75 gl1000 spark but cylinders not firing


Information and questions on GL1000 Goldwings (1975-1979)
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dezrcr02
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Motorcycle: 1975 gl1000

75 gl1000 spark but cylinders not firing

Postby dezrcr02 » Fri Jan 03, 2014 3:44 pm



Bought a 75 gl1000 from a guy who had the carbs all redone, bike only has 8200 miles on it. Brought the bike home, put a new battery in it, but no spark from any of the plug boots. Cleaned the points with sandpaper, put new ngk boot plugs on, and got a spark to all four cylinders, a strong spark actually, both with a test light and a new plug. Got the bike running, but only cylinders 3 and 4 are actually working, as cylinders 1 and 2 are dead. I tested this by getting the bike running and then pulled the spark plug caps off to see if there was a change is the way it was running, very noticeable change in rpms when i pull off either cylinder 3 or 4, zero change when i pull off either 1 or 2. Pulled the spark plugs from the dead cylinders and there is a spark but again its they are not actually com-busting, and the bike does backfire every 3-5 seconds. What is baffling me is that there is a spark but the cylinders are not com-busting. Compression on all cylinders as well. Cracked the bottom drain plug on all four carb bowls and clear gas came out of all four. Are my problem cylinders not getting any gas? The dead cylinder plugs are dry, even after the bike running on two cylinders for 5 minutes? Are the front carbs, which are my non-combusting cylinders, related in any way?

Thank you for your help in advance.



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WingAdmin
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Re: 75 gl1000 spark but cylinders not firing

Postby WingAdmin » Fri Jan 03, 2014 8:55 pm

dezrcr02 wrote:Bought a 75 gl1000 from a guy who had the carbs all redone, bike only has 8200 miles on it. Brought the bike home, put a new battery in it, but no spark from any of the plug boots. Cleaned the points with sandpaper, put new ngk boot plugs on, and got a spark to all four cylinders, a strong spark actually, both with a test light and a new plug. Got the bike running, but only cylinders 3 and 4 are actually working, as cylinders 1 and 2 are dead. I tested this by getting the bike running and then pulled the spark plug caps off to see if there was a change is the way it was running, very noticeable change in rpms when i pull off either cylinder 3 or 4, zero change when i pull off either 1 or 2. Pulled the spark plugs from the dead cylinders and there is a spark but again its they are not actually com-busting, and the bike does backfire every 3-5 seconds. What is baffling me is that there is a spark but the cylinders are not com-busting. Compression on all cylinders as well. Cracked the bottom drain plug on all four carb bowls and clear gas came out of all four. Are my problem cylinders not getting any gas? The dead cylinder plugs are dry, even after the bike running on two cylinders for 5 minutes? Are the front carbs, which are my non-combusting cylinders, related in any way?

Thank you for your help in advance.


It's more likely you have an electrical issue, because cylinders 1 and 2 share the same coil. I would try swapping the coils and see if the problem moves to cylinders 3/4. If it does, then the issue is the coil. If it doesn't, then the issue is the wiring.


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ct1500
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Re: 75 gl1000 spark but cylinders not firing

Postby ct1500 » Sat Jan 04, 2014 1:52 pm

Take a good quality can of carb clean with straw (not the foaming type) and give it a couple spritzes into plenum aiming at dead cylinder carbs' intake. If the RPM's pick up it is fuel related.
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tlbranth
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Re: 75 gl1000 spark but cylinders not firing

Postby tlbranth » Mon Jan 06, 2014 8:13 pm

If you pull a plug wire from 3 or 4 and it stays running, 1 & 2 ARE firing - maybe not well but they are firing. If you pull #3 wire, it stops spark to 3 AND 4. You may have fuel problems but it's a cinch you have coil problems because THEY'RE 40 YEARS OLD!

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Fred Camper
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Re: 75 gl1000 spark but cylinders not firing

Postby Fred Camper » Sat Jan 18, 2014 11:08 am

I too do not suggest working the carbs until you are certain the ignition is outstanding. 40 year old coils and wires are trouble and carb work is very frustrating if the ignition is the real issue. Had a mechanic tell me when I was 16 that "them automakers should put the carb in the oil pan, cause when it is on time it is the first thing you dingbats mess up when you have an ignition issue". I have never been able to prove him wrong. When the ignition is outstanding, fixing anything else is seldom difficult.




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