TB42 stuttering under load

Good morning,

I’m having an issue at highway speeds on long trips when changing altitude where the revs with randomly drop to 0 and bounce back up almost instantly, the car stutters and feels like it’s going to stall when this happens. It’s usually just as it drops under 2.5K revs under load, almost always on inclines and almost always on long trips, although I have experienced this once or twice around town.

Thinks I’ve gone through so far
- Replace all vacuum lines on carby
- replace air filter and pcv
- clean carby and replace gaskets
- reset idle speed and mixture
- check spark plugs (they were still clean)
- check timing (correct to Haynes manual)
- check and set automatic choke (tried setting it all the way to lean too)
- changed distributor points

I’m not sure what it could be, I’ve read a couple similar issues but haven’t had any luck yet. It happens very occasionally, but always on a 4+hr drive and very rarely around town. It never happens sitting over 3K rpm.


Many thanks for any advice.

Cheers,
Mitch

G`day Mitch.
Me, Well I`d stick it on an oscilloscope. May well be fuel related but to me it sounds electrical. An oscilloscope will pick up most electrical problems in the ignition system,most of which you cannot see or find even by jiggling cables and connections.
My Daughter had a Land cruiser which cut out going around sharp right hand turns , but not left. The problem turned out to be an internal problem in the coil. When turning right the internals (which had come loose some how) would short out on the coil body then when you straightened up they moved back in their normal position. this movement was only a couple of thousands of an inch. Found the problem with an oscilloscope only after doing a complete carby rebuild and fuel system check.

Hi Pearcey,

Thanks for getting in touch, that’s a great idea. I’m not sure where to find or how to use one, could you send me in the right direction? Should I talk to a auto-sparky or purchase one myself?

G`day Mitch.
Been a few years since I`ve used mine, (my unit is some fourty years old) but any good tune up shop should have one. It should only take about five to ten minutes to diagnose any faults. As for buying one, there are plenty on EBay but how many times would you use it.