Carb tuning...for dummies please

Displacement activity

An unnecessary activity that you do because you are trying to delay doing a more difficult or unpleasant activity.

Nippy Zipper said:

Displacement activity

An unnecessary activity that you do because you are trying to delay doing a more difficult or unpleasant activity.

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100% accurate! I believe your advice was to clean the carbs, especially the pilot. That is my last resort because I just dont see how my carbs can go from working to not overnight. I have verified fuel is flowing to the bowls and fuel pump works. Bike starts and revs to 3k every time.

@ducvet do you know if the enricher bypasses the idle circuit completely? I ask because I was fiddling around with the idle speed screw so I was thinking perhaps I may have messed something up that is now causing these odd starting issues. If the enricher does bypass the idle circuit completely then it wont matter what the idle speed screw is set at, as long as the enricher is engaged.

Yes they are separate circuits in the carb this is why you can some times start with a enrichener sooner after running out of fuel.

ducvet said:

Yes they are separate circuits in the carb this is why you can some times start with a enrichener sooner after running out of fuel.

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Thank you @ducvet. Ok there goes that theory. However, since they are separate circuits I believe I dont have a fueling issue, at least with the enricher circuit. Enough fuel is getting there to start the bike and rev it to 3k so it seems fuel is being delivered to the enricher circuit. Do you agree?

tboooe said:

Sorry, lets try that again.

Ducati Superlight startup

youtube.com

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Static read off the battery is in need of a charge. 12.8v to 12.99v is well charged for acid. I forget if those are static at 13-14v somewhere?

So diagnostic wise, would be the same as compression. Do not do any tampering of the bike until you have a well charged battery of 12.8v or above.

Your load drop hits 10.9v. Should read in the 11's. So right there, (processor) that TPS or whatever evolving change from carb to injector, something needs 5v to run the numbers off the crank to spark to ignition curve.

Can you keep the engine running with throttle once the engine turns on? I'm just guessing from the video, but it sounds like you have proper spark.

BOTT said:

Static read off the battery is in need of a charge. 12.8v to 12.99v is well charged for acid. I forget if those are static at 13-14v somewhere?

So diagnostic wise, would be the same as compression. Do not do any tampering of the bike until you have a well charged battery of 12.8v or above.

Your load drop hits 10.9v. Should read in the 11's. So right there, (processor) that TPS or whatever evolving change from carb to injector, something needs 5v to run the numbers off the crank to spark to ignition curve.

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I have a lithium battery so that voltage reading is ok. The voltage does dip but once the bike starts you can see it rises to 13.9v. I assume that means the stator and voltage regulator are working fine but I do have a suspicion that the issue is electrical or ignition related.

J.B. said:

Can you keep the engine running with throttle once the engine turns on? I'm just guessing from the video, but it sounds like you have proper spark.

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I do not know because the bike dies so quickly once it fires up. Last weekend, the bike would start and run fine with the enricher engaged but once I turned it off, I had to give it some throttle to keep the bike running, it wouldnt idle by itself. Now the bike only starts but dies pretty much right away.

tboooe said:

I have a lithium battery so that voltage reading is ok. The voltage does dip but once the bike starts you can see it rises to 13.9v. I assume that means the stator and voltage regulator are working fine but I do have a suspicion that the issue is electrical or ignition related.


I do not know because the bike dies so quickly once it fires up. Last weekend, the bike would start and run fine with the enricher engaged but once I turned it off, I had to give it some throttle to keep the bike running, it wouldnt idle by itself. Now the bike only starts but dies pretty much right away.

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I feel like I’ve had a very similar issue. I’m trying to remember…I think mine was like that, and it wouldn’t idle and stalled really easily till engine is properly warmed up. With mine, though it didn’t idle, it started, so I tacked the carbs first by thoroughly cleaning every part of it. Did you say you already cleaned the carbs?

J.B. said:

I feel like I’ve had a very similar issue. I’m trying to remember…I think mine was like that, and it wouldn’t idle and stalled really easily till engine is properly warmed up. With mine, though it didn’t idle, it started, so I tacked the carbs first by thoroughly cleaning every part of it. Did you say you already cleaned the carbs?

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PLEASE PLEASE remember!

I have not cleaned the carbs. The reason is that just 2 weeks ago the bike started and idled fine so I find it hard to believe that during that time the carbs ceased to work properly. Plus I verified I am getting fuel to the bowls and when the enricher is fully engaged, there is enough fuel to start the bike and have it rev to 3k consistently, before dying. Now, that isnt to say the pilots or jets or some other parts of the carbs dont need some cleaning or adjustment. But at this point, I am just trying to get the bike to keep running with the enricher engaged.

Tommy you need to start a check list here so each step can be verified good bad I don't know.
I am sticking with your loosing power to the ignition circuit or bad ground on that connector to the coils.
Why ? when the bike starts it sounds good and most of the time your cranking in your video it does not kick or backfire. If you let the fuel pump run for 30 seconds and then can you get say at 2 shot glasses of gas out of the bowls if so it should run longer tan 4 seconds. also when it did run if it had that little fuel in the bowl it would most likely pop through the intake lean.
Just my two cents.

jdaniele said:

Just do it! View attachment 1062291

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Yes yes I definitely intend on doing as you suggest. I actually agree with you that I think the issue has something to do with ignition/electrical. Most likely I will have time tomorrow. I am just waiting on the my induction timing light gun so I can use it to also visually check for spark.

jdaniele said:

If you let the fuel pump run for 30 seconds and then can you get say at 2 shot glasses of gas out of the bowls if so it should run longer tan 4 seconds. also when it did run if it had that little fuel in the bowl it would most likely pop through the intake lean.

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This is an excellent point and why I dont think my carbs are the issue and its ignition/electrical related.

I hate to burst your logic bubble but the carbs could absolutely work one day and not the next. There are some very small fuel passage in there that can clog easily. I had a car that stalled at the same spot every day, because a flake of paint was in the float bowl and would cover the hole that fed the carb when the float bowl level got low enough . Strange shit happens.

duc96cr said:

I hate to burst your logic bubble but the carbs could absolutely work one day and not the next. There are some very small fuel passage in there that can clog easily. I had a car that stalled at the same spot every day, because a flake of paint was in the float bowl and would cover the hole that fed the carb when the float bowl level got low enough . Strange shit happens.

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Fair enough and I totally acknowledge I am far from being an expert. This is why I sincerely appreciate any and all help I can get, so thank you and others for taking the time to reply on this thread. To help isolate the issue, lets just focus on the enricher circuit. If there is consistently enough fuel flowing from the enricher circuit to always start the bike and have it rev to 3k, is it safe to assume that this specific circuit is working properly and supplying adequate fuel?

Timing light coming should show as soon as you hit the starter button. No action or sporadic action blinking, meaning it shuts off, shows up again as it cranks, then for sure you could point to electrical and maybe narrow it down to the crank sensor. Say spark shows up and it lights the bike up.

But continual spark... time to head over to NAPA auto store, by a can of carb clean. The quick and dirty is no dipping of rubber, plus fresh and new takes like 20 minutes, hose off with water, blow dry, eyeball the jet holes, assemble and install.

Say both bodies have a connect bar, the other is the linage bar. Rather than take that all apart and mess with the sync linkage, dip the one body in the dip, then swap carb bodies. Saves a lot of parts flying, tiny cotter pins rebent and might break on assembly. Crap like that.

I know nothing about those carbs, mine came with FCRs fitted. If it's possible to remove the float bowls and remove the pilot jets with the carbs in situ to check and clean them, I'd absolutely recommend doing that. With the FCR's that is a 30 minute job, can't comment on the Mikunis.

I'm now going to shut up.