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Unread 02-10-2019, 05:13 PM
crunchbucket's Avatar
crunchbucket crunchbucket is offline
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Default Midrange Missfire - RS50

Hi all.

I am experiencing a consistent misfire in my midrange RPMs at all throttle except for full throttle. I have wideband 02 on the bike and everything looks good there.

2000 RS50 with Athena 80CC Powervalve kit, dellorto 21mm, Stock exhaust. Stock Airbox.

AFRs in the 12.5 - 13 range.

I just installed the Top Performance Ignition box in hopes that it would have solved the problem, but the bike is behaving basically the same as it did with the stock ignition.

Is this a common problem? Could it be related to squish setting?

The bike has a B10EG plug on it at the moment. BR9ES on its way from Amazon at the request in the Top instructions to go "R".

Any thoughts?

thanks!

MG
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  #2  
Unread 02-10-2019, 06:39 PM
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Clint Eastwood Clint Eastwood is offline
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Needle taper or atomiser too rich. PHBG 21's usually run W7 needle / 262AU atomiser.
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  #3  
Unread 02-10-2019, 06:39 PM
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twinturba twinturba is offline
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Welcome to Bats!

My .02

Not familiar with the Athena powervalve kit, but I have owned a Cagiva Mito with similar mid range issues caused by a powervalve in need of adjustment. It appears the kit uses vaccuum to activate the powervalve so the first thing I would do is double check that system.

The stock pipe canít be helping the situation either.

I believe you want an AFR closer to 12-12.5 for a two stroke. What jetting do you have in the carb?

Have you measured the squish?
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  #4  
Unread 02-10-2019, 08:01 PM
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jkv357 jkv357 is offline
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Is the problem new, or has it been doing it for a while? Did you do all the mods yourself, at one time, or did you buy it like it is?

Have you tried temporarily running it without the air filter, airbox lid, or tried moving the clip on the needle? Something to lean out the mixture to see if it makes the issue better or worse?

I would think you would benefit from a less restrictive intake and exhaust system.

What does the plug look like?

What fuel are you running? Is it absolutely fresh? Premix or injection?

My Derbi absolutely fell on its face, bucking and stuttering, in the mid-range until I leaned the mixture significantly.
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  #5  
Unread 02-11-2019, 04:53 PM
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crunchbucket crunchbucket is offline
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@TwinTurba - thanks!

Powervalve is suspicious for sure. Doesn't run off of vacuum, but based on exhaust gas pressure essentially. But he AFRs seem right. Like they stay essentially the same under and over this range of RPM and no misfire there. I was given 2 springs with the PV, perhaps I should try the other and see if the problem shifts RPM range.

It has been a while, I would need to open the carb and get my setup. I know I should write this down in a logbook. I have to pull the tank off to put the Airbox back in as I left it out just to make sure the Top ignition box was installed correctly on a test ride. FWIW, all that did was lean it out like one would expect. It didn't change the nature of the misfire or the range of it.

Squish was just at 1mm.

@JKV357 - thanks as well.

Fuel has been in there for a while, but no difference when fresh. I moved the needle and the jetting until I felt I was in safe zones. Light throttle I am good with anything under 13, under medium to full throttle, I try to keep it around 12:1. Injected oil.

Plug looks good. Clean on one side and small amount of carbon on the other.

Did all the work myself.

I need to get my Arrow pipe fitted with an 02 bung so I can keep an eye on AFR with that pipe. It is just too loud for me.

Cheers fellas.
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  #6  
Unread 02-13-2019, 10:04 PM
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crunchbucket crunchbucket is offline
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Squish measures 1.17 with the solder test. Kit calls for .95 to .85. I think they gave 3 gaskets that are all .25 different in thickness, so hopefully I am on a bigger one.

They also call for 96 Octane gas, so I need to mix in some 114 I have in a 5 gallon tank.

Didn't pull the carb to check the jets and needle given that I can monitor AFR.
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  #7  
Unread 02-14-2019, 08:16 AM
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jkv357 jkv357 is offline
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Quote:
Originally Posted by crunchbucket View Post
Squish measures 1.17 with the solder test. Kit calls for .95 to .85. I think they gave 3 gaskets that are all .25 different in thickness, so hopefully I am on a bigger one.

They also call for 96 Octane gas, so I need to mix in some 114 I have in a 5 gallon tank.

Didn't pull the carb to check the jets and needle given that I can monitor AFR.
I haven't worked with AFR, but I don't know if that alone is going to tell you everything you need to know to get it fuelling properly.

Because of specific engine design factors, and in certain conditions and loads, the "correct" AFR may not be right.

I tend to go by sound and feel for carb tuning.

Just an idea...
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