So received the bike yesterday and already discovered that it’s not charging like it should, but that’s covered in another of my many questions.
Rode the bike briefly yesterday until the battery died and seemed to go well considering it’s been off the road for around seven years.
I do know that it’s running very rich and the plugs are black.
I received the new battery today and it started straight away and it ran for 5 mins to get warm for a compression test. All good so far.
Tested the compression on both and they were showing close to 155-160 which is ok……relief.
Now the troubling bit. I checked the plugs again and they were both black and one of them had the ground electrode bent over and touching the centre electrode an there were small marks on the top of the ground electrode where something had been hitting it. Is the compression that high to limit the clearance?
I’m guessing this can only be piston? Does the MK1 use standard length plugs and not specially shortened ones……really puzzled.
I guess the only option is to take the head off and check. Anybody have any ideas?
Just put that cylinder on TDC and roughly measured the distance from the spark plug thread to the top of the piston and it is quite a lot more than the 19mm of the spark plug. There did appear to be some scratches on the top of the piston that would coincide, but I can’t believe that the piston is moving that much in the bore to hit the spark plug?
Well it is possible that something has gone through the engine - eg a stone and marked the piston and bent the plug?? (Most often you see that damage to a plug when someone drops one on the ground!).
On another note it looks terribly rich - were the chokes on?
Even if not unless there is slack in both choke mechanisms they will still be on and it will run much too rich at low throttle
Well an interesting update. I removed the left hand head today and all looks good apart from being very sooty with the rich running. There are some definite light scratches on the piston top where it looks like it’s been hitting the plug.
More interestingly, the bore measures at 90mm and has a relatively flat top piston compared to standard, which means it’s at least a 950 conversion.
Question is, with this conversion (maybe by Raceco), do I need a shorter or different plug. I’ve placed a call with Gutsibits who are phoning me back.
Anyone know anything about these types of conversion?
The rich running is almost certainly a carburettor fault - most likely the choke plungers need slacking off or replacing. Worth checking the jet sizes are correct too as these may have been swapped at some stage.
Agreed they look like Spada and American Le Mans CX100 barrels/pistons, these are 88mm bore - 950cc - the OP measured them at 90mm (possibly innacurately)
Have a good look around the barrels. I do believe that the replacement Gillardoni barrels have the makers name and capacity cast in between the fins somewhere lower down.
The only markings on the barrel is this FUGAT or FUGATI. It is reading as you say, more like 88mm than 90mm.
The piston is Mondial 2639 and has a star, a B and 10.
The valves are Le Mans spec at 44mm and 37mm.
It’s running a 152 main jet and I’ll check the other carb parts tonight. The bike has competition exhausts, so I guess it could have been set-up as a bit of a racer
The carbs are in the ultrasonic as they are pretty bad and I’m struggling to get the other barrel of at the moment and I’ll have another go when I ge my strength back.
I still can’t see how the piston would hit as there is virtually zero piston slap and no vertical movement in the connecting rod…..very strange.
With the heads off, it’s really hard to see how the pistons can be touch the plugs as there appears to be quite a large gap between the two. I’m scratching my head now as I was not making it up, and there was a definite scratching on the top of the piston in the correct location and the electrode was bent over.
The plugs are standard long reach and do not protrude much into the combustion chamber. Going to take the heads over to the local engineering shop (T&L Engineering in Bedford are great for older engines) and get them to clean them up and discuss what could be causing it.
If you look at the scratches on the piston crown they are all similar and too thin to be the plug electrode, also they are at random rotation to each other. If they were from the electrode they would be all in the same place, not be randomly rotated and would be wider. I think you have screwdriver marks on the piston, and the bent electrode is a red herring, possibly bent by the same careless previous owner! I would be very surprised if the two were linked from the evidence of the photographs.
Definitely looks like screwdriver marks, too random to be contact with the electrode - I’ve inserted one to check the flywheel TDC mark is correct in the past. The plug may have been knocked/dropped and inserted without havingthe gap checked.
PS do not use a pencil down the sparkplug hole to test for TDC someone on here did that a couple of years ago and the pencil snapped leaving half of it in the piston!
I usually take the rocker cover off and watch the valves open and close to gauge TDC.
