replace the plugs and leads......and make doubly sure there are no supressed components anywhere ,but in the lead from coil to dist(if you must have one)............supressed leads or plugs will carbon track the little bosch dist cap double quick.
I've resealed the manifolds now for the third time, so carefully that I'm convinced it cannot be a manifold vacuum leak. Even ground down the locator rings a few mm like someone suggested. Sprayed fluid over them all, underneath you name it with no change to poor running.
Tried an alternate carby, to rule out the rebuilt one and it ran exactly the same.
Cannot be a stuck valve given the 130 on all cylinders, but I manually checked again and reset the gaps yet again. (3x - they're so perfect now)
So I was rechecking timing and noticed the timing mark jumping around all over the place. Reconnected the vac line and it got even worse. I suspect dizzy is worn. (These motors don't have a timing chain do they, it's gears right?). So dizzy rebuild is next.
Quick check of the dizzy is to see if the centre spindle is loose ,and then the point gap will be all over place.....this used to cause problems with the forklifts ,....I dont think theres anything can be done with the Bosch......anyway ,beware of the so called disributor reconditioners.....they will stick you $200,and do nothing but put a bit of wax in the bearings.....it will run Ok for about a day,if that.......My cure with the forklifts was an electronic dizzy from TVH forklift spares.......but last time I bought anything off them,their prices had gone skyhigh...they used to be dirt cheap.
Just had my 1941 straight 6 Dodge brought home on the back of a RACQ tilt tray.
With newly rebuilt engine has not been running right at high revs. Starts missing.
Complicated diagnosis with rubbish in the fuel tank causing blockages and regularly changing in line filters. My Carburetor genius said look at fuel starvation. When filters are clean same problem, fitted a back-up in-line electric pump same problem.
Knowing full well that 90% of fuel problems are electrical fitted new leads, condenser, coil, plugs - same problem.
Took the truck to him, removed and cleaned carby, checked fuel flow and spark (at idle) all OK. Bloody thing stops dead at traffic lights on way home, call RACQ.
The only thing I never changed were the brand new points. I pulled them off to find that the spring had detached - broken at the points end- and the only pressure to close them came from the thin brass secondary conductive strip so obviously jumping the lobes at high speed and finally giving up entirely.
New points and now runs like a dream.
I, like most people have stuffed around with carburetors all our lives finding nothing wrong only to discover crook points, condenser, coil, plugs, leads or connections are the culprits.
I would certainly be delving further into the electrical world of International.
Similar situation with my Morris 6. Carby kit and tune-up. New plugs, leads, points, condenser, vacumm advance unit. It would start and run sweetly, but get to 1500 revs and it would start to miss. Get it up to 2,500 revs and all was good again.
Re-check every thing with the aid of a timing light, I was able to determine that it was only number 6 plug which was breaking down.
Replace plug... same problem.
Replace the lead...... ditto.
Run an extra lead from No 6 distributor cap to plug held external to the engine....... same problem
Replace rotor button.... ditto
Check dizzie for wear... no side movement in the shaft and breaker plate and earthing pig-tail all good and secure.
Remove and dismantle dizzie only to find a slight wear mark under the breaker plate where bob-weights had been touching.
How this caused the miss and why only on number 6, I don't know, nor do I care because the problem has gone away.
When I install new points ,I always open and close them with the ignition on,and check if current is flowing......do this because when I workd on cars ,new points were often coated with varnish or something,and the car wouldnt start with the new points .....if they dont spark when opened,out comes the diamond nailboard,and all is good.
John, when I worked on cars last century, I used to wear the front of my overalls because I would rub the points up and down with the overalls seam between them to clear that very coating you mentioned.