Avs2 650 tuning on a 340

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Fez,
Post #14. 800 rpm idle with 25* initial. Was the 800 rpm an increase over what you had? The idea of the test was never to leave the timing 'there', merely to test what the engine liked for idle. For idle & off idle tuning, you will much more success by leaving the AF & vac gauge back on the shelf...
 
In my opinion a nice street 340 with a DP intake loves 750 CFM , SP keep smaller like 650. Anyway you have to live with what you have. Leaning out ( to safe gas) means you need more advance to compensate, but you dont have the VA.
A nice fast MA and a richer fuel curve gives you almost the same fuel consumption, you need less throttle for the same amount of power!
Follow the good advices from the other guys.
 
The 800 gave me more wide open power but the 650 had better driveabilty and throttle response.

So it sounds like the Rev-O-Nator is adding advance as rpms rise to kind of mimic the VA or to compensate for latency . I think it would help if you plotted your timing in 200 rpm increments up to 3800 or whenever it stops advancing . Then we can figure out which VA can you have and start tweeking that.
The reason timing is important to A/F is that if your spark is late there will be unburned fuel (or still burning) passing the O2 sensor making you think the jetting is rich .
 
fez440 said:
Hi. I am looking for help with my edelbrock avs2 650 carb. The engine is a 340 4 speed mildly modified. Air gap intake,aluminum heads, headers, comp cam 231 duration. 480 lift. Vacuum at idle is 10" cruise 15".

Timing is set at 18 initial and 32 total. I have tried different timing spots From 20 intial to 35 total with no change. No vacuum advance as per my recommendations from ignition box company which is a rev n nator with a firecore distributor and their coil. Has summit plug wires and autolite plugs 3924 .035 gap

I have been through the carb and Manuals and believe i understand this carb well even though I'm new to carbs.
I have a o2 gauge with a vacuum gauge next to it which I can watch will driving.

The issue I have is from when i 1st installed this carb it run very rich. Cruise was 10.8:1 wot about 11:1. I have jetted it down much more then their calibration carts shows. Right now I have 98 jet with 73 37 rod and 95 jet in secondary. Orange spring. Middle pump shot.
Still cruises at about 12.8:1 wot about 12.5 which is good. Idle screws react well. Idle is about 13.8.
Now if I try and lean out cruise any more say to around 13.5-14 I get a very bad lean spot while under load. I still get get this lean spot now but it is not as bad. While accelerating with 15" vacuum down to say 5" (before power mode kicks in) my air fuel will start to lean out almost 3 points. I'll go from 12.8 to 15.0 ( once the power mode kicks in air fuel goes to about 13.5) if I lean out cruise to around 13.5 then when accelerating it goes to almost 17:1.
Engine will hesitate above 15:1.

I have tried to use to stronger spring but with the low idle vacuum it doesnt work right. Will bounce even if I turn up the idle more right now it's at 800rpm. I can make the pink work ok at 1000rpm but still will bounce if leaving from a idle as vacuum will drop a bit.

I have tested for vacuum leaks to the best of my knowledge I can't find any.
Have a psi gauge set to 5.5. Floats set to factory specs 7/16" and 1 "

Is this normal for it to lean out this much while under load? Any way to solve this?

Hoping someone has some ideas that way help me out as I have tried all I can think of.
I am new to carbs and older car but I feel like I know how this carb works but cant seem to figure out this issue. I have had no luck trying to find help online so I thought I would try here
Thanks for your time
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I see you are running 3924 Autolite. I would try a heat range or two hotter and see what happens. That spanked me a few years back.
 
Bewy said:
Fez,
Post #14. 800 rpm idle with 25* initial. Was the 800 rpm an increase over what you had? The idea of the test was never to leave the timing 'there', merely to test what the engine liked for idle. For idle & off idle tuning, you will much more success by leaving the AF & vac gauge back on the shelf...
Click to expand...
Yes it was. Was at 750 before but rpm will keep increasing if I keep adding more timing
 
Last edited:
mbaird said:
The 800 gave me more wide open power but the 650 had better driveabilty and throttle response.

So it sounds like the Rev-O-Nator is adding advance as rpms rise to kind of mimic the VA or to compensate for latency . I think it would help if you plotted your timing in 200 rpm increments up to 3800 or whenever it stops advancing . Then we can figure out which VA can you have and start tweeking that.
The reason timing is important to A/F is that if your spark is late there will be unburned fuel (or still burning) passing the O2 sensor making you think the jetting is rich .
Click to expand...
I'll look into doing this. Thanks for the idea
 
Fez,
The idle rpm increasing with more timing is telling YOU that the engines likes the added timing.
 
Have you verified TDC with a piston stop to make SURE your timing marks are correct?
 
Bewy said:
Fez,
The idle rpm increasing with more timing is telling YOU that the engines likes the added timing.
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Yes but the starter doesnt seem to like it. Maybe I'm wrong but at a lower initial timing it starts better when warm. Had it at 22 to 24 initial and the starter would kick back when warm. So I put it back to 18. Even with the added initial timing it made no change to my air fuel while cruising. Total was at 35
 
fez440 said:
Yes
Plus engine was build but a professional shop and he marked the balancer for me
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Ok, so then YOU verified tdc YOURSELF? I don't care WHO assembled it. What I'm getting at is if it's not been verified and seen by then end user who is checking timing.....that's YOU, you will not be 100% sure where your timing marks are.

I make that point, because it seems to want a LOT of initial timing and you want to be sure that's correct. Sometimes that's the case, though. I've seen a few like 25* initial. It's rare.

Then of course, there are those who lock timing out to "whatever" the total is. 32, 34 , 36....."whatever"......but I don't think that's what we're talkin about here.
 
RustyRatRod said:
Ok, so then YOU verified tdc YOURSELF? I don't care WHO assembled it. What I'm getting at is if it's not been verified and seen by then end user who is checking timing.....that's YOU, you will not be 100% sure where your timing marks are.

I make that point, because it seems to want a LOT of initial timing and you want to be sure that's correct. Sometimes that's the case, though. I've seen a few like 25* initial. It's rare.

Then of course, there are those who lock timing out to "whatever" the total is. 32, 34 , 36....."whatever"......but I don't think that's what we're talkin about here.
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Ok thanks for the idea. I will try verifying tdc again just to be sure.
 
fez440 said:
Ok thanks for the idea. I will try verifying tdc again just to be sure.
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If it was mine, I would.....and remark if necessary. Because if TDC is off, so is everything else.

Do you have any idea what static compression is? I'm guessing dynamic is LOW since it wants so much initial timing.
 
RustyRatRod said:
If it was mine, I would.....and remark if necessary. Because if TDC is off, so is everything else.

Do you have any idea what static compression is? I'm guessing dynamic is LOW since it wants so much initial timing.
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Compression is 10.5 : 1
Cylinder psi range from 158 to 162
 
at 10.5 : 1 your engine shouldn't need that much initial. 15 max maybe to run nice.
Who would recommend not to run vacuum advance?
Long duration cams can be difficult.
 
I checked timing. Hopfully you can help me out if this sounds correct. Bumped engine till it pushed my finger off #1 spark plug hole. Moved balance to line up Mark's ( groove in blancer lined up to 0 on tab. Rotor is pointing just past #1 plug. Less than half way to #8
I don't have a piston stop to try it that way.
 
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fez440 said:
I checked timing. Hopfully you can help me out if this sounds correct. Bumped engine till it pushed my finger off #1 spark plug hole. Moved balance to line up Mark's ( groove in blancer lined up to 0 on tab. Rotor is pointing just past #1 plug. Less than half way to #8
I don't have a piston stop to try it that way.
Click to expand...

Sounds about right

The problem with giving it as much initial as it wants it your throttle plates end up closing too much which can mess with driveability. Which is why you might want to hook the VA to a ported source... that will artificially advance timing while idling but drop back once you crack the throttle .
 
fez440 said:
I checked timing. Hopfully you can help me out if this sounds correct. Bumped engine till it pushed my finger off #1 spark plug hole. Moved balance to line up Mark's ( groove in blancer lined up to 0 on tab. Rotor is pointing just past #1 plug. Less than half way to #8
I don't have a piston stop to try it that way.
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That didn’t tell you anything. You need a positive stop to verify TDC.

And as I mentioned earlier it appears you are beholden to a certain A/F number. And I would say again unhook or ignore that gauge and make it run correctly and then hook up the O2 sensor again. That gauge can and will lie to you.
 
Do you recommend Vacuum Advance on a street car ? Yes, the engine will be more responsive and run cleaner.
 
448Scamp said:
That didn’t tell you anything. You need a positive stop to verify TDC.

And as I mentioned earlier it appears you are beholden to a certain A/F number. And I would say again unhook or ignore that gauge and make it run correctly and then hook up the O2 sensor again. That gauge can and will lie to you.
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Sorry no disrespect but I dont agree. I am not soley looking at the gauge but using it as another reference tool. When the engine hesitates under slight load and the gauge shows a lean condition I feel like that is only helping determine the issue.
 
I know that in a perfect world A/F should be xx.x but just fatten the thing up so it doesn't hesitate.
 
fez440 said:
Sorry no disrespect but I dont agree. I am not soley looking at the gauge but using it as another reference tool. When the engine hesitates under slight load and the gauge shows a lean condition I feel like that is only helping determine the issue.
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I never did get my gauge to read as lean as I was hoping but my eyes stopped stinging from excess fumes.

fez440 said:
I have tried hooking up the vaccum advance with 0 changes to the issue I am having
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The VA wont fix the stumble but it will help your car run better overall once tuned properly. Your stumble is a mix of springs / transfer slot exposure / initial timing .

Try removing your carb and setting the transfer slot to a square window then set your intial timing to where the idle rpm is where you want (750ish) ... then recurve the dizzy so that mechanical advance comes in like you want. Then start changinging jets and rods...
Oh yeah ... make sure you are using the correct jetting chart. I downloadsd the wrong one once and chased my tail for a day ...lol
 
Where is A/J when we need him ?

Really ... has anyone heard from A/J lately ?
 
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