No spark, left side and updated project.

avenue

avenue

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Hello all,
It's been a while. After a first go-round of my full project build ('12-'13), riding it daily for almost a year, a secondary teardown for proper paint and odds (spring'14), it's now back together again.

I had the bike together and running strong last summer/fall (after the 2nd teardown) for about two months, ran into some carb problems/busy with life...let it sit for months, and finally made the time this weekend for a full carb overhaul and tune up.

yesterday, after a full carb cleaning/re-assymbly, sync, and mix screw adjustment close to where it was before 2 3/4 turns, the bike fired up first kick (3/4 choke), and idled nicely. After a few minute warm up, the bike ran strong for a 10 minute neighborhood cruise, pulled pretty strong, and only showed slight hesitation at take-off. This morning, I took it out for a slightly longer ride to make finer adjustments. It was pulling hard, decelerated smooth, and sounded good.

But, two blocks from the house I noticed more hesitation at two stop signs before pulling into the driveway.

pull the plugs to check for signs (I had cleaned them while doing the carb work).
left plug is completely black, not sooty, not really oily, just a satin-like black finish.
right plug looked fine but could probably use a slight mix adjustment.

the carbs are sync'd (yardstick) and mix screws set the same.

checked for spark with alligator clip and tester plug grounded to the fins. spark good outside of the cylinder.
I swap the L/R plugs and still the left side won't fire but the right side will with the fouled-up left plug.

next, I throw in two new NKG BP7ES plugs and still no spark on left side (bike still starts and idles).

Any thoughts?

old plugs NGK iridium BPR7EIX
NGK resistor plugs
bs34s with new butterfly seals last fall,
full teardown, clean, air compressor, reassembly.

I've had no spark on left cylinder before. Once was a improperly grounded pamco pickup, the other time was a faulty plug. This time, I'm lost.

any help is appreciated. and, it's good to be back even if for a frustrating problem.

these are brand new plugs results after 3-4 minute idle.
 

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no spark on the left side meaning, cold exhaust pipe and the sound of only one cylinder firing.

that, and the plug is clearly not burning anything. the photo is a brand new plug only after a few minute idle.

I'm a bit confused, too.
 
Haha, I get confused easily. Assuming that you actually have "spark" on both sides, but the left cylinder fails to fire, it may be a simple carb problem. I've experienced similar, usually caused by an errant speck that plugs the idle jet, or similar speck that plugs the air bleed. With the black sparkplug, I'd lean more toward a blocked air bleed.

A quick test is to remove the mix screw, shoost some carb cleaner into the mix screw hole (trying to reverse-blast a suspected blockage outta there), reassemble with mix screw back to original setting, and try a startup.

If it runs differently, that would point to a carb problem...
 
might be worth doing a compression test to compare both cylinders. It might identify a sticking or non-seating valve.

How do the two exhausts compare if you use your hand to compare the exhaust pressures ? it will give you a good comparison between combustiuon in both cylinders.

Have you used WD40 or carb cleaner etc to spray around the stubs and inlets to check for air leaks .?

If you have to remove your carbs you can do a very effective sync by putting each venturi to your mouth and comparing the back pressure of each inlet and adjust the butterflys sync screw until the pressure feels equal.:thumbsup:
 
the hand to the exhaust is what tipped me off about the cold left pipe, first at the tailpipe and then at the downpipe.

TwoMany's might be onto somthing with the air mix screw blockage. THat's one thing that didn't get the shot of compressed air as it skipped my mind while I still had the compressor out. I'll give that a shot but more suggestions are helpful.

thanks.
 
a cold exhaust pressure at the tip and the ability to grab a handful of header pipe after a few minutes of idling tells me the left cylinder is not sparking. yet, the engine will fire up and idle with a hot right side.
 
If the throttle is cracked open very slightly and held at 1200rpm ,does the cold cylinder start to work ?

if the butterflys are not synched accurately and the idle is set very low, then one butterfly would be closed with the other slightly open. :wink2:

This could prevent the venturi drawing sufficient fuel/air through the pilot jet of one carb .

Have you tried adjusting the idle slightly higher to see if the dead cylinder starts to work properly ?
 
chizler62, is that an Anvil bicycle jig in your avatar? If so, I have an early Henry James model for personal projects and have always admired the Anvil fixtures. nice stuff.

peanut, thanks for the tip. I should be able to check it out tonight and report back.

avenue.
 
2015-03-10_09-00-27.jpg
yup! Its a "Don went overboard" frame jig. If you're building 3-4 frames a year the HJ, Brew, etc is more than good! When you have a 18 month wait list. 5k for an anvil is necessarily.

Imagine if the motorcycle fellas caught up? LOL I've actually laughed out loud at the Indy show a few years back at a frame jig system someone was selling.
 
awesome. I'd like to see more photos when you have a chance, or a website if you have one.

an interesting turn with the spark/carb issue. TwoMany was right about the mix screw. There was some trash in the left. I blasted it out with a shot of carb cleaner but it probably needs a proper disassembly. The left cylinder is now firing, although still rough. I pulled the yardstick out again and tweaked the sync, too. Bike fires up and idles. throttle response in neutral feels great.

But, when I went to dial the mix screws with the dead cylinder method (plug pulled and grounded), the right cylinder stayed running the same while I drove the mix screw all the way in and out. no change. That, and the plugs were damn near black after a few minute idle, again. this was after a plug clean, warm start, and no-throttle 2 minute idle.

now, I'm thoroughly confused. I'll re-read the carb guide for the countless time and will go through the full tune up motions, again, but any input in the meantime is appreciated.

thanks.
 
if the mix screw makes no difference in or out wouldn't that suggest an inlet air leak somewhere ? The right cylinder must be drawing excess air somewhere surely.?
If I screw my mix screw fully in on either of my cylinders it cuts right out on idle
 
No response from the mix screw can also indicate the float level is off. From the way that plug is turning black, my guess would be too much fuel in that bowl.
 
No change when the mixture screw is turned fully closed, indicates to me that the pilot jet is larger than it should be. The mixture screw is just a fine trim on what flows through the pilot jet. The mixture screw is "out of range" and cannot affect the rpm.

In other words, if the pilot jet is too small, then the mixture screw needs to be fully open such as 3 to 4 turns. If the pilot jet is too large, then the mixture screw can be turned completely closed with no effect. When the correct size pilot jet is found, its like the Goldylocks story, not to big, not to small, but just right.

Try going one size smaller pilot jet and then re-do the dead cylinder test.
 
Yeah, what the guru said! Sounds like you caught something in the jets... But it must be something big if you lost all firing and can touch the pipes.

And why does that seat look familiar?
 
the seat is my favorite part of the bike, especially right now. at least I can sit on the thing when it's not running and make vroom sounds. also, the upholstery is often the center of attention.

CounterBalance seat, for the win! I'll send some better photos your way.

I'll report back about the carb issue when I can make more wrenching time.

thanks.
 
Hi Avenue, did you ever find a solution to the issue you experienced.? Im having a similar situation and would really like to know if you found a solution. Thanks
 

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