikes to get to the ECU’s.  Is there anything else I should look at / test before blaming the ECU?

[Neil955i]

Hold your horses on the ECU until someone more knowledgeable comes along to advise.  I say that because in my (limited) experience of ECU problems, you're more likely to see a complete failure of the unit.  As a result, I'm betting on something else being the cause?

[CROSSBOLT]

Hold your horses on the ECU until someone more knowledgeable comes along to advise.  I say that because in my (limited) experience of ECU problems, you're more likely to see a complete failure of the unit.  As a result, I'm betting on something else being the cause?

I agree with Neil on this. Of all the components the most reliables seems the ECU. Recommend starting with simpler stuff first.

My suspicion is you have some ethanol "snot" in your injector. I bought a new, old stock 2013 DT300i in 2016 that had the EXACT same symptoms as yours. I was led to devise a plan to backflush the injector with the on board equipment.

What that means is:
1.  Remove fuel hose from injector
2. Remove injector from engine but leave harness plugged in
3. Attach fuel hose directly to injector nozzle and tighten clamp
4. Cycle ignition on and off several times while collecting fuel from the inlet of injector
Note: Very little fuel is passing through the injector each time the key is turned on and off so you gonna do this a LOT to get much fuel though there. You may want to hook a charger or second battery. I did this about ten cycles and the problem went away. Yours may be different....

[Stig / Major Tom]

Are you using ANY throttle when doing a hot/warm start?
EFI works best if the throttle is not touched!
EFI also likes a very healthy battery.
Stig

[Beaker99]

Thanks for the input everyone. I swapped the injector over from the known good bike to the bike with the intermittent starting issue and ran the bike around the neighborhood a few times on Saturday hoping like crazy that it would fix it. Unfortunately, late on Saturday afternoon after leaving he bike for around 15mins post a ride, it again failed to start.

So on Sunday morning I bit the bullet and set about stripping the fairings off both bikes to get to the ECU’s. I swapped them over and did the procedure to reset the throttle sensor position and idle speed control valve.

I haven’t had much of a chance to test it yet, but I’ll ride the faulty bike for the next week and see what happens. I’m almost hoping this doesn’t fix the issue as a new ECU will be at least $500 here in New Zealand. I’d much rather the fault was in a cheaper part.

@Stig, I never touch the throttle when starting and the battery in this bike is relatively new.

[CROSSBOLT]

Thanks for the input everyone. I swapped the injector over from the known good bike to the bike with the intermittent starting issue and ran the bike around the neighborhood a few times on Saturday hoping like crazy that it would fix it. Unfortunately, late on Saturday afternoon after leaving he bike for around 15mins post a ride, it again failed to start.

So on Sunday morning I bit the bullet and set about stripping the fairings off both bikes to get to the ECU’s. I swapped them over and did the procedure to reset the throttle sensor position and idle speed control valve.

I haven’t had much of a chance to test it yet, but I’ll ride the faulty bike for the next week and see what happens. I’m almost hoping this doesn’t fix the issue as a new ECU will be at least $500 here in New Zealand. I’d much rather the fault was in a cheaper part.

@Stig, I never touch the throttle when starting and the battery in this bike is relatively new.

Eliminate the simpler and cheaper and easier to access parts first....

[mousejunks]

Here is information from the Kymco Downtown workshop/service manual.

One of the specific procedures requires you to open or rev the throttle to start which increases air flow to clear excess fuel that could wet the spark plug. Does the issue happen more often with short rides? Try the 'anti-flood procedure below'.

[roxyflash]

Try venting the gas cap

[Ruffus]

@Beaker99, on your case I would suspect:
-killswitch (do NOT use any WD40 or similar, for it demages plastic parts, better alcohol and pressure air, then silicone grease)
-sparkplug, cable and cap incl. coil
-fuel supply/pump

[Beaker99]

A bit of an update. After swapping over the ECU’s I then proceeded to ride the “faulty” bike for 4 days straight, commuting to work and doing all my normal riding. I consistently checked it after each ride by trying to start it back up after 5, 10, or 15mins and the bike never failed. I definitely would have had it fail to start previously within those 4 days if the problem was still present.

I then started riding my usual “good” bike which now had the “bad” ECU in it, and I was fully expecting to have that fail to start at some stage, but it seems it too is running perfectly and I can’t it to fail to start either!

At this point my working assumption is that the issue was ECU related but I fixed it when I performed the reset of the throttle sensor position and idle speed control valve. Aside from swapping the ECU’s between bikes, that’s the only other thing I did on both machines. I’m still riding the “good” bike and I haven’t tested it as much as I would like, but so far it doesn’t seem to have inherited the problem.

Finger crossed I've had a lucky solution. I can now put one of the bikes on the market, which will please my wife immensely!

[Neil955i]

A bit of an update. After swapping over the ECU’s I then proceeded to ride the “faulty” bike for 4 days straight, commuting to work and doing all my normal riding. I consistently checked it after each ride by trying to start it back up after 5, 10, or 15mins and the bike never failed. I definitely would have had it fail to start previously within those 4 days if the problem was still present.

I then started riding my usual “good” bike which now had the “bad” ECU in it, and I was fully expecting to have that fail to start at some stage, but it seems it too is running perfectly and I can’t it to fail to start either!

At this point my working assumption is that the issue was ECU related but I fixed it when I performed the reset of the throttle sensor position and idle speed control valve. Aside from swapping the ECU’s between bikes, that’s the only other thing I did on both machines. I’m still riding the “good” bike and I haven’t tested it as much as I would like, but so far it doesn’t seem to have inherited the problem.

Finger crossed I've had a lucky solution. I can now put one of the bikes on the market, which will please my wife immensely!

Well, whatever it was, glad you've found a solution!

[CROSSBOLT]

A bit of an update. After swapping over the ECU’s I then proceeded to ride the “faulty” bike for 4 days straight, commuting to work and doing all my normal riding. I consistently checked it after each ride by trying to start it back up after 5, 10, or 15mins and the bike never failed. I definitely would have had it fail to start previously within those 4 days if the problem was still present.

I then started riding my usual “good” bike which now had the “bad” ECU in it, and I was fully expecting to have that fail to start at some stage, but it seems it too is running perfectly and I can’t it to fail to start either!

At this point my working assumption is that the issue was ECU related but I fixed it when I performed the reset of the throttle sensor position and idle speed control valve. Aside from swapping the ECU’s between bikes, that’s the only other thing I did on both machines. I’m still riding the “good” bike and I haven’t tested it as much as I would like, but so far it doesn’t seem to have inherited the problem.

Finger crossed I've had a lucky solution. I can now put one of the bikes on the market, which will please my wife immensely!

Could it be a slightly corroded or dirty contact on the ECU plug and socket? That is why a few car manufacturers have started lathering all connectors with silicone dielectric grease. I have copied them with every bike since the early 2000's....

[Neil955i]

Could it be a slightly corroded or dirty contact on the ECU plug and socket? That is why a few car manufacturers have started lathering all connectors with silicone dielectric grease. I have copied them with every bike since the early 2000's....

Good advice Karl.

[stuo]

I had the exact same problem with the 2011 DT300 I owned and although it seemed to solve itself i never trusted it completely so I sold it despite many months of flawless performance. Please keep us posted on your experience with this mysterious ailment/hiccup.