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Old 10-07-2009, 09:10 PM   #1
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Default Mysterious lean bog

After breaking in my JPX .21 Plus and looking of a race tune, I can't seem to fine a tune where it doesn't lean bog. It is the weirdest thing because it will run fine for 5 minutes and then suddenly pick up a bog at WOT but the engine doesn't run hot. I bring it in for a quick needle adjustment and temp and try it again. Each time it started to bog I would richen it a couple of click and it seem to help but a few minutes later it would bog again.

I spent all night chasing this bog and it keeps eluding me. Engine is sealed, exhaust seals are good, clutch assembly and fuel line checks out. Engine seems to idle okay and it does blow smoke. Bog would come and go at all fuel levels in the tank.

My next step is to run the engine in another car just to see if it is capable of running right. This would eliminate the possibility that the tank or other part of the car is causing this problem. I am not a very good tuner, but I had someone that knows his business try and tune it with no luck.

Any ideas on what to look for?
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Old 10-07-2009, 09:24 PM   #2
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The Carbs are known for air leaks between the aluminum and plastic by the high speed needle. Some guys use JB weld over that area to stop the leak.
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Old 10-07-2009, 09:27 PM   #3
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Quote:
Originally Posted by petevette View Post
After breaking in my JPX .21 Plus and looking of a race tune, I can't seem to fine a tune where it doesn't lean bog. It is the weirdest thing because it will run fine for 5 minutes and then suddenly pick up a bog at WOT but the engine doesn't run hot. I bring it in for a quick needle adjustment and temp and try it again. Each time it started to bog I would richen it a couple of click and it seem to help but a few minutes later it would bog again.

I spent all night chasing this bog and it keeps eluding me. Engine is sealed, exhaust seals are good, clutch assembly and fuel line checks out. Engine seems to idle okay and it does blow smoke. Bog would come and go at all fuel levels in the tank.

My next step is to run the engine in another car just to see if it is capable of running right. This would eliminate the possibility that the tank or other part of the car is causing this problem. I am not a very good tuner, but I had someone that knows his business try and tune it with no luck.

Any ideas on what to look for?
usually when it bogs like that at WOT it too lean on the HSN... try fatting the top 1/4 turn..
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Old 10-08-2009, 05:11 AM   #4
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usually when it bogs like that at WOT it too lean on the HSN... try fatting the top 1/4 turn..
What he said. After that you may have to lean the bottom a bit to keep it idling right.
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Old 10-08-2009, 06:42 AM   #5
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I will give that a shot, but I am afraid the HSN needle is going to fall out. It is already quite a bit higher then flush.

I am not sure if these Jammin Plus engines tune with the HSN out that far. I think I will post this question about the HSN on the Jammin thread.
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Old 10-08-2009, 06:48 AM   #6
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I think your low end is way to lean and you compensating by trying to richen up the top....

Go back to factory settings and tune from there.

Seal the carb
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Old 10-08-2009, 08:00 AM   #7
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What is the response from dead stop? Is it near flooding on the low? I know you can very easily have the low end too rich and the high end too lean and it will still idle fine. You're basically masking the lean high end due to having it very rich on the low end. What you need to do to fix this is start by leaning out the low...usually quite a bit...dont worry about the idle yet..get the low to where its not bogging off the line and you have good response...then richen up your high end...finally get your idle in check and it should be good to go. You can check out
http://www.rctech.net/forum/nitro-of...ing-bible.html

They explain this better than i can. Good luck.
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Old 10-08-2009, 09:11 AM   #8
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Quote:
Originally Posted by petevette View Post
After breaking in my JPX .21 Plus and looking of a race tune, I can't seem to fine a tune where it doesn't lean bog. It is the weirdest thing because it will run fine for 5 minutes and then suddenly pick up a bog at WOT but the engine doesn't run hot. I bring it in for a quick needle adjustment and temp and try it again. Each time it started to bog I would richen it a couple of click and it seem to help but a few minutes later it would bog again.

I spent all night chasing this bog and it keeps eluding me. Engine is sealed, exhaust seals are good, clutch assembly and fuel line checks out. Engine seems to idle okay and it does blow smoke. Bog would come and go at all fuel levels in the tank.

My next step is to run the engine in another car just to see if it is capable of running right. This would eliminate the possibility that the tank or other part of the car is causing this problem. I am not a very good tuner, but I had someone that knows his business try and tune it with no luck.

Any ideas on what to look for?
it sounds like you need to put more stall in the clutch. if you are running .9 springs try 1.0 if you have 1.0 in it try 1.1you may need to lighten the shoes up some.just dont know for sure without knowing what you have and see it run.
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Old 10-08-2009, 09:40 AM   #9
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Picco carbs are very sensitive to idle gap. Pull the air filter off and see how much of a gap you have at idle. It should be about .9mm. If it is more than that, the bottom is too rich and top too lean. Back the idle down, richen the top a quarter and lean the bottom until it idles right.

If it is less than that, the bottom is too lean. Increase the idle gap, richen the bottom until the idle comes down and re-tune the top.

If you have a smaller venturi in the carb, you may need to remove it to see if the idle gap is right.
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Old 10-08-2009, 09:45 AM   #10
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Alot of great advice here guys. I am going to try your recommendations ASAP.
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Old 10-08-2009, 02:36 PM   #11
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If all else fails ,take the carb completely appart clean it ,flush it and try again I've heard about picco carbs having minute metal shavings in them from the factory.
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