My bike suddenly lost a cylinder

[tkent02]

Dumb question:

If I have good compression does that mean my valves are working OK?

It does, but they could still be very tight and on the verge of getting burnt, it just hasn't happened yet. Or they could be set perfectly. Or too loose. You don't know unless you check.

[littleroot]

It does, but they could still be very tight and on the verge of getting burnt, it just hasn't happened yet. Or they could be set perfectly. Or too loose. You don't know unless you check.

I just have to pull the cam cover and I'll be able to tell if they are working? Or does one really have to pull the head?

If I understand correctly what I have read I adjust the valves with the cam cover off but I'm not sure if I can tell if they are actuating.

Thanks for any more info you can share.

[tkent02]

How did you get from a spark problem to pulling the head?
Slow down a little bit.
Did you test to see if your petcock is leaking fuel down into #2?
You said your vacuum line comes up from #1, is this correct?

[littleroot]

How did you get from a spark problem to pulling the head?
Slow down a little bit.
Did you test to see if your petcock is leaking fuel down into #2?
You said your vacuum line comes up from #1, is this correct?

Hi, just pulled the vacuum line off the petcock and it is not leaking fuel.

I feel better about not pulling the head after reading that there is no reason if my compression is 170 (on all four actually).

I've taken a few pictures to show what I am looking at with regards to the vacuum and the scene overall.

I just learned something though. When I have the plug wire off and get the revs up to 7000 the engine is a LOT more rough than when the plug wire is on. So I've probably got a bad, block jet. Is that right?

[littleroot]

How did you get from a spark problem to pulling the head?
Slow down a little bit.
Did you test to see if your petcock is leaking fuel down into #2?
You said your vacuum line comes up from #1, is this correct?

Not sure you can see anything useful in these three shots but the vacuum line is definitely on carb 1. All other carbs have rubber plugs in the same position.

The petcock is not leaking. I did another test and seems OK.

I also replaced the spark plug in #2 with a brand new one, and hooked it to the cable and verified it is sparking held close to the head.

Did you see my note about the #2 cyclinder seems to be firing at high revs? When I give the throttle a healthy twist up to 7000 RPM with the spark plug wire on it sounds a LOT better than with the wire off. So it seems the cylinder is firing at high revs. But at idle and low revs it makes no difference if the wire is on or off. weird. And the idle does not sound too bad - hard to tell it is missing, to my untrained ears. The idle gets really bad when I pull off any other plug wire while idling.

Back to the high revs, if I knew what I was talking about I would say one of the jets in carb 2 is clogged. I dumped about 8 more ounces of seaform in a half-full tank and did another 10 miles, trying to keep the revs low where it runs really rough. At times it seemed to clear up a bit, but it still sputters and backfires a lot whenever I close the throttle.

I rode over to the parts store and got some more seaform and some "chem"(?) carb cleaner just in case I wanted to spray it somewhere and I ran into a guy who said it may be a stuck floatbowl from the backfire description. I'm not sure it's a real backfire - it does not go "bang", but more of a sputtering and popping when I close the throttle. Especially when closing the throttle and onto engine braking it sounds like it's running rough, and out of tune, I'm guessing only 3 cylinders.

Not sure what to do next. I know it's been 6500 miles since a tune up on the carbs and valves (as that is when I bought it). Maybe all this is is that they both need attention? I just never thought that would cause a cylinder to fail on idle.

One more thing, I also swapped the pods around and no difference.
Here are the pix.

[Steve]

If it has been 6500 miles since your last valve adjustment, they are about 2500 miles past due.

If you have a valve that is just a bit too tight, it could mis-fire a bit at idle, but respond OK at higher speeds.

Is your bike easy to start when cold? Is it easier to start when warm?
Classic sign of tight valves.

.

[littleroot]

If it has been 6500 miles since your last valve adjustment, they are about 2500 miles past due.

If you have a valve that is just a bit too tight, it could mis-fire a bit at idle, but respond OK at higher speeds.

Is your bike easy to start when cold? Is it easier to start when warm?
Classic sign of tight valves.

.

When cold I choke it and it starts immediately. When warm I get same results without choke. That's all I have ever done. I'm not sure I answered your question. Should I try some other test? I am in the SF Bay area and have not owned the bike in the winter yet. As owner of the bike has never seen lower than 55 F degrees since I've owned it and always garaged.

Thanks for the reply

[littleroot]

another photo



Just a picture of the overall view and the coils.

Any more ideas? Do we think it is just a valve adjust and carb rebuild to fix?

[Steve]

When cold I choke it and it starts immediately. When warm I get same results without choke. That's all I have ever done.

If it starts that easily, it's not likely a valve adjustment issue, but it wouldn't hurt to check them.

.

[lucabond]

Just a thought the carb thats not firing at idle maybe to rich which at idle just floods the carb at higher rpm the rickness isn't as much of a problem.
Is the #2 pipe cold at idle then warms up at high revs ? That would be a good indicator, Good luck.

[Nessism]

Sounds like a plugged up pilot jet since it's not firing at idle but runs at higher speed. The compression indicates the valves are ok, although they should be checked soon. I'd pull the carbs and remove the pilots and look for junk in there. If you have rust in the tank it's very easy to plug a pilot.

Good luck.

[littleroot]

Sounds like a plugged up pilot jet since it's not firing at idle but runs at higher speed. The compression indicates the valves are ok, although they should be checked soon. I'd pull the carbs and remove the pilots and look for junk in there. If you have rust in the tank it's very easy to plug a pilot.

Good luck.

Yeah I guess something got into the carb. The tank looks really clean inside, but anything can happen. There is no fuel filter. Shouldn't there be?

[Skunky]

Sounds like you said there was fuel...I had the same issue with #1 cylinder...it was a clogged jet. Try pulling the carb and using a wire (pulled from a wire brush) to poke thru the holes in the main jet. Once I did this I ended up doing all carbs while they were out. Ran better then ever after I was done.
Good Luck,
John

[littleroot]

Sounds like you said there was fuel...I had the same issue with #1 cylinder...it was a clogged jet. Try pulling the carb and using a wire (pulled from a wire brush) to poke thru the holes in the main jet. Once I did this I ended up doing all carbs while they were out. Ran better then ever after I was done.
Good Luck,
John

I really want to do this but I have no idea where the jet(s) are. And I am stuck at the moment wondering how to get the carbs off the bike and on a workbench because I do not know how to get the throttle cable off. My carbs are not stock so I think I need to post some pix and get advice. I did notice when the pods are off I see fuel is squirting OK. Is that the jets you mean or is it further inside somewhere?

Please let me know.

Thanks!

[littleroot]

It is working!

It sounds like something pluged in the carb, you could try some seafoam in the gas to clean it out..

Son of a gun: I kept putting more seafoam in her (read this thread for how much and when) and running the engine for a while on and off while gathering data Saturday and then today after just sitting all day while doing other things the #2 cylinder decided to work when I fired her up this afternoon. I don't have as much power as I used to but the #2 is now firing at idle!!!!

Now I can just hear a slight difference when I put on/take off the #2 plug wire while idling. I took my wife for a ride tonight and out for dinner - a great 23nd anniversary present for us both.

From reading all the posts from everyone trying to help me here I learned so much. I bet after I do a real carb cleaning I'll get all my power back and more.

THANKS EVERYONE!