Timing is changing!

80Bu355

Weekend Racer
Oct 30, 2003
99
0
0
Greenville,SC
Had my q-jet rebuilt (big mistake) by a local speed shop. Ever since its been back on the car the idle is going up and down. Started messing with the idle screw on the carb but idle never got right. idle would go so low at times it would cut off. Well i decided to stick my timing light on the sucker to see if I needed to adjust it. While i had the light on it as the idle went up and down...the timing started going up and down as well.

Could the timing going up and down be caused by the carb being screwed up or am I looking at a potential timing chain issue? There is no spit back in the carb while it trying to idle but if you try to give it and gas it wants to bog pretty bad and then it will rev. Any one have any ideas or direction? I appreciate any help that is given. ](*,)
 

t5montecarlo

MalibuRacing Junkie
Oct 21, 2007
4,632
31
48
Lederach, PA
garage-scene.com
several items come to mind:

Timing will change with rpm due to weights in the distributor and or due to vacuum applied to the distributor.

How is the condition of the throttle shaft? Does it wobble around in its bore? If so, it will cause a vacuum leak and will cause the idle to change depending upon how hard the blades close after being opened.

If the bog is while mashing the pedal, it is likely due to the secondaries opening too early: not being controlled by the secondary diaphragm, secondary diaphragm faulty, spring set to loose.

If the bog is while blipping the throttle, there may be something wrong with the accelerator pump circuit.

There may be several other reasons, so please listen to others who reply.
 

80Bu355

Weekend Racer
Thread starter
Oct 30, 2003
99
0
0
Greenville,SC
t5montecarlo said:
several items come to mind:

Timing will change with rpm due to weights in the distributor and or due to vacuum applied to the distributor.

How is the condition of the throttle shaft? Does it wobble around in its bore? If so, it will cause a vacuum leak and will cause the idle to change depending upon how hard the blades close after being opened.

If the bog is while mashing the pedal, it is likely due to the secondaries opening too early: not being controlled by the secondary diaphragm, secondary diaphragm faulty, spring set to loose.

If the bog is while blipping the throttle, there may be something wrong with the accelerator pump circuit.

There may be several other reasons, so please listen to others who reply.


Thanks for the reply. I will check for the wobble on saturday. I am about ready to go and get a new carb but i dont want to do that if there is a chance its not the carb.
 

Doober

Moderator
Jun 2, 2003
14,704
1
38
Catalina, AZ
www.cardomain.com
You also have the advance disconnected when checking with a light, correct? If not, vacuum will cause the idle to change as well as t5 said... beyond that I don't have a lot to offer in the carb dept.
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
Is it a stock engine? If so the distributor should be on "ported" vacuum, not manifold vacuum. That will mess with idle speed, too.

Tommy
 

80Bu355

Weekend Racer
Thread starter
Oct 30, 2003
99
0
0
Greenville,SC
LS6 Tommy said:
Is it a stock engine? If so the distributor should be on "ported" vacuum, not manifold vacuum. That will mess with idle speed, too.

Tommy


No Tommy its a mildly built 355 with a retro roller cam.
 

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