Ok, I’ll start with a little background on the engine. About a year ago it was taken out of the car running perfectly.
It has since been rebuilt with all new bearings, 30thou oversize forged pistons, datsun rods, new oil pump, oversize valves, adjustable cam pulley, BF63 cam, new rockers, some porting work, shaved head, etc... It has a compression ratio of 10.8:1 calculated with current original head gasket, and over 11:1 with the felpro that is soon to be put on.
I have twin dellortos to go on, but as they have not been jetted correctly yet I figured I would run the cam in on the standard 32/36 that I was running before the rebuild, and then swap to the dellortos when it was ready for the dyno.
Now, my issue is...
I can start the car, and it runs on 4 cylinders, but it will only start on full throttle, and when it does start on full throttle it will only rev to about 1000rpm and that’s it. I can back the throttle off to about ¼ when it is running but it will still only sit on about 1000rpm, throttle position doesn’t make a difference above ¼ opening, and below ¼ it dies. But it won’t start on anything but WOT. I have tried 2 different 32/36’s both with the same result, and both came off perfectly working engines previously.
These are the things I have checked so far,
Ignition timing – I am using the pertronix ignition, and originally I thought that this may have been the problem, so I changed back to standard points, but this made no difference. I timed it originally to 10deg BTDC but tried turning the distributor as it was running and 10deg seemed to be about the smoothest spot, advancing the timing from 10deg made it throb like crazy until it stopped, and retarding it made it die. Now for those of you that say “maybe you have the timing 180 degrees out” I have tried that, and the fireball that launched itself out of the carbies say I had it the right way!
Plug leads and plugs – I have tried replacing all the plug leads for brand new ones and this made no difference, replaced all the spark plugs with new iridium NGK DPR9’s. I have tried placing the plug on the engine while cranking in all of the leads and they are definitely all sparking. I cannot see any cracks in the distributor cap and although it’s not new it is in good condition, same as the rotor.
Cam timing – cam timing I have double checked and is in correct position but decided to adjust it slightly by using the pulley anyway and either way I went it made no real difference.
Fuel – car has electric fuel pump and is definitely supplying enough fuel, float bowl if full and return line has fuel in it.
Exhaust – definitely not blocked, have checked extractors, and from there it has a pipe going straight out the side, so no muffler to block up.
The engine itself is definitely not ‘tight’ as it spins fine on the starter and can be turned over by hand without any issues. Compression, although I have not checked with a gauge, is fine with the old finger on the plug hole test, plus it is a rebuilt engine so I have no reason to believe it is that.
I think the problem lies in the ignition/carby department, but I am out of ideas to try so am hoping someone has had a similar problem, or can throw me some ideas. Now I realise that the 32/36 with standard jetting is going to be on the small side, but I’m sure that I should be able to get more than 1000rpm out of it.
Sorry for all the writing.
Thanks
Garry

I wouldn't run untuned carbies on a fresh engine. You wash the bores and the piston rings don't bed in.
Cam timing is needs advancing and the total ignition timing should be around 30°.
Have you used the correct marks on the bottom Pulley? It might be advanced too far at the crank.
Goodluck with it Garry.

10deg timing is the bare minimum I would run with that cam, more like 16-18deg initial timing.

Have the carbys been unused for a long time? The idle jets etc, could be blocked due to corrosion.

If it looks ok, just pull the spare secondary idle jet out and put it into the primary to see how that goes. It may be just enough of a difference to help if its lean.

What you are decribing sounds like the cam timing is out.

Cam timing sounds like its not right which will also make iginition timing out.

Set the cam up properly so you are 100% it is right and then set the ignition timing from there.

ok, got it sorted now.
it was the cam timing. I've had to advance it 1 tooth. it was set up originally using the 'E'bar method, which i have never had problems with before. it looks like it is all wrong now, but for some reason it works. here is a photo demonstrating,



the marks were pretty close to 6 o'clock when it was in the initial 'correct' position, and this is where they are now when it is working. not a great photo but hopefully you can tell.

TDC is definately correct, that was set with dial guage when engine was being built. can only put it down to cam profile.

thanks all for the replies.

Bit hard to tell from that pic with a vernier gear. Id be keen to see where the keyway is pointing

Using the E-bar method is a waste of time, probably invented when dial indicators and stands were expensive. When you can get a dial indicator & stand for less than $100 why would you bother.

FYI a set orifice size will only pass "x" amount of air so "camming" up the motor will not automatically lean out the carby. Generally the fuel curve will shift around but the total fuel consumption will stay about the same. This is of course using the same carby and some common sense.

Keyway lines up with the 0 on the vernier dial. when i take it apart again ill measure it to see how far out it is.

im not going to start a debate about the merit of the 'e'bar method, i have used it previously to good effect and esslinger recommended it, so it must be fine in most applications. why would i go and spend the money buying dial indicators when a flat peice of aluminium plate can do the job, i couldnt justify doing that.
anyway, cam timing is sorted now.