Help Correcting Strange Idle Issue

[kryptik]

Hello everyone,

Lately I have started to experience an interesting idle issue on my newly built zz383. Searching google and the forums turned up nothing...



Basically, the car runs strong, has good power, etc etc. The problem presents itself most notably when I'm getting off the freeway. I'm in 5th gear at ~2000rpm, as soon as I push in the clutch and put the car in neutral (while braking), the engine drops to a 400rpm shudder and wants to die. Only my right foot moving off the brake and tapping the accelerator will return the engine to a normal idle. After that it will behave fine until I have to coast to another stoplight and put the motor in neutral, it will want to do the same. And when I give it a tap of gas it will return to a normal stable 900rpm idle.

Carb is a Quickfuel 680VS, floats are set about halfway up the glass, timing is 10-12 initial 31-33 all in at 3200 rpm (no vac advance).

Any suggestions would be greatly appreciated...

Thanks,
Matt

[Nessumsar]

I don't know if it has anything to do with your issue, but your timing looks a little retarded. Without knowing the engine specifics I would think you can run 14-18 initial with ~36 total in by 3000. I'm running 18* initial, 38 total + vacuum on my 268-cammed 383.

[kryptik]

GMPP Specs for ZZ383 with mild cam (222/230 @.050) and FastBurn Heads are 10 initial and 32 all in @4000 (the @4000 seemed way too conservative so I bumped it to 3200). I believe that the heads require less timing because of their efficient chamber design.

[MrQuick]

Hello everyone,

the engine drops to a 400rpm shudder and wants to die. Only my right foot moving off the brake and tapping the accelerator will return the engine to a normal idle.
Carb is a Quickfuel 680VS, floats are set about halfway up the glass
Any suggestions would be greatly appreciated...

Thanks,
Matt

Try putting your float levels (front and rear) down to the base of the glass. You might be getting a slight rich situation on decel due to high floats.

Where are your transfer slots as relation to throttle blades?


I also agree on the timing setting, you are just going to have to tune it to get your sweet spot. Increase total till you are on the edge of detonation.

[Nessumsar]

It could also be improperly set throttle blade stops. I would check to make sure the throttle blades are not closing. You mentioned it happens when getting off of the freeway, so I would assume you are coasting with high vacuum pulling on the blades; you push the clutch in and the engine is no longer being spun by the weight of the car...?

[kryptik]

1. Alright Mr. Quick I'll try dropping my float levels a little bit.

2. My transfer slots are exposed as little as possible, I made sure to turn the idle speed screw out as far as possible and tune from there...also, the engine does not diesel when hot so I do not think the throttle blades are open too far.

3. Jon, I am not sure what you mean by lower and upper throttle blades. And yes, the the engine is spinning on the car's momentum, then I clutch in. It doesnt make too much sense I would think that the engine would easily return to idle, but it does not.

Thanks in advance for any further assistance,
Matt