Car tries to die when coming to a stop..ideas?

[jrhone]

Here are the specs on the motor.....

Head Gasket replaced about 2k miles ago...previous rebuild maybe 50k miles ago. New Weber 38/38 1 year ago, new intake manifold, Tii distributor with Pertronix, Piano top pistons. Plugs, cap and rotor and oil changed recently.

So the car seems to be running good and smooth. Lots of power, instant throttle response, no hesitations or flat spots. I have the carb not quite dialed in perfectly, maybe 85% there. I am not sure I even want to spend the time on the weber 38/38 when I plan do switch to DCOE's soon, like maybe next week. So its running good enough...smooth idle, lots of power. The last few days though I have noticed that when I pull to a stop with my foot on the clutch the rpm goes down to about 400 or so....idles rough...then levels off to a smooth idle at about 800 RPM...which is where I set it. Ideas? Happens more when it's cold. It doesnt do it all the time...sometimes not at all...it died once yesterday...which is the first time in 2 years it has stalled on me...hasnt died since, but it has come close...seems like if I slow down with the foot off the clutch until about 5 mph it doesnt do it at all...if I put the clutch in from a higher RPM and come to a stop with the clutch in t does it more frequently....so if I am getting off the freeway from 80...I slow down...step on the brake and stop with the clutch in from 40 mph....it will try and die. Same exit, but I downshift from 4th to 3rd to 2nd and keep it in 2nd with the clutch out all the way to 5 mph the step on the clutch just before I stop, it doesnt do it and idles perfectly at 800 RPM....ideas? Its not a HUGE thing right now...I am just very anal...The ONLY thing done since this started was a carb adjustment. Was running rough...adjusted the carb, and tightened it up...sees it was VERY loose on the manifold and I had a slight leak. One thing I noticed was I adjusted one barrel more than the other so they may not be balanced? Would that cause such an issue?

[c.d.iesel]

....... idle circuit of the carb

clean idle jets and idle mixture screw passageways

[BillyRay]

Check valve between brake booster and engine? Booster may be pulling a vacuum off of the engine when you are on the brake?

Just another possibility. "Z"

[KFunk]

Check valve between brake booster and engine? Booster may be pulling a vacuum off of the engine when you are on the brake?

Just another possibility. "Z"

I'd also check this... losing any brake fluid, or see any smoke behind you when you brake? (leaking brake fluid could get sucked thru booster and into engine)

[rover1]

intermitant vacuum leak or progression circuit problem.

[jrhone]

Check valve between brake booster and engine? Booster may be pulling a vacuum off of the engine when you are on the brake?

Just another possibility. "Z"

NICE! I am also experiencing a change in idle if I pump the brakes...its slight but does point to vacuum issues with brake booster. I'll look at that area. If I am slowing quickly, I am on the brakes harder....

[Guest Anonymous]

My car with a 32/36 Weber was doing the same thing. The situation improved when I went through the hoses between the base of the carb and the distributor.

Make sure there are no leaks and the lines are clear and connected properly.

Then make sure that they are drawing vacuum from the correct port at the base of the carb. I have three ports at the carb. One is manifold vacuum below the throttle plates. Second is valved off by the closing throttle plate. And third is above the throttle plate.

I connected the advance/retard lines at the port above the throttle plate and the problem improved.

My car still need the smog equipment on it and has the mag valves and push/pull dizzy. I forgot to look at which are you have but I think that this stalling at the red light has to do with ignition, specifically vacuum advance at idle. Good Luck.

[jrhone]

Thks for the advice...I have no vacuum coming off the distributor as its a Tii mechanical advance dizzy....

[Guest Anonymous]

I guess the car is a '76 and you live in CA, therefore it must pass smog? I think it is the smogg eqt. that produces that flat spot at idle.

If not that look at your float chamber. It might be that the fuel level isn't controlled properly and main jets choke at the low rpm due to a momentary low fuel condition in the float chamber.

The 38/38 isn't progressive if I remember. Its sequential. Maybe your secondary linkage isn't set correctly to cover the transition from medium rpm into low rpms.

Last thought is that the mechanical advance bottoms out at a higher rps than it should. Just like the dashpot on the solex carbs, you need a bit of enrichment in fuel or timing advance remaining after the throttle plates are closed and you get into idle. Maybe lean out your idle mixture screw and run a bit more throttle 'stop' screw. That would keep the idle rpm from dropping through the floor. Good Luck

[jrhone]

no smog equipment on my car at all...exhaust is straight headers....38/38 isnt a progressive carb, 32/36 is...38/38 is asynchronous so both throats open at the same time all the time. I'll check mixture again...I was fooling around with that before this problem came up...maybe I need to dial it in a bit more....thx!

[Lee]

but does point to vacuum issues with brake booster.

Your carbs aren't properly set-up, hence the low idle when braking. You need to tune idle mixture.