View Full Version : now, PTO cylinder not firing.

profqwerty - n/a
14-Feb-09, 05:29 PM
Hi all,

My craft has suddenly developed this problem where at about 4000rpm the engine starts really jumping around.

It wobbles a lot and I'm a bit tentative about taking it higher in case something breaks. By hand you can't move the engine much, the centaflex looks/feels fine and it runs absolutely fine up to 3500rpm. Belt tension is as it has been, and seem ok.

The only difference is, one of the nipples came off the pto carb cable (not carb end) as it was running which initially caused it to vibrate massively, so I changed the lot.

Does anyone have any ideas? I'm thinking of changing the engine frame to something better over the easter holidays so I'm hoping it'll fix itself then...



hovmart - n/a
15-Feb-09, 10:47 AM
are you sure its running on both cylinders, try removing plug leads one at a time

profqwerty - n/a
15-Feb-09, 04:09 PM
It seems to be an intermittant fault http://hovercraft.org.uk/images/icons/smiley_icons/icon_mad.gif

At low rpm (1000-2500) it runs only on the MAG cylinder; taking the plugs out both have a strong spark so i'm thinking the ignition timing has gone way off for it.

At 3000 it runs smoothly for about 10secs then dies off (as above when it hits ~2500rpm) and stalls at a constant throttle setting.

At 4000 it's starting to vibrate, the hull is shaking, >4000 the vibrations just get stronger so I close throttle a bit.

leaving it with chokes on it runs rough but at least does idle pretty consistantly.

Sometimes, it starts then idles smoothly for ~10secs then stalls.

Have cleaned both carbs and set air screws to 1/2 turn out, idle screws where they were before, both carbs open/close simultaneously, changed ignition coil, both are sparking strongly.

I ran out of time / light and haven't been able to take a look at the points yet...

Kipmac - n/a
15-Feb-09, 05:33 PM

Reading what you say it is quite possible the problem is not the engine but some point in the transmission or something out of balance.

Possibly the belt,but more likely the frame bending under load.

Maybe your frame is cracked.

I would certainly give more thought to the frame which is obviously something you are considering.



nickyd - n/a
16-Feb-09, 01:05 PM
Check your electrical connections. Intermittent contacts can lead to the engine jumping about as it turns on and off... Just a thought

profqwerty - n/a
17-Feb-09, 09:08 PM
Thanks for the replies...more to think about http://hovercraft.org.uk/images/icons/smiley_icons/icon_sad.gif

I won't be home til the easter holidays now, so it's going to have to wait...

hovmart - n/a
19-Feb-09, 03:25 PM
447 did suffer with generator coils breaking down