#1 not working until warm up.

[Guest]

I just finished going through a 1980 1000GLT, maybe you saw my recent post in the "GS Owners" section. That post tells the work done that may affect this problem. Cylinder #1 does not want to engage until the motor has warmed up for a couple of minutes. Once warmed up, it never misses a beat. Usually doesn't miss the rest of the day, but every now and then it takes a minute when starting the engine warm. I've hooked up a spare plug to #1 lead on cold start and plug is firing happily away. I've cracked open the #1 float drain screw and it's got gas. once warm, the motor runs strong and smooth through the range, and idles nicely. Thanks.

 

[londonboards]

Most likely is that the choke circuit is not working on this cylinder. Takes carbs off and remove float bowl on the affected cylinder.

From the carb body you will see a brass tube sticking down. This has a very small hole in the bottom of it. Make sure this hole is clean - use a very fine piece of wire - I use a thin guitar string.

Then in the float bowl you will see the hole in which this tube goes down into. This tube sucks up fuel from the bottom of the float bowl for the choke circuit. Now get some carb cleaner spray and spray it down this hole. You should see the carb cleaner come out of the hole in the bottom of the carb bowl. This is usually the first place a carb gets bunged up and its the most difficult to clean.

Also try spraying the carb spray in the opposite direction. You need this passageway to be free flowing. If it is gummed up, then you will need to ultrasonnicaly clean it or immerse the bowl in some strong carb cleaner.

To be sure it's not an electrical problem as well, change over the plug leads between cylinder one and cylinder four. If the problem is still on cylinder one then is defo the carb.

 

[Rob S.]

Could it be that #1 needs a colder or warmer spark plug? Of course, that would still leave the question: why?

I'm not advising, just asking. I'm trying to learn.

 

[Tom R]

The spark is the same... it’s the hotter or colder is the temp of the plug.

 

[Guest]

Thanks for the replies. It's not the spark for sure, plug is firing fine. Enricher circuit sounds logical. I have gone through the carbs using the carb cleaning tutorial on this site. I was thorough, and a guitar string is what I used for the tiny holes. I will go through #1 again and see if I wasn't quite thorough enough. Is it possible the vacuum circuit to the petcock could cause this, or would that continue to affect it after warm up?

 

[Nessism]

The vacuum line to the petcock won't cause the issue you describe.

Did you vacuum sync the carbs? Where are the pilot screws set?

 

[pdqford]

I've hooked up a spare plug to #1 lead on cold start and plug is firing happily away. Thanks.

Good test. But it doesn’t take a whole lot of voltage to jump the correct gap at atmospheric pressure.
And it doesn’t prove the ability of the original plug to provide a ground for the voltage. But it does show that your coil is able to produce a spark.
Now if you could insert an inline spark checker between the spark plug wire’s boot and the tip of the spark plug, and the inline spark checker doesn’t show a spark when cranking, you know the issue is either with the spark plug, or low coil output when the ground is under compression.

 

[TxGSrider]

Sometimes tight valve lash can act like that.

 

[Guest]

I did vacuum sync the carbs. Pilot screws I believe are between 2.5 and 3 turns from soft seat. I used a method somewhere deep in the pages that says blip the throttle and how it returns to idle tells if it's rich or lean, and to put all 4 in the same adjustment for CV carbs. It idles great and returns to idle correctly when warm

The vacuum line to the petcock won't cause the issue you describe.

Did you vacuum sync the carbs? Where are the pilot screws set?

 

[Guest]

The valve clearances are in spec.

Sometimes tight valve lash can act like that.

 

[Guest]

If it was the coil, would #4 also misfire? Could the problem disappear when warm? I know coils can be funny, and it seems like every time I throw a coil at a problem, that's not it. The coils are original, so 40 years old and all. I haven't tried switching 1 and 4 plug wires yet, and I'd sure rather do that than pull the carbs again. The plugs are new, and the symptom persists with any plug. The boots are new and I snipped 1/4" off the wire before installing.

Good test. But it doesn?t take a whole lot of voltage to jump the correct gap at atmospheric pressure.
And it doesn?t prove the ability of the original plug to provide a ground for the voltage. But it does show that your coil is able to produce a spark.
Now if you could insert an inline spark checker between the spark plug wire?s boot and the tip of the spark plug, and the inline spark checker doesn?t show a spark when cranking, you know the issue is either with the spark plug, or low coil output when the ground is under compression.

 

[pdqford]

I know coils can be funny, and it seems like every time I throw a coil at a problem, that's not it. The coils are original, so 40 years old and all. I haven't tried switching 1 and 4 plug wires yet, and I'd sure rather do that than pull the carbs again. .

Swap the coils around?

 

[Big T]

Switch the #1 and #4 coil wires first
If the symptom doesn't change, swap the coil trigger wires and the coil wires