here goes i have a 57 f100 with a 292CI and 4 speed manual,the motor ticks over smooth at around 500 rpm,but on acceleration it seems to go lumpy{sorry its an english term]when you take your foot off the throttle at speed it is back to normal.i have checked the usual timing/plugs/leads/points etc,maybe an iffy battery.living in england you cant pop next door to someone who has one for advice

thanks gary

 

Have you looked at your accelerator pump? When you mash down on the throttle there should be a healthy stream of gas dumped into the intake.

 

Is your vacuum advance working? Check to make sure the vacuum line isn't leaking.

 

Yea i would make sure all of your vacume lines, it sounds like thats the prob.
Ridin

 

thanks for your replys.there is a tube facing upwards at the rear of the inlet manifold there was nothing on this so i plugged it [should this go to the rear of the air filter which is currently blocked off] i'll run through the vacuum system and accelerator pump
thanks fellas.
gary

 

dixiefied -

No, no vacuum goes to the air cleaner. If it is a small diameter line, it may be the one that is supposed to connect to the dizzy, although that line usuallu comes from the base of the carb, so that it is reactive to throttle position.

 

thanks randy,the line you are talking from the dizzy to the metering block is in place,also when i turn the dizzy the timing marks do advance and retard,it says it should be 3 BTDC but i have read it is better set between 8 & 10 btdc. i just need to work out where that is as i only appear to have one mark.

 

dixiefried -

My balancer has only one mark also. I bought a Craftsman timing gun. It has a dial on the back that lets you set the advance you want on the gun, then shoot the TDC mark on the balancer. Works really well. My eyes aren't good enough to read those little numbers dancing around down there. But lining a bright white line on the pointer is no sweat.

Setting the static timing at idle (8-10 BTDC) is fine, but it doesn't tell you anything about what the dizzy is doing. I start with the static idle timing, then have a buddy run it up to 2500+ rpm and like to set mine around 36 degrees advance (total) at that rpm.

If there is any problem with the dizzy vacuum advance (diaphragm, springs, etc) it will show up doing it this way.

 

thanks again for your advice,looks like i'm gonna have to upgrade my timing light

 

There are three timing circuits for you to check - the static, the mechanical, and the vacuum. You have set the static about right.

The mechnical is the weights and springs that live under the plate that holds your points. As the engine speeds up the weights fly outward, moving the plate and advancing the timing. You should check that these are working smoothly and not locked in place with rust and dirt.

You don't normally adjust the mechnical, but you can by playing around with the weights. This is called "recurving" the diz. I think there is a technical article on this.

You should, however, verify that it is working by watching the advance (use the timing light) as you speed up the engine. As your engine speeds up you should fire more and more in advance of TDC. As Randy said you should see a total of about 36 degrees in the 2500 to 3500 RPM range.

The vacuum advance should also be checked. Actually, it should be called a vacuum retarder as it is spring loaded to retard the timing when engine vacuum drops.

What happens is that you are running along at a steady state and then shower down on your gas. The accelerator pump in the carb dumps extra gas into the fuel/air mix, making it rich. At the same time the vacuum in the engine drops because the throttle plates are open more, causing the vacuum advance to retard the timing which makes this rich mix burn better. The increased gas makes your engine accelerate, and you back off the throttle - so vacuum increases, causing the vacuum advance to overcome the spring pressure and advance the timing to the normal setting.

If it does not work correctly your engine stumbles when you mash on the gas.

 

You should set the base timing with the vaccuum line removed from the advance mechanism and temp plugged. after setting, reattach the hose and the timing should jump up several degrees. As you rev up the engine it should advance more until it reaches 30 degrees or so.

 

hey ***** b thanks for the info

 

thanks AXracer, i shall be checking all advice given.

 

Just a thought better check plugs& wires + dist cap & points. Could be high resistance in plug wires or a carboned up plug , or points went shut, or weak coil
or bad condensor. Just some thoughts -- Good Luck Hotwrench

 

thanks for your thoughts,i have checked the plugs,wires,cap etc changed the coil but will check on the condenser.