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Montesa 315R - starting issues

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doggone
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PostPosted: 00:19 - 14 Feb 2020    Post subject: Montesa 315R - starting issues Reply with quote

Friend has bought a reasonable looking one of these but it has stood unused since about 2017 and won't start on the kicker so far despite having good spark and fuel.
In desperation we towed it behind a quad bike and after several minutes it suddenly roared into life at full throttle resulting in a minor crash but only minor damage.
Still not been able to start it on kicker but at least we know it can run!
Any insight about what's wrong?

Typically for him he's already splashed out on new tyres (surprisingly expensive) as old ones were perished, and is wanting to get new front and rear mudguards/seat they are a bit battered.
But it won't start yet... Rolling Eyes
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stinkwheel
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PostPosted: 00:44 - 14 Feb 2020    Post subject: Reply with quote

Has a slide carb yeah?

If it went full throttle on a slide carb without you holding it at full throttle, that means the throttle valve is being held open. Throttle valve stuck (or idle screw screwed all the way in), cable stuck/poorly routed or the needle sticking in the emulsion tube or (if it was owned by an idiot, and I have seen this done before) throttle valve in backwards.

Or a dead rat in the carb venturi?

I've seen cables pop the ferrules up out of the seat at one end or the other so they are resting on top instead of seating in. Especially if they get sticky. This has the effect of holding the throttle halfway open.

You should be able to hear the throttle valve hitting the idle stop when you snap .the throttle closed.
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Easy-X
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PostPosted: 03:13 - 14 Feb 2020    Post subject: Reply with quote

Another possibility along those lines: someone in the past thought they were cute and cut down the main carb slide spring to get a lighter throttle response and, over time, the spring has weakened and now doesn't have enough strength to fight the vacuum. Ask me how I know...

Anyhoo, as for not starting (but vigorous pull get's you going*) my money's on a blocked pilot jet or something similar.

*as the actress said to the bishop
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doggone
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PostPosted: 08:23 - 14 Feb 2020    Post subject: Reply with quote

stinkwheel wrote:
Has a slide carb yeah?

If it went full throttle on a slide carb without you holding it at full throttle, that means the throttle valve is being held open. Throttle valve stuck (or idle screw screwed all the way in), cable stuck/poorly routed or the needle sticking in the emulsion tube or (if it was owned by an idiot, and I have seen this done before) throttle valve in backwards.

Or a dead rat in the carb venturi?

I've seen cables pop the ferrules up out of the seat at one end or the other so they are resting on top instead of seating in. Especially if they get sticky. This has the effect of holding the throttle halfway open.

You should be able to hear the throttle valve hitting the idle stop when you snap .the throttle closed.



Bolded bit sounds plausible.
We weren't happy with cable routing it seems jammed between frame and tank, but looking at pictures online most if not all seem to go that way and it appears to twang shut on it's own as expected.
Air inlet and airbox have been cleaned it did look like it had muddy water in at some point.

Anyway it's in my shed at the moment TBH he's trying to get it going for his 14 y.o. lad so it needs to be 'safe' to use.
Quite taken with it myself will definitely have a go on it.
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steve the grease
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PostPosted: 01:12 - 15 Feb 2020    Post subject: Reply with quote

Classic issue , >>>>> slide put in back to front. Full throttle only. Nearly killed me once that one.
Seriously.
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Easy-X
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PostPosted: 02:01 - 15 Feb 2020    Post subject: Reply with quote

steve the grease wrote:
Classic issue , >>>>> slide put in back to front. Full throttle only. Nearly killed me once that one.
Seriously.


First move: always fit the kill switch Shocked
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doggone
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PostPosted: 08:45 - 15 Feb 2020    Post subject: Reply with quote

Easy-X wrote:
steve the grease wrote:
Classic issue , >>>>> slide put in back to front. Full throttle only. Nearly killed me once that one.
Seriously.


First move: always fit the kill switch Shocked

It's only a 250 but he was caught out by the instawheelie effect when it fired - while being towed
I wish I'd put a gopro on the back of quad.
They might both be tinkering today will stress that back to front slide risk
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doggone
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PostPosted: 18:09 - 24 Feb 2020    Post subject: Reply with quote

It was grim outside this morning so had the carb apart but didn't see any problems, put it back together and it seems to be starting and running as you'd expect now.,
Clutch plates were stuck together but just wiping them off seems to have fixed that too, so he's ready to go ... except the rear wheel is away for respoking - a few days yet.
New tyres are to put on too.
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Old Thread Alert!

There is a gap of 1 year, 66 days between these two posts...

doggone
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PostPosted: 14:44 - 01 May 2021    Post subject: Reply with quote

A year on he is still playing with this old bike.
New tyres are on, brakes bled through, new fluid and working well but clutch plates seem stuck together.
We wanted to start it and try to free them by slipping it in higher gear.

It has been running Ok briefly in the shed - but today kick started first go then it suddenly revved its nuts off flat out and would not respond to kill switch or even disconnecting wires to coil which are easier to access than pulling plug cap off.
Apparently two stroke engine runaway is not that unusual but I didn't know they could do it!
They can get so hot that the plug itself can ignite fuel without spark.

Normally you could have stalled it out but with no clutch couldn't get it in gear.
Anyway that was pretty scary as it started to get so hot coolant began to blow out onto red hot exhaust then it did somehow die on it's own.
Initially we thought nothing too serious had happened as it still turned over but when it is cold it feels locked up but could be coolant in cylinder or something daft.

Must admit this was one of the scariest bike relate incidents I was ever involved in as I thought it might catch fire or literally blow the engine apart somehow!
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Suntan Sid
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PostPosted: 00:01 - 02 May 2021    Post subject: Reply with quote

Serious air leak into the crank cases.
Or, less likely, air leak on the fuel inlet.
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thx1138
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PostPosted: 17:58 - 02 May 2021    Post subject: Reply with quote

My beta 2T revved its nuts off and wouldn't stop, even with the kill switch once. There was a rubber shroud halfway down the throttle cable that had got damaged , though not obviously, and the cable snagged on it.
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doggone
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PostPosted: 18:18 - 02 May 2021    Post subject: Reply with quote

We had a quick look at it again this morning and though at first it couldn't be turned on kickstart it was possible to free it by getting it in a higher gear and turning the wheel backwards at first - it doesn't look good but probably still well worth repairing when he has spent so much on it already.
He had just put the tank back on it wouldn't be surprising if the throttle cable wasn't routed correctly because when it was run previously on blocks it was just sat in place loose (it's fiddly to secure).
Otherwise some kind of air leak must be first thing to suspect.

What troubles me is the plan was to get this in usable condition for his lad to use, he is only 12 but unusually big and strong for his age, but has only ridden mountain bikes before - he's very accomplished on that even on really tricky going.
It seems kind of temperamental and if every time he tries to ride it something breaks down it might put him off for life Laughing
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