Cota 247 Running Lean and Overheating

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Went for a good ride over steep hilly country all was well then it suddenly died - appeared hot, plug was browny grey. A 2 km uphill walk in bike boots to get phone signal to call the cavalry (wife with trailer).

I read recently that too much oil in the mix makes for a lean burn and overheating - has anyone experienced this? I am running 5% or 20:1 which is what it says in manual although sticker on tank says 4% - but I wouldn't expect that much difference.

[Reinald]

Hi, No expert on things mechanical but 20 : 1 is a fairly full on. I always run 40 - 50: 1 and yeah more oil leans out the mixture, contrary to popular belief. Not sure that would make a big difference tho'. Wheres the Gladstone Guru ? [David L may add some of his wisdom here]

[TriCub]

Oil mix is always hot topic. You go into your local bike shop and the kid behind the counter tries to sell you some super oil that only needs to be mixed at 50 or 60 to 1, and tells you that the less you put in the better it goes.
I'll throw in my opinion. Air cooled trials bike from the seventies 25 - 32 to 1 with a good 2 stroke oil. It will drip oil out the exhaust but the maun bearings and piston will last.
At 20 to 1 the jetting should be spot on as that is what the manufacturer set it up for. But there wouldn't be much of a change going to 25 to 1. Even though the fuel mix would be a bit leaner the extra oil would cut down the friction and make it cooler.
The plug colour sounds ok. Was the plug the reason it stopped? I have had a problem with a stator coil that shorted when it got hot and if you let it cool down for 30min or so it would fire up again.
A good idea is to take a spare plug with you next time! If that was the problem.

[scrivo]

Be very careful of going leaner than 32:1 oil mix with '70's Montesa bikes (now I will get dozens of people tell me that they run 50:1). The main bearings are a little marginal and also easily starved of oil due to shrouding of the bearings. The 348 was the first of the trials bikes (to my knowledge) that had the larger mains. I have been unable to locate main crank bearings for any of my Montesa bikes in Australia and have ended up buying from RM Montesa, SWMontesa or in motion trials in the UK. I have not tried Don or Bully parts Australia. Order and have them in a week. The non drive side will cause leaning out and erratic running while the drive side will naturally suck primary drive oil (auto transmission fluid is the best for that) which does not burn well at all and claggs (is that a new work) everything up quickly.

The other area to check very closely on Monties is the carbie to cylinder sealing. Monties seem particularly sensitive to intake side air leaks. I have double checked things seven times (how do you double check things seven times? ) bike ran like crap stopping when hot and overheating etc. Replaced intake connector and clamps and bingo.

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Oh Scrivo, I too have double checked things about seven times - it only occurred to me today that this post has evolved into a continuation of my post from 1st of May "Cota 247 Carbie" where I report carbie recon and lean running and no matter what I do since I can't get a rich appearance on the plug and engine appears to be running hot - today I made another adjustment advancing timing. Making it harder to cold start but runs fine a bit less tweaky in power delivery ( felt a little more like Brownie's Bultaco M49) then 20 minutes of long steep climbs and descents and after that the engine is racing (say 1000 rpm) at idle, feels hot and the plug is as lean as. Here is the tally so far:

1. replaced all carbie parts with genuine Amal - some of which were incorrect eg: idle adjust screw too long
2. replaced many of the new carbie parts with old parts ie: put the old idle jet and idle screw back in
3. ground carbie mounting face level and replaced o-ring and gasket
4. checked carbie sealing with WD40, water and most recently LPG gas - no indication of leaks
5. checked, double checked and hectruple checked the timing
6. advanced the timing about 3 degrees (today)
7. replaced the points
8. replaced magneto side engine seal with correct seal - ( existing seal was not correct double lip) - the engine is not excessively smokey. David mentioned refitting the shim however the new seal was at least 1mm wider and when I refitted the shim and new seal the engine felt tight (cranking by hand) I spoke about it with Greg Harding who suggested maybe the shim was to compensate for the incorrect seal I carefully removed the shim and engine felt normal ... please don't tell me to put the shim back, can I do it without buggering the seal?
9. checked and tightened exhaust manifold
10. raised the needle
11. raised the float - then lowered the float - then replaced the float.
12. checked fuel flow and replaced inline filter

The plug always appears dry - even after kicking and pumping the throttle for 5 minutes it never looks wet. If I put my finger over the plug hole the suction appears very strong and yet there never appears to be any fuel vapour when cranking with the plug out. When I remove the air filter there is always a small amount of fuel on the filter inlet mount. The tickler pours fuel freely. As I say I first reported this after installing an Amal carbie kit - I think it's time I just reverted to the original everything - what can I lose?

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no one has mentioned fuel - and yet I read elsewhere that unleaded runs hotter and an old engine may need to be retarded to compensate. What fuel do other old Monty riders use ? I read that premium runs even hotter, although the higher octane should be better suited to the relatively high compression of the 247 at 10:1 - I am running on standard unleaded (no ethanol) - could this be my problem? If so what should be trying first;

- * a few degrees?
- run an even cooler plug? specs sat B6 I have tried B7 with no obvious gain
- run higher octane?

Any other ideas

[David Lahey]

I'm not convinced that the problem is overheating, or oil type, or fuel type, or sparkplug heat range.
It just sounds like something is causing the bike to run strangely and stop after you have been riding for a while.

Your description of the compression, lack of fuel spraying out the plug hole and fuel sitting in the inlet tract when you pull the carby off, are all completely normal observations. "Pumping" the throttle on an AMAL concentric does not do anything except wear out the throttle slide, and unless you flood the motor with petrol and kick it over with the throttle fully open, you should not see anything spray out the plug hole.

Please tell us the important things like:
Is there still fuel in the carby float bowl when the bike motor stops unexpectedly?
Is there still a good spark when the bike motor stops unexpectedly?

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David

Yes still has spark - the motor doesn't idle it races and is tweaky at low revs sort of threatens to die then surges forward (makes for nightmare for a novice) and if it does stop (stall or switch off) it's an absolute mongrel to restart. The plug is as dry as my mouth after 50 kicks.

[David Lahey]

As soon as it stops next time, turn the fuel off at the tap immediately and pull off the float bowl. I'll bet there will be no petrol in there.

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Ok will do - but I have fitted an inline see through filter and wouldn't that also be empty - coz it isn't and the breather isn't blocked so no air lock