Modern Vespa

With the season approaching, I am taking another final attempt at troubleshooting my (now) permanent crank but no start GTV. It showed similar symptoms to what I went through in 2019 (2017 GTV 300 no start. Read a lot, checked a lot, need help (Post 2343004)) and so I did many of the same steps but finally decided to start over one more time with the basics:

Check spark, fuel, air, battery and compression. Results:

- Spark: Bright. See pic and video link. Hopefully the video link(s) to my dropbox work ok.
- Fuel: Nice looking spray cone. Don't have a way to measure the pressure but the pic and videos provide decent visual checks of injector squirting and pump priming.
- Air: I can lightly feel air drawn in while trying to cover the throttle body intake by hand.
- I also sprayed short bursts of starter fluid into the intake while cranking the engine. Nothing...
- Compression: I stuck the tip of my finger on the spark plug hole and pushed it in pretty good. First compression stroke pushed the finger right off the hole. I don't have a compression gauge for an exact measurement.
- Battery: To eliminate any questions (voltage, cranking speed) around my aging battery, I installed and charged a new battery. You can hear the cranking speed in the spark plug and pump videos.

- Observation/question about the spark and injector videos: It seems that there is a repeating pattern of several impulses followed by a very brief pause, impulses and pause, impulses and pause, etc. I noticed this for the spark as well as the injector. Does anyone know if this is normal?

- Additional info: When this crank but no start first started happening about a year go, it was rare and seemingly random. It would happen maybe one out of every ten times starting. At the end of last season, it eventually became permanent. Ie it happens every time now and does not start anymore at all.


Any suggestions on where to go from here besides hauling it to the closest dealer (150mi one way)? Thank you!



Spark while cranking video:
https://www.dropbox.com/scl/fi/7m7a5bge6d38457aqp4pq/IMG_2727-1.mov?rlkey=700g7jxqbv0v4lp2o5j008njt&st=a9xfeo5b&dl=0

Injector squirting while cranking video:
https://www.dropbox.com/scl/fi/w65sopmtl7v8swecignt3/Fuel.mov?rlkey=vzen3fboy9ekuzz00doih6evg&st=dylli2o1&dl=0

Fuel pump priming with key on:
https://www.dropbox.com/scl/fi/2t3zjc35yj9o23v8rpr5k/IMG_2725.mov?rlkey=z6k93wpqcslyvv9gocb5l25wm&st=23lkz34k&dl=0[img][/img]

And you *have* checked valve clearances?

Thx, good question. I have not.

I just went out to the garage to take another look at the clearance between body and valve cover. Not sure I want to undertake that myself....

Something I could have mentioned in my earlier post: I am the original owner (purchased 2018) and the odometer currently reads about 5700 miles.

OK.
So you are the original owner.
Bought it new in 2017.

In 2019 you wrote:
"My 300 GTV is just over a year old (2017 model year) and has around 3000 miles on it. It ran fine until I shut it off one night and the next morning it would not start (cranking over fine but not firing)."


But now you write it did 5700 miles.

Does it mean this 2019 problem was solved, but now you run into a similar problem?

I read it that the problem's been intermittent, gradually getting worse, until it finally won't start at all.

You have to undo the rear shocks and raise up the body so the engine swings down at the back - the engine front swings up and around to let you get at the valve cover. Just make sure no wires or hoses get stretched while doing this - the spark plug one in particular.

But before you do that - ensure the throttle body idle bypass passage is clean and clear. Read this:

https://cheekythoma3.wixsite.com/itsme/idle

If that's blocked, then you'll have great difficulty getting the bike to start, as any twist of the throttle and the ECU will not allow a start.

I purchased it new in 2018 and still own it. Yes, current mileage is about 5700 miles.

Sorry for any inconsistencies in my timeline. I should not have written 'last year' (last year was when it started again...). Also, when i wrote 'still' instead of 'again' I was thinking of my unsuccessful efforts last year and not those back in 2019. Thanks for catching that.

Back in 2019, the root cause if I remember right was a spark plug boot not seating correctly. Last year then, similar symptoms to those in 2019 started. After making sure it was not the boot again, I started down a similar path of troubleshooting as in 2019. The difference is that it occurred more and more often to where it now refuses to start at all. Last fall I eventually just walked away from it.

With the new season approaching, I decided to have another go at it a couple days ago.

Hope this clarifies the timeline.

Check the valve clearances as per jimc. Really not that hard but buy the feeler gauges used in Scooterwest video (YouTube) which makes it easier. Buy new gasket and bolt gaskets.

I released the throttle body far enough to get some carb spray and compressed air into the bypass. Both made it through. It will still not start BUT.... it sounds like it is trying to here and there. During the few seconds the starter turns the engine over (while holding the stater button) there are probably 2-4 times where it sounds like it is close. It did not do that before!

I will try a couple more rounds of spray and air and see if things continue improving.

Succes! It started Only problem: Now it smokes pretty bad...

I did the spray/air combo a few times and it still wouldn't start. However, I could tell I was getting closer and so I decided to 'assist' the air going through the bypass by aiming compressed air (after dialing the pressure way down) into the bypass hole while cranking the engine. A couple seconds later the engine started right up. I started / stopped it a few times since and it started without hesitation each time.

So that's awesome! THANK YOU for the suggestion of cleaning out the bypass.

However, it started smoking pretty bad soon after startup and I would like to get some thoughts on the possible cause and whether or not this could turn into a bad situation (fire):
- About twenty seconds into idling with the seat up and the liner still out, I saw smoke coming out of the liner opening.
- I looked for the source and, to the best I can tell, it is starting around the first section of the exhaust that also houses the oxygen sensor (see diagram). This section of the exhaust was already very hot after the first idling.
- I shut the engine off and the smoke slowly diminished over about 30-60s.
- I repeated this (start, wait for smoke and shut down again) a couple more time with the same result (smoke after 15-20s or so) each time.

Any thoughts on what might be causing the smoke? My only suspicion is that, with the injector squirting while cranking during the numerous times of trying to start the engine, a fair amount of unburnt fuel could have made it into the exhaust....? Should i be concerned about a fire?

Any thoughts? Thx....

Personally, as long as I could convince myself that there wasn't an active gasoline link I would just let it idle for two or three minutes and see if the smoke cleared. If it stayed the same or got slightly better I probably take it for a ride. My operating assumption would be that some oil had somehow gotten on the exhaust pipes and that a ride would probably clear it off. But I'm not particularly risk-averse.