Jump to content

300St 2014 Throttle Over Run


magsy
 Share

Recommended Posts

Hi all just joined TC been meaning to join for years. I recently parted with my 2004 290 and bought a second hand 2014 300 ( big jump I know). Went out for first play and found a few things not right with throttle.

It started with the bike not settling back to tick over when shutting off the throttle and almost stalling on down hill decents. I decided I would give the bike a good once over and switch to a slow action throttle anyway.

I removed the carb and gave it a good clean but didnt change any settings. I put everything back nice and clean with airbox/filter spotless. It seems to have got worse with the throttle bouncing back and forth now. I've read about air being pulled in through crank seals and inlet manifolds but wasnt sure if this was the case as the bike is quite new. Does anyone know of any issues this model might have and if there are any tips or mods worth doing.

Thanks M

Link to comment
Share on other sites

 

Could be a blocked pilot still, The hole is minute so check it again and maybe pass a thin piece of copper wire through it to make sure it's clear.

Also an air leak is still possible, do a search on here to see how to test.

Is the fuel pipe pinched under the air box?

Check the 1 way tank breather under the rear mudguard.

Check the float height, There is a diagram on splatshop's website.

The sherco's are jetted quite lean anyway from standard but you should not have a hanging idle.

I'm betting on air leak or fuel shortage.

Good luck!

Link to comment
Share on other sites

 

See what comes out the float bowl, catch it in a clear plastic vial. Only takes a drop or two of water in the fuel to do this.

Might ring splatshop Chris, I think manifolds could possibly be an issue, not sure on the year.

Spray about the flywheel with carby spray lightly, that is once you are sure of pilot jet, as better than you have been fooled, trust that!

Link to comment
Share on other sites

 

Hi thanks for the advice, have checked with previous owner and turns out the main throttle spring above slide had been modified and halved in length to make it lighter. It measures 55mm or 21/4" in length. This may well be the problem but have checked all jets etc again and given a good clean. New spring on order.

The float height was a little high so tweaked that as per splat shop pics. Have checked with fuel and seems ok, not overflowing.

The main jet is 128

pilot 48

Needle JJH

slide 4

Needle setting second from bottom out of 5

Mix screw 1 turn out from full in

Not sure if these are standard settings, any advice would be good.

When I get it all back together will test for leaks around manifold etc if problem persists.

Link to comment
Share on other sites

 

Its probably the spring, the manifold was an issue on earlier models 2010 / 2011 but 2012 onwards they were changed and seemed ok.

id take the one way breather of the tank vent just to try it if the spring doesn't cure it, they can stick closed which then creates a fuel starvation issue.

Link to comment
Share on other sites

 

Cutting the spring isn't a good idea, The throttle is very light anyway compared to the dellorto setup, You're wise to get a new spring.

Your jetting seems rich enough so should not be a problem. The slide is leaner then the normal 3.5. (unless they changed on the 14 models) I found the sherco's run best with the same jets and needle you have but with a 3 slide to cure the lean bottom end at 0 to 1/4 throttle.

Change the spring and double check for air leaks again, Check the fuel pump vacuum pipe, I believe on the 2014 they are taken from the crankcase instead of the manifold check for leaks and make sure it's not pinched. Also check all the fuel pipes and make sure they are connected the right way round.

Link to comment
Share on other sites

 

found on my 2012 290 that the nipple in the Reed case leaked causing the fuel pump to not work correctly ( i.e. the mixture leaned out , which made the throttle like an on /off switch with not a lot of modulation.also it was a pain in the a** to start. the old nipple was cut down and drilled out and a new nipple fitted , after this was done the carb needle was dropped a couple off clicks as it was over fuelling, the bike is now a totally different machine so controllable . I have Chris at Splat shop to thank for diagnostic ,

Link to comment
Share on other sites

 

Hi guys thanks for all the advice, I will be looking out for all the things mentioned in the future. Just rebuilt bike with new throttle spring, carb set to as near standard as poss ad it runs perfectly. Measured new spring and this is 82mm compared to the one that had been modified which was 55mm. The throttle snaps back and still feels nice and light. Bike ticks over with no over run when throttle blipped. Just need to test fully next time out to make sure. Didn't spray for air leaks around manifiold or crank seals as bike seems fine but did make sure manifold was put back together with sealant just to be sure.

Thanks again Magsy

Link to comment
Share on other sites

 

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...