Hi,
a friend of mine got a new 68 C3 BB with a Tripower on it.
It seems that it was originally a L36.

The Engine has a rough idle and shakes.

He asked me to help because I have some experience,
I checked this:

Ignition:
- vacuum advance canister is working and is full pulled when 12Hg are applied (but the engine is only producing 8Hg in idle, what seems pretty low for me)
- timing adjustet to 36° @ 3000 and at idle we have 17°

Carbs:
- first cleand with running engine and carb cleaner, no improvement
- then adjusted the mixture screws, found that both need to be turned out ~1 turn. When turned more in the engine is going to die and vacuum also drops. When the screws were turned more out there is no change of the vacuum visible. The pointer needle is als flickering all the time. Only if you rev it up and let it come down you get a clean reading on the vacuum gauge. And then 15Hg vacuum is reached. But after some seconds the problems start again.

- (un)pluged the vacuum hoses to see differences. Found none. Only if you pull the hose from the PCV its sucking so much air that the engine is going to die. (While my Engine just revs up if you do so)

- sprayed brake cleaner around the carbs, searching for leaks. Found that it was reving up a bit when spraying to the socket of the rear carb.
So removed all 3 carbs, disassembled them into all parts, cleand everything inside and that holes and put them together again with new gaskets. But this didn´t solve the problem, despite now you can spray the rear carb outside without any rev changes.

- during the carb-rebuilt I saw that the throttle blades where much too far open.
Usually you should see the transistions slots as a "square", but in this case the idle
was so high adjusted to keep the engine alive. I could not screw it down, because the engine would die. The secondaries were correct closed.

- fuel level in the bowls is checked and ok

- engine is running on all cylinders

- I found some oil in the intake runners of 2 cylinders. Checked the according sparkplug and found it "good oiled"

Now we assume a vacuum leak at the intake to the crankcase because of the oil in the intake and on the sparkplug.
But I am not sure if a leak there can be so bad that it is causing this.
What do you think?
At idle the engine has only 8Hg vacuum, I think it should have 14Hg or sth like that.
Opinions?

 

Hydraulic or solid lifters? Is the PCV valve good?

 

We don´t know the lifters.
Still bad results if the PCV hose is unhooked.

But knowing the previous owner had done something with the engine it´s possible that there is a larger cam in it. The flickering vacuum gauge could be a hint for this.

I found in another thread that replacing the vacuum canister to get more advance can help. And also the change of the airbleeds for the idle circuit.

 

The 'end' carbs must be completely closed during idle for the tri-power to be set up properly. Only the center carb is used for idle, low throttle and normal cruise operation. Therefore, neither end carb can be opened AT ALL during those periods of use. Check to see that those two end carbs have NO idle air entering them by blocking off their airhorns and then opening them up to the air, while the engine is idling (warmed up completely). If the engine runs differently whether the air horns are "open" or "closed", excess air is getting into the fuel charge via those end carbs.

If the carbs on your buddy's intake are not the proper center/end carbs for a tri-power system, they will never work properly.

 

Hi,
as mentioned above, the end carbs are closed correct, saw it when the throttle bodies were removed.
The center carb is the one that is adjusted much to high, just to keep the engine running.
I told him to put a piece of wire into the air bleeds to reduce the diameter and maybe get an improvement.

 

Don't put wire into the air bleeds. This will make the carburetor run rich and you don't know if it's rich, lean or just right. A quick and accurate method to test rich or lean on the idle circuit: Raise the engine rpm with the idle adjustment screw to a stable 1200-1500 rpm. The carburetor will be running on the idle and intermediate circuit. Turn the mixture adjustment screws in. If the rpm comes up, the carburetor is rich. Turn the screws out. If the rpm comes up the carburetor is lean. If the engine falters turning the adjustment screws both in and out, then you are probably not dealing with a carburetor idle circuit issue.

Please Google something like: "vacuum gauge readings for engine troubleshooting" to understand what the gauge is trying to tell you. It's possible the engine has a big camshaft and what you're seeing is normal, but we're not there looking and listening to it so that's hard to say.

 

Thanks a lot, learned much about reading the gauge.
But our problem is not included:
The needle is flickering very very fast, you can´t see it clearly with your eye anymore.
You can only determine the end position of the needle. And this is -8 and +4 (yes it goes to the plus side when it flickers around). Would this indicate a big cam?

My zz502 shows the same (similar) flickering at idle, but my engine is running good so far.

 

Found this:


it´s not from us, but shows same flicker frequency and smooth out when reving up.
From all what I have read now it would indicate something with the valves not ok.
So next step would be a compression test.

 

Today we took the intake of, sealed it new and put it back on.
Adjusted the lifters (solid) and tried it again.
But no improvement, it has still the same behavior as before.

We took a video to show you what it does:


You can see the flickering needle at idle.
If you rev it up it gets a clean reading of -5" at ~1100rpm and vacuum increases
up to ~ -15" maximum with increasing rpm.

The only thing i can imagine is that there must be a realy large cam inside or the valvetiming is wrong. Maybe the chain is one step skipped?
What do the Experts say?

 

Did you block off all other vacuum feeds from the engine while doing your tests?
Have you read this? http://www.secondchancegarage.com/public/186.cfm

 

yes and yes

Our problem is not included. But what about worn vavle guides?

 

That or leaking head gasket per the chart here: http://www.gregsengine.com/using-a-vacuum-gauge.html

Just a thought.

Pete

 

Have you done a compression and/or leakdown test? It sounds like you have one cylinder acting up. Maybe a wiped cam lobe.

 

My 244/244/110 cam in my 427 is hard to read on the vacuum gauge but it does not bounce that fast.

I too would do a leak down test.

 

Wanted to give update here: compression test was ok. Then another issue came up with a defective lifter, so he decided to tear down the heads and check everything.
He also pulled the cam and checked its number. Turned out that the cam in this engine was way too much for the complete engine setup and totally wrong.
Currently he is putting everything back together but going for the right cam now

 

 

Did you check if the center carb throttle shaft is loose in the bore of the carb main body? The shaft & bore tend to wear and allow a vac leak at the shaft/bore interface. I have repaired a multitude of these.