Re: IML: 68 No-start when hot

[randalpark@xxxxxxx]

Black smoke means TOO MUCH GAS. I suspect you may be pumping the pedal 
to get it started, or the car may be flooding itself after you turn it 
off. This would be due to a carb malfunction. The floats could be set 
wrong, or some other incorrect adjustment. If you aren't "pumping" it, 
then gas must be continuing to flow from fuel pump pressure after shut 
down. It is not suppose to do this. Check the rebuild.

Paul W.


-----Original Message-----
From: Greg Krueger <box_89krueger@xxxxxxxxxxx>
To: mailing-list@xxxxxxxxxxxxxxxx
Sent: Tue, 11 Sep 2007 2:58 pm
Subject: RE: IML: 68 No-start when hot



       Yes the car is in running condition i have driven it 100 miles 
at a time. I am fairly certain it is in the fuel system not the 
electrical.  Black smoke will blow out of the tail pipe momentarily 
after I get the car finally started.  We have replaced the coil, 
ballast resistor, spark plugs, and wires.  We have checked for spark 
and it is there even when the car will not start.  Also emedietly after 
I have realized the car wont start i check the carb's choke it is 
working as it should.  I am fairly certain this is a boil over problem 
on a rebuilt holly carburetor. any advice. 

From: sosmi@xxxxxxxxxxx
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: Re: IML: 68 No-start when hot
Date: Tue, 11 Sep 2007 19:52:14 +0000


Since there has been a lot of very good input, I would only add, spark, 
and fuel. The two easy tests. It is possible the accelerator pump is 
in-active. The 68 should have a Holley carb, it's possible the cold 
start is good because the choke is closed, and vacuum during cranking 
will draw enough fuel to start, once the engine is hot it may be too 
lean to start. Then when the engine cools enough the choke may close 
enough to start. A simple check to see if the accelerator pump is 
working would be in order. And as others have stated, check for spark, 
however I have the impression the engine will start, only with delay. 
If that's the case,it's most probably a carb/fuel issue. A very low 
fuel pressure, or blocked fuel filter may also be a problem. You also 
didn't say if the car was driveable .Ya'll have a nice day, Dave.

 

-------------- Original message --------------
From: "Geoff Fors" <wb6nvh@xxxxxxxx>

> It sounds like the fuel is boiling and/or vapor-locking in the 
carburetor
> bowls. I presume that once the engine is running, it doesn't stall 
when
> hot, it just won't re-start when hot? That points to a fuel system 
problem.
> I also presume this is running a Carter AFB series carburetor.
>
> Sounds like the heat riser valve is frozen in position, and its 
thermal
> clock spring may be rusted away or missing as well. The spring keeps 
it
> closed until the engine heats up, then it holds it open after that. 
The
> exhaust force will also push it open when the engine is brought above 
idle.
> It's possible to wire the heat riser open, especially if you live in 
a warm
> climate. However, the heat riser assists in rapid warm-up and reduces 
the
> time that excess gasoline enters the combustion chambers during 
warm-up.
> You may have a valve which is rusted closed, even though it appears 
to be
> open from an exterior view. That would certainly account for this 
problem.
> Sometimes the paddle moves on its shaft. The only way to tell is to 
drop
> the exhaust pipe from the manifold and look, rather a pain.
>
> It's not unheard of for the heat riser paddle to come off the shaft 
and fall
> down the pipe, jamming at some point, plugging that side. I haven't 
seen
> this on Imperials but on 1960's Buicks it will totally plug the 
exhaust
> system!
>
> The gasoline sold today tends to vaporize far more quickly than 1968
> gasoline and thus older cars without fuel injection can vapor-lock 
easily.
> This is a perennial subject in other make car clubs at the moment.
>
> The paint always cooks off on the heat r iser path section of the 
intake
> manifold after awhile. That's normal. It shouldn't come off the rest 
of
> the manifold, however!
>
> If we were to take a survey, I think you will find that there are 
quite a
> few of us running stock '67-'68 setups with working heat riser valves 
and
> original carbs and gaskets, and we don't have this hot-start issue. 
Thus I
> think something is wrong. It wouldn't hurt to make sure the choke is 
fully
> pulled-off when the engine is warmed up. The setup worked fine 
originally,
> so if it isn't doing so now, something is not right.
>
> I don't see any point in changing the intake manifold. The heat comes 
from
> the riser tube, not the manifold design. If you really want to 
eliminate
> the heat, use a gasket that blocks the riser tube holes, and you can 
retain
> the stock manifold. And, it wouldn't hurt to use a thicker gasket 
under the
> carb. Bu t, it should run fine as a stock setup, and not get too hot.
>
> Geoff
> Monterey CA
>
>
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