Secondary diaphragm

mark77 · 08-01-09, 06:38 PM

Hi Guys,
I've had a problem with my '83 2f cruiser (180000 orig km's) since i bought it a few months ago which is starting to frustrate me. It seems to ping the valves up hills under very little load or acceleration. Also been hard to start after a highway run and it's using a bit of oil.

The previous owner said the engine had been set up for unleaded, and it is obvious that the head has been off. Despite this now run it on 95 unleaded with valve lubricant added. Didn't help. Next i changed points, plugs and did timing. Helped a tiny bit. Next i took carby off and sprayed heaps of cleaner through it. Checked the secondary butterfly and it seemed to be a bit frozen. I freed it up thinking it might have been not opening causing the engine to run lean at highway speed. Next i checked the vacuum hoses which all looked ok. Finally, i'm not sure why, but i took off the secondary vacuum unit off and opening it up. The secondary vacuum diaphragm has a crack in it. Could this possibly be causing the issue?

I'm struggling to work out what exactly is does. From looking at it it appears that when the secondary opens up a certain amount, the stem gets pushed up by a fitting on the shaft which would push a small amount of air through a jet and into the carby. But what does this do?

Curiously too after looking for a replacement, one site stated that the "bent" stem type is for 3F. My motor is definitely 2F but carby has a bent stem and can't see that a straight stem one would fit. Maybe someone has put a 3F carby on?

Any help would be appreciated.

Cheers,
Mark

inkpot · 08-01-09, 10:02 PM

Howdy! I thought all Landcruisers were on unleaded long before 1983. If the secondary has a cracked diaphram, the that will cause a vacuum leak, leading to a overly lean condition. Secondly, it means you are not getting the second barrel open at the right time, so your pretty much running on a one barrel carb. Also, in the U.S. all of the 3F engines were 3FE = fuel injected. No carb. Johyn

FJ40Jim · 08-01-09, 10:37 PM

The secondary was sticky because the diaphragm has not been opening it up for a long time. The mechanical linkage does bump open the secondary, but then if there is sufficient airflow through the carb, there will be vacuum at the diaphragm, and the diaphragm will continue opening the secondary until the load demand is satisfied. The diaphragm is cracked, so the secondary is not opening.

The bent stem diphragm is used on all 81-later 2F and all 3F.

The pinging is probably ignition timing that is overly advanced, or overly advancing due to a dissy problem.

Putting the hardened seats in the africa spec head would probably raise the compression a little, by moving the valves out into the chamber a bit. But I don't think it would be enough to get the comp ratio up to 9.5:1, which would be the minimum to get detonation w/ 95 octane.

mark77 · 08-02-09, 04:56 AM

Thanks alot for that info, it clears things up alot. No wonder performance hasn't been the best. From what FJ40Jim says then the pinging sounds like a separate problem. I'll check timing and points again but don't know where to go from there. What other probs might be happening with the dizzy? Could it be the vacuum advance? What is the best way to check it's functioning correctly?

2mbb · 08-02-09, 08:36 AM

You can purchase timing lights that have advance knobs on them, but I don't think you will really need it.

1. Before setting your timing you should disconnect both vacuum tubes from the distributor advance diaphragms and plug them. The timing is then set so the pointer is on the "bb" for 7 degrees BTDC.
2. You can check that your diaphragms are working by removing the distributor cap (truck is off, now) and applying vacuum to each port. The plate below the rotor should rotate as vacuum is applied.
3. Check that your high altitude compensation (HAC) is working properly. If you are at low altitude and the outer distributor diaphragm is getting vacuum, this will provide additional timing advance which could cause pinging at low altitude.

FJ40Jim · 08-02-09, 09:10 AM

Quote:

Originally Posted by 2mbb

You can purchase timing lights that have advance knobs on them, but I don't think you will really need it.

1. Before setting your timing you should disconnect both vacuum tubes from the distributor advance diaphragms and plug them. The timing is then set so the pointer is on the "bb" for 7 degrees BTDC.
2. You can check that your diaphragms are working by removing the distributor cap (truck is off, now) and applying vacuum to each port. The plate below the rotor should rotate as vacuum is applied.
3. Check that your high altitude compensation (HAC) is working properly. If you are at low altitude and the outer distributor diaphragm is getting vacuum, this will provide additional timing advance which could cause pinging at low altitude.

Mark 77's truck is not equipped w/ the dual vac advance and HAC systems referenced above.

mark77 · 08-06-09, 11:28 PM

Hi,
I have replaced the secondary diaphragm but wanted to check the timing before i test drive it. I put timing light on it and i can't even see the BB in the window. I haven't plugged up any vacuum hoses before i checked.. should I? There seems to be 1 hose from the vacuum advance diaphragm on the side of the distributer. I don't understand why it would be out as i was set by a mechanic who knows these cars very well and owns one himself. Is it possible he has set it to a different setting thats suitable but that means i can't see the BB in the window at all? The only things i've done since he did the timing was adjust valves and fix the secondary diaphragm.

Thanks guys

2mbb · 08-07-09, 08:04 AM

Yes you need to disconnect the vaccum lines from the advance diaphragm(s) and plug the lines. Then you set the timing.

Some people do advance the timing to get a little more performance. I think they may put the bb just at the edge of the window. However, if you are having problems with pinging, then the corrective action is to retard the timing, so you need to set the timing to stock conditions first and see if your problem persists.

mark77 · 08-07-09, 06:42 PM

Great advice mate, will do that. Other thing i have done which i forgot to mention was clean the carby out. Not sure is this can affect timing though.

Cheers

mark77 · 08-08-09, 06:02 PM

Success! I adjusted the timing. As suspected the BB was the window out of sight. The bracket on the dist was not that tight so am wondering if it may have moved. I retarded it so that it was only slightly below the line. Took it for a drive and.. no pinging. I drove it up quite a steep hill and didn't ping in 3rd. Even changed to 4th and despite not being able to accelerate in this higher gear still no pinging. Thanks alot for your help.