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Cota 315 Engine Problem


chrisinspain
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Hi all,

I have 2003 Cota 315 which has developed some kind of problem with the engine.

Over the past few rides I noticed a noise at lower rpm which sounded like kind of a ratchet, but deeper. Hard to explain!

Anyway, today things got worse. In neutral, the bike starts and runs well without unusual noise. But under load, at low rpm the noise is apparent, then, when I open the throttle more, the engine looses all power. Perhaps the noise and power loss are unrelated?

The engine oil is fine, it has a new spark plug ( surely this couldn't be the problem), and the fuel is new at 80:1.

Yours thoughts please!

Thanks,

Chris

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The olly thing that comes to mind based solely on your discription would be perhaps a loose flywheel on the magneto. And the keyway about to go? Pure speculation, but may be worth a look to insure some basics.

First indication would normally be the fact that tou could thighten the flywheel nut using a hand ratchet I would think!

Someplace to start! :thumbup:

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Hi guys,

The spark plug is the the standard NGK plug as per the manual which I installed a couple of weeks ago. I didn't set the gap when I bought it, just eyeballed it against the last plug and the bike has run well for several rides.

I initially thought it might be a problem with the carb ( the loss of power ) but then what about the noise?

Perhaps the cota makes this noise as standard?

I bought the bike second hand about 6 months ago. Its my first trials bike but I have had motocross bikes before.

Thanks for all replies so far.

Chris

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There is a known fault with the 315 that it "pinks" at low revs and under load. This is solved with high octane fuel and a bit of 'jiggery pokery' with the timing. I never botherd with mine in the end as it didnt really bother me. The loss of power i would say has to be a problem with the carb. Possibly the main jet system? or the mixture is wrong. However it is unlikely to be the mixture if it was running ok previously.

max

Edited by yamahaty250xox
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One thing to be aware of if you aren't already is that on the earlier PHBH carb the little mixture adjustment screw works on the air circuit so unscrewing it makes the mixture weaker (more air). On yours you should have a PHBL where the mixture screw works on the fuel circuit instead so unscrewing it makes the mixture richer (more fuel). On your bike the mixture screw should be 3 - 4 turns out if I remember correctly.

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*Update*

I've just been out riding for the last 20 mins without a problem. Weird.

There was no loss of power when I opened up the throttle - maybe a jet was temporarily blocked last time?

As for the noise, it is still there but is not really audible when the bike is cold. It seems to get a little worse as the bike warms up, but its only at low rpm under load. When the bike gains speed or I open up the throttle, the noise disappears. Could this be the pinking yamahaty?

Another question for you, I rode a friends gas gas txt 250 ( 03 model ) yesterday which I found to be a much sportier bike. It felt lighter, was faster, had crisper power delivery and just felt more manoeuverable. Kind of like a sports car to my truck! The only thing I didn't like was the tendency for the motor to stall at low revs, which my Cota does not do.

Actually, my Cota feels like a bit of a dog compared to the Gas Gas. Is this the general opinion? I'm new to Trials and bought the Cota because it was supposed to be bullet proof and a good beginners bike...but I prefer the performance of the GG. Would a new piston and rings and some tuning breath some life into my Cota?

Thanks for your advice so far.

Chris

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All the various makes and models feel different in different ways. I've always loved the way that Betas ride because they just seem to fit with my style. We are lucky to be blessed with this variety! I wouldn't consider any of the various trait differences between your Mont and a GG as any sort of problem at this stage in your trials journey; what some people consider a problem may be your advantage.

To my style, given what you've said about these 2 bikes; I'd take your Montesa every time! Reliable bottom end power easily trumps zip and zing at the top for me; on the novice route full throttle is the last resort; 'plonk' finds grip; 'zip' flings it at the people behind you!

:guinness:

Graham

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Chris. Yes the noise you describe does sound like the common Montesa knock. Mine does it a tad when it gets hot and when I come off the throttle sometimes. Nothing to worry about too much. You may find you can improve it by altering the mixture screw a bit or by putting the next size up pilot jet in it. You probably need to make sure everything is clean and correct, and that you're running on Super Unleaded, first before you alter anything though.

As to 'truck vs. sports car'. Yes you're right to a degree. The Gassers are much more revvy and generally more flighty. If that's for you then that's great. The Monts give you a bit more time, and as lots of trials is about timing your moves, that's a good thing when you're learning IMO.

I've ridden a '05 GG250 belonging to a mate and yes it feels tighter, and the steering is a lot quicker, but I didn't really like the power delivery after my Mont. It's horses for courses though as there are loads of GGs about and most owners love them.

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Hi Chris,

As the other posts have stated : there are advantages and disadvantages to every bike.

I'm presuming you haven't compared the Gasser and Mont in a fast flowing stream where you can barely see where you are putting the front wheel...I would take the Mont in that situation.

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The Montesa is a great bike for sure, it's just that mine seems to be a little down on power compared to the GG 250. It had me wondering if I need to replace the piston and rings or do something else. I don't think it's performing as well as it could or did.

What would be the first step to get some more performance out of the bike?

Chris

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Have you had the carb off and taken it apart and cleaned everything? Blown all the jets and passages out with compressed air or carb cleaner? Taken the banjo off the side and cleaned the fuel filter? Compared what jets you've got to those specced in the manual? Set the float height? Cleaned and oiled the air filter? Checked the timing? Repacked the rear silencer?

I'd look closely at all them before thinking about rings. It may need rings etc but I'd get everything else working as well as I could first. It's difficult to say anything meaningful, at long distance, about power but the Monts aren't known to be lacking in that department usually. The delivery will definitely be different to the Gassers but it should still have plenty enough power to get you into all sorts of trouble!

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