Re: IML: 68 No-start when hot

[<boboyen@xxxxxxxxxxx>]

I would pull the float level plug on the side of each bowl (front & back), if fuel runs out the 
float is too high. It can be adjusted up or down with the screw on top of each bowl (after 
loosening the lock nut). If it's a rebuilt (scary) Holley the power valve should be OK as you 
didn't mention any backfiring & it's not a motocraft carb. Remember to use rags & be very careful 
because this process will cause fuel spillage & should be done by a trained professional.
Good Luck!


On Tue, 11 Sep 2007 23:51:03 +0000
 sosmi@xxxxxxxxxxx wrote:
> It is possible the floats are set wrong, it's also possible the power-valve (primary side) may 
> be leaking, either the wrong gasket, damaged valve(from a major back fire) or loose.To check the 
> floats, you could  shut the engine off, then look in the carb, if the floats are the issue, then 
> you will see fuel dripping from the venturi boosters.If the power valve is the problem, you won't 
> see the fuel leaking in, until you open the primary throttle valve. Since you have black smoke 
> after start up, then the carb is suspect. Ya'll have a nice day, Dave.
>
> -------------- Original message -------------- 
> From: Greg Krueger <box_89krueger@xxxxxxxxxxx> 
>
>       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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