Could it be vapor lock ?

[Flash]

Okay Team, Flash is in need of some guidance with regards to an irritating issue that I am experiencing with my Toyota 3Y powered Thames van. I've noticed that when I've been on a longer drive and I go to restart the engine after a short stop I have to crank the engine excessively before she will fire up. In these instances, after she has started the engine stumbles a bit especially at lower revs. This stumble clears up after a few minutes of driving. This only happens on longer trips say anything around 20km or further. It doesn't happen on short trips around our village and it also doesn't happen if the van has been left to stand for a longer period of time before restarting.

I'm thinking that I may be suffering from vapor lock and after reading everything that Uncle Google tells me the only cause that I can think of in my case is that I'm getting excessive heat build-up in my fairly small engine compartment which is causing my fuel to evaporate in the lines/carby. I'm considering putting my thermo fan on a delay timer so that it runs for a while after engine shut off, just to try to clear some of the heat from the engine bay, but I'd be keen to hear any other suggestions on how to cure this issue.

Thanks in advance.

[GregT]

Mate put a 1600 crossflow into a Thames and - you guessed it - got vapor lock.  He never really got on top of it but there were less options available in fans etc back then. I remember him leaving the engine cover up when he came to visit.

[tortron]

do you just have a mechanical pump?

a small electric pump with a 5 second relay when ign on would probably help mask the issue

[HighLUX]

Seems to be a common issue with 3Y powered vans. My hiace was the same and needed a bit of finesse to get it to start. Being non cross flow and all that cast iron of exhaust manifold under the inlet doesnt help. An electric prime pump will help as mentioned and maybe making a decent heat shield between the inlet and exhaust

[Flash]

14 hours ago, tortron said:

do you just have a mechanical pump?

a small electric pump with a 5 second relay when ign on would probably help mask the issue

Yep, Toyota 3Y mechanical pump that has the factory return circuit back to the fuel tank. 

Thanks for the electric pump suggestion Tori, it's worth a go.

[Flash]

10 hours ago, HighLUX said:

Seems to be a common issue with 3Y powered vans. My hiace was the same and needed a bit of finesse to get it to start. Being non cross flow and all that cast iron of exhaust manifold under the inlet doesnt help. An electric prime pump will help as mentioned and maybe making a decent heat shield between the inlet and exhaust

Thanks for the heat shield suggestion @HighLUX. I am running a Weber 32/36 carby instead of the factory Aisin and I did retain the factory spacer between the carby and the inlet manifold, but the factory heat shield that sits on top of the exhaust manifold does look a bit flimsy and thin, so I'm going to give some thought to fabricating something more substantial. Do you think wrapping the exhaust manifold might help too ?

[Flash]

14 hours ago, GregT said:

Mate put a 1600 crossflow into a Thames and - you guessed it - got vapor lock.  He never really got on top of it but there were less options available in fans etc back then. I remember him leaving the engine cover up when he came to visit.

Yikes, interesting to hear that it happens with a crossflow engine too. In that case the common denominator seems to be the confined engine box. I've lifted the engine cover a few times after a run and the heat that seeps out into the cabin is epic.

[HighLUX]

Wrapping it could help but also might make it more prone to cracking. You could look into getting it hi temp ceramic coated

[cletus]

Have you got somewhere you could attach a vent pipe to the engine box?  

Ie something like a 3" flexible hose with a fan in it to suck the hot air out when you park? 

[Flash]

Just now, cletus said:

Have you got somewhere you could attach a vent pipe to the engine box?  

Ie something like a 3" flexible hose with a fan in it to suck the hot air out when you park? 

Thanks Clint, that's a bloody good idea.

[GregT]

3 hours ago, Flash said:

Yikes, interesting to hear that it happens with a crossflow engine too. In that case the common denominator seems to be the confined engine box. I've lifted the engine cover a few times after a run and the heat that seeps out into the cabin is epic.

Mate's 1600 crossflow used a 28/32 Weber. To all intents a Cortina GT engine. The accelerator pumps on the downdraft twin chokes seem vulnerable to heat. Possibly the lighter alloy used vs cheaper OE carbs heats up faster.

From having a Thames myself - a long, long time ago - And from memory, a duct into the cover above floor level wouldn't be easy. Have you got a roof vent ?  Straight up and out might work.

[locost_bryan]

Most BMC stuff had a heat shield between the inlet and exhaust manifolds, or between the carbs and manifold on one-piece cast manifolds.

Some MGs had a carb cooling fan.  This is one for a MGC.  The Maestro 1600 did something similar for its twin Webers, had a wee microprocessor that turned it on when the temp got too hot and kept it on until a set time after it had cooled down.

[ajg193]

Have you definitely ruled out bad head gasket? Won't hurt much to check for excessive milky buildup under oil cap

[sleeektoy]

21 hours ago, tortron said:

do you just have a mechanical pump?

a small electric pump with a 5 second relay when ign on would probably help mask the issue

bang on the money, especially with a return line it will shove colder fuel through and hopefully solve this issue

[GregT]

1 hour ago, sleeektoy said:

bang on the money, especially with a return line it will shove colder fuel through and hopefully solve this issue

You're using the tank capacity as a heat sink.

[Flash]

5 hours ago, GregT said:

Mate's 1600 crossflow used a 28/32 Weber. To all intents a Cortina GT engine. The accelerator pumps on the downdraft twin chokes seem vulnerable to heat. Possibly the lighter alloy used vs cheaper OE carbs heats up faster.

From having a Thames myself - a long, long time ago - And from memory, a duct into the cover above floor level wouldn't be easy. Have you got a roof vent ?  Straight up and out might work.

Yep, my Weber is visually almost identical to a 28/32 so what you are saying makes sense. Might be worthwhile me checking in with @yoeddynzas I know he fitted the same carby as mine to a customer's HiAce. I wonder if that van also suffers from vaporlock since the conversion.

No roof vent unfortunately and I don't fancy fitting one. I had a good look under the van earlier today and ducting the air out won't be that easy. Lazy Flash thinks maybe just use the main radiator thermo fan to blow the hot air out of the engine box after engine switch off.

[Flash]

4 hours ago, locost_bryan said:

Most BMC stuff had a heat shield between the inlet and exhaust manifolds, or between the carbs and manifold on one-piece cast manifolds.

Some MGs had a carb cooling fan.  This is one for a MGC.  The Maestro 1600 did something similar for its twin Webers, had a wee microprocessor that turned it on when the temp got too hot and kept it on until a set time after it had cooled down.

Thanks for the info Bryan. I'm still running this factory spacer between the carby and the aluminium inlet manifold:

But the factory heat shield on top of the cast exhaust manifold is just a thin piece of shaped metal, so Making something similar to your BMC example might be the answer.

[Flash]

2 hours ago, ajg193 said:

Have you definitely ruled out bad head gasket? Won't hurt much to check for excessive milky buildup under oil cap

Thanks for the suggestion @ajg193. I'm pretty sure it's not a head gasket issue. No milk in oil, and no oil in coolant. Thermostat opens at 85C and engine stays at a constant 95C in both traffic and the open road. Well within factory spec. Compression across all 4 cylinders is good too.

[Flash]

2 hours ago, sleeektoy said:

bang on the money, especially with a return line it will shove colder fuel through and hopefully solve this issue

Thanks @sleeektoy. My current mechanical pump has a return line fitted so would you suggest that I look at substituting the electric pump for my existing mechanical one or somehow running the electric as an auxilliary? I'm thinking it would be a simpler exercise from a plumbing point of view for me just to replace the mechanical pump with an electric job. Unless you have a cunning plan that I haven't thought of.

[Flash]

21 minutes ago, GregT said:

You're using the tank capacity as a heat sink.

Yep, sounds like a really good solution.