7 replies to this topic

[Native beats]

Hello, I finally got round to buying myself a timing strobe, so i could set my dizzy properly, because i've not been able to stop my mini from running way too rich.

Found TDC with a screw driver in No.1 cylinder just to make sure i didnt end up 180 degrees out, and then set it up.

According to Haynes book of lies, my 1275 (electronic Ignition) should have been 5 + 1 degrees at 1500rpm
i didnt really know what it meant by 5 + 1 so i set it to 6 as best i could.

thing is i disconnected the vacuum advance and plugged it to set the timing, and it just makes no difference whatsoever.

sitting still and idling after i set it, i tried disconnecting it again, and she still made no difference, and then i drove it up the road......no difference to the way she drove.
so the vacuum advance really is doing nothing, and i cant work it out. no blockage in the carb, though it has weak suction, but thats the thing, if the vacuum was weak then shouldn't my timing be experiencing problems all the time?

and could this be the reason i cant lean my engine off enough without it choking when i put my foot down
even when the carb mix is clearly set way too high, when i push the carb piston lifting pin up the engine drops in revs as if it were too lean.
im running an HS4 by the way

sorry if my description is a bit all over the place

[Ethel]

It could, if there is a fault, the vacuum take off on the carb is located above the throttle disc to help the idle by limiting advance until the throttle opens. Suck on the end of the vac pipe: you should just be able to move move the vac advance mechanism.

[Native beats]

cool, cheers man, will give it a go when i get home, and when i do that, i guess the revs should go up a little? if not dizzy problem? or just diaphragm?
also was i correct to set the timing to 6 degrees if it said 5 + 1?

Edited by Native beats, 22 September 2011 - 12:24 PM.

[Ethel]

Sorry I didn't explain that well, I meant with the dizzy cap off so you can see any movement. You'd need very good lungs to pull the advance any real amount & it can be hit 'n miss to judge power on an idling engine as there's no much for it to push against. Less advance helps idle as it ensures the push will come after tdc and push the pistons down the bore no matter how weak.

Vac advance only really kicks in under load at part throttle, you can check the dizzy baseplate moves freely and the vacuum can doesn't leak (suck test) which should be enough to ensure it does what it says on the can - literally, you'll find the vac can is stamped with the maximum advance it gives.

[dklawson]

There may be nothing at all wrong with your vacuum advance.

First, vacuum advance is typically used for part-throttle fuel economy. It is not there to affect power. Excluding part-throttle cruising, the ignition advance is controlled mechanically by bob weights beneath the plate in the distributor.

Over the years the carburetor connection point for the vacuum advance has moved. In some installations you will find the connection behind the throttle butterfly, in some it will be in front of the throttle butterfly. The location determines when and how the vacuum advance is used by the engine. Since the manuals have to cover "all" variations of the car it is easier to simply tell you to disconnect and plug the vacuum advance tubing while setting the timing.

Try this test instead of simply revving the engine. Disconnect and plug the vacuum tube as you did before. Take a second, clean tube and connect it to the vacuum canister on the distributor. Connect your timing light and start the engine. Shine your timing light at the timing marks. While you are watching the marks, "suck" on the piece of tubing you connected to the distributor. Depending on the spring in the dizzy vacuum canister... you should see at least a little advance on the timing marks. Ideally you would have one of those hand-pump vacuums that you could use instead of sucking on the tubing... but you have to work with what you've got.

By the way, to hook up the timing light you do not need to bring the engine to TDC.

[Native beats]

ah cool that makes sense, yeah will try that when i get home, ill try using a syringe or something to do the sucking if it fits.

just one more thing, was i right to set the timing to 6 degrees? i didnt understand what haynes meant by saying 5 + 1 degrees.

thanks for all the help, makes lots more sense now.

[finch661]

sorry to hi-jack, but how far should the timing move when the vac advance is connected (and a timing light shining on the marks?)

[Ethel]

Are you sure it wasn't 6 + or - 1 degree, giving you a range of 5 to 7 degrees.

As above, the amount of advance is stamped on the vacuum can, if it's not given in your Haynes, but you're unlikely to see that much advance just by sucking - it may well create more advance than the timing marks cover anyway - or stall an idling engine. Even a degree or two will prove the system works, again as above, you can move the baseplate by hand as well to prove it will move freely. Advance is given in crank degrees, the dizzy does 1 lap to every 2 the crank does so 20 degrees advance equals 10 degrees of dizzy movement, for example.