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clunk noise when starting

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  #1  
Old 1 Week Ago
Encyber Encyber is offline
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Default What's that Clunk?

2005 XL 1200.

Happens nearly every time. I usually gas up in the morning on my way to work. The gas station is about 10 miles from my home so the motor is warmed up pretty good by then. I shut it down at the pump, gas it up with 93 octane and then when I go to start it up again, the engine turns over once and quits with a loud and very heavy CLUNK. Sounds terrible and freaks me out every time. So, WTF is it?

I live in Florida. Bought the bike in March and it is now October so I don't believe weather plays a part in the problem. Battery is new (several months). Carb was rebuilt before I bought the bike in Feb and the motor otherwise runs like a top.

For the record, the only time it does this is immediately after refueling. Cold starts and warm starts not related to refueling are normal

Is this a vacuum thing? What can I do to stop it from doing that.
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  #2  
Old 1 Week Ago
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bustert bustert is offline
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i cannot see any correlation.
throw this out:
if while sitting, the manifold some how get a little extra fuel (atomized vapor) and it fires off and causes a mild kick back.
every time i have starting issue with the starter and ratchet, it was the battery, starts and get progressively worst. being new doesn't rule it out but also look at wiring connections.
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  #3  
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John Harper John Harper is offline
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I believe I've read that 1200s can cause momentary starter stall, depending on where the pistons ended up when you shut down. I forget exactly what the issue is, but I do recall it was 1200 size engines, maybe combined with a weak starter or a cylinder under compression (?). Maybe someone else has some better idea.

John
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My first Dyna did that all the time. Still worked OK.
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I've found that mine does that sometimes and if I just 'tap' the start button once (fraction of a second) and then push the start button, it won't clunk. I just have to remember to do that when the station is full of people!
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The ignition is on while the starter is, it doesn't shut off for the first revolution while the crank gets started rotating. The engine is fighting the starter. My BT EVO had the original "small starter" before Harley upgraded them. We'd go into the right handlebar switch and change one wire so the engine would crank with the kill switch OFF. Hit the starter with kill switch off, turn the kill switch on as soon as the engine was spinning. Made life much easier on the starter and battery. I think Canbus etc has removed that option and Harley chose not to build it into the ECU.

Or are you referring to the exhaust backfire they do while starting? Seems IAC settings and cranking fuel adjustments can help that. I find that more annoying.
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Default

Thanks everyone for your insight.

Toejam503, I thought about doing that. Haven't tried it yet but will.

Tomcat, your solution will be option two, mostly because I'm not sure what wire I'd change. Oh, and it's definitely not backfire.

Bustert, you think it would help burn off manifold fuel if I rev the throttle a couple of times before hitting the kill switch? Or would that just make it worse?
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It's called heat soak.

It happens to a lot of 1200's. When you kill the engine while it's at temp, it naturally rotates until it comes up against compression as it dies. So, when you try to fire it up, you are already against the compression, the starter and battery are right on the line as far as being strong enough to do the job and the fuel mix that is in the jug is hot and expanding from sitting there for the short time.

When we push start a speedway bike, we roll it backwards in gear to rotate the engine to where it is up against compression in the opposite direction of the running engine. That way as the rider lets out the clutch the engine can rotate some before it gets up against compression and it's more likely to rotate through that part of the stroke and fire off.

The cure for your bike is an "all balls" starter with more torque, paying attention to battery condition, connections and condition of cables.

If you hold the button, it will come to a stop then rotate through and start, so it may suck but the bike usually can overcome it.
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Quote:
Originally Posted by Encyber View Post
Tomcat, your solution will be option two, mostly because I'm not sure what wire I'd change. Oh, and it's definitely not backfire.
We did this in the 80's. I remember it did involve de-soldering / soldering switch connections. It was easy to see what to do as the FSM had a wiring diagram that showed the actual switch circuitry in the switch assy. We did it because the "small" starter could really balk on hot starts.
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Default

Wedge, thanks for explaining the physics behind the problem. That makes so much sense to me now. It a way, the symptom of this problem reminds me of the symptom of a low battery. Before I replaced the battery, the motor would do something similar. It would try and rotate, hit hard compression immediately, pause and then jump to a start. This is just more of the same on steroids.

Battery's a good quality high-cranking amp model. Starter is original and old. Think I'll look at getting a high-Torque replacement as you suggest.

Thanks again to everyone who took the time to comment. I love this site. A million years of combined experience and counting. Great community!
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