Vapor lock?
Banned
Joined: Jul 2008
Posts: 1,036
Likes: 67
Battery checked out ok. I have a theory that it's the lower grade gas I've been running. I would normally run the mid grade but the last couple times I filled up with the recommended premium. No problems since. Lower grade gas will more easily combust under extreme pressure and heat which is why you get "spark knock" or "pinging" so this must be it. That's the only answer I can come up with. Thanks for all the input!
4th Gear
Joined: Mar 2014
Posts: 8
Likes: 0
From: Howards Grove, WI
I'm having the exact same problem with my bike. Happened twice in the last 3 days, both times I started it up after riding it for a bit and then shutting it down for about 15 minutes. 09 Street Glide, Rhinehart slips ons and that's it. I've had the compensator replaced and the battery seems good. Starts right up when it's cold, but doesn't want to start when hot.
Let me know if you find anything with yours, I'm going to try to figure out what is going on with mine, it's a new problem this year.
Let me know if you find anything with yours, I'm going to try to figure out what is going on with mine, it's a new problem this year.
Outstanding HDF Member
Joined: Nov 2008
Posts: 2,034
Likes: 127
I have not seen a late model Harley vapor lock since Shep was a pup. The new fuel pumps put a lot of pressure in there. If you are having problems with the engine turning over when it is hot, I would suspect you have a weak battery. When you turn the engine off on a hot engine it comes to rest on the compression stroke. At this point it actually builds up pressure in the combustion chamber since there is no cool air going over the jugs to cool it off. If your battery does not have enough "oomph" to overcome the inherent pressure in the compression stroke it won't spin it until it cools off and the pressure drops. I think I would suspect a weak battery before anything else.
At 80 degrees ambient temperature anything below 12.6 volts is not 100%. 12.2 volts is actually at a 50% charge. It goes down real fast.
At 80 degrees ambient temperature anything below 12.6 volts is not 100%. 12.2 volts is actually at a 50% charge. It goes down real fast.
Thread Starter
|
Intermediate
Joined: Aug 2008
Posts: 43
Likes: 0
From: Catawissa, Pa
I have not seen a late model Harley vapor lock since Shep was a pup. The new fuel pumps put a lot of pressure in there. If you are having problems with the engine turning over when it is hot, I would suspect you have a weak battery. When you turn the engine off on a hot engine it comes to rest on the compression stroke. At this point it actually builds up pressure in the combustion chamber since there is no cool air going over the jugs to cool it off. If your battery does not have enough "oomph" to overcome the inherent pressure in the compression stroke it won't spin it until it cools off and the pressure drops. I think I would suspect a weak battery before anything else.
At 80 degrees ambient temperature anything below 12.6 volts is not 100%. 12.2 volts is actually at a 50% charge. It goes down real fast.
At 80 degrees ambient temperature anything below 12.6 volts is not 100%. 12.2 volts is actually at a 50% charge. It goes down real fast.
Outstanding HDF Member
Joined: May 2013
Posts: 2,059
Likes: 4
From: Florida
2009 SG 30, 600 mi. Since the end of riding season last year the engine kind of locks up if you try to start it when its hot. Eventually it does fire up and seems to run fine and I doubt the starter is bad. I am suspecting a leaky fuel injector is causing the thing to vapor lock when hot. Never happens when cold. Like it won't turn over, ya know? Anybody else ever had this happen? Is it a known issue? The dealer (as usual) doesn't have a clue.
Thanks!
Thanks!
Grand HDF Member
Joined: May 2008
Posts: 4,585
Likes: 673
From: Rolla
That quick disconnect fitting can keep your bike from starting, but it won't have any effect on the engine cranking over.
What the OP is describing is when hot, his bike won't crank over very easy.
Just like when you have a low battery, but he says his battery is good.
You can completely disconnect your fuel fitting, and the bike will still crank over (starter will spin the engine). It just won't start.
Road Warrior
Joined: Nov 2014
Posts: 1,962
Likes: 140
From: NY
I'm having the exact same problem with my bike. Happened twice in the last 3 days, both times I started it up after riding it for a bit and then shutting it down for about 15 minutes. 09 Street Glide, Rhinehart slips ons and that's it. I've had the compensator replaced and the battery seems good. Starts right up when it's cold, but doesn't want to start when hot.
Let me know if you find anything with yours, I'm going to try to figure out what is going on with mine, it's a new problem this year.
Let me know if you find anything with yours, I'm going to try to figure out what is going on with mine, it's a new problem this year.
The most likely reasons your HD will start better cold (not 30 deg ,meaning 55-60+ deg out) then hot is when hot there is more resistance in electrical items like starter/battery cables,battery so if any 1 or 2 of those items are not at or close to 100% of their operating efficiency when new thats when a hot lrg air cooled v-twin will have an issue spining over when heat soaked like for example stopping for fuel & trying to refire 5-8 mins later when everything heat soaks to bit higher temp 5 mins later when you try to fire it up .
So you can IN FACT have a battery tests within allowed spec that can still be at the root of a hot start issue,same goes for the starter that could also pass test spec of amp & voltage draw when tested but still be part of the issue if the battery & starter just happen to just make spec when tested but are operating at 80-85% of their full operating power/efficiency which was enough to pass spec but since they are both collectively down a bit on output is just enough to collectively together cause a hot start issue.
Been there done that many times over the past 4+ decades wrenching bikes and 60's to very early 70's classic muscle cars.
Scott
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Tourer
Joined: Mar 2010
Posts: 428
Likes: 35
From: Calgary Alberta Canada
As stated above engines stop on the compression stroke. With my old roadking when it did that I learned a trick. Bump starter button . That makes it bounce back down lessening compression and then hit it again and it can overcome the compression with a little inertia. As stated above as well, with a good battery and starter short of it being seized it should at least turn over?
