2.8 Timing & Distributor Questions

[AMC86Kid]

Ok so my 3.4 needs the timing set on it 

I can get it running but it idles high and it sounds off timing 

 

my questions are :

 

What is the proper timing on the 2.8 ?

Where is the timing tab or degree indicator on the 2.8 ? 

 

 

My 3.4 was originally fuel injected so the computer of the Firebird set the timing correctly there for I have no timing degree indication on my rebuilt engine 

 

[Green Mesa XJ]

Bud, I believe I posted the best pics I could at the time of what the 2.8 timing cover and markings looked like. Search some of your old threads I’m sure it’ll be there.

Original timing would be something like 10 degrees btc. With vacuum disconnected at idle, (700 rpm? )

don’t have those pictures on my phone or I’d repost them.

No idea how to guess set without those marks, best guess would be make a mark on the 3.4 cover based on where the 2.8 marking are, then fine tune by driving it.

But this is a little out there for internet mechanic online stuff. Hands on I’m sure I could set it, or get it close enough. Telling somebody how to do it is another matter.


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[Green Mesa XJ]

Well I found them. Hope this helps


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[AMC86Kid]

Thanks Green Mesa 

is the pic from a 2.8 MJ ??

also where is that tab located ?   is it on the top right of the bottom crank shaft 

and how big is the crankshaft pulley ?   do you think the 3.4 is the same size pulley ?

[Green Mesa XJ]

Honestly I don’t know 2.8 vs 3.4 pulley, ought to be similar.
, timing mark it’s on the top left side, right hand standing in front, below the water pump
About where the 3.4 should have mounting points for its crank sensor, if that’s what that sensor is.




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[AMC86Kid]

do you have a 2.8 ?

can you measure the harmonic balancer and i can measure mine so we can see if there the same size ?

 

and for location you mean when your standing in front of the engine looking at it 

its on the top right side of the harmonic balancer wheel ??

[Green Mesa XJ]

Yes it’s a 2.8 timing cover

I don’t have a frame of reference, the 3.4 has a different water pump , if I had to guess I’d say between the two bolts( in the last picture of the cover and crank pulley) for the water pump, closer to the left side (bolt nearest your right hand) , that’s if they are anywhere near the same bolt location .

If you look at the 2.8 pictures you can make out where 10 btc is by counting the notches. That’s where 10btc is going to be regardless of the timing cover, mechanically that’s where it should be on those engines, I’d look for bolts or something similar on both covers to make a guess on where it is in the 3.4 cover.

Bigger question is does the 3.4 crank have markings for timing the engine and did you ever set tdc? If you set zero you should be able to make slight adjustments to get it close enough.


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[Eagle]

1 hour ago, AMC86Kid said:

Thanks Green Mesa 

is the pic from a 2.8 MJ ??

also where is that tab located ?   is it on the top right of the bottom crank shaft 

and how big is the crankshaft pulley ?   do you think the 3.4 is the same size pulley ?

 

The timing mark isn't on the pulley, it's on the harmonic balancer -- and you can;'t swap that from the 2.8L to the 3.4L because the two engines are balanced differently.

 

What you can do is manually rotate your engine until the #1 cylinder is at TDC (top dead center) on the compression stroke. To find that, remove the #1 spark plug and probe inside the cylinder with something like a length of solid (not stranded) copper wire while a friend turns the engine with a wrench. (It'll turn easier with all the spark plugs removed.) Use a toothpick and some bright white or yellow paint to mark a line on the damper and on the block.

 

Then calculate how far away from the first line you need to be to get 10 degrees, mark a second line on the damper, then wipe or scrape off the first line. Now replace the spark plugs, attach the timing light, fire it up and set the timing.

 

 

[AMC86Kid]

Thanks Eagle 

and yes I understand that the 2.8 is externally balanced and the 3.4 is not 

so it makes sense that the harmonic balancer can not be swapped 

I was just trying to see if the diameter of the harmonic balance is the same on both engine sizes since this will determine if the timing tab would be around the same location and the distance in degrees would match also 

 

 

i also found this : 

Base timing should be in the 10*-14* BTDC ballpark before adjusting the carb.

 

[AMC86Kid]

Green Mesa is right the water pumps are different

but i looked up the info on the harmonic balancers

and they are both the same size (6.406 in. OD)so this means that TDC should be the same 

and the timing tab on the 2.8 will work on the 3.4

since the angle of the 2.8 will match the curve of the 3.4 Har-Bal

and the spacing from zero to 10 degrees would be the same too

[AMC86Kid]

I found this 

F7A70931-5042-4B92-B94A-F7D808D90ED1.jp

 

instead of getting a timing tab 

I can just use timing tape

find TDC like eagle said 

mark it and line it up with zero on the tape then when I use a timing light I can see where 10 degrees before zero is and I can get real close to where I need to be  

[AMC86Kid]

Now my other problem is getting the rpms down so that it can be easier to adjust the distributer 

the engine idles at like 2000 rpm right now 

if I can get it down to 700 like Green Mesa said would be nice but I got to learn how to tune down my Weber carburetor 

[Green Mesa XJ]

The Weber is simple to tune. Right now i would leave the fuel mixture alone, should be set from factory more or less where you’ll need it. I’d leave it alone unless it has to be adjusted. The last Weber I bought I just threw on, reconnected it and set the idle.

 

After the cold idle releases, you can set the warm idle. I’m kind of assuming idle was bumped up to keep the engine running, but if not double check the basics.

 

Make sure you don’t have any vacuum leaks or leaks at the base where the carb mounts, then it’s a matter of adjusting the idle down.

On the side of the carb where the linkage is for the throttle, there is a screw that can be adjusted up or down to set the warm idle, maybe some call it curb idle.

 

The screws at the center front and back are for the mixture, at this point I’d leave them alone unless they’ve been adjusted way out of spec already.

Not hard to retune them just unnecessary at this point.

 

Here is a link for the Weber instructions

 

http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm

 

 

First thing I do is set tdc and find zero.

Then I’d double check the carb is set up right, no leaks, correct vacuum lines, good fuel pressure, and wired up correctly not that you’ll need much wiring. Should be all in the instructions the kit came with.

 

Far as timing without markings I have no idea, but I’d follow what eagle said.

 

Did you ever get the federal emission distributor set up? As I remember it your MJ had California emissions.

 

 

 

 

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[Eagle]

1 hour ago, Green Mesa XJ said:

Far as timing without markings I have no idea, but I’d follow what eagle said.

Did you ever get the federal emission distributor set up? As I remember it your MJ had California emissions.
 

 

What's the diameter of the harmonic balancer? Figuring out the offset from TDC for 10 degrees isn't difficult.

 

Let's say the diameter is 6 inches. The circumference is Pi x diameter, or 3.1412 x 6. That's 18.8472". The full diameter occupies 360 degrees, so divide 18.8472 by 36 and you have 10 degrees occupying 0.5235 inches.

 

Substitute the actual diameter where I used "6" and go from there.

[AMC86Kid]

i printed this out to set my timing on my harmonic balancer 

 

 

i should be able to just cut it out and glue or tape it to my Har-Bal

it is for a 6 and 13/32 size wheel which is what i need cause my wheel is 6.406 inches

[AMC86Kid]

by the way Green Mesa your link doesn't work for me 

and right now I'm just using the electronic distributor since thats what i already have

and i want to learn how to set it up correctly 

after this i do want to spend the extra money and get the vacuum controlled one

 

now for my carb it shouldn't have an air leak since it comes with a new thick black gasket 

the instructions it comes with are not the best it just has this one pic 

 

 

i still need to look up how to hook up the electric choke 

and when it should be on or off (maybe my choke is just not turning off and running it to rich)

also i deleted almost all the cali emissions crap since i don't need it 

[Eagle]

Choke should only be on for initial, cold start. Immediately after start it should go to half choke, and then very quickly go to no choke. Some choke might be needed for warm restarts in cold weather. No choke should be needed for warm restarts in hot weather.

 

If your carb has an electric choke -- hook it up.

 

[Green Mesa XJ]

http://www.redlineweber.com/html/Tech/38_dgas_tunning.htm

 

Try this link.

 

Powering the choke was a matter of tying in to something that only powers up with the key on run. I’m not sure what your wiring look likes but there should be one or two sources near the carb that only become hot (powered) while the engine is on run.

 

As fir keeping that distributor I dunno. It ties back to a computer, somewhere, even as limited as it is, it controls a lot of how that engine runs. I know nothing about that set up, I’m sure there’s a write up somewhere of somebody putting Weber on a California Mission S10 or jeep

 

 

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[AMC86Kid]

Eagle so you think that the choke is normally open and after it gets power it turns closed to allow more gas build up 

 

see from what I’ve read and seen online everyone says it’s a normally closed choke and you have to send it power so that it opens and allows the engine to breath warm up and idle down 

 

I guess I will find out today as it’s the first time I hook it up to power, I will take a look and see if the rpms go up or down 

 

and Green Mesa the new link works but it’s the same info as what my instructions say so it’s not much help for me I need pics to be able to see what there talking about 

there assuming that I know where all the ports are and exactly what there used for

i will post pics of it and show what I understand about it so far 

[Eagle]

I didn't say the choke is normally open. I said if it has an electric choke, hook it up.

 

Let's go back to basics. The old, mechanical chokes from the 50s and 60s had a bi-metallic coil spring that closed the choke flapper. There was a heat tube up from the exhaust manifold to the choke housing that fed heat from the exhaust up to the choke. As that heat warmed up the spring, it lost tension and allowed the flapper to open as the intake air flowed past it.

 

I don't know specifically how the Weber electric choke works, but those I have seen simply substituted an electric current for the heat tube. The electric current flows through some kind of resistance coil, which generates heat, which then causes the choke flapper spring to lose tension and allow the flapper to open.

 

So if you have an electric choke and you don't have power to it, more than likely the choke is always on (closed).

 

[Green Mesa XJ]

Um, the Weber choke is supposed to get power when the ignition is on, otherwise it’s a power drain and always on when the Jeep is parked

When running it gradually opens the choke as the engine warms.

Looks like I powered mine from the plug that used to go to the warming element that was under the carb, junk, got rid of it long ago, I bought a gm pigtail plug to use the plug instead of splice into to bring power to the electric choke.



You should have one big vacuum line and one small line the Weber requires, should be easy to match up as the old carb had used the same lines. Getting rid of the factory carb means you don’t need most of the vacuum lines under the hood.

This it the idle screw



I remember you had over heating trouble before. Hope that’s fixed.

Far as the cpu the adjusts the timing instead of vacuum advance find the factory instructions for timing those engines either Jeep or whatever gm had for those 2.8 carbureted.





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[AMC86Kid]

Ok I found TDC 

 

 

The line on the Har-Bal

seems to line up with this bolt

[AMC86Kid]

And I glued down the timing tape I printed out

 

Now I'm gonna let it dry so it says in place when it spins around 

and I got to go get a timing light 

 

I’ll update you guys after I get the timing gun but for now I can start a new post on the carburetor since I did manage to hook up the choke 

[Ωhm]

Maybe I'm all mixed up with all the photos, but could that be ATDC? Put a directional arrow on the pulley face.

[AMC86Kid]

No it’s set up for BTD the wheel spins clockwise