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Old March 10th, 2021, 03:11 PM   #1
clakmurrick
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Unhappy Choke raises revs to 2k RPM, then bike begins to stall.

Hey all, I'm looking for some help with the choke on my bike. Full disclaimer, I have some problems with the bike, and I'm going through any problems to limit them. I made a post previously about the problems I'm having, specifically lower RPM problems, because I modded the bike under the advice of a fellow bike enthusiast. I can't return it to stock at the moment since the airbox was broken. I have converted to velocity stacks, a jet kit, washer on the needle, and an exhaust. I can provide more details later.

Anyways, the bike never really needs the choke to start. I usually get away with cranking it while cold, and it starts. It usually has a pretty low RPM (like 800 RPM) until I give it some throttle and let it warm up, and then it usually stays where I set the idle (about 1300 RPM). The temperature around here is 65-70 F, and we're about 400 feet above sea level, so not high altitude.

When I do try and use the choke, the bike still starts, but the behavior is odd. If the bike is idling, but still cold, and I apply choke, the RPMs usually raise to about 2000 RPM for a second or two, then the bike begins to stall and will die unless I turn the choke off. I understand that the choke on the Ninja is really just an enrichener since it adds fuel, but I'm not sure why the bike decides to stall. My hypothesis is that perhaps one cylinder is getting fuel, trying to raise the RPM, but the other cylinder is not (perhaps it's clogged), so the engine is upset since there is an imbalance.

Any help is appreciated. I tried my best to clean the carbs. I've had the carbs apart 3 times to clean them, each time letting them sit in carb cleaner for hours, using needles to clean passageways. I must be missing something.
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Old March 10th, 2021, 06:13 PM   #2
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It sounds like the mixture is very rich. All my carb engines stall when they are warm and I apply the choke. Modifying many variables at the same
time always leads to a risk of messing up things with follow up difficulties of understanding what is wrong as they compound. The only way to have a successful modification while modifying many things at the same time is when you have proper diagnostic tools.
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Old March 10th, 2021, 07:55 PM   #3
clakmurrick
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Do you have any tools you'd recommend?
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Old March 11th, 2021, 07:57 AM   #4
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Quote:
Originally Posted by clakmurrick View Post
Do you have any tools you'd recommend?
I am no expert, but If I was doing it myself I would at least use the carb wet flow bench, dyno test bench and air/fuel mixture analyzer. Plus a bunch of other small tools to make sure your carbs are in sync, you valves gaps are on etc.


Hopefully the experienced guys here would chime in.
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Old March 11th, 2021, 08:21 AM   #5
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Have you adjusted the Idle Mixture Screws?

Did you install larger Pilot Jets?

Overall, it sounds rich. You should need some amount of choke/enrichment to get a cold engine to idle reasonably.

The carbs should be synced as soon as you get it to run decent.
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Old March 11th, 2021, 09:38 PM   #6
clakmurrick
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Quote:
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Have you adjusted the Idle Mixture Screws?

Did you install larger Pilot Jets?

Overall, it sounds rich. You should need some amount of choke/enrichment to get a cold engine to idle reasonably.

The carbs should be synced as soon as you get it to run decent.
Yes, I did adjust the idle mixture screws. I found that the best setting for me was about 2.5 turns out, when below 60 F out. Revving it at that setting wouldn't have any hanging, nor would the RPM go below my idle. The pilot jets are upgraded to a number 40. I have synced the carbs. From another post, I was told that my 117.5 jet is likely too large.

Quick question, how much throttle am I using under no load to get to 6k RPM? It seems a lot of my problems are down low for now. I wouldn't doubt that a smaller jet would help. I have a 112.5, so I'll swap to that and see what happens. What pilot jet would you recommend?

Thanks!
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Old March 12th, 2021, 07:03 AM   #7
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Quote:
Originally Posted by clakmurrick View Post
Yes, I did adjust the idle mixture screws. I found that the best setting for me was about 2.5 turns out, when below 60 F out. Revving it at that setting wouldn't have any hanging, nor would the RPM go below my idle. The pilot jets are upgraded to a number 40. I have synced the carbs. From another post, I was told that my 117.5 jet is likely too large.

Quick question, how much throttle am I using under no load to get to 6k RPM? It seems a lot of my problems are down low for now. I wouldn't doubt that a smaller jet would help. I have a 112.5, so I'll swap to that and see what happens. What pilot jet would you recommend?

Thanks!
The larger Pilot Jets should be fine, but 2.5 turns out on a bigger Pilot seems too rich. That's about the range with a stock 38. I would expect you to be closer to 1.5 turns out.

You really can't tell much by revving to a certain RPM in neutral. It takes minimal throttle opening to produce high RPMs when not under load - so it doesn't really tell you anything. You need to ride it (fully warm) and note at what throttle position the problems occur. That tells you which carb circuit is causing the problem.

Having 2 similar threads going is making this more difficult. Maybe we could merge them or something?

https://www.ninjette.org/forums/showthread.php?t=354327
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Old March 12th, 2021, 07:24 AM   #8
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Was the engine fully warmed up when 2.5 turns was best?
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Old March 16th, 2021, 03:51 PM   #9
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Was the engine fully warmed up when 2.5 turns was best?
It should have been. Let me do some more testing.
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Old April 2nd, 2021, 05:28 PM   #10
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Ducatiman fixed all my problems! I posted more about it in the other thread. Thanks Gordon!
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Old April 3rd, 2021, 06:11 AM   #11
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just for you, C
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Old April 6th, 2021, 01:58 AM   #12
clakmurrick
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just for you, C
Haha you're the man!
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