Dead cylinder?

[Guest]

I have the symptoms of a dead cylinder. On my 84 Interstate, when I pull plug #2 while running nothing happens. When I pull the plugs one at a time, there is a signifigant stall on the engine and usually dies - as it should be. I've pulled the carbs and rebuilt #2 thinking it's a fuel issue. I thought this because I can pull the spark plug and connect it/ground and I get a good spark. Totally disassembled #2, soaked it and put it all back together and get the same symptom. I had a spare set of carbs and totally rebuilt #2 on that set and installed. Same symptoms. I thought it was the carb because if it is getting good spark, the other option is fuel. I've rebuilt the carb and a completely different one and still have the same results. Where should I go now to start troubleshooting this issue?

Thanks,

Ken

[Guest]

Run a compression test on all cylinders. It "seems" you don't have a spark or fuel issue. Compression is all that's left. It's not a timing belt problem if you are only experiencing the condition on one cylinder.

[Guest]

I forgot to add that compression is good all around.

Ken

[Guest]

I thought this because I can pull the spark plug and connect it/ground and I get a good spark.

Did you actually pull the spark plug, or just the wire? Try swapping #2 and #4 spark plug and see if the symptom follows the component. Let us know if the plug was wet or dry.

[Guest]

I thought this because I can pull the spark plug and connect it/ground and I get a good spark.

Did you actually pull the spark plug, or just the wire? Try swapping #2 and #4 spark plug and see if the symptom follows the component. Let us know if the plug was wet or dry.

Definitely look into that bad plugs can spark while in a free air situation and lose all spark under pressure.

[Guest]

Thanks for the replies.
I swapped plugs (2 & 4) and had them both sitting out on the cylinder at the same time. I turned it over and they both sparked pretty good - as well as one can desimate without getting too close. I'll go up to the auto store and get some raw solid core cable and some new plugs and see what that does.

Stay tuned.
Ken

[Guest]

So I went up to Napa and purchased 4 new plugs and 5 feet of 7mm solid core to replace the wires. (PS - You may want to purchase 6 1/2 feet to replace all four. It was only enough for 3 - oops). Anyway, I swapped out the plugs (and gapped them). Swapped two of the spark plug caps with a different cylinder to rule that out also. End result is that when I pull #2 plug while running, it does not affect the engine idle/performance at all. Just runs as normal. The kicker is that it really doesn't sound that bad - Idles pretty smooth. But something in the back of my mind thinks that there is still something wrong with #2 cylinder. I'm at a loss. When I remove the #2 plug cap and start getting it closer to the installed spark plug, I can hear a pretty good arc like it's firing. I still think it may be fuel related as that should be the only other componet to this issue. I know the carb is getting fuel. I can twist the drain plug and fuel drips out. I know the float is set correctly (@ 7.5mm) per the manual - Air screw 3 1/2 turns out also (84). Soaked the carbs after completely disassembling them. I have compressed air and ensured that all of the jets and passage ways are free and clean. I'm open to any suggestions.

Thanks,

Ken

[Guest]

Have you checked compression? you might maybe have a bad/stuck valve? or it might not be sealing good? I've had 2 bikes with this problem.

Let us know, Wes

[Guest]

Just curious.......for clarification, while sitting on the bike, which cylinder are we calling #2?

[Guest]

Just curious.......for clarification, while sitting on the bike, which cylinder are we calling #2?

As your sitting on the bike, left front. I don't think it really matters though, does it?

I did do a compression check and they all fell around 170ish. No signifigant difference between the four.

[Guest]

bump

[Guest]

As your sitting on the bike, left front. I don't think it really matters though, does it?

The reason I asked is because #4 has a vacuum tube that could have been leaking causing a lean situation.
So, in review....you have 170# compression, you have known good resistor caps, new wires, and new spark plugs. You've cleaned and/or replaced #2 carb. You have fuel in the float bowl. We asked wether or not the plug was wet or dry. This is important. If the plug is wet, you may still have a spark issue. If it's dry, you don't have fuel being introduced into the cylinder (needle/seat?)
The one thing that stands out to me is you say when you pull any other plug wire, the engine nearly dies or does die. You should see a noticeable drop in rpm and some roughness, but it shouldn't try to die. This indicates #2 is being "over supported" by the other three cylinders.
Get a can of carb cleaner, remove the sync port screw at the bottom of the intake runner. Spray the carb cleaner into the hole (with the bike running) and see if you get an increase in rpm. This should indicate wether or not it's a fuel related problem.
How are you syncronizing the carbs? One thing that hung me up a few years ago....do a visual inspection of the throttle plate opening between #2 and #4. They should be very close.