hot start question
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Tourer
Joined: Apr 2018
Posts: 315
Likes: 154
From: Upstate NY
hot start question
I saw previously mentioned (and it works) that when the bike is hot, hitting the starter before the fuel pump is primed makes the bike fire easier when hot. Like I said, it works, no argument there.
Here is my question..... Why does this work?
My background is cars/trucks, and I just cant seem to wrap my small brain around this.........
Does the fuel injection system give the cylinders a shot before the engine starts cranking or something???
BTW, I did do a search and could not find a reason as to why this works....
Here is my question..... Why does this work?
My background is cars/trucks, and I just cant seem to wrap my small brain around this.........
Does the fuel injection system give the cylinders a shot before the engine starts cranking or something???
BTW, I did do a search and could not find a reason as to why this works....
Tourer
Joined: Jan 2018
Posts: 319
Likes: 139
From: Seattle
Must admit I'm more versed in carb than EFI but my take is the ECM won't/can't (not enough fuel pressure) fire the injectors until the pump priming sequence is complete. By then you have the inertia of the flywheels swinging away. Thus, no charged cylinders to kick the pistons back. Hopefully someone else will chime in and have a better explanation.
Last edited by FPV; Sep 15, 2018 at 10:01 AM.
Grand HDF Member
Joined: Jan 2012
Posts: 4,459
Likes: 2,900
From: Oklahoma
My theory is questionable at best. When mine began to do that, I figured there must be some seepage from one or both fuel injectors that is minimized when the starter is used quickly after power up. What makes that questionable is that the same bike starts by the book after a new battery is installed. Now, I assume this is the first indication of the battery no longer being able to provide the big current push needed for a hot start. Next theory, my bike has over 92,000 miles and I assume the starter solenoid contacts are no longer "like new" so I will be rebuilding the solenoid this winter to ensure maximum current flow with new contacts. Your guess is as good or better than mine.
Road Warrior
Joined: Jun 2008
Posts: 1,344
Likes: 173
From: Watertown, CT
Same solution to a common problem as you have. I figure as you do that there is a little fuel being injected into the cylinder more for cold starts than hot.
By hitting the starter the way we do indicates fuel being dumped into the cylinders .Been starting my '10 RK like this for years.
By hitting the starter the way we do indicates fuel being dumped into the cylinders .Been starting my '10 RK like this for years.
Club Member
Joined: Dec 2007
Posts: 4,192
Likes: 168
From: Knoxville, Tn
Hot Starts
I'll tell you what I think happens with a hot start on a HD fuel injected bike...When the fuel pump primes and the bike is hot, there isn't enough oxygen to support combustion in the cylinders until the pistons pull in cooler and cleaner air. That's why it has to turn over a few times before it starts when hot and primed. I also have been starting my bikes for years without letting them prime and it works the same for automatic compression releases or with the manual ones. On both, I put the run/stop switch on the run position and then turn the ignition on and immediately hit the starter before it has time to prime. I thought about why it works so well, this way rather than with the SOP that Harley prints. Really, it's the only logical solution I can think of.
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HDF Community Team
Joined: Nov 2012
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From: USA
I agree, it works. Not hugely different, but it is noticeable.
Something Ive noticed, albeit mild, is that with a full pump cycling/priming, the bike starts with a lumpy surge. Makes me wonder if the injectors go through a cycling while priming and making ready.
Something Ive noticed, albeit mild, is that with a full pump cycling/priming, the bike starts with a lumpy surge. Makes me wonder if the injectors go through a cycling while priming and making ready.
