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Car wants to die under deceleration/braking

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100DashSix

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The current problem I'm facing: if I've been driving along for a few minutes (highway or street speeds) and then have to come to a full stop, I decelerate and then put it in neutral, and the revs just plummet below my normal idle speed and don't stop. I have to tap the accelerator a few times to get it to live. The idle speed after it does this is pretty high, probably 900 to 950.

(The car normally idles pretty roughly below 900..has new plugs, gapped points, I plan on changing the cap, wires, and coil soon, as I don't know how old they are.)
 
Re: Car wants to die under deceleratoin/braking

Sounds like a fuel problem to me. Have you checked the carb linkage? Dashpot oil?
 
Re: Car wants to die under deceleratoin/braking

Ah, converted it to the Weber 32/36 recently, and going through the process of tuning it properly now. That's why I'm fiddling with the carb in the first place.

Hmm, and please elaborate on the fuel problem.
 
Re: Car wants to die under deceleratoin/braking

By fuel I meant carbs, but you've changed to a Weber so I can't help. I've never owned one!
 
Re: Car wants to die under deceleratoin/braking

Ah, I see...a carb problem makes more sense to me than a fuel problem. Hmm. Could the mixture be so rich that the engine is asphyxiating?
 
Re: Car wants to die under deceleratoin/braking

A lovely rust coloration. Oh, you mean the gas out the muffler, not the downpipes? As it warms up it's steam-colored, and as it settles down I don't see any coloration.
 
Re: Car wants to die under deceleratoin/braking

how about a vacuum leak?? maybe the manifold adapters aren't seating properly. I had that problem when I converted a datsun to a weber carb. the carb wasn't seating properly and i had a huge vacuum leak.
 
Re: Car wants to die under deceleratoin/braking

Hm, that's a good point, and one that I've been concerned about. A few times now I sprayed the end of the intake manifold with starting fluid and listened to the revs. If there was a change, it was very slight.. Nothing drastic that I could tell, or maybe nothing at all.

To get the intake to bolt on I did have to file down the back of the mounting tabs to get them even with the exhaust. I was careful about it, and figured the fender washers would make sure it was pressed evenly, even if there were small errors in thickness.
 
Re: Car wants to die under deceleratoin/braking

--100-6; Sounds like you may be runing just a tad bit lean. try runing with just a tad of choke on and see if the problem goes away. If it does just richen her up a bit.--Fwiw---Keoke
 
Re: Car wants to die under deceleratoin/braking

About to go out, Keoke, so I'll give that a shot. A bit surprising if that works, though...if anything, I thought I was running rich.
 
Re: Car wants to die under deceleratoin/braking

Actually, I've thought of another thing. It feels like there are two idles.. When I've been driving for a bit and just coast to a stop, it idles about 600 or 700, but when I push the gas and let it settle itself in, it's back up at 950. The 'fast idle' wouldn't change this, would it? As I understand it , adjusting that would only change behavior when the choke is engaged.

Another thing..the car only runs well when the timing is fully advanced, and even then doesn't idle completely smoothly. Would a worn cam explain these problems?
 
Re: Car wants to die under deceleratoin/braking

One, check that the fuel pressure isn't over 2 lbs. Less is better. Webers do not like excessive fuel pressure. Second, make sure the carb isn't varnished up inside. Third make sure the float setting is right and not to high where the bowl will have to high a fuel level. Better to be slightly low. The color of the exhaust sounds ok. Keep us posted. I've had two Webers and had no problem with either one. I'm not knocking Webers BUT, I like SUs. To most peoples surprise, tuned right, thier almost bullet proof and run trouble free for years. /ubbthreads/images/graemlins/cheers.gif PJ
 
Re: Car wants to die under deceleratoin/braking

First of all check thoroughly for vacuum leaks ,around base of carb and after the car has stopped pull the vacuum hose valve out of the servo -should hear a hiss showing it retains vacuum and the internals are ok if all ok-Sounds like the second choke is sticking open,could be to do with dirt or the bodies tend to distort and don't let the throttle spindles run freely
 
Re: Car wants to die under deceleratoin/braking

I checked for leaks where the manifold meets the car and wasn't able to find anything.. I'll spray the base of the carb and make sure something isn't wrong there.

There's no servo either--if I understand you correctly--the only line that holds vacuum would be the one that runs to the distributer, which is currently plugged off on the carb side.

And Paul, is there an easy way to check fuel pressure? I could buy a fuel pressure tool I suppose, if there is a good possibility that the pressure is the culprit. I don't think it's some electronic aftermarket fuel pump (which, I imagine, could cause higher than normal pressure).

I think it might be something else.. If the timing is off, could it have this problem? Once moving the car runs well, but at low revs it isn't very powerful, and needs much gas to keep it from dying.

I tried as Keoke said, and more choke will prevent it from dying. On the other hand, I also tried increasing the idle speed (as the choke does) w/ the choke off, and this will keep it from dying as well.
 
Re: Car wants to die under deceleratoin/braking

Sounds like a classic vacuum leak. /ubbthreads/images/graemlins/iagree.gif

What jet sizes are you running?

I run 150 fuel & 165 air for the primary
160/160 for the secondary

(Can't believe I'm telling anyone this /ubbthreads/images/graemlins/smirk.gif)

Also....Are you sure your linkage is nice & tight?
 
Re: Car wants to die under deceleratoin/braking

Hmm, I've very throughly sprayed starter fluid where the intake manifold bolts onto the engine and heard no change at all. Is there something I should do to test further? (Like turn idle down to near stalling, and spray then?..hmm..now that I think of this, it sounds like a good idea.)

The jet size, WhatsThatNoise, I'm afraid I don't know. Might be able to find out, but don't have the time now..

And which linkage should I check for tightness? It's just the single carb..only linkages I can think of are the choke and accelerator cable connections.

One good thing that happened this weekend is I got the heat working! Quite a skillful fix, really..tapped on the heater valve with a screwdriver and hammer. In fact, it works so well that I have to turn it down or open the windows!

Alas, I won't be able to work on the car again until next weekend.. Don't feel good about keeping it off at school, due to the area I live in.
 
Re: Car wants to die under deceleratoin/braking

This may not be pertinent but I have been having a bit of problem with idle, also, with my DGV Weber. The PO used a rather weak idle return spring. Coupled with a throttle cable that was a bit sticky, I could set the idle at 700, then when I goosed it it would fall back to maybe 300. Installing a slightly stiffer spring cured the problem.

Guinn
 
Re: Car wants to die under deceleratoin/braking

That is a really good insight, Guinn! When I installed the Weber I put in an extra return spring, one that had been used for years on the car already. At the time I wondered whether it would be stiff enough, but I forgot about that thought until now.

Let's see if I have this right: say that the throttle was held open for a while as I was driving along. Then I let my foot off the pedal but--due to the spring--the throttle assembly link doesn't fully close, leaving one of the throttle discs open further than it would be at idle. The engine has a suddenly relieved load, however, and is spinning independently of the transmission (the wheels no longer helping it turn).. Thus it revs down on its own, but--due to decreased suction--it cannot suck in enough air to pull through the fuel? If the disc were further closed, on the other hand, the open surface area would be less, thus the air faster-moving and the fuel more readily delivered. Is this a valid theory?
 
Re: Car wants to die under deceleratoin/braking

Basically what I meant was that if you take your foot off the throttle at almost any speed and let the engine slow down with the car, it will return to the idle speed allowed by the idle screw setting - unless the throttle cable is binding and the spring just isn't strong enough to pull the throttle back against the idle stop.

Try stepping on the throttle, then releasing it slowly. Now using the mixture screw only, set the idle speed to about 700 or 800. Step on the gas then release the throttle quickly. Your idle should be the same as before. Goose and release several times and see if there is any change in idle speed.

It's worth a try as most other possibilities either take a lot of time or time and money. Keep us posted.

Guinn
 
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