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Minuki pumper carb running lean?

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If your pretty much stock for the motor, a 17 might be a too rich. It is on mine anyway. I have a stock motor with a UNI filter and the 96-97 exhaust SA with the bigger outlet. When I tried the 17.5 in the summer (warm weather) it didn't respond as well from low rpm's under a load. I would suggest tuning the fuel screw position first before putting the 17.5 in there. Good luck!

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20 minutes ago, michigan400 said:

If your pretty much stock for the motor, a 17 might be a too rich. It is on mine anyway. I have a stock motor with a UNI filter and the 96-97 exhaust SA with the bigger outlet. When I tried the 17.5 in the summer (warm weather) it didn't respond as well from low rpm's under a load. I would suggest tuning the fuel screw position first before putting the 17.5 in there. Good luck!

I will try that today. I'm at sea level with an open air box( Gordon's mod is what it's called I think) with a UNI filter as well, and a XR's only Exhuast. Ever since I put the carb on, it has had slight popping on the deceleration. It sounds cool, but I'm sure it's doing that because it's lean. Also thanks for your input

Edited by Caleb Barger

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Out is richer. Don't go more than 3 total turns out.

Determine how far out it is currently.

Popping thru the exhaust on decel is a sign of a lean pilot circuit. Always check the tuning of the fuel first before dropping in another jet.

So you installed the Mikuni as is and have been running it without tuning the fuel screw for your elevation and weather. You can't do that with any carb and expect the engine to run right.

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1 hour ago, Trailryder42 said:

Out is richer. Don't go more than 3 total turns out.

Determine how far out it is currently.

Popping thru the exhaust on decel is a sign of a lean pilot circuit. Always check the tuning of the fuel first before dropping in another jet.

So you installed the Mikuni as is and have been running it without tuning the fuel screw for your elevation and weather. You can't do that with any carb and expect the engine to run right.

No, I looked up the recommended amount of turns out for the screw when I put the carb in, but from the looks of the plug it's lean. But thanks for your info! I will do this when I get home.

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The recommended is a starting point. It's impossible to predict what the optimum setting is for every bike configuration and conditions, so a recommended setting is a starting point to get the bike running, then you fine tune for your specific bike setup and conditions.

It's entirely possible you need a 17.5 pilot, especially given the the XRs Only exhaust. Is that exhaust the header or muffler or full system?

And it can be a little presumptive trying to give you a definitive answer on the plug condition without knowing how much time it has on it.

Edited by Trailryder42

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8 minutes ago, Trailryder42 said:

The recommended is a starting point. It's impossible to predict what the optimum setting is for every bike configuration and conditions, so a recommended setting is a starting point to get the bike running, then you fine tune for your specific bike setup and conditions.

It's entirely possible you need a 17.5 pilot, especially given the the XRs Only exhaust. Is that exhaust the header or muffler or full system?

And it can be a little presumptive trying to give you a definitive answer on the plug condition without knowing how much time it has on it.

It's just the muffler, and the plug is about 6-8 months old, I'm going to re-adjust the fuel screw and put a new plug in her and ride her.

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About what I thought on plug age.

You should put the new plug in first, then ride the bike, get it warmed up, then work on tuning the fuel screw.

Just saying, for future reference, all the info you've revealed in your subsequent posts should have been said in the initial post. It all makes a difference in determining what people recommend to you. When you make folks drag info out of you, the process takes a lot longer. I understand a lot of people don't know what info to include. That's why you're here, to learn.

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58 minutes ago, Trailryder42 said:

About what I thought on plug age.

You should put the new plug in first, then ride the bike, get it warmed up, then work on tuning the fuel screw.

Just saying, for future reference, all the info you've revealed in your subsequent posts should have been said in the initial post. It all makes a difference in determining what people recommend to you. When you make folks drag info out of you, the process takes a lot longer. I understand a lot of people don't know what info to include. That's why you're here, to learn.

Thanks for your help! Had no clue the plug age had any role in determining. 

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18 minutes ago, Caleb Barger said:

Thanks for your help! Had no clue the plug age had any role in determining. 

When talking about the amount of time on a plug, it means engine hours of running/riding. So like, if you rode every weekend for 3 hours, in 8 months it would have about 96 hours on it. Trying to determine how well the bike is jetted "for today" is iffy on a plug that's been run for 96 hours.

After changing the plug and getting the carb tuned, go ride for a few hours. Then check to see what it looks like.

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Sea level to 8000ft.   I have posed this many times people bolt  on pumper carb. Then have restive pipe/muffler/airbox/air cleaner. Then jetting problems some even say little power difference with pumper.

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She was definitely lean. I threw the 17.5 pilot jet in. I no longer get a slight bog off of throttle. seems to be running cooler but I'll test it tomarrow mid day and check the plug again. (The plug in the pic has around 2 hrs of road speeds on it)

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