surge at idle

working on my tune. heres the combination i'm working with:
351w 0.060" over
apprx 10:1 comp ratio
world jr no mods
comp XE274H
hedman 88300 headers
pro products rpm knockoff intake
holley 4777 out of the box
toploader 4-spd

got my LM-1 up and running last night and found a surge at idle. it'll idle fine for about 30secs at 14.5:1afr and about 10.5" of vacuum then it goes lean 17:1 vacumm drops to 5-7" for about 5secs then does the whole thing over again. i had a transparent fuel filter right before it goes into the pump and it never filled, it actually had very lttle gas in it with very little visible flow. my thouhts were maybe the filter was causing the air in the line so i took it off and blew compressed air back towards the tank to make sure the pick up wasn't clogged. no change. the fuel pressure gauge at carb reads between 3-4psi. checked the float bowls and both trickled when i removed the screws. today it has to be some sort of fuel distribution problem. its parts store fuel pump. any help would be appreciated.

So many things could be the cause, a vacuum leak is what I'd look for first.

If you have a vacuum canister on your distributor and you are hooked up to it....

Disconnect it, and plug the vacuum port untill you have your engine tuned. It will be impossible to get your engine ruinning correctly while it is hooked up. After the engine is tuned and your happy with the way it is running, a few weeks from now... then you can connect it back up to get better gas mileage.

Secondly, please take some timing readings for us ( with the vacuum can disconnected.)

My guess it your too close to TDC with your initial timing, and your pulling fuel out of your booster venturies in your carb, and this is causing the surge. It often is the first thing I would look for.


If this is happening, it is bacuse your throttle plates are open too much at idle. The only way to close them back up is to set your engine timing to be near 15 - 18 degrees BTDC at idle. Once you have your timing set correctly, then you can tune your carb for best idle vacuum and richness.

Those are your first steps. But lets verify this first, please take a reading of your timing at idle as it is now. Buy a timing light if you don't have one, cause you will never be able to tune your car without one.

Mike

[addsig]

Hey thanks for the commits guys i was begining to give up hope.
At first, I thought it was a vacuum leak, but i think i've pretty much eliminated that using the carb cleaner trick, unless its leaking below the manifold... and i'm sure thats possible.

i've had the vacuum canister disconnected for sometime now.

intial timing is at 16-18 degrees. I took the carb off and checked the throttle blades, they are slightly open. didn't measure although i will. however since then i've swapped on a Proform main body and haven't had much time to tweak it yet.

Friday night is "Torino night", so i'll try to see if the surge is still present adn post update.

mikes66, nice car i had a buddy in high school with a red one like yous. man that car was fast. also, i'm kinda green with these forum details, but how do you paste an image of your car at the end of your posts?

Thanks for the comment. There is still snow ice and salt on the ground here, so it will still be a while till I can start driving again.

So, you did a Proform change over, that is great. There are great main bodies, the casting is done much better then Holleys version.

New Questions. Do you have four corner idle main bodies on your carb? The proform is set up for 4 channel idle. So, if you only have idle adjustments in the front, and none in the back. You will need to change the size of the rear idle airbleeds. They are the outer brass looking airbleeds at the top. The outers should be set at 75 from the factory. With two corner idle, they need to be set yo 46. rears only.

Secondly, the possision of your secondary throttle plates when at idle are very important. The secondary plates should not be fully closed.
There is an adjustment screw on the back throttle plates. If you turn the screw to the fully closed position, then turn the adjustment to start opening the plates. Make that screw 3/4 of a turn from full closed. Range is 1/2 turn to 3/4, but you should use the high end.

Then on the fronts. The front plates should be set so the very bottom of the transfer slot is showing.

It is a long rectangular slot, and when the plates only show the bottom of it when closed, so the slot looks like a little square.

Then put it back on the car and giver a go. It is possible the main body may have been put on the throttle plate assembly backwards. There are two vacuum holes that don't line up if you do. So, maybe worth taking the bottom plate off, and checking everything matches the gasket.

Have fun....

hey, I looked at your car, on your photo page here..... Cool car.
I built one like yours about 20 years ago, but it was a 1:24 scale.....
I drove a 70 version for a long time.

Heres a link explaing it. posting pic...
http://www.fordmuscle.com/forums/the...ned_56608.html

then add it in your signture in your account
Tim[img]/forums/images/smiles/icon_spin.gif[/img]
_________________
ALWAYS THE RED NECK WAY
61 Comet W/200
http://img522.imageshack.us/img522/6415/comet2bj.jpg
64 International 4dr. truck w/466


<font size=-1>[ This Message was edited by: pedal2themetal45 on 3/23/07 3:04am ]</font>

i've got the idle adjustment on the primary metering blocks only. you know, i looked at the secondary adjusting screw and backed it a bit, "eyeballed it", just so a slight opening existed between the plate and the wall of the passage. and there was a commit in the instructions for the proform install about a changing airbleeds, i'll go read them i guess.

i appreciate the info, gonna chisel on it tomorrow. i'll post update.

pedal, plan on taking some more recent pics this weekend, i.e."car pose", then post as signitutre, thanks!!

Since this is a new carb, if nothing works, you might have to take it apart and check the metering blocking for crap. Could have something it them from the factory.

While you have the carb off, take the throttle plate body off of it to make sure it is installed with the correct orientation to the main body. You should be able to re-use that bottom 4 hole gasket if your carfull. If you get a new gasket, make sure it is thin between the holes.