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Montesa 315R tuning?

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Hey there, 

 I've been playing around with my new to me 99 315R. 

 Got it cleaned up and running pretty well, the previous owner didn't use it much and it''s been run rich for along time. 

 I cleaned the carb well, removed the difuser jet and tossed it. Cleaned the packing in the silencer and it's running nicely.
I notice that it does some to pop and stumble a little more then it should imo. and the "Hit" seems to be quite high, I'm wondering if there is some obvious adjustments I can make to try and move the "hit" down lower in revs. If I was to try and explain it, it's almost feels like the bike wants to walk away from under me once it starts to rev.

I'm coming from an older 96 Gas Gas 370 which was a fair bit heavier and not as nicely balanced but it was a little more predicable. The 315 is ten times the machine even though it's an older trials bike, I'd just like to smooth it out a little down low. 


Any tips much appreciated! 


Hope that makes sense, typing on my damned Iphone :p




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The Montesa forum on Trials Central has some stuff on smoothing out the 315R.


The Delorto carb has some jetting issues causing part throttle richness that results in the popping, different pilot and needle clip position can help.


Some have also converted to Keihin PWK 28 carbs or the Chinese knockoff OKO in a 26mm size.  One poster said the Delorto was the best $15 carburetor in the World.


Boyesen last years introduced a new reed set for the 315R.

Edited by Chuck.

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Run race gas or AV gas in it for starters and advance the timing. You need to be creative with a file to advance it but I did it to mine on the advise of Lewis from Lewis moto sports. That fixed it right up. The air box lid on those also collapsed down. Make sure it's open. Those bikes also supposedly came with two or three removable restrictions in the pipe and mid pipe. Make sure they have been removed. They were some kind of import only item and most dealers removed them but you never know until you look.

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I should have mentioned fuel and oil, you didn't mention if you also have the Owner's Manual:


My 04 manual recommends 80:1 = 1.6oz of oil (47.3cc) per gallon  of Elf Moto 2XT 100% synthetic (OC flash point @  108°C)

1 oz = 29.57 cc

The manual also specs gas with a  RON of 92-100,  

RON value is about 8-10 points higher than  MON, and 4-5 points higher than the AKI (Anti-Knock Index) shown on pumps in the U.S. (R+M/2): So U.S.  pump premium with a AKI of 91 will be about 95-96 RON, and should be OK.

You can raise the octane by blending in race gas.

VP110 Purple has a MON of 107, a RON of 113, so R+M/2= an AKI of 110

Blend with pump premium (91 AKI):

               25% VP110 yields about 98 RON,  50% VP110 yeilds about 104 RON


Alcohol gas should be avoided because the alcohol softens the resin used in the fibreglass tank, I sometimes run E10 gas but I don't store the bike without  a drain and flush with pure gas. 


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