Odd fart

I was trying to start the 750 this morning, when the starter was going and turning the engine it would not start and also heard a sound like when you open a soda can "PSST" very short but it did it a couple of times.

I looked under the gas tank and everytime the starter cranked it looked like either somewhere from the intake manifold (or the vacuum port) a little bit of air and/or steam would pop out and then stop.

I have had no time to look into it but wanted to share and find out if somebody has experienced the same hiccup.

This weekend I will take the tank off and try to find out what is going on there. a few days ago I did the propane torch test and the idle stayed put but this hissing has me thinking twice about it.

 

Start at the exhaust manifolds before tank removal

 

The same process may be at work here:

Why does my engine sometimes backfire when I first turn on the key (without attempting to start the engine)?:

- When you kill the engine, the intakes will still have some remaining (un-burned) air-fuel mixture remaining in them. Upon powering up the bike (turning the key on), the ignition system will apply 12 volts to the coils, thus charging them. Of course, that constant current is not good for the coils, so few seconds later (if the engine is not started) the TCI shuts down the coils by grounding them (to protect the coils from overheating) which cuts the current to the coils and thus triggers a spark to the plugs. If there is enough un-burned fuel in the intake manifolds or the combustion chambers, and if the valves are held open by the camshafts, a backfire thru the exhaust header and/or thru the intake manifolds/carbs/airbox can result.

 

Chacal.... very interesting!

 

Thanks,

Today I looked under the gas tank and while cranking I heard the same noise. It seems like it came from vacuum port # 3. I thought the vacuum ports would "suck air" into the manifolds not push air out through the hose.

It did that a couple of times but I was unable to get the bike to start. I check for spark and that was ok, got new plugs, new oil, I had it hooked up to my car battery to make sure that there was plenty of juice turning the engine.

I was hoping for some easy troubleshoot but so far no answer so I will have to stop trying shortcuts and go through the service manual every step of the way.

Darn it, PO said that the only issue was the starer clutch slipped when engine was hot, I guess there goes that. And one again I have another bike on the driveway that won't run

 

Haven't learned this already?

Never believe a PO!!!

 

I do know better but the bike started a few times since I got it, sometimes without a hiccup at all some others gave me a hard time to start. I guess it called it quits until I go through everything

 

the only time i've heard that, the intake cam was one tooth off. that bike didn't try to fire
backfire, the cylinder fires with the intake open? valve way tight, blowing past a closed valve or during overlap?
starter clutch slips, could this be how starter clutches crack? the starter isn't powerful enough to crack them but a backfire trying to spin the engine backwards could be.
i'd try to not let it start, crank it and watch the intake rubber manifold, look for it to swell up in pulses as it cranks with the throttle closed

 

Now I need some translating.

I can't quite tell where statements end and questions start. When you say "I would try to not let it start, crank it and watch the intake as it cranks with the throttle closed". How should I crank it without letting it start?

I am not trying to be a smartie, I'm just trying to figure this one out because I am quite puzzled.

 

Pull the two Plug-in's to the TCI.