I figured out today that my bog is caused by my timing getting retarted 10 degrees off idle to around 2500 I think. I noticed that when I wring it out some that the timing drops form 18* with the vacuum advance on to 4* when I rev it WOT. I assume it is taking until 2500 for the timing to catch up with the RPMs. how do I keep the timing up? could I be rich or lean?

Make sure when you set your timing you do it with the vac advance unplugged, and cap off the vacuum line.

The timing dropping off when you gas it is normal - if you have the vacuum advance hooked up.

I've been checking everything plugged, unplugged, backwards, and forwards trying to find out why I'm bogging so bad. I've replaced the ignition wire from the fuse block and before the fuse block with 18 guage, carb baseplate gasket, three jet sizes, ALL the secondary springs, with and without air filter, raising and lowering the floats, advancing and retarding the initial timing, total timing, and centrifugal timing. idle mix, idle speed. A,m I missing something? could my carb not be matched to my combo since it's intended for stock replacement and a cam with less than 220* duation @.050? I have 224* @ .050. the only thing left is if it is flooding or starving right? :confused: :confused:

I have no idea what your engine is, but you should probably always want more than 4 deg timing. If your timing drops off from 18 to 4 when you gas it, I think you'd be best off by trying to retime it.

Pull off the vac advance hose and plug it. I don't know your engine, but time it to 8-12 deg or so at idle (your engine may even like more than that). Then plug in the vac advance again and reset the idle on the carb. If you don't hear it pinging at all under load at higher rpms you're probably ok at this point. You could try an advance timing light, or timing tape to further tune the timing at rpm, but not totally necessary.

By setting the base timing at idle at say 10 deg, you are setting the lowest point that your timing will ever be at. It will never go lower, only higher as rpms rise, or vacuum advance kicks in. So basically, if your timing light shows 4 deg when you gas it, your base timing must be at 4 deg or lower. Try bumping it up to 10 or so and see how it goes.

Worry about the carb later once the timing is pretty close.

Chris

Your vacuum advance was connected when you did this check right?

The vacuum advance is doing it's job then.
When you go to WOT the vacuum drops and the vacuum advance drops out as it should.

You need more initial advance
"with the vacuum advance Disconnected".
16 Degrees would be a good figure to shoot for.

Setting the total advance is the correct way to time a performance engine.Do the following.

Get a dial back timing light or borrow one from a friend.Disconnect the vacuum advance and time the engine at a high enough rpm where the distributor stops adding advance.This is known as total timing because the distributor is not capeable of adding more advance.
This rpm point will probably be around 3000-4000rpm.Set the total advance at 36 degrees.

Leave the vacuum advance disconnected and let it idle back down.Note how much advance is showing.

If it is something like 8-10 degrees you need to modify the distributor so that it has less mechanical advance.Mechanical advance can not be changed with springs.Springs only make the advance come in at a higher or lower rpm.

P.S-
Your lack of gears and higher stall is probably causing some of the bog.On a small block that cam should be used with a gear of "at least 3.08" with a 26 tall tire.I am assuming that your tires are taller, probably something like 27-28inches.This reduces the gear that you actualy have.For instence it would make a 3.73 seem more like a 3.50.
This means that you will require at least a gear of 3.50.
An 11inch converter would also help.

I think I will redo the rear end this summer when I get more money. my tires are 26" tall with my 2.73.
Bulb, my combo is in my sig

Do you have the vacuume advance hooked to port or manifold? If it is hooked to manifold you will see a drop when the throttle is opened, where as ported source the vacuume will rise on initial throttle tip in. GM on most cars uses ported vacuume for the vacuume advance.

manifold.

Are you using a carb spacer? I had a bog problem with my truck a while back when I tried to change over to a Holley DP. Turns out I put an open spacer for a single plane on it and it needed a 4 hole spacer. According to the guy at the speed shop the change from the open plenum spacer to the dual plane manifold cause a low pressure and and my bog. Switched it out and my bog went away. Not sure if it helps or not but thats one fix I had for a bog.

no spacer either.

I think you should try hooking the vacuume advance to the port vacuume source, after you have set the timing to 8° to 10° BTDC. The port source on the Q-jet is in the front of the carb on the left side about half way up the main body, it is the place Chevy put the hose to the vacuume advance. If your using a Holley carb, the port vacuume is the nipple that is in the side of the primary metering block. I don't remember the port source for Edelbrock/Carter carb but it is easily check with a vacuume gauge.

get rid of the vacume advance for now, don't factor the vacume advance in at all. Tune your initial and mechanical curve with different weights, cams and springs. when she pulls hard from low to high rpm you'll know you've got the right combination----------then connect the vacume advance and tune that in to your combination. Some combinations that are running on the edge of detonation won't like vacume advance and will live happier without it. Tune one thing at a time instead of jumping around. This takes awhile. Powervalve, squrter size, jetsize, pumpcam selection are also very important when tuning for acceleration--I'm sure a good air/fuel mixture guage would be handy for this but I've never had the opportunity to use one. Good luck. graemlins/beers.gif Bob

Have you re-checked the timing or adjusted it yet?

One thing I didn't notice in your reply was pump cams? Have you tried some different ones? Something I do to check to see if it needs more fuel is run the idle real rich. If the bog gets better then you need more pump cam or sooner, bigger squitter. Worse then less fuel.

For timming, it seems most SBC like around 36deg. I don't set timming at idle. Unhook vacum advance, plug the hose. Spin the motor up untill the mechanical advance is all out, and set it at 36. On my car I have 36deg by 3000 (I used some lighter advance springs) that puts initial at 22deg on my motor.

Steve

I have rechecked my timing and it seems to like 12* initial the best (without the vacuum).I have the stock pump cam that is pink I believe. I tried the mixture screws that Baddbob71 and steve recommended and it seemed like it needs a more delayed cam. I guess my next paycheck will go to a better mechanical advance set, vacuum guage, and pump cams :D .Thanks for the ideas guys I'll fill you in on what happens. graemlins/beers.gif

Originally posted by wanarace:
For timming, it seems most SBC like around 36deg. I don't set timming at idle. Unhook vacum advance, plug the hose. Spin the motor up untill the mechanical advance is all out, and set it at 36. On my car I have 36deg by 3000 (I used some lighter advance springs) that puts initial at 22deg on my motor.

Steve Gee, seems like I heard something similar ;)

Ever thought about trying it?

I guess I need to add timing tape to my list. I promise I read everything several times graemlins/thumbsup.gif .

Haha, sorry missed your post thrasher. But you are one smart man. :D

Just a thought. Do you by any chance have a Summit HEI that's about 6 months old? We put two of them in my buddy's Elco because the first one was retarding the timing instaed of advancing it (without Vac Adv hooked up). After we called Summit the second time, they said they discovered they had a problem with that lot of distributors and sent us an Accel unit - It worked fine. Just throwing that out there in case you are seeing the same thing because you cant fix it.

Troy.

Originally posted by wanarace:
Haha, sorry missed your post thrasher. But you are one smart man. :D I just wanted to emphasize that this was mentioned twice... with no reply.


P.S
I not that smart.Just love to mess with shiznit.

Bit of a perfectionist too smile.gif and :(