Big bang while trying to start.

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K9Sicem
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Big bang while trying to start.

Post #1 by K9Sicem » Wed Oct 09, 2019 8:37 am

I have a 76 LTD that I just got a week or two ago. I have driven it 50 to 75 miles without issues. I tried to start it last night without luck. When I shut off the key it back fired loud. I tired again and it did the same think. This bike has an electronic ignition. This is my first bike so I have little knowledge of what to look for. I have restored several old trucks. Based on that it is my thought that it is loading up with fuel and only getting spark when I tried to shut off the key. Any help would be appreciated.

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Re: Big bang while trying to start.

Post #2 by rcmatt007 » Wed Oct 09, 2019 9:04 am

First of all. Have you changed the timing belts?
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Re: Big bang while trying to start.

Post #3 by K9Sicem » Wed Oct 09, 2019 9:47 am

I have not. It was changed when the bike was rebuild. It should be almost new.

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Re: Big bang while trying to start.

Post #4 by dontwantapickle » Wed Oct 09, 2019 10:31 am

I have had that happen on a Norton I had with an electronic ignition.
It turned out to be a bad key switch that only worked when in the perfect position or made contact when the key was turned.

It may not be your issue, but it might be worth checking out.

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Re: Big bang while trying to start.

Post #5 by Sagebrush » Wed Oct 09, 2019 11:22 am

Seems to me I remember something about a low voltage situation where the coils didn't have enough juice to fire while the starter was turning over but just as you released the starter button removing the starter amperage the coil fired one time and started the bike. Seems to me it was a classic symptom on a 1500 of a weakening battery. I'm not very clear on what the final cause was but I would check for spark while turning the engine over to see if it there our just too weak to fire.
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Re: Big bang while trying to start.

Post #6 by ericheath » Wed Oct 09, 2019 11:16 pm

My 77 will kick back when I turn the key off sometimes, but not a Big Bang, and not when just releasing the starter button. The motor is dead still when switched off. It has Dyna Ignition.

Looking forward to theories.

I have wondered about the Hall effect of the Dyna triggering a signal to a coil as a result of the power drop as the key is switched off. The bike is supposed to fire ahead of TDC and with the piston stopped ahead of TDC, it would have to backfire.

The loud bangs could be from the waste spark touching off unburnt fuel in the opposite cylinder on the exhaust stroke.
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Re: Big bang while trying to start.

Post #7 by robin1731 » Thu Oct 10, 2019 7:45 am

K9Sicem wrote:snip...…... thought that it is loading up with fuel and only getting spark when I tried to shut off the key.


First step. Verify if you have spark or not while cranking the engine. Pull all the plug. Place one plug in a plug wire and ground it to the engine. Crank engine over. You should have spark. And yes, installing just one plug will give you spark. You do not need two plugs installed to check spark with a Dyna.

Actually do this first. Before doing that turn the engine over with the starter with the run switch in the off position. Just to make sure there is no fuel in the cylinders. Have the fuel petcock turned off too.

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Re: Big bang while trying to start.

Post #8 by K9Sicem » Thu Oct 10, 2019 8:06 am

I took the plugs out and checked for spark. No spark while turn over the engine, but after I shut off the key I got one spark. I'm think the bang is coming from the burn off of unburnt fuel. How do I check the switch?

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Re: Big bang while trying to start.

Post #9 by Shadowjack » Thu Oct 10, 2019 8:12 am

Do you know if it ever ran with the Dyna? This is exactly what a stock ignition does if the ballast resistor gets unplugged. Some Dynas bypass the resistor, I think, but do you know if it was installed correctly?

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Re: Big bang while trying to start.

Post #10 by robin1731 » Thu Oct 10, 2019 8:14 am

Shadowjack wrote:Do you know if it ever ran with the Dyna? This is exactly what a stock ignition does if the ballast resistor gets unplugged. Some Dynas bypass the resistor, I think, but do you know if it was installed correctly?



Depending on how it was wired though it should still have spark while cranking. But that is a good thing to check.

And yes, the ballast resistor should be removed if using both Dyna ignition and coils. But if you are still using the stock coils you still need the resistor. A new one comes with the Dyna.

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Re: Big bang while trying to start.

Post #11 by gltriker » Thu Oct 10, 2019 11:21 pm

K9Sicem wrote:I have a 76 LTD that I just got a week or two ago. I have driven it 50 to 75 miles without issues. I tried to start it last night without luck. When I shut off the key it back fired loud. I tired again and it did the same think. This bike has an electronic ignition. This is my first bike so I have little knowledge of what to look for. I have restored several old trucks. Based on that it is my thought that it is loading up with fuel and only getting spark when I tried to shut off the key. Any help would be appreciated.


As this Topic progresses, there are quite a few mentions of Dyna.

Has this LTD's 'electronic ignition' actually been visually identified as a Dyna unit? :-?
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Re: Big bang while trying to start.

Post #12 by gltriker » Thu Oct 10, 2019 11:34 pm

K9Sicem wrote:I have not. It was changed when the bike was rebuild. It should be almost new.


Two timing belts. Not just a single, It . ;)

It's a best practice to remove both timing belts' covers, now, and check for correct camshaft pulleys' static timing alignments. tumb2

Timing belts are very inexpensive.

See this Timing Belt Replacement tutorial from NGW Club's Shop Talk.
viewtopic.php?t=3544
Cliff

Keep your eyes and ears open and you'll learn something new, everyday. tumb2

New users please visit our "Shop Talk" for common tips and help: <---jdvorchak
http://www.ngwclub.com/forum/page/ST :oldies

RE: a thorough fuel tank cleaning
"And your carbs will thank you. They no longer live down stream from a sewage plant." -gregforesi tumb2
"Can't see the paint when your looking thru the handlebars..........." -Oldewing ;)
"I'd rather Ride than Shine" -RAT tumb2 Me Too!!

Cliff

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October,2017 BOTM :shock: https://nakedgoldwingsclub.com/forum/page/Welcome

previous rides:
1953 H-D Servi-car, naked, 1969-1978 (serial#53G1559 committed to memory!)
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Re: Big bang while trying to start.

Post #13 by K9Sicem » Fri Oct 11, 2019 8:14 am

Both timing belts are good. Yes, it is a Dyna unit. Ran fine. Next night I wanted to ride and that is when it would not start. I checked for spark. Will not spark while turning over. It will give off one spark when I shut off the key. Battery is near new and has good voltage.

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Re: Big bang while trying to start.

Post #14 by robin1731 » Fri Oct 11, 2019 8:17 am

Have you done any of the suggested tests/procedures/diagnostics?

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1975 GL1000 parts bike (parts for sale)
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder

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Re: Big bang while trying to start.

Post #15 by ericheath » Fri Oct 11, 2019 8:46 am

Could be a worn ignition switch. The one of mine that exhibits this had a bad switch and I pulled it apart and tightened up the rivets inside.

Have you probed the wires at the Dyna to see if they are getting power with the switch on?
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
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