Timing help with the 2.8

[MadMax_636]

Ive set my motor at 10 and 12 degrees BTDC and Im getting a crappy manifold vacuum. So I raised the initial timing to around 13-14 BTDC and Im getting a decent 19-20 inches of vacuum. I tested my total mechanical advance and it seems like a decent 28-30 of total timing.

I have tested it with vacuum advance and it goes way above the timing marks on the balancer.

I am mainly asking what is the safe total timing for this motor as well as what could be causing the low vacuum at 10-12 BTDC. I'm thinking maybe a worn out mounting gaskets that are leaking but I can't seem to find a point where it could be leaking from. I have had a power valve gasket leak a whole bowl of fuel down the neck a few times but idk if that could have anything to do with it. That is it getting into the oil but the oil level looks right. I have fixed the leaking of fuel. The main reason was a power valve that for some reason that kept blowing the gasket and causing it to run very rich so I reverted back to the original one I was using.

Any help would be awesome. I have not test driven the truck yet since I was doing this in the middle of the night due to not being able to sleep.

 

[kimcrwbr1]

Are you setting the air mix needles with the vacuum guage. The 2.8 likes a rich idle air mix start the engine after setting the idle air needles out 3 1/2 turns from lightly seated then set the base timing at exactly 10 degrees. Bring the engine up to temp then set the idle around 750rpm and then one at a time turn the needles in slowly wait about five seconds each 1/4 turn. If the idle speed goes up keep it around 750rpm using idle speed. Your goal is to maintain the highest vacuum pressure at 750rpm. Turn the needles in until vacuum pressure decreases then back out for the highest pressure. Every time you adjust the timing you must redial in the slow needles GL.

 

[kimcrwbr1]

BTW if your running the autolite 2150 just go ahead and get some #42 high speed jets that will bring that mo fo back to life.

 

[MadMax_636]

BTW if your running the autolite 2150 just go ahead and get some #42 high speed jets that will bring that mo fo back to life.

#42 high speed jets? Do you mean put #42 sized jets in the carb? Ive seen this carb have #50 sized jets stock.

 

[MadMax_636]

Are you setting the air mix needles with the vacuum guage. The 2.8 likes a rich idle air mix start the engine after setting the idle air needles out 3 1/2 turns from lightly seated then set the base timing at exactly 10 degrees. Bring the engine up to temp then set the idle around 750rpm and then one at a time turn the needles in slowly wait about five seconds each 1/4 turn. If the idle speed goes up keep it around 750rpm using idle speed. Your goal is to maintain the highest vacuum pressure at 750rpm. Turn the needles in until vacuum pressure decreases then back out for the highest pressure. Every time you adjust the timing you must redial in the slow needles GL.

I adjusted my timing and I thought I had it right. When I took it for a drive when I gave it the beans it started to spark knock/detonate but would go away once I laid off the throttle. I thought it was my trans or clutch since its know to make some noises since it is a truck trans haha. I checked my idle timing it was WAY TOO high. I was sure it was at 10 BTDC.

I'm thinking my stock vacuum can might be sticking high. Since a few times, it wouldn't drop in the vacuum gauge as if the timing was high though it was at idle rpm (No choke/high idle)

The main piece of info I'm looking for in the safe range for MAX total advance for this motor. If I know what other people's safe rage is it would help me which knowing what is TOO much and too little. I can't find anything about that anywhere.


Thanks for the help BTW! I recently bought an adjustable vacuum advance can. I just haven't had the time to install it due to weather being hotter than satan's balls and having to go to work. Haven't really had much time off lately which sucks. I will probably be asking for a week and a half off just to relax and work on my truck.

 

[kimcrwbr1]

#42 high speed jets? Do you mean put #42 sized jets in the carb? Ive seen this carb have #50 sized jets stock.

Yes the #50 high speed jets made mine bog down pulling a mountain pass an belch black smoke. Once I put in the #42 jets it give me plenty of power pulling a hill. I never had a issue with total timing either just disconnect the vacuum advance and set the timing at 10 degrees. If your carb is not ported just connect the distributor to manifold vacuum that will give you about 20 degrees at idle speed. The key is adjust the carb needles after you adjust idle speed stop screw. Start with the 3 1/2 turns out of both idle air needles, set the timing at 10 degrees base and adjust the needles for the highest rpm or vacuum pressure after the engine warms up. Connect the vacuum advance then adjust idle speed only using the idle stop screw. The #42 jets will greatly improve upper end performance. I am going on four years with the autolite platinum plugs and a set of splitfire plug wires. The best two things I did was pull the water pump and blast the rust out of the engine block and replace the valve guide seals. You can replace the seals without pulling the heads it is time consuming but well worth the wear and tear on the plugs.

 

[kimcrwbr1]

With the original feedback carb they had the #50 jets and the feedback solenoid controlled the air bleed into the high speed circuit. The computer would allow more air into the venturi cluster reducing the amount of fuel in the mix. If your still running the feedback carb just pull the feedback solenoid and punch two holes in the diaphram with a needle. That will allow more air into the venturi cluster to vaporize the fuel better.

 

[franklin2]

I disagree with putting the vacuum advance on manifold vacuum. It makes the engine very difficult to tune. The stock vacuum advance advances the timing way too much to set it up like that.

I have never measured the total advance on my engine. I would imagine it's in the 30's like any other engine. Like the other poster mentioned, set it on 10 or 12, and go for a test ride. If it doesn't ping, you can move it up a little bit till it does.

And a note; Most all engines are run around 50 degrees BTDC total advance with the vacuum advance hooked up. You can run engines that high WITH NO LOAD on the engine. It's done for efficiency and fuel mileage. As soon as you press the gas pedal the vacuum drops, so the advance drops back to a more normal timing number so the engine will not detonate.

I mentioned before on the original computer style carb, there is a port on the very front driver's side corner of the carb that has a hard plastic cap on it from the factory. If you take a knife or screwdriver and pry this cap off (it's on there pretty good) I found this port is a ported vacuum port and is where the distributor can be hooked to. You idle needs to be slow enough so this port has no vacuum on it at idle.

 

[Blmpkn]

Size of jets is real dependant on elevation. A #42 might work in Denver but sea level might need the #50