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Mikuni pumper from XR's only for XR4 worth it?

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Hey mate,

 

For what it's worth, Id definitely pay the extra money to buy it direct from XR's only. Bought mine second hand off here and have had an absolute nightmare setting it up. Least if it's new you know it won't have been butchered by previous owners.  Mine definitely pulls better than with stock carb, I didn't really have troubles with the stock, started easy minimal bog, but it definitely an improvement. If you do do it, find some of the posts from Trailryder on here it will make it heap easier for you.

 

Good luck

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It was definitely worth it for me, as I couldn't get the stock carb to feed my big bore 440 acceptably. I think it's also more forgiving between elevation extremes than the stock carb, as far as if you don't get it tuned/rejetted perfect, it still runs decent enough.

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They work great on stock motors also. Gives a little more snap to the low end and should you end up dumping the bike somehow, it won't stall out on it's side.

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My best freind had a 2000 XR400R he loved but hated the hot starts and starts after a fall. He stuck on e of those pumper carbs on from XRs only and said if he ever got another XR400 that is the first thing he would order. Major difference in low end snap, better mid and top end and even less picky to jetting for altitude changes than the stock carb which isn't bad.

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I ride from 7000' where I live to sea level and maybe turn the screw 1/2 turn but haven't messed with the jets ever.  You need to tweak the alignment of the carb with the adapters to fit completely inside the boots and the throttle linkage to be completely free.  

 

I lied, My brother in law took it out with us on a ride and had some missing and popping on the way out to the trails, maybe started 5 times this year before that.  Pilot jet was clogged and now back to bullet proof.  I am always thinking about selling the bike then I ride it and it is too much fun....

 

So YES, get the pumper!

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I recently installed (8/22/13) the Mikuni pumper carb. I had planned to do a photo install. I got carried away and before I knew it. I was done, about 1-1.5hr installation, including cleaning around carb area. My 2003 XR400 fires right up after sitting for 5yrs. The original carb was froze. I flushed tank with new gas. I have yet to ride as of yet, but kicking it over has never been so easy. Carb was purchased through XR's Only, cables were included.

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I have one on my bike.  It's a completely stock motor with Uni air filter and free flowing exhaust.  I did it several years ago, got out of riding for a few years, now getting back into it.  I have no bias any more to justify why I spent $400 on a carb like I might have recently after I bought it.

 

I don't notice any difference in performance with the pumper.  Maybe a tiny bit improvement off idle.  I didn't have any bog with the stock carb after getting jetting advice and parts from Carmichael Honda in Sacramento.  Stock carb ran great.

The biggest difference for me is the starting.  I hadn't started my bike in over 6 months.  I'm getting ready for a ride next month and decided I better pull it out of the corner of the garage and start going through it to make sure it's ready to go.  My 8 year old son was in the garage with me and asked to go for a ride before I put it up on the stand and started working on it.  I reluctantly said OK, as I really didn't want to kick on it for a long time for a trip up the street and back.  Choke on, gently pushed the motor through getting to the compression, let the kickstarter back up to the top, gave one half twist of the throttle, one good kick, and it started right up.  More than 6 months in the corner of the garage between the last start.  If that had been stock carb, I would've wheeled it out in the gutter for a little more leg room, let the sun shine on the engine for awhile, gone through the whole routine, and pray that if I got it to fire I could keep it going. 

 

I do find I have a harder time with the tuning of the pumper than the stocker.  The mid to upper range is fine, my problem is idle circuit.  I can't get the lean popping out of it on deceleration.  If I crack the throttle just the tiniest bit as I'm decelerating, no popping.  If i just let it close all the way, pop pop pop pop.  If I adjust the fuel screw any, it just makes it run worse where it matters.  The decel pop is not a big deal, just annoying.

 

I think I agree the pumper is less sensitive to altitude and weather changes than the stock carb.

 

Edited to add... I guess I'm getting old and busy with life, 3 kids.  I just want my bike to run and be fairly low maintenance, (which is why I still have my XR400).  If I can't have electric start, I'll take easy kickstarting.  To me that's where the pumper is worth it. 

Edited by michaelxr

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They work great on stock motors also. Gives a little more snap to the low end and should you end up dumping the bike somehow, it won't stall out on it's side.

Wonder where u saw that?????

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I had an '01 400, stock engine, installed an Edelbrock. Huge improvement across the board, I'm sure the FCR would work just as well if not better. Cheaper alternative, the stock engine '96 I'm riding now has a Mikuni TM34, non pumper. Although not quite as good as the Eddy in off-idle throttle response, it is a significant improvement over the stock carb throughout the RPM range. I have attempted to fine tune 3 400 stock carbs, never could get them to suit me.  

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Wonder where u saw that?????

 

Ohhh,,,, here and there,,, and over there,,,, and back that way again. LOL!!

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Its hard to see when you are in the thick of it, but human nature is highly influenced by confirmation bias and the Placebo Effect. We tend to see what we are looking for. Spend $400 bucks for a pumper and you want to see that your bike runs much better. Same with a cam, pipe, etc. Bottom line is, you get the right air/fuel mixture to the cylinder and its going to make the power...dosen't matter if that mixture is from the oem carb or a gold plated, ten thousand dollar carb. I realize that transient period when you crack the throttle does need a shot of fuel from a pumper, but in steady-state operation, no fundamental difference. I wish it was different, but in truth, there isn't that much difference in performance when you do the Gord mods, replace oem filter with twin air, etc. The bikes may run slightly better, but "much better"? No way! I remember a news article I saw some time ago where in a blind test, tasters showed no preference for expensive wines over cheap.

Edited by oldmanrip

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old man rip has a good point. I see no difference with an aftermarket air filter on my xr 400. if the stock carb is tuned properly the stock engine will pull just fine. I would get a pumper if I was rich for the 1% increase in performance, or maybe if i had a big bore 440 which might need a little better breathing.cant justify 400 bones for a pumper right now. I had slight improvements in the mid to high rpm range with pulling the snorkel and richening the needle one notch and of course slightly bigger jets. went from getting passed by a drz 400s to slowly passing the drz with the gordon mods. so the cheap gordon mods were worth it. not buying a $400 carb anytime soon

Edited by XL100allnightlong

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I have to agree with those that have no problem with the stock carb with the bike in stock form or with the Gordon mods. I never had an issue with it. I just learned to tune it. It wasn't til after I did my 440 kit that I actually "needed" to consider the Mikuni.

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Its hard to see when you are in the thick of it, but human nature is highly influenced by confirmation bias and the Placebo Effect. We tend to see what we are looking for. Spend $400 bucks for a pumper and you want to see that your bike runs much better. Same with a cam, pipe, etc. Bottom line is, you get the right air/fuel mixture to the cylinder and its going to make the power...dosen't matter if that mixture is from the oem carb or a gold plated, ten thousand dollar carb.

 

I never tried a pumper carb, but couldn't imagine why I'd ever want to.  My XR4 pulls like a freight train from idle through WFO with absolutely no off-idle bog.  I think most folks have their pilot circuit setup too lean - I jet specifically for explosive off-idle throttle response, and found the stock carb more than adequate.

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Hey mate,

 

For what it's worth, Id definitely pay the extra money to buy it direct from XR's only. Bought mine second hand off here and have had an absolute nightmare setting it up. Least if it's new you know it won't have been butchered by previous owners.  Mine definitely pulls better than with stock carb, I didn't really have troubles with the stock, started easy minimal bog, but it definitely an improvement. If you do do it, find some of the posts from Trailryder on here it will make it heap easier for you.

 

Good luck

I had the same experience. Get a new one from XRsonly.

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Its hard to see when you are in the thick of it, but human nature is highly influenced by confirmation bias and the Placebo Effect. We tend to see what we are looking for. Spend $400 bucks for a pumper and you want to see that your bike runs much better. Same with a cam, pipe, etc. Bottom line is, you get the right air/fuel mixture to the cylinder and its going to make the power...dosen't matter if that mixture is from the oem carb or a gold plated, ten thousand dollar carb. I realize that transient period when you crack the throttle does need a shot of fuel from a pumper, but in steady-state operation, no fundamental difference. I wish it was different, but in truth, there isn't that much difference in performance when you do the Gord mods, replace oem filter with twin air, etc. The bikes may run slightly better, but "much better"? No way! I remember a news article I saw some time ago where in a blind test, tasters showed no preference for expensive wines over cheap.

I would disagree. There is a reason EVERY new MX bike has a pumper carb. (Before the switch to fuel injection.) To some degree it is a crutch. You shouldn't be grabbing a handful of throttle off idle. Or you should know how to clutch the bike. But if you need to, the bike will wheelie forward, rather than stumble. Nice if you need to wheelie off a ledge on a slow single track. The throttle response is better. The cheap plan B for MX tracks is just turn up the idle a bit.

As for the UniFilter. Jet you bike spot on for the UniFilter, then put in the stock filter. The stock filter makes the bike feel plugged up, just a bit. The fix might be a quick turn of the fuel screw, but it is noticeable. My XR400 is plated, so test runs are often done on the street or freeway.

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I have one on my bike.  It's a completely stock motor with Uni air filter and free flowing exhaust.  I did it several years ago, got out of riding for a few years, now getting back into it.  I have no bias any more to justify why I spent $400 on a carb like I might have recently after I bought it.

 

I don't notice any difference in performance with the pumper.  Maybe a tiny bit improvement off idle.  I didn't have any bog with the stock carb after getting jetting advice and parts from Carmichael Honda in Sacramento.  Stock carb ran great.

The biggest difference for me is the starting.  I hadn't started my bike in over 6 months.  I'm getting ready for a ride next month and decided I better pull it out of the corner of the garage and start going through it to make sure it's ready to go.  My 8 year old son was in the garage with me and asked to go for a ride before I put it up on the stand and started working on it.  I reluctantly said OK, as I really didn't want to kick on it for a long time for a trip up the street and back.  Choke on, gently pushed the motor through getting to the compression, let the kickstarter back up to the top, gave one half twist of the throttle, one good kick, and it started right up.  More than 6 months in the corner of the garage between the last start.  If that had been stock carb, I would've wheeled it out in the gutter for a little more leg room, let the sun shine on the engine for awhile, gone through the whole routine, and pray that if I got it to fire I could keep it going. 

 

I do find I have a harder time with the tuning of the pumper than the stocker.  The mid to upper range is fine, my problem is idle circuit.  I can't get the lean popping out of it on deceleration.  If I crack the throttle just the tiniest bit as I'm decelerating, no popping.  If i just let it close all the way, pop pop pop pop.  If I adjust the fuel screw any, it just makes it run worse where it matters.  The decel pop is not a big deal, just annoying.

 

I think I agree the pumper is less sensitive to altitude and weather changes than the stock carb.

 

Edited to add... I guess I'm getting old and busy with life, 3 kids.  I just want my bike to run and be fairly low maintenance, (which is why I still have my XR400).  If I can't have electric start, I'll take easy kickstarting.  To me that's where the pumper is worth it.

What are the jetting specs you used for the stock carb? Can you post them for other people.

The popping on deceleration was driving me nuts. Otherwise the Mikuni worked great. I tried bigger and smaller jets, nothing worked. Then I found the tip of the fuel screw was broken off in the carb body. I pushed out the brass tip with a dental tool and bought a new fuel screw. Now I can tune out more popping.

The gasoline in California will turn your bike into crap in a month. I never used Stabil before, but now I do. Gone are the days of parking an XR for years and starting it up. Not if you didn't use Stabil. I had to buy new jets for my small XRs. The ethanol turned them into corroded junk.

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