90 replies to this topic

[triple_x]

Hi

Excellent job Greeves.

Got the Cota ready and gave a run at the Bath Classic event last week.

As with all new projects they need running to find the faults.

1 Clutch was like an on off switch so this week I replaced the plates and springs. Item that confused be is that the brass pressure bush is available in two lengths. Can anyone advise why???

2 The carburation was off so would appreciate if any of you guys know the standard jetting, needle and slide for a 21M1824 Mk 2 with a Amal 627 concentric.

Once I get it running the way I want will then strip down and powder coat the frame, respray and seal the tank.

Apart from that it was nice to ride and bring back memories from 1968.

Regards

Martin

[vintagecota]

Nice job Greeves, just one nit to pick. The kicker is mounted too far forward, you'll kick a hole in the case through to the magneto if you stroke through with it like that. The kicker should be parallel to the frame tube by the carburetor.

[keychange]

vintageCota, on 30 April 2012 - 12:29 PM, said:

The kicker is mounted too far forward, you'll kick a hole in the case through to the magneto if you stroke through with it like that.

I made the same mistake when I first got my Cota and indeed do have a hole ...not good for creek crossings .
I used JB weld and mesh reinforcing and it seems to work fine.

[jon v8]

Triple_X, on 28 April 2012 - 03:01 PM, said:

Hi

Excellent job Greeves.

Got the Cota ready and gave a run at the Bath Classic event last week.

As with all new projects they need running to find the faults.

1 Clutch was like an on off switch so this week I replaced the plates and springs. Item that confused be is that the brass pressure bush is available in two lengths. Can anyone advise why???

2 The carburation was off so would appreciate if any of you guys know the standard jetting, needle and slide for a 21M1824 Mk 2 with a Amal 627 concentric.

Once I get it running the way I want will then strip down and powder coat the frame, respray and seal the tank.

Apart from that it was nice to ride and bring back memories from 1968.

Regards

Martin

Martin,that Mont was looking very smart,it was a suprise to see it.Once I get all my British scrap and the Yams sorted I'll get onto sorting my Mk1 out.Most of the cycle parts should be easy enough,all that worries me is things like getting a rod kit and piston etc.I guess I should slowly start amassing bits for it.I notice mine is a bit different to Greeves bike,mine has steel fork yokes and the first part of the exhaust was chromed.
I just looked through all the pics my son took at the trial last week,sadly there are none of you or I would post it up or mail it to you.Shame I couldnt get to ride my "new" Ajs.... the sections felt good when we tested them on saturday. The joys of running an event eh ?

[chris_]

jon v8, on 01 May 2012 - 09:33 PM, said:

I notice mine is a bit different to Greeves bike,mine has steel fork yokes and the first part of the exhaust was chromed.

Hi Jon

From what I have seen, the early 247 models (mk 1 & 2) had yokes like the ones on Greeves' bike, with the bolts on the side. Later yokes (mk 3 onwards) have the fixing bolts recessed on the front.



I also think that the first part of the exhaust would originally have been chrome




Could you post a picture of the yokes on your bike to have a look at?

[triple_x]

Hi
John

My 1968 Cota had the steel yokes finished in Hammered Silver with the side bolts as shown in Chris's picture.

I believe the alloy yokes came in at the same time the mod to the primary drive cover when they removed the extra flywheel and narrowed the engine.

Thank you for the comments on the Mont, makes it all worthwhile.

Am trying to get it ready for this Sundays Golden Valley trial then Ringwwod evening meet on Thursday.

Regards

Martin

[jon v8]

Here you go,Montesa must have thought the front end was too light to have specced yokes as heavy as that !

[triple_x]

When I rode the Mont the other week I had a mid range hesitation and the motor would not clear and 4 stroked at the mid to top end as though it is too rich. Symptoms tick over fine, rev then hesitate clear and 4 stroke!!! then fine on tickover.

So I did the following.

• Cleaned the carb
  
• Replaced float and viton tipped needle valve and checked the float level, all good.
  
• Checked for air leaks, none that i can see
  
• New crank seals.

So I am thinking that the jets are wrong.

• Currently fitted Amal 627 has 40 Pilot, 150 Main and 2 1/2 slide and needle on the middle groove. No excessive wear on slide.

So PLEASE can anyone advise what the standard carb jetting was for a 1970 Concentric 627, I can then at least go back to basics and start again before i look at the electrics

I have already fitted a new coil, condensor and points and timing is at 4mm BTDC.

Hope you can help, sure it is something simple and I cannot see the wood from the trees.

Regards

Martin

[woody]

Don't have the jetting for the 247 but for the Bultaco of the same age with the same carb, from memory, they were 25 pilot, 106 needle jet, 160 main, 3 1/2 slide. Same sizes also for the 250 Ossa with same carb. So the Mont must be very close to that.

Would be a good starting point.

40 for your pilot is very rich for MK1 Amal (generally)

When I can next get to it I'll check my Clymer and see if the 247 spec is in there, but won't be until the weekend.

[keychange]

The standard jets are 150 main 35 idle and U2 needle. You can still get complete 627 kits from Amal

Standard timing should be 2.5mm (21 degrees), points 0.4mm - my Cota is very touchy about timing and points gap - too advance won't start and too retarded easy to start cold but a bugger when warm ( doesn't make sense but that is what I find)

Also check your plug gap as they really do not like a wide gap standard is 0.40

[triple_x]

---

Don't want these Ads? Why not help support TC and sign-up as a Trials Central Supporter

[triple_x]

Hi Dave - Andrew

Thank you for the the feed back.

I have bought 25, 30 and 35 pilots to play with.

Interesting comment today from a colleague who just happened to say "Don't forget that when these bikes were made we were using 16/1 or 20/1 ratio fuel oil mixture.

So the viscosity of the fuel was thicker needing bigger jets to get the flow rate.

So today at 60/1 or 50/1 the fuel will flow at the same rate through a smaller jet!"

Seems to make sense!!!!

Anyway thank you, will advise progress.

Martin

Edited by Triple_X, 03 May 2012 - 10:05 PM.

[keychange]

I run standard jets and 25:1 with excellent reliability and good performance for the last 12 months. I wouldn't listen to the modern oil arguments just run the recommended 25:1 (I use semi-synthetic) and the right plug with the right gap (very important). I also recently fitted an SM replica muffler replacing a crap after market and it makes a enormous difference at the top end - highly recommended.

The Amal works well when set up as it was intended but when you start fiddling you start chasing your tail with compensation for previous compensations.
The Amal is reportedly very prone to wear but in my experience, make sure you are using the correct needle and jets and that the manifold facing mount is flat (they warp easy but are easily fixed).

My Cota's reliability is very sensitive to timing settings I now use factory or maybe 2 degrees retarded to improve cold starting and take some of the surge out of the low end power but advance at your peril.

[triple_x]

Hi Chris


The Clymer says time @ 4 deg, which I have done.

However it does kick back which suggests that you are correct it needs to be around 2 deg.

Will see how It goes Sunday and the adjust.

I have got the original system which exits by the r/h shock. Which SM muffler did you buy?

Set the Amal at 25pilot and # 3 slide normall run my Sherpa on 50/1 PJ1 Silverline..

Kind regards

Martin

[greeves]

Hi, just returned from Scotland were I have been racing the pre65. Brilliant trial !!!!

The jets I have in my bike are:

Pilot jet - 25. Main jet - 160. Needle jet - 106. Slide - 3. Needle - middle position.

It is true the position in too forward; but the thing is it has a big gap between where the kickstart starts it action and where it is in the pic. I will need to check it.

[keychange]

We aren't confusing degrees with mm are we? The factory manual says 2.5mm BTDC which is 21 degrees. 4 degrees would be a long way out - I don't trust Clymer - I have a Honda one for my TLR and it has several errors and confuses models.