51M5994 is a 348 Cota, probably a late 1977 or early 1978 model. Here is a chart of 348 Cota improvements from the start of production in 1976 through 1978.
51M000
First mass produced 348 Cota
51M3132
Change in filter housing is added deflator antiwater screen.
51M3699
Step is added chain guard on engine crankcase forwarding. Change speedometer.
51M3790
Change elements of the carburetor.
51M4722
New front fender.
51M5059
The 3rd speed gear on the secondary axis from 15 to 16 teeth to shorten development.
51M5599
Amending the bottom flange of the triple tree to open a passage for the cables.
51M5707
Improved gearshift by ensuring the pinion is free and moveable.
New Telasco “Hydrobag” rear shocks. Improved front suspension with gas. Improved spring tube protectors. New brake and clutch levers. Eccentric chain tensioning step further reduced.
51M10107
New rubber grips on handlebars.
51M11307
New black and gold tank decals. New fixing system and roller rocker gear which ensures the positioning of the new shifter and rear brake rigid optic headlight. New flywheel. New front suspension with air pressure suspension arm protector
I suspect the shift eccentric may not be adjusted correctly. This is easiest to do with the clutch removed. Spin both shafts so that all 5 gears can be selected with a minimum of further turning of the shafts. The shift detent plunger and spring must be in place. Set the eccentric in the middle of its range. Now shift down into 1st and release the shift lever. If you see that the shift drum moves (ever so slightly) as you release the lever, then you need to adjust the eccentric. The plan is to have each downward movement of the lever put the shift drum in exactly the correct position. The shift detent plunger should not "assist" in rotating the drum even slightly, after you let go of the shift lever. Now pull the lever up into second gear. Release the shift lever. Once again, you should not see any further movement of the shift drum after you release the lever. If you do, then you are moving the drum too little, or too much, and that is what the eccentric adjusts for.
World Manufacturer Identifier (WMI)
The first 3 characters of a VIN represent the WMI code that uniquely identifies the manufacturer of a motorcycle:
The 1st character shows the country in which the motorcycle was built. Characters in this spot range from numbers to letters, and each country has a unique character representing it.
The 2nd character shows the brand’s name. For example, "Y" stands for "Yamaha," "S" for "Suzuki," "K" or "S" for "Kawasaki."
The 3rd is the manufacturer’s division or motorcycle’s type (ATV, scooter, superbike, dirt bike, etc.).
The WMI section may have a different structure if the motorcycle isn’t mass-produced.
Vehicle Description Section (VDS)
The next 5 characters create the Vehicle Description Section, revealing most details about the motorcycle. The VDS reveals the brand, engine size, type, and frame style. The meaning and placement of characters in this section depend on the manufacturer.
Check digit
The security check digit is necessary to ensure the VIN is legitimate. This digit results from a special mathematical operation that puts all other VIN characters into a formula. The VIN number is incorrect or fake if the result doesn’t match the check digit. VIN decoders perform this operation during a VIN check.
Vehicle Identifier Section (VIS)
The Vehicle Identifier Section consists of the last 8 characters and tells us the model year, assembly plant, and unique serial number of a motorcycle.
When buying a used motorcycle, you can always check the 10th character, which reveals the model year: "1", "2", and other upcoming numbers represent years "2001", "2002", etc. The letter "A" stands for "2010" while "B" is "2011", etc.
Forget the Chinese copies. They are not made with much precision and often prove difficult to tune. Take a look at an OKO carb. Full details at www.mid-atlantictrials.com.
VM26 is probably a better size for the 348. However, take a look at an OKO carb, as shown on www.mid-atlantictrials.com. They are easier to adjust and are sold all set up for the 348.
Barnesy is correct. The parts diagram is for a later 348 and the 349. To make the adjustment first remove the clutch. Spin both shafts so that all 5 gears can be selected with a minimum of further turning of the shafts. The shift detent plunger and spring must be in place. Set the eccentric in the middle of its range. Now shift down into 1st and release the shift lever. If you see that the shift drum moves (ever so slightly) as you release the lever, then you need to adjust the eccentric. The plan is to have each downward movement of the lever put the shift drum in exactly the correct position. The shift detent plunger should not "assist" in rotating the drum even slightly, after you let go of the shift lever. Now pull the lever up into second gear. Release the shift lever. Once again, you should not see any further movement of the shift drum after you release the lever. If you do, then you are moving the drum too little, or too much, and that is what the eccentric adjusts for.
There are other variables in this issue by the way. If the shift pawls are worn or damaged from impact on the shift lever, then you will not get the expected movement of the shift drum. If internal shimming of the 3 transmission shafts allows too much end movement, then you will not be placing the shift fork where it needs to be to select gears properly. If internal shimming of the 3 shafts puts one or more shaft out of line with the others, then you will not get the positive gear selection you need.
Take a look at www.bobistheoilguy.com/viscosity-charts. Notice that the low number winter viscosity oils [ 5W, and 10W] correspond closely to 75 wt gear lube and the SAE 30 engine oils correspond to an 85 wt gear oil. 75W-90 gear oil is about as close as you will get to 10W-30 engine oil. Why not use use 10W-30 as Montesa recommended.
Sorry, but I have no idea why the hole is there. I've had the clutch cover off on both the Rev3 and Evo series bikes and neither has a hole where yours does.
Similar to what Jonboy883 has said, when cold, I kick it through slowly, two or three times, to kind of prime it. Then give it about 1/4 throttle, get it on compression with the kickstart, and then come down hard and swift. Usually takes two or three kicks like this and it's running. Fast and hard kicks are the secret. You can't baby it.
Clutch - 300 cc - 10W-30 (I use Maxima MTL-XL 75W transmission oil for the clutches in both my modern and vintage bikes)
Front forks - 210 cc per leg, 10W fork oil (any decent brand)
Gas / oil - Montesa manuals recommended a 4% mixture, but with todays synthetic oils 50:1 is fine. I use Amsoil Interceptor at 60:1, again in both my modern and vintage bikes
My 78 Cota 348, which has never been restored or repainted has the black and yellow tank stripes along the lower tank edge and one Made in Spain decal located half way between the filler cap and the top front edge of the tank. However, if you Google Montesa Cota 348 there are a few tank pictures that show additional decals. Might have been based on the market and the whims of the factory.
It makes no difference which wire goes to ground. Connect one wire to the coil lead and the other to ground. All the kill switch does is complete the circuit to ground when depressed.
Sorry to be the bearer of bad news, but there is no service manual for the 348, 349, or 350 series Cota's. Closest you'll find is the Clymer Service Manual for the 1965 through 1975 125 - 360 cc singles. They come up occasionally on Ebay.
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51M5994 is a 348 Cota, probably a late 1977 or early 1978 model. Here is a chart of 348 Cota improvements from the start of production in 1976 through 1978.
51M000
First mass produced 348 Cota
51M3132
Change in filter housing is added deflator antiwater screen.
51M3699
Step is added chain guard on engine crankcase forwarding. Change speedometer.
51M3790
Change elements of the carburetor.
51M4722
New front fender.
51M5059
The 3rd speed gear on the secondary axis from 15 to 16 teeth to shorten development.
51M5599
Amending the bottom flange of the triple tree to open a passage for the cables.
51M5707
Improved gearshift by ensuring the pinion is free and moveable.
51M6828
Chain guide fixing hole diameter reduced. Spacers fixed to prevent wear.
51M7200
New Telasco “Hydrobag” rear shocks. Improved front suspension with gas. Improved spring tube protectors. New brake and clutch levers. Eccentric chain tensioning step further reduced.
51M10107
New rubber grips on handlebars.
51M11307
New black and gold tank decals. New fixing system and roller rocker gear which ensures the positioning of the new shifter and rear brake rigid optic headlight. New flywheel. New front suspension with air pressure suspension arm protector
51M12305
Rear shock suspension modified.