Qjet issue

[trac209]

I have a 305 with qjet that's giving me fits and I'm fresh out of ideas. So when the engine is cold it fires right up. The fast idle,choke and choke pull off work fine. Engine will kick off fast idle after couple min(it's -30c) here right now so it needs a few min warmup. Issue is it will die the second you try to drive away in gear if it's not warmed up longer than I feel it should need. If the engine is cold if you try to rev it up it will have a flat spot off idle circut and die out. And if you rev it up to around 1200 or so and hit throttle briskly it sounds like it just sucking air.

Carb has a fairly fresh rebuild but this is the first winter with it on,accelerator pump was changed and I have no idea why cold it would drive like this but warmed up it's ok.. It does have a delay when floored from a slow speed even warmed up but pulls hard once it kicks in. Engine is stock only egr is blocked off idk if that would make it act like that though. Thx for any insight .

[geezer#99]

Engine is stock!
Do you mean everything right down to factory exhaust, heat riser valve working, hot air to air cleaner from exhaust manifold kinda stock or have you modified any of that?

[trac209]

Originally Posted by geezer#99

Engine is stock!
Do you mean everything right down to factory exhaust, heat riser valve working, hot air to air cleaner from exhaust manifold kinda stock or have you modified any of that?

Yes everything is in place and functioning

[geezer#99]

Try richening up your choke!
Turn the black cap ccw.

[trac209]

Originally Posted by geezer#99

Try richening up your choke!
Turn the black cap ccw.

Choke is operating as it should and is fully open after a few min running. Problem has nothing to do with choke setting. My initial post explains the issue and all the basics have been addressed.

[geezer#99]

What's your timing set at?

[68gmsee]

Originally Posted by trac209

Choke is operating as it should and is fully open after a few min running. Problem has nothing to do with choke setting. My initial post explains the issue and all the basics have been addressed.

Won't hurt to try it anyway. I have a manual choke on mine and when it's cold it hesitates until I choke it more.

Minus 22º c sounds cold. Is that pretty normal up there?

[trac209]

Originally Posted by 68gmsee

Won't hurt to try it anyway. I have a manual choke on mine and when it's cold it hesitates until I choke it more.

Minus 22º c sounds cold. Is that pretty normal up there?

Yes that's normal lol. The issue is not the length of time choke is on for IMHO besides it's the choke pull off you would adjust in that case. With the choke spring set too tight it would take far too long for the fast idle to kick down as they are inter connected. I'm not a newb with qjet or carbs in general Ive just never seen an engine behave this way until it reaches a specific operating temp before.
Once engine is warm it's awesome so it's not the chokes fault. Car starts excellent in very cold temps it's the long warmup time to be able to drive away that's the issue.

[geezer#99]

Originally Posted by trac209

Car starts excellent in very cold temps it's the long warmup time to be able to drive away that's the issue.

It's simple then! Your heat riser's not closing or the passage under the intake is plugged causing the fuel to puddle in the intake until the intake gets warm enough to keep the incoming fuel vapourized.

[68gmsee]

Originally Posted by trac209

.... Car starts excellent in very cold temps it's the long warmup time to be able to drive away that's the issue.

Yep. That's the way mine is. I can drive away once it warms up but if I do it while cold it hesitates -unless I choke it more.

If it were mine, I would take the carb apart and double check everything including running wires through all the little openings (I use a cut guitar string), spray cleaning and air blowing all the small passages. Maybe another kit to insure the one in it is not defective.

[trac209]

Originally Posted by geezer#99

It's simple then! Your heat riser's not closing or the passage under the intake is plugged causing the fuel to puddle in the intake until the intake gets warm enough to keep the incoming fuel vapourized.

I thought of that too and it's seems to be closing via vacuum when cold and opens with the air cleaner door when warmed up. I would guess it's possible the flap in the riser is rusted away? I would guess I would need to take it apart to see for sure. I suppose I could disconnect it to see if the problem is no worse and it would give me an idea. Thx

[geezer#99]

I'd be more inclined to suspect a plugged intake passage. When you start it up cold and just before you'd normally kick it down, put your finger on the intake where the crossover is closest to the plenum and test for heat. If all is working right with the heat riser you should feel heat right away. No heat tells you it's plugged or the heat riser valve is not working.

[trac209]

Originally Posted by geezer#99

I'd be more inclined to suspect a plugged intake passage. When you start it up cold and just before you'd normally kick it down, put your finger on the intake where the crossover is closest to the plenum and test for heat. If all is working right with the heat riser you should feel heat right away. No heat tells you it's plugged or the heat riser valve is not working.

Ok thanks I'll give that a shot

[trac209]

Well I checked there and it was warm but not as warm as I'd think so it's a possibility that's the issue.

[geezer#99]

If everything is working like new you should at least feel some heat right away. At least in the first minute.
Does the flapper close completely on the air cleaner snout?

[trac209]

Originally Posted by geezer#99

If everything is working like new you should at least feel some heat right away. At least in the first minute.
Does the flapper close completely on the air cleaner snout?

Yes

[geezer#99]

If you suspect the intake passage is plugged or the heat riser is gone you could set the flapper on the snout to stay closed all the time. Warm air fulltime won't hurt.
If the flapper is opening at 30 below the sensor on the air cleaner might be hooped.

[Wrenchbender Ret]

Make sure the accel pump is working OK. Try raiseing the float level a little. If it has adjustable metering rod, raise the rods a little from the low position.

[Gumby]

WOW at -30C you should have problems hehehhe



at single digits temps in F mine gets to be a picky girl that wants more heat up time a good 5mins+ and lots of rev's to clear her up to go. [ was 9F today, thermo stuck, coolant all over, fun]