Hard starting Downtown 300i

[JaydeeFL]

I think I have read about all the forums on this subject, and pretty much checked them all off, and I am still stuck.  My problem is a no spark issue.  I have a spark checker that I have used on small engines for years, if the spark will jump the gap, it will fire under compression.  With the plug out, I have good spark, plug in,  no spark. These are some of the things I have done with basically no change in the problem.  I had bought a new battery when I got the scoot before I knew about this problem.  Once I got into it, and reading all the blogs about batteries, I bought another one with the CCA of 175, the same as what came with it.  I fought with the theory of possibly starving the ECU while cranking with the plug in.  Voltmeter proved that wrong, but still I used another battery to power everything but the starter, no change. Okay, so it is not voltage drop, it does crank slower with the plug installed, so could it be the signal from the pickup/pulsar/crank position sensor.  It ohmed out correctly and I really hated to do it, but pulled off the crankcase end to get to it.  It was melted pretty badly.  Oh boy, thought I had it, replaced the coil , checked the gap, running about .015, perfect, buttoned her back up, no change.  I have ohmed out the ECU and connector to the manual, everything checks, removed and replaced all ground wires and have used dielectric grease on everything. Checking the output from the pulsar coil, it is showing about .45 volts AC cranking without the plug installed and maybe .42 with it in, not enough to make a difference one would think.  I am showing over 12 volts going to the hot side of the coil as well as the power to the ECU while cranking.  The only code she is throwing right now, is the O2 sensor because the exhaust is still off from changing the pulsar.  I keep thinking it is something stupid and when I find it, she will purr like a kitten, because I have about left no stone unturned, including valves.  I have checked continuity from the ECU to the signal side of the coil along with about every wire in the harness.  I am starting to look real hard at the ECU but everything says it is okay, it performs the precheck perfectly, throws a code when it should, but what else is there. I have cranked it long enough on a couple occasion that it has started, once running, it runs perfect.  You can tell when she is going to start as the tach starts to jump. Any and all suggestions will be truly appreciated.

[Ruffus]

@JaydeeFL,
I know it sounds strange, but try to take a new spark plug and put a simple short piece of stiff blank electrical cable from your ignition cable (sparkplug cap taken off) onto your sparkplug. Try to start. Check this blank cable piece is not touching anything.

[CROSSBOLT]

Welcome and you seemed to have done EVERYTHING that can be harped on in a situation like this! I think Ruffus is on to something simple like a faulty plug wire or cap except for it runs great once it starts! The normal for this and the People GTi300 with the same engine is two revolutions on the starter and it runs.

Sounds like the only thing left is to plug in a "known to be good" ECU to at least rule out that possibility. The only problem with that is NO ONE just happens to have any of those laying about!

Have you tried a new plug yet? Or did I miss that?

[JaydeeFL]

@JaydeeFL,
I know it sounds strange, but try to take a new spark plug and put a simple short piece of stiff blank electrical cable from your ignition cable (sparkplug cap taken off) onto your sparkplug. Try to start. Check this blank cable piece is not touching anything.

Let's see if I got this straight.  I think you want me to try a plug wire without the resistor?  I will try that, Thanks.  I had considered that, knowing when the circuit is broken in the coil, it unloads into the secondary winding looking for another ground, this time through the plug and that resistor in the cap only ads resistance.  I always thought that resister was just a noise suppressor for  the radio, if so, what is it doing on a scooter??  Anyways, I did purchase another coil to try even though the original coil ohmed out correctly. No change.  The spark checker I use forces the spark to jump about 5/16s of an inch, spark plug out, no problem, spark plug in, it will not even jump the ,035 gap on the plug laying on the block.  I don't think my meter is quick enough to pickup if a signal is being generated by the ECU, could try a test light. I know in both cases a signal is going to the ECU from the crank position sensor, I just don't think one is coming out to the coil when the spark plug is in, and not that much seems to change, just a few cranking RPMs.   Ruffus, thanks for the suggestion, I'll go out and try it, at this point, I'll try anything.  I will let you know! Thanks!!!  I just hate to condemn the ECU, that is an expensive part with a long lead time, without exploring all options.

[Kansas kymco]

Just curious when the plug is out of the engine you are laying the plug on the block of the engine so the plug base is grounded correct?

[Ruffus]

Yes, want you to try this without resistor.
High peak noise is not so significant on our scoots, but on other traffic members which have GPS, HIFI, radios in their transports..

[JaydeeFL]

Just curious when the plug is out of the engine you are laying the plug on the block of the engine so the plug base is grounded correct?

Yes, it is grounded solid.  Thanks!

[JaydeeFL]

Welcome and you seemed to have done EVERYTHING that can be harped on in a situation like this! I think Ruffus is on to something simple like a faulty plug wire or cap except for it runs great once it starts! The normal for this and the People GTi300 with the same engine is two revolutions on the starter and it runs.

Sounds like the only thing left is to plug in a "known to be good" ECU to at least rule out that possibility. The only problem with that is NO ONE just happens to have any of those laying about!

Have you tried a new plug yet? Or did I miss that?

Oh, I have tried a half dozen different plugs, finally ended up with the nine dollar titanium plug that the electrode comes to a point. Nothing.  I wish I knew someone who had a 300 with easy access to the ECU .  I certainly would pay shipping both ways to have someone plug this thing in and either thumbs up or thumbs down it.

[JaydeeFL]

Yes, it is grounded solid.  Thanks!

I went over everything again and nothing changed.  Tried the plug wire without the resister, nothing.  Maybe when the pickup coil did it's melt down thing, it damaged just that circuit in the ECU.  Strange I can see the signal going to the ECU from the pickup, with the spark plug either in or out, but only the signal comes back with the spark plug out.  Powered the ECU separately, no change, so it's not voltage drop, only the slight difference in cranking speed.  I guess I'll have to bite the bullet and order a new ECU.  I am about half temped to order a AC powered CDI box and just separate that circuit from the ECU and see what happens. That box is like 7 bucks from Amazon and two day delivery, but I am sure the ECU would be throwing codes.  Might be an interesting experiment.  Thanks guys for all your your help.

[Ruffus]

Sorry to see there is no progress.
Yes, why not trying to bypass your ECU with an external CDI-box. Would be interesting whether it works. Pls keep us posted about any outcome whatever.

[JaydeeFL]

Sorry to see there is no progress.
Yes, why not trying to bypass your ECU with an external CDI-box. Would be interesting whether it works. Pls keep us posted about any outcome whatever.

Okay, ordered a DC CDI box and coil today, under 20 bucks, should be interesting.  The only thing that may throw a monkey wrench into the equation is the amount of tabs on the flywheel.   The little gy6 scooters have but one tab on the flywheel where this puppy has them all the way around, evenly spaced, with one tab being larger.  The gy6 scooters seem to fire once per revolution even though they are 4 stroke.  So I am not sure just how the CDI is going to interrupt the signals coming up from this setup, should be interesting.  Ordered a ECU this afternoon, it is a month out, I could not find a used one.  Not very optimistic on the CDI, but I'll keep you posted. Thanks!!

[JaydeeFL]

Okay, ordered a DC CDI box and coil today, under 20 bucks, should be interesting.  The only thing that may throw a monkey wrench into the equation is the amount of tabs on the flywheel.   The little gy6 scooters have but one tab on the flywheel where this puppy has them all the way around, evenly spaced, with one tab being larger.  The gy6 scooters seem to fire once per revolution even though they are 4 stroke.  So I am not sure just how the CDI is going to interrupt the signals coming up from this setup, should be interesting.  Ordered a ECU this afternoon, it is a month out, I could not find a used one.  Not very optimistic on the CDI, but I'll keep you posted. Thanks!!

I thought what happened would  happen,  On the GY6 scooter there is but one tab on the outside of the flywheel, and that is what the pickup sees going by and tells the capacitor to unload.  The Downtown has at least a dozen tabs on the flywheel, with one being about double size.  I have to assume that is the tab the ECU is looking for.  The little CDI was putting out constant sparks, looked like a welding arc. It was a strong spark and should have been firing in the hole,  but I got nothing.  I know the timing would be way off, it acted like a glow plug, but nothing, I was at least hoping for a backfire.  I have compression, fuel and spark, even though it's in the wrong place, but the darn thing would not even give me a pop.   New ECU is ordered, but a ways off,  this thing is really getting to me, wish me luck.

[JaydeeFL]

I think I have read about all the forums on this subject, and pretty much checked them all off, and I am still stuck.  My problem is a no spark issue.  I have a spark checker that I have used on small engines for years, if the spark will jump the gap, it will fire under compression.  With the plug out, I have good spark, plug in,  no spark. These are some of the things I have done with basically no change in the problem.  I had bought a new battery when I got the scoot before I knew about this problem.  Once I got into it, and reading all the blogs about batteries, I bought another one with the CCA of 175, the same as what came with it.  I fought with the theory of possibly starving the ECU while cranking with the plug in.  Voltmeter proved that wrong, but still I used another battery to power everything but the starter, no change. Okay, so it is not voltage drop, it does crank slower with the plug installed, so could it be the signal from the pickup/pulsar/crank position sensor.  It ohmed out correctly and I really hated to do it, but pulled off the crankcase end to get to it.  It was melted pretty badly.  Oh boy, thought I had it, replaced the coil , checked the gap, running about .015, perfect, buttoned her back up, no change.  I have ohmed out the ECU and connector to the manual, everything checks, removed and replaced all ground wires and have used dielectric grease on everything. Checking the output from the pulsar coil, it is showing about .45 volts AC cranking without the plug installed and maybe .42 with it in, not enough to make a difference one would think.  I am showing over 12 volts going to the hot side of the coil as well as the power to the ECU while cranking.  The only code she is throwing right now, is the O2 sensor because the exhaust is still off from changing the pulsar.  I keep thinking it is something stupid and when I find it, she will purr like a kitten, because I have about left no stone unturned, including valves.  I have checked continuity from the ECU to the signal side of the coil along with about every wire in the harness.  I am starting to look real hard at the ECU but everything says it is okay, it performs the precheck perfectly, throws a code when it should, but what else is there. I have cranked it long enough on a couple occasion that it has started, once running, it runs perfect.  You can tell when she is going to start as the tach starts to jump. Any and all suggestions will be truly appreciated.


Crud, I haven't gained a thing.  I have now another ECU and I have replaced the stator and pickup coil.  I have wrung out every wire, powered the ECU separately from the starter, checked all grounds, and still, using a spark checker, have spark with the plug out, no spark with the plug in.  Plug is not hooked up,  using the spark checker is both cases, plug just fills the hole like a plug and raises compression.  Engine turns over a little slower under compression, but still quick enough.  Have jumped it with a car battery.  Have two new coils, two ECUs, new pulser and stator, and I am right where I was a year ago.  I assume it is the ECUs job to determine which of the flywheel tabs trigger the coil.  I assume the square tabs, might be 6 of them are for the injectors and possibly timing advance, where the big rectangle one is for ignition.  I just can't see that much of a change between cranking with the plug in or out, only a small difference in the strength of the signal generated by the pulser coil.  Hate to drop another $372 for another ECU, if any of you guys have the hood off your 300 and wouldn't mind plugging in a couple of ECU to see if they are any good, I'll gladly pay shipping both ways.  Thanks!

[CROSSBOLT]

One thing you said somewhere: it sounds the same while cranking with the plug in as it does with it out...or similar  to that statement. Have you checked compression?

[JaydeeFL]

One thing you said somewhere: it sounds the same while cranking with the plug in as it does with it out...or similar  to that statement. Have you checked compression?

I don't think I have put a compression gauge on it, never got that far.  Until I can figure out why I have no spark under compression, and there is compression, as that is the one and only thing that changes. there is no sense.  I have had it running about 4 times over the past year and when it does fire off, it runs fine.  In the beginning, I may have checked compression as I did do the valves, but that was many, many, frustrating hours ago..  Once I realized I had no spark under compression, and good spark with an open hole, that's about all I've worked on.  If it would fire under compression, I'm sure it would lite right off.  I have bypassed all the wires going from the pulsar to the ecu and back, and the wires going to the coil, bypassed the ignition switch. I have checked the tilt switch, powered the ecu separate from the starter using another battery, ran new ground wires.  Swapped out the ecu relay. I have checked continuity from the sources through the ecu plug, used dielectric grease on all connections.  After everything, two ecu's, two stators and pulsar coils, two coils, not one thing has changed  Using a simple spark checker that forces the spark to jump to ground about a quarter inch, plug out, blue spark, plug in, and not even tight, no spark.  Freaking unbelievable......Dynamite?