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Mikuni Pumper HEADACHE!

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Mikuni Pumper HEADACHE!

I purchased a mikuni pumper from XR's only and have experienced nothing but headaches. I am in Utah, 4400 feet, and the jetting came as 15 pilot and 130 main. The bike ran a little rich, but had a horrible bog if I cracked the throttle open. It was worse than stock! I checked for air leaks at the carb connections and carefully adjusted the valves. No change. *I called XR's only and they suggested the leaned jetting. No change. They then suggested that I make sure the pumper was squirting fuel next to the needle and not at the wall and that the pumper engagement screw was bottomed out. I made the adjustments, but that didn't change anything. Then the needle and I have since tried it in EVERY position. I spent a lot of dough to fix a problem and have only created a bigger one! I have since gone back to a 15 pilot and that seems be a fraction better, but the bike still falls on its face when I crack the throttle.

My set up:

99 xr400

Uni filter and snorkel removed

9 small holes drilled in exhaust

Mikuni headache...I mean carb from XR's only

I am thinking I have a lemon because the consensus is that this is the carb to have on this bike. Please help! What do I try from here?

Edited by Behubert
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Mikuni Pumper HEADACHE!

I purchased a mikuni pumper from XR's only and have experienced nothing but headaches. I am in Utah, 4400 feet, and the jetting came as 15 pilot and 130 main. The bike ran a little rich, but had a horrible bog if I cracked the throttle open. It was worse than stock! I checked for air leaks at the carb connections and carefully adjusted the valves. No change. *I called XR's only and they suggested the leaned jetting. No change. They then suggested that I make sure the pumper was squirting fuel next to the needle and not at the wall and that the pumper engagement screw was bottomed out. I made the adjustments, but that didn't change anything. Then the needle and I have since tried it in EVERY position. I spent a lot of dough to fix a problem and have only created a bigger one! I have since gone back to a 15 pilot and that seems be a fraction better, but the bike still falls on its face when I crack the throttle.

My set up:

99 xr400

Uni filter and snorkel removed

9 small holes drilled in exhaust

Mikuni headache...I mean carb from XR's only

I am thinking I have a lemon because the consensus is that this is the carb to have on this bike. Please help! What do I try from here?

I also live in Utah and had similar problems when I installed the Mikuni pumper on my XR400 last month.

1st problem I found is that I was drawing air in past the intake manifold on the engine side because I ripped a piece of the o-ring off when installing manifold with carb. Replacing o-ring solved problems with bogging, high idle, and hard starting.

With a new o-ring I went 1 size smaller on the pilot (13.5 I believe) and that helped off idle response to throttle input. Mikuni recommends the pumper spray of fuel hits the needle. Not sure how much that helped when I re-directed the spray but the bike starts and runs well now.

Hopefully one of these suggestions will be of help to you.

vk

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does it do this all the time ? when bike is in neutral or jut when riding ?

is your filter clean ? is there too much oil on your filter. The bog says you are getting too much fuel for the amount of air going through. Have you tried adjusting when the pump sprays ? try making the pump pump a little later so the air can increase some first.

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Thank you for the ideas. My o-ring looks fine, so I don't think it is that. I can adjust the spray to hit the needle, but XR's only said to have it spray past the needle, close but not on it. I found out tonight that the carb came with the 9DZH6-50 needle and a few people are saying that the xr4 needs the 9EBY1-50 needle to run properly. Can anyone comment on this?

Also, I made sure that the filter was clean and even tried removing the filter to make sure it wasn't the problem. Unfortunately it didn't help.

Edited by Behubert
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for some reason that 9EBY1-50 sounds familiar to me. Cant say for sure. I live in denver, so similar elevation but ride utah without rejetting. I run the next step down from a 15 pilot as far as i Know and its a 12.5.

I run a 122.5 main, 12.5 pilot, and the third position on the main clip. hope that helps

I have a variety of jets from 120 through 130 i think, and this worked best for me, but its pretty opened up as far as gordon mods and what not

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I can adjust the spray to hit the needle, but XR's only said to have it spray past the needle, close but not on it.

I don't agree with that recommendation. By the stream hitting the needle, it is broken up from a solid stream to finer droplets, which vaporizes better.

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Finally, a resolution! Called XR's only and talked to Seth. This is the guy to talk to! He used some notes and gave me the perfect settings.

12.5 pilot

127.5 main

Needle in second to lowest clip

It worked! I ripped around the neighborhood and made a few small tweaks, but it works. Yahoo! Thank you all for your help.

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Your settings confirm my new proper jetting, air filter and exhaust similar to yours - but I'm at sea-level, and Mikuni recommends 1 size smaller for each 2000 feets altitude change:

17.5 pilot

135 main

Needle in middle position

I was running 15/125 till now, and it worked fine (but not great), only minor bogs very seldom. Now it's much better.

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Im also out of Utah. Ive been considering getting the Mikuni pumper carb. My question is this good upgrade? I luv the bike but would like to get a little more out of it. I would also like to get rid of the stall when I romp on it right at first. Is upgrading to a Mikuni worth it?

Thanks for any advise.

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people with pumper carbs will say it is definitely worth the money.

People without pumper carbs will say if you properly set up the stock carb, that is just as good.

Coarse, if they have never ridden with a pumper, how would they know it is just as good ?

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Don't buy one unless you want to take it off and on and rejet it at least a few times before it runs right. You don't gain enogh power to make it worth it dollar wise. Whore out your ehaust pipes right where they bolt to the head put a good air filter and jet the stock carb. That's my opinion, but I have had bad luck with two of the pumper carbs now!!

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Thanks for your input cr5xr4. I am going to grind the exhaust out this winter sometime. I just wanted to get a few opinions on it. I dont want to through $400 at something that I wasnt sure about. Especially if its not going to give me more performance. Im considering doing the ATJ_Number_1 carb mod. Ive been looking around and if it really performce like they say it does, I may go that route. That's around $100 to $200.

Thanks

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Well thats just not true.I can understand to bad mouth the carb,because your having problems.They can be fixed.The power from a stock carb with the right jets(I have 12 or more xr4s)To Pumper(I have three xr4s)you would not even think they are the same bike.When my bike was stock only the pumper.It made more power with only the carb,then with 440 kit and cam.Too bad I already had the 440 kit and cam sitting in my shop.Yes the BSR42mm carb does make more power than the pumper.Only thing I dont like about the BSR 42 carb it does not get the MPGs like the pumper.My last ride (125 miles)I have 3.8 gallon tank,I had to carry extra gal on my belt.It used 4 gal gas not good.

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Baja trail Rider are you saying to save my money and get the pumper? I just bid on a BST 40 on ebay. And it looks like its very possible i will be getting it. Could you give me your thoughts on the carb situation? You seem to have plaint of experience with the XR.

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I would have got the 42mm carb as it fits with out many mods.As long as you can get or make the parts needed for the 40mm it works great.Also buy the time that carb works and all the parts you need to make it fit and time working.The pumper is well worth the money.Since your 40mm is on the way,once it works.You wont ever put the stocker on.Another note bigger carb,so one will say Wow this does not make more power than stock carb.Bigger carb,now opened up airbox,large air filter,large big tube header,muffler that flows.Than it works I learned the hard way.

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Thanks for the information Baja trail Rider. I do work at a machine shop so I will be able to make the 40mm work. I was looking for the 42mm but didnt see any on ebay.

Right now i have only done the gordon mods. Do you suggest that I should up grade in pipe or just grinding out the welds and putting a new tip sufficient enough?

Thanks for your input, it helps alot.

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You can try for now grind stock header,get 96 xr4 or copy Ex tip that you can remove tip.Also open up airbox,put in 10 pro vents up high on box 5 each side)Let me check my bikes to see how many.We also use 84xr500 uni air cleaner(but you need to do mods to get it in.The tricks for airbox and header muffler,where shown to me years ago by honda factory rider.We could not understand why his bike ran away from ours.Also on hillclimbs he would pull one gear higher than ours.The stock header is good,but we have found out the larger headers make more power.You would think that it would take away bottom end,but mine is like a tractor down low.

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Those are some good tricks, to give the bike a little more. Im going to get some vents order and the XR 500 air filter. When I get the carb ready I will make all those mods. Finally the XR will be running like it always should have. I will just need to figure the jets and Im set. Thanks a ton Baja. I appreciate it.

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Would you mind PM me instruction for this mod? Thx. Also the vents comes with 6 vents. Is this plenty or should I get another set.

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