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Pumpercarburetor Just installed a Mikuni carburetor on my XR400R, bike is pain in the ass to start, what did I do wrong?

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Before I installed the Mikuni carburetor, I rode my bike around with the stock earlier in the day, it was fine. The XR kicked over and I was able to ride, in context the bike had adjustment issues with the carb and idling with the stock and for many other reasons and as a gift I got the Mikuni Carburetor for my 2002 XR400R. 
 

I just received my package and I instantly go to install it. I get everything in the proper place, gas tank connected, and it just doesn’t kick over. I feel like I am missing something here. since the carburetor did not come with any real instructions, I went with how I put in the stock, and adjusted the mixture screw to the 1 1/4 as stated in my manual for California. 
 

I am sure I am missing something, anyone had a run into with this pumper carb? 

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Which Mikuni? The TM36 as sold by XRs Only? You typically find the TM36 set up with 130/15 jetting.

California, so......near sea level? 130/15 jetting is often found to be too lean for sea level. Depending on how the intake and exhaust is configured, you typically see guys needing to run at least 135/17.5 jetting and often richer.

What if any, airbox, filter and exhaust mods are done?

This is the .pdf we use for tuning/working on the TM36. https://mikuni.com/pdf/hs40_manual.pdf

I suggest setting the accel pump timing screw (screw #1 in the .pdf) turned in all the way, bottomed against its spring to start with.

You should also verify the float level is set properly.

The Mikuni has an actual fuel enrichment circuit for cold starting, unlike just the choke flap of the stock carb. Pull up the knob to set it to ON, I still like to hold decomp and kick the engine over several times to prime the system, then bring to TDC and make every starting kick from there. Only difference is, unlike the stock carb, the MIkuni responds well to wicking the throttle open at the bottom of your kick.

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55 minutes ago, Trailryder42 said:

Which Mikuni? The TM36 as sold by XRs Only? You typically find the TM36 set up with 130/15 jetting.

California, so......near sea level? 130/15 jetting is often found to be too lean for sea level. Depending on how the intake and exhaust is configured, you typically see guys needing to run at least 135/17.5 jetting and often richer.

What if any, airbox, filter and exhaust mods are done?

This is the .pdf we use for tuning/working on the TM36. https://mikuni.com/pdf/hs40_manual.pdf

I suggest setting the accel pump timing screw (screw #1 in the .pdf) turned in all the way, bottomed against its spring to start with.

You should also verify the float level is set properly.

The Mikuni has an actual fuel enrichment circuit for cold starting, unlike just the choke flap of the stock carb. Pull up the knob to set it to ON, I still like to hold decomp and kick the engine over several times to prime the system, then bring to TDC and make every starting kick from there. Only difference is, unlike the stock carb, the MIkuni responds well to wicking the throttle open at the bottom of your kick.

I bought it from nichecycle. I’m also going to switch the jets to those sizes in the morning.

 

as far as mods, I have the entire bike stock. Thank you for the pdf. I will study this. 

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4 hours ago, Jayesfoo said:

Before I installed the Mikuni carburetor, I rode my bike around with the stock earlier in the day, it was fine. The XR kicked over and I was able to ride, in context the bike had adjustment issues with the carb and idling with the stock and for many other reasons and as a gift I got the Mikuni Carburetor for my 2002 XR400R. 
 

I just received my package and I instantly go to install it. I get everything in the proper place, gas tank connected, and it just doesn’t kick over. I feel like I am missing something here. since the carburetor did not come with any real instructions, I went with how I put in the stock, and adjusted the mixture screw to the 1 1/4 as stated in my manual for California. 
 

I am sure I am missing something, anyone had a run into with this pumper carb? 

Did you try opening the fuel screw a little more? 

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2 minutes ago, ossagp1 said:

Did you try opening the fuel screw a little more? 

Yes I did, even went as far as 2 1/2 but I’ve noticed that when screwed all the way in, u can’t even see the tip of it sticking out, not sure if that’s a problem 

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They do just about disappear, and require a smaller size of screwdriver to get them bottomed than anything else needs on my bikes. If the carb slide is even up enough to let light from a flashlight in, my xr 250 and my xr600 get really finnicky to start with the same pilot jets that work when they are warmed up. Cool days I used to open the 600 up to 3.5 just to start it. Warm it up and make it sensible again. First start can be rough.

Prime it and see if it runs. I do it through the plug hole rather than through the carburetor.

Edited by ossagp1

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39 minutes ago, ossagp1 said:

They do just about disappear, and require a smaller size of screwdriver to get them bottomed than anything else needs on my bikes. If the carb slide is even up enough to let light from a flashlight in, my credit 250 and my xr600 get really finnicky to start with the same pilot jets that work when they are warmed up. Cool days I used to open the 600 up to 3.5 just to start it. WRm it up and make it sensible again. First start can be rough.

Prime it and see if it runs. I do it through the plug hole rather than through the carburetor.

Man I am sort of new to bikes, but learning fast, however I can’t even comprehend what you just wrote to me lol

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Well if you never heard of priming them, let me explain. Common when one is starting one with a new carburetor. Maybe 1 in ten times I do it or need to do it when I have had a carburetor apart. 

Put about a teaspoon full of gas directly into the cylinder just before you try to start it. This should get it running, and if you have the fuel turned on it should stay running. That seems to help purge air out of the low speed circuit of the carburetor. Gosh knows why they don't vent out on their own.  Sometimes I lay one on it's side until the vent hose let's some dribble out.  

Now if all you did was stick the carburetor on or you never looked at one at eye level, the throttle slide part of my post probably lost you completely. All I am suggesting is that you carefully set the idle screw so that the slide is not so far open that you lose vacuum. Now I am sorry if that confuses you more, and I should have known that when you used a manual for the OEM carburetor to set a totally different brand that you are very very very new to modifying anything internal combustion.  Good luck getting yours running. 

Edited by ossagp1

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So, you got the Mikuni TM-68 Pumper carb from nichecycle. Did it have the proper size airbox and intake manifold adapters pre-installed?

Have you installed a larger pilot jet yet?

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6 minutes ago, Trailryder42 said:

So, you got the Mikuni TM-68 Pumper carb from nichecycle. Did it have the proper size airbox and intake manifold adapters pre-installed?

Have you installed a larger pilot jet yet?

It’s the TM36 for the 2002 Honda XR400R

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4 minutes ago, Jayesfoo said:

It’s the TM36 for the 2002 Honda XR400R

That didn't answer any of my questions.

Niche sells the TM36 in both a pumper and non pumper versions.

Mikini doesn't manufacture the carb with different size bell housings for different applications. Those that sell the carb have to install adapters to the carb for different bike applications. If you got a standard carb with no adapters and tried to fit that to your stock airbox and intake manifold, that could be a problem.

Niche sells the pumper with a 12.5 pilot jet. That's too small for sea level. The non pumper TM36 is totally different jetting than what we've been talking about.

 

Edited by Trailryder42

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7 minutes ago, Trailryder42 said:

That didn't answer any of my questions.

 

Sorry, but I wasn’t aware that I would have needed an adapter for it to be installed. I came from the Perspective that it would easily be able to be installed and go, just as it was marketed. Where would I be able to get the adapters at anyway?

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5 minutes ago, Jayesfoo said:

Sorry, but I wasn’t aware that I would have needed an adapter for it to be installed. I came from the Perspective that it would easily be able to be installed and go, just as it was marketed. Where would I be able to get the adapters at anyway?

I don't know where one can get just the adapters. I would call Niche and tell them you bought one and ask if they sell it with the bell adapters preinstalled to fit your bike, that is, if you can't tell by looking at it.

Edited by Trailryder42

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