No way to get engine to work

Hello community,
I apologize for my English, I'm not native English speaker.
There are few weeks I'm trying with a Mecatronic friend to overcome the problem that the engine isn't running anymore.
Sometimes it is possible to start, the engine idles a bit and badly then turns off. When the engine is idling and you try to accelerate, the engine stops.
EVERYTHING was checked! We tried also to change the motor control unit.
Sensors were checked by oscilloscope. The sensor on the left side between the engine and the frame seems not working regularly as the wave on the oscilloscope does shrink regularly, but who knows. To take off this sensor is a hardship, it seems we have to dismantle a lot to take it out. But what about the ignition pulse generator / pic-up 1-000-576-226? We are thinking to change also this part.
Reporting the top dead center and the lower on the left side and using a stroboscope lamp we realized that using the old motor control unit the ignition point is moving sometimes when you start the engine with spark plugs taken off. We realized also. that in this situation if you accelerate there are no sparks anymore.
Fuel pressure is also good and the injects seems to work properly.
It's a SW 400 2006 with 45000km kept in very good conditions.
We have also the original Honda SW repair manual.
I looked around a lot in the net without finding any suggestion. It seems this engine always run without problem.
Does anyone of you have a suggestion?
Many thanks and greetings from Switzerland

Hi, if you don't have a "MIL" malfunction light, is probably not an electrical issue?, maybe a fuel delivery issue, bad fuel pressure regulator (Bad regulator could cause a rich/lean condition), tank or fuel pump issue. Do a fuel flow and pressure test, remove injector make sure is spraying, etc. Check for bad vacuum hoses or leaks around throttle body.

Is this a sudden problem, has the scooter sat, etc.

@zrx212
Many Thanks for your reply.

Fuel pressure is 3 bar, injectors seems well spraying.
Fuel pressure regulator wasn't checked.
No MIL flashing or code.

In the last time I didn't ride the SW regularly. In winter if we have salt on the road I don't ride it. I usually let him sleep without starting the engine. After winter this time he didn't start well. The engine stopped and didn't want to come back, but tben suddenly the engine came back and I moved ride away to not make it stop again. The engine worked normally after. The SW stayed again some time. I wanted to start it, he coughed a bit started and died. No way to get it at live again.

Welcome aboard the board Snapy.  Sorry to hear about your challenges with your scooter.

A few thoughts:
Is the battery strong enough?
What is the condition of the spark plug and spark plug wire?
Is the fuel/gas good after sitting?

@ Sonuvabug
Fuel regulator checked and OK.
For all the work on it a big car battery was attached, so no way that there isn't enough power?
Spark plugs were not bad but we changed them. Resistance of spark wires checked and one substituted. Spark aren't very impressive with the stock spark coil, so we tried also an other one wich gives an very good spark.
Fuel is good.
Next step: change of pulser assy. cam (1-000-552-851) and ignition pulse generator / pic-up 1-000-576-226. Maybe someone has the data to check these components?
Many thanks and best regards

Hello,
work in progress: pulser assy. cam (1-000-552-851) and ignition pulse generator / pic-up 1-000-576-226 were checked and seems OK.
NO IDEA WHAT TO DO now.
Any help from you?
Many thanks

It seems that all the components you have checked are okay. However what you haven’t mentioned is “fuel”. Fuel is known to deteriorate over time. Especially fuel containing ethanol: E10, E15, etc. So now drain the fuel tank -completely- and add some fuel system cleaner additive (Redex, etc) then refill with fresh fuel.

Clean/check the air filter. Rodents are known to enjoy nesting in there.

Also, when you are starting the bike have the throttle twisted to wide open. That’s a known technique for clearing a flooded engine, not that you have a flooded engine, and it also somehow alters the ECU programing map.

Try running it with the fuel cap off, vent may be blocked

So the bike has gone from running nicely to not running over the storage time. It would be unlikely that a sensor has decided to fail while it was parked up, and as suggested that should generate a fault light. The suggestion about the air filter being blocked sounds possible. It might also be worthwhile loking at some other electrical interlocks specifically the sidestand switch (which can be bypassed for testing) and the tip-over switch mounted under the front cowl; both of those would cut the ignition, maybe there is a corroding connector that is intermittent. Lastly, check the vacuum hoses around the injection system are leak-tight.

Many thanks for suggestions.

@ Cosmic_Jumper: fuel was added few months before and there is no alcohol in. But we will try also this option. Air filter is new and there is no obstruction. Trottle open was also tried.
@ Kitchenman: Fuel pressure is 3bar, injectors are working. So blocked ventilation should not be the problem, but we will try also this option.
@ Terry Smith: sparks are always there, so it should not be the side stand or the tip over switch? Vacuum hose are checked.

We will try a new ignition pulse generator.

Best regards from Switzerland

If the fuel is there and the spark is there and it doesn't run, all I can think of is that they're not there at the same time.

After cranking for a while, is there a smell of fuel? Is the fuel coming out unburnt?

I might have missed a mention of checking fuel flow. There is an easy way in the shop manual to check it. Since pressure is possible even with poor flow it seems worthwhile to test the flow rate. You won't need to disconnect the fuel return line at the tank but just unhook it at the regulator and use another piece of hose to feed from the regulator to a measuring cup or an old baby bottle with measurement markings.

Dear all,

the new ignition pulse generator didn't change the situation.

Lastly we tried compression of the cold engine only 8 bar instead of 14. Couldn't believe this.

The scooter was always perfectly serviced. The only thing I did not respect was the motor oil: I always used Motul racing oil the same a friend of mine uses in his Honda racing motorcycle for about 20y.

Please, has anyone of you tried the compression of his SW, just to have an other data to compare to my 8 Bar and the Honda reference value? MANY THANK for this.

@Smellybeard: We had the same thinking about not having spark and fuel at the right time. Not really fuel smell after cranking for a wile. But spark plugs are a bit wet.

@1Wingman1: flow wasn't really measured. We tried pressure and tried to look at the fuel spraying from the injector ramp. The fuel sprayed for about 2 m away.

The story so far is rather puzzling. Low compression would not normally prevent the engine from starting, a low reading may be caused by sooting of the valve seats, worn/broken piston rings or head gasket failure. Even then, I would expect the engine to start and maybe produce excessive smoke out of the exhaust and popping noises.

If the plugs are wet it would suggest insufficient spark or too much fuel but you seem to have covered these items. Smellybeard asked if the fuel and spark are there at the same time....could the electronic ignition 'timing' be out-of-sync?

I think we are all sharing your frustration

Snapy:  Your post reminded me that I wanted to check my compression because I have noticeable
            oil usage.  Nothing to worry about.  My compression gauge measures in PSI only and may be    
            20 years old but my readings are 170 PSI on both cylinders rather than the 199 PSI in my
            manual.  The bike has 29,000 miles and runs great.

           To the best of my knowledge the proper procedure has always included holding the throttle
            wide open during the tests.  It definitely makes a difference.

Snapy said:    Sensors were checked by oscilloscope.

An oscilloscope can tell you a lot but I doubt that there is any manufacturer info about signal timings and amplitudes.  Honda provides only resistance readings for the sensors under Fuel System near the front of the manual.  If you haven't already, you might see if there is a resistance problem in a sensor.

I remember the day when an engine that would start and then stumble the problem was usually a fuel delivery problem of some sort.  Alas, modern engines and electronics are not always easy to diagnose.

The only other low tech thing I can think of is to check the fuel flow over a longer period. Maybe it's getting starved after running for a short time.

Oscilloscope? A perplexing problem indeed, but holy cow, it seems like you’ve gotten too far into the weeds with this.

Sorry to say too but it seems as if we here seem to have exhausted our ideas. Best suggestion I have now is for you to pose your problem to the legendary Stevefano Bonacasa (Stevenb) of the SWCI in Italy. Here is a link to his FaceBook forum. https://www.facebook.com/groups/hondaswt/

Thank you for bringing this “won’t start” problem to our attention. Please let us know Stevenb’s response and how you resolve this.

"This is like the worst episode of Scooby-Doo, ever"!

Curiouser and curiouser said Alice...

Some reasons for low compression may be:

1. Poor fitting adaptor to gauge, or butterflies not full open during test
2. Corrosion/carbon on valves preventing a good seal
3. Corrosion or other damage to rings/bore
4. Rings gummed up from standing
5. Camshafts out of phase with crank

There is a technique called leak-down testing where compressed air is applied through the spark plug hole; the escape path should allow you to narrow down where the leak/low compression is coming from.

The compression is good enough to start and could easily be down to sitting unused. It's not really an issue that needs to be dealt with now. If there's an issue, the regular emissions test will see if there's muck coming out the exhaust.

Purge the fuel line as it sounds like it could be blocked with debris, poor quality fuel. I had the same problem and that cured it for me.....good luck

Hello again to you all,

no really news. But the SW started without any problems making a desperate trial after doing nothing for days. The engine idled normally for about 15 seconds, then my friend tried to accelerate. Doing so the engine died immediately. And no way to get it to start again.

It seems it is not a fuel problem. Can it be that there is to much fuel wich prevents the spark plugs to build an effective spark??? Any idea?

Thanks a lot to you all

@Cosmic_Jumper: Stefano Bonavita seems not so cooperative to me, he wrote back that "he should se the SW" ...

... just to show how far we went and how wrong we are :-)))

Here my friend is checking the ignition coil.

I could not load MP4 file???

My Moto Guzzi has developed a similar issue.

I'm doing some work on my garage and the Guzzi and sidecar has been outside for a few weeks and it did get wet. I went to use it on Saturday and found it difficult to start and completely unable to do anything but tick over when I did get it going. Opening the throttle causes it to cut out or spit back through the carbs - once so violently that it blew the carb off the inlet stub.

One thing I intend checking today is if a charging fault is causing the voltage to drop dramatically when reaches the rpm when it should be beginning to charge. I've noticed the red battery light going out just before it cuts. I need to check the wiring diagram and maybe pull the relevant wire off the regulator.

Carbs going in the ultrasonic bath too. Fuel in the float bowls is crystal clear but who know where there might be gick.

Snapy wrote:

Hello again to you all,

no really news. But the SW started without any problems making a desperate trial after doing nothing for days. The engine idled normally for about 15 seconds, then my friend tried to accelerate. Doing so the engine died immediately. And no way to get it to start again.

It seems it is not a fuel problem. Can it be that there is to much fuel wich prevents the spark plugs to build an effective spark??? Any idea?

Thanks a lot to you all

You posted a very nice oscilloscope pattern but I suspect that it was the input of the ignition coil that you measured.  I once had your problem with an automobile.  The ignition coil was giving a weak output voltage and the introduction of more fuel into the cylinders extinguished the sparks just as you suggested in the quote above.  The coil could be your problem.

@1Wingman1: many thanks for your support/suggestion. Coil was changed with an other not Honda giving even a better spark. As you can immagine engine doesn't come to live. :-(

If your replacement coil came from another application the following from MGAguru.com might apply concerning coil polarity and the failure of the replacement coil to run the bike:

"Why then do we worry about coil polarity? Because the spark plugs do care which way the electrons are flowing in the high tension circuit. The spark plug has a thermally insulated center electrode (surrounded by ceramic). With engine running the center electrode runs substantially hotter than the exposed end electrode. Design of the ceramic insulator determines how hot the center electrode will run, leading to the designation of hotter or colder spark plugs. As electrons go, they love to jump away from a hot surface and fly toward a colder surface, so it is easier to drive them from hot to cold rather than from cold to hot. End result is a difference of 15 to 30 percent in voltage required to make spark "initially" jump the gap on the plug depending on which way it is going. So the spark plug prefers to see a voltage potential that is negative on the center electrode and positive on the end electrode for the very first hop of the spark."


This is a last ditch attempt to pin the trouble on the ignition coil. Desperate situations require desperate measures. Your problem has to be fuel or ignition. Good luck.

Have you purged the fuel lines where they go into the injectors?

Search for Silverwing Down and you will see the crud that appeared when I purged my fuel lines and cured my starting issues. I'm very confident that this may sort your issue.

ANd dont worry happy to help

If the engine started after being left alone for a while and then died when the throttle was opened, could there be a fault with the cold start system? Now I have no idea how this works on the SW but I had a similar problem with one of my old cars which had the mechanical type automatic choke.

I've sorted my Moto Guzzi and the issue was interesting and you never know, might be relevant.

My first problem was a bit of dirt in one of the carbs but I also had an issue with my battery. It had no problem buzzing the 1000cc engine over but the RITA ignition system absolutely must have at least 11.5 volts. It would start a lot of the time but when I revved it up, the alternator field coils energized and dragged the voltage down, killing the spark.

You might have a look for this happening. Maybe you have a regulator or alternator fault.

Mine is not caused by a fault - just 40 year-old electrics.

Dear all,
unfortunately no news to the subject.
For now we stopped with the SW. As soon as I have news I let you know.
@smellybeard: with the spark plugs outside of the engine they are giving a spark. I don't know il for some reason as I insert the plugs in the engine they could stop to work?
Best regards

Snapy wrote:

(Snip) @smellybeard: with the spark plugs outside of the engine they are giving a spark. I don't know il for some reason as I insert the plugs in the engine they could stop to work?
Best regards

If the plugs won’t fire under compression it might very well indicate a weak coil.

Update and end of the problem
Hello community, SW is working again!
Just as we were near to replace the entire engine he came back to life almost on his own after more than a year in repair.
The fuel in the its tank was used for an other vehicle, this vehicle started to have problems. The tank was than filled for the third or fourth time. Just trying to start like "millions" of time he came back to life as some times before, but stayed working, even if coughing. The engine didn't augment revolutions as gas is turned but it stayed alive. The engine was let idling for a 20 minutes than turned off. After cooling down he was restarted and did the job still coughing. The next time wen started again he was able to augment revolutions coughing didn't improve. He was let idling about 30 min than turned off. After cooling down he was restarted and taken on road. The SW did his job as nothing has been.
No idea wat really was the problem.
The fuel was changed repeatedly with fresh one and before having the problem SW was stopped only for about 3 month, not time enough to alter the composition of the fuel in its tank.
So a lot of work without knowing what was really the problem
Have a nice riding to all you.
Best regards from Switzerland

Hi Snapy.

Having read the full story about your problems getting the Swing to run properly I believe your problem is caused by Ethanol build up due to petrol evaporating while unused.
The Swing engine was never designed for mixing Ethanol with petrol as a fuel.
I also understand your petrol in Switzerland has a higher amount of Ethanol mixture than here in the UK.
Having got your Swing to run properly now I would treat/ clean the fuel system with injection cleaner.
There are also additives and fuel enrichers you can add on filling up with fuel to reduce the effects of Ethanol.

Hope this helps.

Be safe, be seen!