4k Jerking/cutting Off Under Light Throttle

[marlon]

hey guys,

long time reader first time poster.

 

straight to the problem.

my car started off with a miss early last week which has now gotten much worse to the point of it being undriveable.

 

the problem is if i give it any less than 3/4 throttle the engine cuts off every second or so (it sounds similar to a bridgeported rotary engine). if i however give it more that 3/4 throttle then it revs as it should at 3/4 throttle.

 

the 3/4 point to me felt like the opening of the secondarys in the carby so i replaced it- the problem still remains.

 

The engine is stock but has no air filter and a very bad exhaust leak.

 

Please let me know what you think some potential problems could be.

 

thanks in advance, marlon

[philthy30]

hey guys,

long time reader first time poster.

 

straight to the problem.

my car started off with a miss early last week which has now gotten much worse to the point of it being undriveable.

 

the problem is if i give it any less than 3/4 throttle the engine cuts off every second or so (it sounds similar to a bridgeported rotary engine). if i however give it more that 3/4 throttle then it revs as it should at 3/4 throttle.

 

the 3/4 point to me felt like the opening of the secondarys in the carby so i replaced it- the problem still remains.

 

The engine is stock but has no air filter and a very bad exhaust leak.

 

Please let me know what you think some potential problems could be.

 

thanks in advance, marlon

 

hey,

 

Have you checked the timing at all I'm no advanced mechanic but maybe the problem is in the advance in the distributor ? i had a similar problem when i first bought my corolla and the distributor was completely seized up.

[marlon]

na i havnt checked the timing, il play around with that tomoro. anyone else got any ideas of what it could be?

[seabiscuit]

Take your dizzy cap off and you will see that your points will be almost non-existent. This happened to me a little while ago.

 

If not, it could be a broken coil, leads, spark plugs, something.. Points is the number 1 guess though.

[altezzaclub]

Sounds like a general tuneup and service needed before you hunt any further. Check points, good spark, timing, timing advance on throttle.. get that side sorted.

 

Where is the exhaust leak? At the manifold or down the pipe?

 

Could it be an inlet leak as well that is leaning it out?

 

Let us know how you go...

[marlon]

Philthy30 looks like you got it right.

 

i pulled the vacuum hose off the dizzy and the car ran similar to usual (it now has a slight pause from once i apply throttle to when the engine revs)

 

i did a little reaserch and apparently the vacuum advance is mainly responsible from low to mid engine load conditions but mechanical advance is solely used for harder stuff (in my case 3/4 to full throttle). Pretty much explains my problem.

 

so il just replace the dizzy and all should be sweet.

 

thanks for the help guys!, marlon

Edited December 22, 2009 by marlon