Big Bang on startup
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Tourer
Joined: May 2014
Posts: 299
Likes: 40
From: Eastern foothills of Shenandoah Mountains, Virginia
Big Bang on startup
Yesterday when I started the bike cold ( 60f) it made one loud BANG and then ran.
Never did that before.
Then today engine got hotter than I've ever felt in 20 city blocks of stop-go-stop-idle in DC after Rolling Thunder. Then rode 20 cool miles at 60mph, shut down and it dieseled 2 strokes.
After a 2-hour cool stop, one loud BANG on startup, then minor sputtering at stops for ten minutes.
Did not bang at various other stops both days.
FLSTC Heritage 99
Is the bang damaging? How to fix?
Any Big Bang Theory?
Never did that before.
Then today engine got hotter than I've ever felt in 20 city blocks of stop-go-stop-idle in DC after Rolling Thunder. Then rode 20 cool miles at 60mph, shut down and it dieseled 2 strokes.
After a 2-hour cool stop, one loud BANG on startup, then minor sputtering at stops for ten minutes.
Did not bang at various other stops both days.
FLSTC Heritage 99
Is the bang damaging? How to fix?
Any Big Bang Theory?
Seasoned HDF Member
Joined: Dec 2012
Posts: 6,673
Likes: 502
From: Orange County
Mine does that occasionally, however, I believe it is due to the high compression 98CI big bore that was recently installed.
Any recent engine work? If not, it could be the starter, or the starter gear.
I'm sure others here will chime in...
Any recent engine work? If not, it could be the starter, or the starter gear.
I'm sure others here will chime in...
Last edited by Road Star; May 30, 2016 at 12:50 AM.
Road Master
Joined: Feb 2014
Posts: 913
Likes: 5
From: indiana
The loud bang out the exhaust is un burnt fuel in the cylinder at startup it will cause a backfire but running hot and sputtering and dieseling is running lean and overheating like said above check for a intake leak
Seasoned HDF Member
Joined: Oct 2012
Posts: 11,226
Likes: 3,049
From: St.Louis Mo.
does it seem to be a fuel or electrical problem ? make sure the vacuum line for the voes is stiil hooked up. could be bad gas or i've seen the timing plate slip alittle over time in evo's changing the timing. how many miles ? bad plug wire or old plugs ? i'm assuming it's carbed.
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Tourer
Joined: May 2014
Posts: 299
Likes: 40
From: Eastern foothills of Shenandoah Mountains, Virginia
One sharp short BANG, almost a CLANG metallic sound, from the right front at the moment engine started.
Not out of exhaust, not exhaust type sound.
Details:
New plugs and plug wires 500 miles ago.
Had Samson Long Shots, too loud so I put stock pipes back on 700 miles ago. No carb adjustment.
Fuel mileage 39 - 40mpg.
Heritage FLSTC 99 EVO carburetted. 42,000 miles
Bike was sitting 3 weeks, had Seafoam in tank. 93 octane
First BANG was after 3 weeks sitting: Choke, twisted throttle 6 times before hitting Start. The engine started the same moment of the BANG.
Then 100 miles of 35-50 mph twistish 2-lane.
Power as usual (but I don't know if its 'usual' power is on par with 'normal' for this engine. My only comparisons are an 883 and two twinkies, all 3 faster than my 99 evo).
After Rolling Thunder I rode 20 city blocks in DC clogged with cars, stop, go, idle, engine hotter than I've ever felt.
Then rode 20 miles 60mph in cool air, shut down and it dieseled two strokes. Never dieseled before.
After 2 hours, started with a BANG almost as loud as day before. Just half choke, no twists pre-start.
Starter engages fine. Could it be dis-engaging too slowly after I let go the button?
I'm not sure if my thumb was still pushing on the start button at the bang moment. Talking a fraction of a second there. I'm not someone who keeps spinning starters too long. My thumb muscle memory lets go when I hear the engine catch.
Still scratching head
Not out of exhaust, not exhaust type sound.
Details:
New plugs and plug wires 500 miles ago.
Had Samson Long Shots, too loud so I put stock pipes back on 700 miles ago. No carb adjustment.
Fuel mileage 39 - 40mpg.
Heritage FLSTC 99 EVO carburetted. 42,000 miles
Bike was sitting 3 weeks, had Seafoam in tank. 93 octane
First BANG was after 3 weeks sitting: Choke, twisted throttle 6 times before hitting Start. The engine started the same moment of the BANG.
Then 100 miles of 35-50 mph twistish 2-lane.
Power as usual (but I don't know if its 'usual' power is on par with 'normal' for this engine. My only comparisons are an 883 and two twinkies, all 3 faster than my 99 evo).
After Rolling Thunder I rode 20 city blocks in DC clogged with cars, stop, go, idle, engine hotter than I've ever felt.
Then rode 20 miles 60mph in cool air, shut down and it dieseled two strokes. Never dieseled before.
After 2 hours, started with a BANG almost as loud as day before. Just half choke, no twists pre-start.
Starter engages fine. Could it be dis-engaging too slowly after I let go the button?
I'm not sure if my thumb was still pushing on the start button at the bang moment. Talking a fraction of a second there. I'm not someone who keeps spinning starters too long. My thumb muscle memory lets go when I hear the engine catch.
Still scratching head
Last edited by Kayakeur; May 30, 2016 at 01:02 PM. Reason: clarify
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Seasoned HDF Member
Joined: Mar 2010
Posts: 21,116
Likes: 7,639
From: Poolville
You are going to need to put up a video. 6 pumps on the accelerator with a choke to boot is a lot of fuel... And not rejetting the carb after a change in exhaust like that will also create issues. I'll bet the right front bang is fuel coughing back out the carburetor because of all the above.....
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