TOPIC:

bump, anyone? What could cause 3 of the four cylinders to not fire, related to ignition? Should I be checking something farther upstream of the coils?

Thanks again
-J

just guessing

resistor plug caps that have had their day and gone out for lunch, I get an old bike sometimes that has them and change straight over to non resistor plugs and caps as a first step.

Might have missed this in the thread, but did not see results posted following installation of the new coils and plug wires (which presumably included new non-resistor plug caps on solid copper core wires). May the diagnosis proceed from this point on the assumption that there is no problem with the coils, plug wires, plug caps and plugs?

I installed new NGK plugs, Dyna suppression 8mm wires, and 2.2 ohm Dyna coils yesterday. Bike now is running on 4, most of the time. I'm still getting one that drops out occasionally, generally either at low speed (and hot) or when first started cold.

Yesterday right after I had finished installing the new parts I took it for a ride. When I got back, Cylinder #1 stopped firing but only at idle, and gasoline was coming out of the overflow tube. But only at idle, if I revved the engine the cylinder began firing again and the gasoline would stop dripping out.

I cranked it a few hours ago cold, cylinder #1 wasn't firing. Pulled the plug, it was wet. After I ran the motor a little longer it came to life and the bike was running on all four.

What could still be causing one cylinder to keep dropping out? I also took apart the carbs today and cleaned them, seemed fine. Float levels seem ok, and I put in new float valve needles. I checked compression the other day as well, registered ~180 psi on all cylinders.

iM NOT SURE YOU CAN RULE OUT THE CARBS.wHEN IT DROPS A CYL YOU NEED TO PROVE TO YOUR SELF IF THE PLUG IS FIRING EACH TIME.(oops , CAP LOCKS).Then you will know if it is wiring or carbs.I wonder if it could be flooding out the cyl.

If its flooding the cylinder, im guessing the plug will be too wet to fire? Is that true? What is the best way to determine if the ignition or carb is at fault?

I took my bike on the interstate today. The new ignition components revived my top end. A HUGE improvement over the old hardware. Just throwing that out there if anyone else is having a similar stumbling-at-high-rpm (almost felt lean) problem.

Have you measured your valve clearances? What voltage are you getting at your coils?

masospaghetti wrote:

Bike now is running on 4, most of the time. I'm still getting one that drops out occasionally, generally either at low speed (and hot) or when first started cold . . . Cylinder #1 stopped firing but only at idle, and gasoline was coming out of the overflow tube. But only at idle, if I revved the engine the cylinder began firing again and the gasoline would stop dripping out.

I cranked it a few hours ago cold, cylinder #1 wasn't firing. Pulled the plug, it was wet. After I ran the motor a little longer it came to life and the bike was running on all four.

What could still be causing one cylinder to keep dropping out? I also took apart the carbs today and cleaned them, seemed fine. Float levels seem ok, and I put in new float valve needles.

Just some thoughts --- fuel dripping out the overflow tube only at idle could result from a poorly seating float needle which becomes less symtomatic at higher RPM. Even with motor off and fuel being supplied uninterruptedly to the carb, a poorly seated float needle may allow fuel overflow from the float bowls ("prime" petcock position, if applicable). When changing the float valve needles, were the seats also replaced? (Believe the usual recommendation is to replace both needle and base as a set -- in other words not use a new needle in an old base, or vice versa). Will presume the seat base fiber gasket is in place. Also, have you checked the actual fuel level in the float bowls via the clear plastic tube method (motor off) -- which may likely prove impossible while the bowls are overflowing and dripping from the overflow tubes. In short, I would suspect leakage at the float needle seating as being consistent with the conditions you have described. Keep the faith.

when you feel that a cyl is not firing pull that plug insert it into wire, place plug against head to get it grounded ,and turn eng over(with egnition on),watch for spark at plug gap.If you have spark it is likly a carb problem.
masospaghetti wrote:

If its flooding the cylinder, im guessing the plug will be too wet to fire? Is that true? What is the best way to determine if the ignition or carb is at fault?

Here are some updates, still need some help:

Wiredgeorge: I haven't measured valve clearances or voltage at the coil yet. Correct me if i'm mistaken, but the latter seems unlikely given that only one cylinder is not firing? The other three fire off just fine. Compression is 180 psi in cylinder #1.

Patton: I should have gotten the seats also, you're right. That will be the next step.

This morning has gotten me very concerned, however.

I went out to start the bike, it turned over (choked) but with the throttle partially open, but it was running on all four cylinders, I could feel all four pipes heating up. I shut it down, came back about 5 minutes later and tried to fire it up. Cylinder #1 would not fire for the life of me and it was backfiring like CRAZY. I sat there and tried to warm it up but this didn't help. I pulled the plug, it was wet.

What I dont understand is that, Cylinder #4 (on the same coil) is doing just fine. They're new coils, wires, and plugs. So this seems to me like a carb issue?

I'm pretty much fed up with this set of carbs, they've been no end of trouble since i've had the bike.

Post edited by: masospaghetti, at: 2006/11/21 15:18

Post edited by: masospaghetti, at: 2006/11/21 15:22

I'm not familiar with your year of bike and I don't know what area of the country you are in, but:

IF your bike has the smog pipes coming off each side of the exhaust valve cover, that may be your problem. Look to see if there is a smog valve under your gas tank and in fromt of the coils.

If there is, that's likely your problem. My bike had one and it had all the problems you are having and more. Back-firing, hard starting, poor idle, etc...

Disconnect the two hose's to the smog valve, then run a single hose from one valve cover to the other.

Start the bike and if your problems go away you've located the problem.

Throw the smog valve away. Cap off the two vacuum connections on the carbs that go into a tee leading to the smog valve.

I replaced the two plates on the exhaust valve cover with plain flat aluminum ones that I made myself. Problem solved....

Bob

Post edited by: Bob_79KZ, at: 2006/11/21 16:18