My vehicle while at idle will "hiccup" for about a second and engine shakes. When I drive from a complete stop, the engine will hesitate (usually three times) while my foot is on the pedal. Also, there is a rattling sound coming from under the hood as I press on the pedal but stops once I ease off the pedal . (I suspect valve train noise.) I built this engine 5 years ago and only put 3300 miles on it since it was built. These issues started last july. The vehicle idled fine but the rattling sound upon taking off from a complete stop was always there. (I installed 1.6 roller tip rockers and wonder if that is the source of my rattling) Then one evening, it began to idle poorly and seemed to lose power. I checked for vacuum leaks and none were present.

Since then I have changed spark plugs, replaced the cap and rotor on the dizzy. I put a vacuum gauge on the manifold fitting to see what was going on and the gauge needle flutters back and forth between 10 and 15 inches of vacuum and when I rev the engine it moves up to 20" and flutters between 19-20 inches This morning I adjusted the valves, changed the oil and removed the spark plugs. Did not install the new ones yet. After I pulled them I noticed that plug #8 looks like it had not been firing. The insulator core still looked white and the electrode was still shiny with a little soot on it. Plug #3 was fouled, the others looked normal.

Since I have more than one problem, I am seeking advice on where to begin. The valve train noise if it has not gone away, could it be that the cam has wiped lobes. As for the vacuum gauge readings, could I have burnt or leaking valves. Should I do a compression /valve leak down test? I'm a bit frustrated and I want to get this thing running as it should. I hope I have not lost anyone with my gibberish. Thanks for all advice in advance.

 

Yes run a compression test. Needless to say, make sure all of the plugs ar out and the throttle is open, and make sure the engine is warm.

You may want to check the timing and possibly pull the distributor and check the gear to see if it is worn or almost wiped out ( not knowing what type of cam you have and the required bronze distributor gear for some cams) Just thinking and writing...

Keep me (us) posted.
"DUB"

 

Today I adjusted the valves and put a vacuum gauge to the manifold fitting at the rear of the manifold. I now have a good, steady needle with 21" of vacuum and the needle drops on the vac gauge drops to zero and returns to 21" when I release the throttle. However the vehicle still stumbles (three times) when I put my foot on the pedal to move from a complete stop.

 

The rattling is probably pinging from too much timing advance either from initial timing, or vacuum advance. Temporarily disconnect the vac advance tube and plug it. Try driving it. If no more rattle, then you need to retard the initial timing - you don't mention what it is set at, or reduce the vac advance, if your distributor is adjustable. Also, check for burned plug wires or boots which are arcing and causing a miss in your ignition. This is common if you have headers. This might help part of your problem.

 

Yes I have headers. I will have to check the timing to see exactly where it is set at. Thanx for the suggestion about plugging the advance tube. I did not think about that. If the rattle disappears with the vacuum advance tube plugged (hope so), I will be very lucky I did not burn a hole in any of the pistons. I will set the timing at factory specs for now. However, since I now have 64cc heads on the engine I may have to retard the initial from it's factory setting. Did not think about plugging the vacuum advance unit tube. If this helps,I will get a dizzy re curve kit and set timing to my engine's potential. My dizzy is not adjustable. I checked for burned wires and boots. The plug wire on the #6 was burned. I replaced the wire with a new wire (from the universal wire kit I had purchased) the boots on either end of the wire were not burned. As for the arcing, I will do that at night so I can really see any arcing clearly. I'm glad someone else replied, after 62+ views I no longer feel ignored Will let all know what is happening.