Hitchcocks Forum

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Bullet go BANG!



Help!, Tornado and I were just pulling up at a road junction when he made a very loud bang. I guess some kind of backfire through the carb or maybe the inlet valve stuck open?


The video cam declined to record the explosion. It seems that it's automatic record volume works well!




The explosion blew the carb off the engine and was so hard, the air caddy was also blown backwards causing the caddy bracket to swivel; anti-clockwise!





Notice gap between carb and engine rubber mount.


Having opened and checked the air caddie in case the air filter was full of fuel (wasn't) I put him back together and re-connected the fuel pipe. I forgot to check the throttle cable before starting and it was not seated correctly. No idea how fast the RPM got up to for 5-6 seconds, but it gave me the frights. Decompress hardly works at that speed, but the ignition key soon sorted it.



Does not seem to be any additional oil leakage since the explosion and engine run-away, and the engine seems to run and sound ok (including the now legendary rattle), except that it runs a little faster on tickover now! Probably cleaned all the crap out?



It was several miles home from there, an Tornado ran perfectly, so no idea what might have happened except that occasionally on tickover, the engine will run slow if starting after an hours rest or so, and stop with a "PHUT' type noise in the airbox, but this never happens during normal running at junctions, etc.





Please see attached vid, and any advice on anything that maybe it would be wise for me to check please? Got push rod adjustment on the list, but it raining now.


According to my RPM listening app, which works just as well from the soundtrack on the video replay, the engine got up to 4895 RPM for those very few seconds. Is that fast enough for me to be concerned or did we probably get away with it?







If no vid showing... http://youtu.be/_k4gfbe5SJo

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probably better to see on youtube at full HD quality.

Well that went with quite a pop! Inlet must have been open to do that . Cam follower temporarily stuck in the up position maybe? Rocker spindle stuck down for a fraction of a second? I don't think your timing slipped because it started and ran ok after....

Or maybe a bit of carbon propped the valve open a tad - then got blown away in the explosion (cheapest diagnosis)

4895 RPM = fast cruising, don't worry about it !

Could have been worse if it had happened as you drove into the Hollyville café that would have gathered a crowd, glad it was an easy job to get Tornado going again

"Gathered a crowd" ???



More like, blown the bloody windows out!, my ears are still ringing with the memory of it!

Actually, I guess I'm lucky that it did not set the fuel in the carb on fire. Losing Tornado does not bear thinking about.



Ever!

These "phut" stoppages could be a clue. I suspect the inlet valve is intermittently sticking open. I've had this on a Ducati, and it was caused by an excessively rich mixture causing carbon to be deposited on the inlet valve stem, which then stuck open.



I would go through the valve gear from inlet valve right back to cam follower with a fine-toothed comb.

When I first got Tornado,it wasn't so much as 'running rich' as drinking fuel like there was no tomorrow, So I guess he needs a de-coke as well.





I will have to let Chris check all that out when I go back to France, due to lack of workshop facilities here in the uk.



ok, maybe I can do it with the toolkit and a few extras? No valve compressor, but I guess i may not need one of those. I will look online for a tutorial. Got spare gasket sets already.