Q-jet hard to start when hot

[terror396]

hi all

when cold it will start with only one try
but if it is hot it wont start unless I pump the pedal several times

it is a 1985 K20 with stock 350
the chock in the Q-jet wasn't functioning properly so i adjusted it to be open (vertical) all the time and blocked the vacuum hose going to it

also last time when I went to the dunes the idle started to be rough

what should I look after

and I have a brand new EDL-1407 750cfm with off-road needle (not installed yet)
is it better to use the edelbrock than fixing the Q-jet

thanks

 

[dyeager535]

Personally I say use the Q-jet.

Obviously if it just started having idle problems, it could be a few things, but check out the basics first. Plugs, wires, cap/rotor. Make sure all of them are in perfect shape.

If you've got the right carb for the engine, make the choke work properly. They aren't that difficult to figure out.

 

[terror396]

it has idle problems only on rough terrain ( driving fast in the dunes )
but in the street it is very smooth


i forgot to say the when it was rebuilt the well plugs weren't sealed with epoxy

 

[vortec]

If you've got the right carb for the engine, make the choke work properly. They aren't that difficult to figure out.

go low-tech. keep the q-jet and do a manual choke conversion. the HELP! kit for it is cheap and simple and pretty much every part store has it. i prefer relying on my right hand instead of parts the general slapped on there 25 years ago.

it has idle problems only on rough terrain ( driving fast in the dunes )
but in the street it is very smooth

if you're going fast enough to bounce the float around at idle, it sounds like the idle is way too high.

 

[rcamacho]

Check for vapor lock in the fuel line. Also, if the carb is excessively hot, you might try a heat insulating spacer 1/2" - I prefer phenolic vs the thick gaskets as the latter contribute to warped base plates.

 

[dyeager535]

Probably not ignition related then if it's only when you've been bouncing around and then goes back to "normal" on flat ground.

Seems a bit suspicious that it starts that easy with no choke. Your idle mix and/or idle speed are two that come to mind as being an issue if that's the case. From what I've seen, no choke+cold motor=runs horrible at low RPM's.

 

[terror396]

Check for vapor lock in the fuel line. Also, if the carb is excessively hot, you might try a heat insulating spacer 1/2" - I prefer phenolic vs the thick gaskets as the latter contribute to warped base plates.

how to check for vapor lock ? ( I have the stock metal fuel line )
and should I stick to the specifications in the rebuilt kit ( float level .. etc )
or are there better adjustments for off-road use ?

 

[terror396]

Probably not ignition related then if it's only when you've been bouncing around and then goes back to "normal" on flat ground.

Seems a bit suspicious that it starts that easy with no choke. Your idle mix and/or idle speed are two that come to mind as being an issue if that's the case. From what I've seen, no choke+cold motor=runs horrible at low RPM's.

I don't think it is ignition related too
even though when it is hot and i don't pump the pedal the starter will hardly turn it and it won't start without multiple tries

but if I pump the pedal or floor it while cranking, it will start immediately but after giving a very black smoke

 

[blazin_blazer]

that sounds like timing to me.......can't explain the rough ground versus smooth ground idleling different tho... i had an engine that done the same thing...turned out timing was advanced to much...but it also had 11.25:1 comp ratio, so its kinda like comparing apples to oranges.

do you have any preignition symptoms? ping while under load? if not, it very well maybe sloshing fuel out of the vent tube, into carb, since only doing it while driving rough....this could be why it does it when warm. b/c when it is cold, air is more dense
and would burn the sloshed fuel better. try using some fuel line and extend the carb bowl vent, see if it helps. if so, get real fuel bowl extensions.


some fair links:


http://www.hotrodders.com/kb/carburetor-articles


http://wiki.answers.com/Q/FAQ/491