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Hot starts ?!

JonathanT

Not normal for Norfolk
Messages
1,317
Location
Wymondham Norfolk
Hello everyone!
not been on here for a while and now here I am with a problem ! (Typical)

Out at the weekend in Womble ( GTL)
Hot day and Womble refused to start when already hot.
Now I have had this problem before but it’s always gone away so I have not bothered
However this time was more problematic and I was in a ‘breakdown’ state for an hour or so.
Closer examination of the carb saw fuel dripping on the manifold .
Took the air box off and looked down into the throat of the Zenith 28if

I could see fuel pouring in and onto the butterfly- quite alarming and all this with the engine and ignition off.
I’m thinking how could this be ? Has the needle valve got stuck open ??

further investigation on the subject of Hot Starts reveals modern fuel is very prone to evaporation and boiling
And fuel lines in older cars would benefit from

1/ routing via a cooler location to the carb

2/ fitting an electric pump with an inertia shut off switch and non return valve



So could it be the fuel passing over the top of the engine and sitting in the filter is boiling on entry to the carb reservoir and causing the needle valve to jiggle and allow more fuel into the carb reservoir and then overflow into the engine

I am thinking the suggestions 1/ and 2/ are good and may take this route but welcoming any thoughts

will post pictures shortly

thanks guys !
 

722stu

Enthusiast
Messages
24
Hot days have left me similarly stranded on occasion, but usually no more than ten minutes and always when the engine has been running in slow moving traffic. This usually involves: engine off, opening the bonnet, waiting 10 minutes and then a restart.

I'm thinking this is likely a very hot carb soaking heat from the exhaust manifolds just a few inches away.

On the one hand I'm thinking, surely Renault would have worked this out by the time they got to my car in 1967? There were thousand of them in Morocco, Algeria, the Mediterranean... I know it's been hot in the southeast of England the past few days, but this is an average day in a Marrakech, right?

Anyway, I'm experimenting:

(1) I wrapped the exhaust manifolds in insulating webbing (bought my the metre from Think Automotive) attached with some stainless cable ties.
(2) I put a 6mm phenolic spacer between the inlet manifold and the carb. I couldn't find an exact one for my Solex but found an Amal carb spacer and gaskets from Burlen Fuel systems that needed 20-minutes of reworking to take the internal diameter out a couple of mm.

I'll let you know how I get on, but long-term thinking this is a sticking plaster to a system that in theory has been tried a tested? Any advice appreciated.

solex carb.jpeg
 

reidalpine

Enthusiast
Messages
1,520
on orig motor I placed a large heat-shield between carb/manifold (large to dissipate lots of heat plus direct evnt drippings past the manifold) and also to "shield" carb best possible from heat pouring up at standstill)
-this worked for me.
Not to make you soil your pants!-but ALWAYS keep a fire-extinguisher within your car-R.
 

mr-reno-139

AKA Paul Cunningham
Messages
2,210
Location
lancing west sussex england
I covered my solution to this on a Renault 4 recently on the Renault classic car club Facebook page
my solution was heat proof shielding on fuel lines
extra spacer under carb
and finally extending air filter intake down through inner wing to the gap below lhd master cylinder
 

angel

Enthusiast
Messages
2,135
Location
Athens, Greece
Over the last year I 've had various issues on customers' cars related to modern petrol being sensitive to high underbonnet temperatures. Haven't experienced it yet on an R4 though.
722stu, be aware that it's not recommended to wrap a cast iron manifold, it may crack.
 

722stu

Enthusiast
Messages
24
"722stu, be aware that it's not recommended to wrap a cast iron manifold, it may crack."
Yikes... no I hadn't considered that. Good advice, let me see how I get on with the spacer alone! I'm guessing there's no issue to wrap the exhaust downstream of the junction with the manifold if this contributes to keeping the carb a little cooler?
 

Piet

Enthusiast
Messages
140
The phenolic spacer is really important. They had them fitted when new but you often find on older cars they have gone missing or just replaced with a normal gasket and nothing else. I had same problem, correct spacer was missing, cut one out of 6mm phenolic sheet. This has so far worked fine but if it still didn't I would have made another one from 8mm sheet, provided I had enough stud length remaining for the nuts. Having said that 6mm was fine and the problem went away.
 

JonathanT

Not normal for Norfolk
Messages
1,317
Location
Wymondham Norfolk
VERY interesting everyone and thank you for comments so far . I’m sure I have a thick plastic spacer fitted - will check. Not sure if it’s the phenolic type material though.
I can see routing the fuel differently to the carb should help. The fact it passes over the top of the engine and a great big metal fuel filter on the top will surely be a heat collector.
im off this weekend with Sweet Pea caravan and not had a chance to make any mods yet. The weather (sadly) is cooler now so hopefully problem free.

I am very much liking the idea of a physical heat shield that also diverts any ‘expanded’ fuel from dripping onto the manifold - that’s scary to watch!
 

petak

Enthusiast
Messages
1,728
Location
Vodice, Croatia
Reading with interest as sometimes have same issue.

Really bad hot start if car is left for 20minutes to one hour.

Luckily it starts after few more cranks of starter but it is followed with strong fuel smell.

In other situations car is starting easily
 

Simon Knight

Enthusiast
Messages
150
Location
Sawbridgeworth
HI all, i have the same hot start problems as noted in previous posts, and once had fuel spilling out over the manifold, as Jonathan said that was very scary. Could the problem be solved by fitting an electric fan near the carburettor that would come on when the engine is turned off, and runs on a timer for a while?

Cheers Simon.
 

L'R4

Enthusiast
Messages
16
Hi everybody, I'm back after a long absence.
I lived in the South of France and in Africa and never heard of this problem. I even had a trip to the desert in one of these and few times at an altitude of more than 2000m with temperatures in high 40s and low 50s with no problem.
I know that in Africa the fuel is generally leaded or at least where I was, and everyone that I know in France used additives including my self.
This might seem a bit simplistic, but could the lubrication of the fuel be the problem?
 
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