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bron yr aur

Help with 2012 290 running rich, not a carb problem

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At least I don't believe so. My bike ran fine last year. The carb was set up by a local trials pro with the usual mods (lowered float height, a little different jetting). This spring, it started acting up. Once warm, the bikes acts as if it's really rich in the pilot circuit. The rpms keep wanting to die. It will sit and idle, but the longer I leave it the lower the rpms. Until I blip it, then it goes back. But when approaching an obstacle I can't just add gas, or its sputters and coughs and I lose my rhythm. Not that I have much. Pretty much every time I go to pop the front wheel I have to whack the throttle and clean it out. And it doesn't seem to respond to turns of the air screw  I went all the way to over 3 turns and it still did it  

In June, I pulled the carb to clean it out and see what's up. I replaced all the jets back to stock, and raised the float to nearly the 19mm stock setting. On a tip from a Beta guy just south of me, I replaced the jet block gasket. He said that he had encountered this a few times and that was the culprit. But it didn't help it. Still the same. I got the gasket from Oko, and it's considerably thicker than the stock one  

 

Any suggestions? I got involved in a full build on my boy's KTM enduro bike, so I haven't even messed with it. Just overwhelmed myself I guess. Now, I'm readying the bike to sell it (just don't have the time right now for trials) and would really love to deliver a sound running bike to the next owner. At this point, I'm simply at a loss  

 

Thanks in in advance for any help. 

Edited by bron yr aur

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Hello hello,

I am not a Sherco tech, but perhaps your bike hasn’t been fitted with the return fuel line from the fuel pump? Wild shot in the dark but I thought I would post up this useful link just in case: https://www.splatshop.co.uk/2010-2011-sherco-preparation

I realize your bike is a 2012, so this should already be done, but perhaps the inline check valve from the gas return line is installed backwards and it’s forcing in extra fuel even when the float valve is closed?

One other thing I can add is that you should make sure your air-box-to-carb isn’t half on/distorted at the carb air-inlet. This happened to me recently and luckily I caught it in time before engine damage (hopefully! Time will tell!) Probably not your issue seeing as it feels like it’s getting more fuel than air..

I’m sure that someone with more Sherco experience than I have will chime in soon, but I thought I would throw out some ideas in the meantime ? I hope you get it going! So far this bike has been the best bike I've ever owned. Good luck on your enduro rebuild, you should post up some pics! ?

 

edit: check this write up as well regarding the fuel piping return line, a few paragraphs down from the top. 

Unfortunately they don’t have any pics of it but perhaps this is indeed your issue?: https://www.splatshop.co.uk/blog/2013/09/a-closer-look-at-the-2014-sherco/

Edited by jackman290
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Thanks for that! At first I thought it wouldn't apply, but I did a full service on my bike last spring. I'm not familiar with the fuel system on this bike, so it's very possible that I routed something wrong when I had it apart. I'll check it out in the next week or 2. The weather has been horrible this entire summer with rain, and it's still raining 4-5 days per week. 

I'll post back when I get it apart. 

PS just a couple pics from the build (since you asked) :)

The first is from June, the second sometime in July, and the last is me and my boy in August. I'm jealous of his height even though he's only 13 there lol. 

image.jpeg

image.jpeg

image.jpeg

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By the way, just wondering exactly how the fuel "pump" works? There's not much info on these bikes. I'm gonna have to look really closely at the routing of the lines. 

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On 10/29/2018 at 7:17 PM, bron yr aur said:

By the way, just wondering exactly how the fuel "pump" works? There's not much info on these bikes. I'm gonna have to look really closely at the routing of the lines. 

Perhaps too late to help you but for future reference, operation of the "vacuum" or "pulse" type fuel pump is describe here: www.walbro.com/wp-content/uploads/2015/12/FPC-pump-8-20-12.pdf

Edited by konrad
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