Hitchcocks Forum

I thought I'd make mention of what happened to my bike last Saturday. I wasn't riding my Bullet...shame on me, but it's not on the road at the moment. Anyway I was two up pushing the 500cc short stroke single mostly flat out into a very strong headwind and a long dual carriageway climb. I tend to push most of my bikes pretty hard at times and I had been nearly flat out for around 5 minutes at least. Then suddenly the engine slowed quickly, and I remembered I was low on fuel and switched onto reserve very quickly. It made no difference, the bike just decelerated as if the brakes were hard on and I then knew the engine was seizing but too late, the damage was done. So on after restarting it after cooling it off I knew what to expect and sure enough there was that unmistakeable clanking of a piston and bore that know had far too much clearance after grating the piston away. Why did it seize…simple. As the fuel ran out at full throttle and maximum power the mixture had suddenly become far too weak and resulted in the engine temperature shooting up to piston melting temperatures. So here is the warning, make double sure you don’t ever ran out of gas when you are caning the motor, it won’t matter usually but not if you are running flat out. Sometimes you are aware that the fuel is low but you also know you have plenty in reserve to get to a station, so you ride on sometimes riding fast, so I hope this warning might prevent any of you doing the same and suffering engine damage.

Hey Les when I push my Bullet I can't get anywhere near flat out - only about 3mph!

Good one Riggers...I should have seen that one coming....

Hello Les,
I am sorry to hear about your engine
Is this a problem for older bikes or all bikes? I know it's not a good idea to run low on juice on a two stroke running a petroil mix as I've owned loads of MZ's over the years.
regards,
Alan

Or don't do what I done last week on the way home from a 10 hour night turn on me Old work Bullet. In a hurry I grabbed the diesel pump at one of those multi pumps instead of petrol petrol gun lucky only had a short squirt probably just over half pint before I noticed so I just filled the tank up with 15 litres of premium 97 it still run OK though. Cheeky sods still charged me a pound for the Diesel though on top of the petrol.

Hi Alan (rado53), Thanks for your concern and sympathy. I was quite annoyed with myself for hammering the bike quite as hard as I did forgetting the petrol was running low, it would have been ok had it not run out, its a pretty tough engine with a good oil pump and I've had it running just as hard before with no trouble, but was unaware how close I might have been to seizing. I haven't seen the piston as yet but I would imagine it's a modern make possibly JP or GPM both of these seem to be prone to seizing and they are usually heavier as well. I can't understand how modern pistons are not as good as the originals but from many stories I've read it does seem that way. So just by running out of petrol, I've suffered an expensive breakdown and as the slap is so loud I will have to buy a new piston. Two strokes are more likely to seize especially pre-mix type engines with lean mixtures. What helps two strokes get by is that the piston is in contact with the cold fuel charge a bit more than four strokes, even allowing that they fire twice as often...they are cooled twice as aften too. I've had no trouble with my two MZ's in that way, but then again they are relatively low powered and not overly stressed...I really like two-stroke engined bikes...Cheers Alan....Les

Might have decoked it a bit Paul :)no damage otherwise I reckon.

sorry to hear that Les, but I saw a holed piston on a very good motor, because a new tank and cap had been fitted and the cap vent didn't work. Ran it lean and also took the head of the exhaust valve off

Having a recent bullet seizure myself and almost another on seeing the resultant piston damage on strip I feel your pain.
If you've been having the kind of heat we have up here then it's easier still to run hot when leaning off.

Hi LES---- we're all still kids at heart, aren't we ?? Enthusiasm over riding common sense at times-- even to-day. Back in my day I was BIG TIME into Speedway and Grass-tracking in the Southern Centre ACU territory...Cutting my teeth on the ubiquitous C15 and B40 machines there came the time when I could afford a spanking new Montessa 250 engine + tuned exhaust.... It ran exceptionally well until it caught me napping one meeting at Blanford Forum when the bottom end let go at max RPM changing from 2nd into top. I didn't have my hand on the clutch lever---a common practice with pre. mix oils---. You can imagine the sight that beheld my eyes when I removed the cyl.head ?/ All the rollers had been pumped up the extra wide transfer ports and danced the Fandango on the crown and head !!............total wright-off. And me still paying the Ex. for maintenance as well. Ah --what joyus behold-aloady !!