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Carb tuning...for dummies please

12736 Views 281 Replies 23 Participants Last post by OddBird, 6 h ago

tboooe

Discussion Starter · 3 mo ago

Preface: I havent messed with carburetors in over 25 years, and even then I was not very good at it so please be gentle. Being a total carb newbie I want to take a methodical, stepwise approach to diagnosing the issue and ultimately identifying the correct fix, otherwise I will likely get overwhelmed making too many adjustments and probably end up making things worse.

I finally got one of my Superlights (#669) running. It is 100% stock. I adjusted the idle so it sits at 1100-1200 rpm. The issue now is that I think it is running incredibly rich. When I rev the bike it starts to pop through the exhaust at around 3500-4000 rpm. Additionally, the ends of the exhaust is covered in dark black soot. Plus based on the exhaust smell I think its rich.

First question, does this sound like the bike is running rich?

141 - 160 of 282 Posts

tboooe

Discussion Starter · #141 · 2 mo ago

OddBird said:
Hmmm. I somewhat agree. But he did say that the engine quits "gracefully" at 3k, which leads me to believe that it is an ignition issue, or a massive flooding situation. I was going to suggest connecting a timing light with an inductive pickup, but I assumed that he did not possess one.

I figured that ruling out fuel starvation would take the carbs out of consideration, as I really don't see massive flooding as a probability, if: turning off the enrichener will not allow the bike to start, and then after starting, turning off the enrichener does nothing to improve the situation. I am also assuming that any changes in throttle input or enrichener plunger positions have had no positive effect during the repeated "climb to 3k and die gracefully" scenario.

When the engine does start, it is apparently running on both cylinders, and it is dying immediately after starting and climbing to 3k. Fuel starvation would seem to be the most obvious choice here, but the fact that the engine dies without even a hiccup leads me to believe that it is ignition. If it is ignition, then it is most likely an issue with BOTH coils, which likely means that it is coming from somewhere BEFORE the coil high tension circuit- a voltage drop on the low tension side due to a bad fuse, connection, dead battery cell, or god knows what else. The chance that both coils are fried seems improbable, but not impossible (and a fried coil could behave exactly like this).

I think that voltage reading was taken with the battery tender plugged-in, as 14.5 volts is unlikely with everything static, unless there is something about these new lithium batteries that allows them to sit at 14.4V when they are unplugged. Dead cell would hamper starting, so I'm not thinking it is battery related.

Yes, this could be troubleshot much more quickly, but I'm not the one hearing the bike run or in control of the probes... so we move at a more careful pace and have to be more patient.

You are correct, without the enricher the bike wont start. I tried giving the bike some throttle before it dies but it did not help. I was assuming this is because then enricher bypasses all the circuits in the carb?

You are correct, when the engine dies it does not hiccup or sputter.

The 14.5v I read from the lithium battery was it off the tender.

As for flooding, when I removed the spark plugs I did see some moisture on the vertical one but the horizontal one was exceptionally clean and dry. I dont understand how it could be flooding if before the bike was starting and idling fine. Last week, the bike started with the enricher but would not idle when I closed the enricher. I had to give the bike a little of throttle or else it would die. Not sure if that is some sort of clue.

Reactions: 1

tboooe

Discussion Starter · #142 · 2 mo ago

duc96cr said:
A simple spark tester will identify if the engine is still sparking when it quits running. If it isn’t , we learned something really quickly.

Yes, looking right now for an inline one with a probe that has a removable terminal cap.

Reactions: 1

tboooe

Discussion Starter · #143 · 2 mo ago

ducvet said:
I would install some better NGK 5K caps and put the old metal caps in a drawer with the other crap oem parts like you ducati electronica regulator.

@ducvet are these the ones you are referring to?

www.amazon.com

Amazon.com: NGK LD05FP Resistor Spark Plug Cap : Automotive

Buy NGK LD05FP Resistor Spark Plug Cap: Spark Plugs - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

tboooe

Discussion Starter · #144 · 2 mo ago

tboooe said:
Yes, looking right now for an inline one with a probe that has a removable terminal cap.

Seems there are not inline spark plug testers for threaded studs so I am just going to buy this and solder a post on the end.

www.amazon.com

Amazon.com: Lisle 20610 Inline Spark Tester : Everything Else

Amazon.com: Lisle 20610 Inline Spark Tester : Everything Else

www.amazon.com

tboooe

Discussion Starter · #145 · 2 mo ago

OddBird said:
I figured that ruling out fuel starvation would take the carbs out of consideration, as I really don't see massive flooding as a probability, if: turning off the enrichener will not allow the bike to start, and then after starting, turning off the enrichener does nothing to improve the situation. I am also assuming that any changes in throttle input or enrichener plunger positions have had no positive effect during the repeated "climb to 3k and die gracefully" scenario.

So I've been thinking about the possibility of fuel flooding more. When I opened the float bowl drain screw, fuel flowed freely even though the bike and fuel pump were off. I am assuming fuel was still being fed to the carbs via gravity. Is this normal?

Also, in reviewing my notes, the bike actually started to exhibit this behavior of starting, revving to 3k, and dying before I changed the spark plugs a few weeks ago. Oddly, after I changed the spark plugs, the bike did start fine a few times but would not idle with the enricher off. I had to give the bike a little bit of throttle to keep it running. Anyway, more data points.

duc96cr

· #146 · 2 mo ago

An inductive timing light would work fine to test spark. Do you have one ? The type that just clamps around the spark plug wire?

ducvet

· #147 · 2 mo ago

You can buy spark plug caps that are for the bling boys who like lights and sparkly things, they come in red,blue or probably other colors and are not sold as a tool but a "upgrade". I have some I use ini the shop for testing not to leave on bikes and they work well to let me know if I lose spark.

LBO5e or F depending on what post type I want. Both are 90 degree but they do have a 45 degree as well. If you use the large stud version you have a better chance if finding plugs in the middle of no where as you can always adapt small stud to large but not always the other way around.

Reactions: 1

OddBird

· #148 · 2 mo ago

tboooe said:
So I've been thinking about the possibility of fuel flooding more. When I opened the float bowl drain screw, fuel flowed freely even though the bike and fuel pump were off. I am assuming fuel was still being fed to the carbs via gravity. Is this normal?

Also, in reviewing my notes, the bike actually started to exhibit this behavior of starting, revving to 3k, and dying before I changed the spark plugs a few weeks ago. Oddly, after I changed the spark plugs, the bike did start fine a few times but would not idle with the enricher off. I had to give the bike a little bit of throttle to keep it running. Anyway, more data points.

Others here would probably know better, but if the in-tank pump allows fuel to flow through it when it is not running, then I would expect fuel to continue to siphon from the tank to the float needle valve after the engine is shut down. What you experienced with fuel flowing from the bowls after shutdown would then be a normal occurrence. Are you able to actuate the carbs slides through the airbox- lift them carefully with a screwdriver and watch them drop? I'm wondering what position the slides are in right when the engine dies- if either is raised, then that is a problem. That said, because both cylinders are quitting, I would be hesitant to consider flooding as the issue. Stranger things can happen, though. Whatever it is, it's right under your nose somewhere! It would be helpful to see and hear a video of the bike starting and dying.

tboooe

Discussion Starter · #149 · 2 mo ago

duc96cr said:
An inductive timing light would work fine to test spark. Do you have one ? The type that just clamps around the spark plug wire?

I am not familiar with this. Would something cheap like this work?

www.amazon.com

Amazon.com: OBDMONSTER Ignition Timing Light, 12V Strobe Lamp Inductive Petrol Engine Timing Gun Automotive Tool for Car Motorcycle Marine : Automotive

Buy OBDMONSTER Ignition Timing Light, 12V Strobe Lamp Inductive Petrol Engine Timing Gun Automotive Tool for Car Motorcycle Marine: Timing Lights - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

OddBird said:
It would be helpful to see and hear a video of the bike starting and dying.

Good ideal. I will do it later today.

tboooe

Discussion Starter · #150 · 2 mo ago (Edited)

OddBird said:
It would be helpful to see and hear a video of the bike starting and dying.

Ok guys here is a short video of some cold starts. I also had my multimeter connected to the lithium battery. The first two start up attempts are without the enricher. The third and fourth attempts are with the enricher at max position. When the bike starts you can see the battery voltage does increase before it dies. Does this video shed any new light on this perplexing issue?

youtube.com

Ducati Superlight startup

youtube.com

BOTT

· #151 · 2 mo ago

Cut and paste the title. It defaults to private so no one can see it. Edit and radio click public. You live in So Cal, tboooe?

duc96cr

· #152 · 2 mo ago

Yes that timing light would work, or the flashing plug caps as Ducvet suggested, or go to Harbor Freight in the Automotive tools and buy one or two cheap firing indicators .

tboooe

Discussion Starter · #153 · 2 mo ago

BOTT said:
Cut and paste the title. It defaults to private so no one can see it. Edit and radio click public. You live in So Cal, tboooe?

Sorry, lets try that again. And yes I am in Socal, the OC to be exact.

Original post:
Ok guys here is a short video of some cold starts. I also had my multimeter connected to the lithium battery. The first two start up attempts are without the enricher. The third and fourth attempts are with the enricher at max position. When the bike starts you can see the battery voltage does increase before it dies. Does this video shed any new light on this perplexing issue?

youtube.com

Ducati Superlight startup

youtube.com

jdaniele

· #154 · 2 mo ago

Tommy just for shits and giggles put a jumper wire from the battery positive to the coil positive wire and give it a go.

tboooe

Discussion Starter · #155 · 2 mo ago

jdaniele said:
Tommy just for shits and giggles put a jumper wire from the battery positive to the coil positive wire and give it a go.

Thank you for the suggestion. What would this do and what problem would it reveal? Also, does it matter which coil (horizontal or vertical or both)? And, how do we know which terminal is positive on the coil? I have the old grey ones with the integrated spark plug wire.

jdaniele

· #156 · 2 mo ago (Edited)

Well it will eliminate the possibility of a bad kill switch all the positive wires come together at the short harness plugged in on the right side frame. Something tells me your loosing power to your ignition system. look at the diagram see 26-27 and 23 the brown wire is positive it goes to the kill switch. you should be able to attach a wire to one of the coils positive to the battery positive now if it starts and stays running look for a bad connection from that harness to the kill switch.
Note on my 93 the wire is red not brown there maybe differences in color.

duc96cr

· #157 · 2 mo ago

Watched the video. That’s what mine does when I’m out of gas.

tboooe

Discussion Starter · #158 · 2 mo ago (Edited)

jdaniele said:
Well it will eliminate the possibility of a bad kill switch all the positive wires come together at the short harness plugged in on the right side frame. Something tells me your loosing power to your ignition system. look at the diagram see 26-27 and 23 the brown wire is positive it goes to the kill switch. you should be able to attach a wire to one of the coils positive to the battery positive now if it starts and stays running look for a bad connection from that harness to the kill switch.
Note on my 93 the wire is red not brown there maybe differences in color.

I have a couple of extra kill switches from my other Superlights that I can try. I wonder if a bad voltage regulator would cause this issue. No right? Because even with a bad voltage regulator the battery should be able to power the spark plugs for at least a little while.

duc96cr said:
Watched the video. That’s what mine does when I’m out of gas.

I am perplexed because if fuel is the issue, why would the bike start and rev to 3k consistently with the enricher engaged? I have confirmed the fuel pump works and fuel is flowing to the bowls. Plus, just last week it started fine. I am no expert with carbs but my experience is that carbs dont just stop working overnight. That being said, I dont want to dismiss any possible solution. I ordered some starter fluid to help verify if it is indeed a fueling issue.

jdaniele

· #159 · 2 mo ago

Carful with that starter fluid you can crack a piston easy. The way the bike sounded when it did start sounds like the timing is ok to run. if you make the little jumper wire like I said you can eliminate the kill switch and wiring check the connector that powers the ignitors and coil just follow the the harness there is a connector there on the right side. Also make sure the ground is good. Do you understand what to jump looking at the diagram?

tboooe

Discussion Starter · #160 · 2 mo ago

jdaniele said:
Do you understand what to jump looking at the diagram?

Honestly, no.

There is a reason why I studied Mechanical Engineering at university and not Electrical Engineering. I will need to go into the garage tomorrow, remove the right side fairing and take a look.

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