Hiss sound when cold starting

838 Views 9 Replies 5 Participants Last post by Mordru, 9 mo ago

Mordru

Discussion Starter · 10 mo ago

Hi everyone, anyone know about a HISS sound when doing a cold start? Ever since I replaced my carb diaphragms, ive been hearing this sound. Is it some sort of a backfire?

It runs fine otherwise.

Here is my thread with my recent work on the bike. Essentially just a carb cleaning, replaced diaphragms, and a new battery.

Loss of power

Hi everyone, hope you are well if you're reading this. Here's the story: Ran the bike in the morning to work, and on lunch just fine. (Hard start when the engine is cold, but my battery needs replaced. Once it's started it runs great) Went to leave work, bike is giving me a real hard time...

www.ex-500.com

Here is a link to a video with the sound.
Hiss sound when starting

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e10_muppet

· #2 · 10 mo ago

Does it continue to hiss when the bike is running or is it just that short sharp pfft on startup? If it's constant then obviously check all of the hoses are seated properly. I have a hiss coming from the back of my petcock when it's running, which i've just taped over.

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Mordru

Discussion Starter · #3 · 10 mo ago

Just a quick sharp hiss/pfft on startup. Doesnt happen while running. Not sure if its something that needs investigating or not lol

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Mordru

Discussion Starter · #4 · 10 mo ago

Just noticed this today; I rode the bike out for a bit, parked it for a couple hours. Going to start it again to leave. Switched the kill switch to run. Put the key in, turned on the ignition. At this point there was a puff/backfire type noise!!! I had not touched the starter. Only turned the key.

Anyone know whats going on here?!?!

P.S. side note Im thinking about getting new carbs boots as mine are stock (im assuming) and are really showing their age (bike is a '93).

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aneiwck

· #5 · 10 mo ago

Did you ever figure out the cause of the electric snap noise that happened prior to replacing the diaphragms?

I would look at electrical parts first, especially since you said it happened with battery voltage, before cranking.

I took a peek at the wiring diagrams, first inspect fuses and the ic ignitor.

In your video it sounds like the starter cuts out with the hiss sound, can you confirm that?

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Mordru

Discussion Starter · #6 · 9 mo ago

Eventually I figured out that I did not seat my carb very good in the boots. I loosened the clamps, pushed the carbs in a little bit more and they seated. Tightened everything back up and now the hiss sound is gone when cold starting. Woo hoo!

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FlipFlop

· #7 · 9 mo ago

Mordru said:
Eventually I figured out that I did not seat my carb very good in the boots. I loosened the clamps, pushed the carbs in a little bit more and they seated. Tightened everything back up and now the hiss sound is gone when cold starting. Woo hoo!

Thank you for updating, over the years so many just don't bother saying anything or they gave up and threw it in the back of the garage. Glad you figured it out and was super simple!

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po18guy

· #8 · 9 mo ago

The key-on Pffft: Due to the engine occasionally stopping just before TDC on the firing stroke, the ignition trigger on the flywheel is tripping the sensor to send the spark siognal to the coils. The ignition is really dumb and does not know if the engine is running or stopped. All it knows is "trigger is close, send spark signal" And there it sits, waiting for the juice to send the signal. Then, when you go key on, the coils are energezied and are immediately told to send a spark by the trigger (only takes a microsecond). But the piston is before TDC, so the combustion that occurs sends the crank backward, causing the starter clutch to make its weird sound.

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Mordru

Discussion Starter · #9 · 9 mo ago

po18guy said:
The key-on Pffft: Due to the engine occasionally stopping just before TDC on the firing stroke, the ignition trigger on the flywheel is tripping the sensor to send the spark siognal to the coils. The ignition is really dumb and does not know if the engine is running or stopped. All it knows is "trigger is close, send spark signal" And there it sits, waiting for the juice to send the signal. Then, when you go key on, the coils are energezied and are immediately told to send a spark by the trigger (only takes a microsecond). But the piston is before TDC, so the combustion that occurs sends the crank backward, causing the starter clutch to make its weird sound.

Oh, that explains it perfectly. Here I thought I was going crazy.

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Mordru

Discussion Starter · #10 · 9 mo ago

FlipFlop said:
Thank you for updating, over the years so many just don't bother saying anything or they gave up and threw it in the back of the garage. Glad you figured it out and was super simple!

I always come back if I get a solution! You never know, it could help someone in a pinch, even if its something stupid simple. Sometimes you just don't think about the small stuff.

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