• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Vapor lock issue solved [RB cars only]

Share this page

G

Guest

Guest
Guest
Offline
I've been fighting vapor lock on my twin euro SU's and came up with a solution. I fitted another transfer type bowl lid to the front carb, then connected the other port to the fuel return line going back to the tank.

This way, fuel runs to both carbs constantly, and the tank now acts as a cool can. Any vapor gets bled off and goes back to the tank and is replaced by fresh cool fuel. The fuel running through the top of the bowl acts as coolant and pulls heat off of the rest of the bowl.


The float bowls are almost cool to the touch now at operating temps. I still have a very slight problem with heat soak back after it sits a bit, but it goes away almost instantly now; before it took a few miles to cool down enough to run right.

I can now finally take that stupid pressure regulator off and there is no chance of overloading the floats with too much pressure. All tests confirm that fuel pressure and supply is good with this method at all RPM ranges and engine loads. It's not conventional, but it works great.

I still might wrap the exhaust just for the halibut.

( no fish were harmed in the posting of this thread)
 
neat! can you post a pic?
 
There are some screw on fuel filters that you could use for this purpose too. The housings have a place for 4-5 fittings.
 
I was going to suggest this solution, but i figgered it would get shouted down. Another nice benefit of your solution is that you have checked off one of your to dos for your future efi project.
 
Never mind, I misunderstood what your are doing. BTW, what are you doing? I think I need a diagram. It sounds like you are purposefully flooding your float bowls.
 
No, I'm not. Fuel is at it's normal level. All I did was to take an extra bolw top from a rear carb and install it on the front carb. I then connected the "extra" outlet ( the one that would go to the front carb if the top was mounted on a rear carb) and connect that to the return line.

So, now the fuel travels in a continuious loop.

From the tank to the rear carb, through the top out of the front bolw feed line to the front carb, through the front bowl feed line out the "extra" bowl feed line to the return line back to the tank.

Does this make sense now?
 
Nope.
I'm more confused than ever!
Got a camera?
 
Took pics but photobucket is not working right. I need to find a new place to upload from.
 
OK I got it now. What type of fuel pump?
 
Did you know that you can upload a photo directly here using the File Manager link at the bottom of the full reply form?
 
Kellysguy,

You were having vapor lock despite switching to an electric pump? Is the pump under the hood or back by the tank?

The reason I ask is because I'm ready to bite the bullet and install an electric pump in the back but I don't think I'll bother if it doesn't cure the vapor lock.

What sort of tape were you thinking of wrapping the exhaust manifold?

Cheers!

PS I installed special heat shielding cloth from Summit on the line from the mechanical pump and applied special tape onto the heat shield and fuel bowl - didn't do squat.
 
Part of my problem is that I didn't cut the car for the euro dual install and made a bracket that moved the rear float bowl further back towards the exhaust. I had the pump both up front and out back but it made no difference. I fyou have a vapor return line like the later cars then this will work for you ( it should depending on what carb(s) you have...which begs the question.)
 
Kellysguy,

Thanks for the info.

I replaced the ZS with a single HS4. A vast improvement but now I'm getting terrible vapor lock and can't relieve PCV gases effectively, leading to bigger oil puddle than before.

Was going to solve both by putting in a rear mounted electric pump and putting on a breather on a plate to cover the mechanical fuel pump hole.

But you have me re-thinking it - fortunately!

Cheers!
 
I'd use a spacer to help keep it cool ( mine is being cut right now). I also plan to use motrcycle header wrap. It's the same stuff as regular auto header wrap just 1" wide instead of two.

Two reasons for 1":

a. stock exhast mainfold isn't that big.

b. $29.99 instead of $44.95 (both 50' rolls.)

I also have my bolws wrapped with foam pipe insulation. They made a rubber one too which I'll probably switch to, although I might not need it anymore.


IMO, if you are having that much trouble w/ PCV issues, your rings are shot. My car did that till I reringed it. Now I get almost nothing out the tube and it just dangles out there.
 
Kellysguy,

Thanks for the ideas!

I'll check out the header wrap - never thought of that.
I'll also try the spacer idea - I think the original one for the ZS will fit but I'll need longer studs - McMaster Carr will probably have them.

As for the rings, I'll take a look at them next time I replace the rod bearings/thrust washers.

Cheers!
 
kellysguy said:
I'd use a spacer to help keep it cool ( mine is being cut right now). I also plan to use motrcycle header wrap. It's the same stuff as regular auto header wrap just 1" wide instead of two.

Two reasons for 1":

a. stock exhast mainfold isn't that big.

b. $29.99 instead of $44.95 (both 50' rolls.)

I also have my bolws wrapped with foam pipe insulation. They made a rubber one too which I'll probably switch to, although I might not need it anymore.


IMO, if you are having that much trouble w/ PCV issues, your rings are shot. My car did that till I reringed it. Now I get almost nothing out the tube and it just dangles out there.
Click to expand...
My experience with wrapping pipes on bikes with that stuff is not good. The heat doesn't get out and it keeps more in the head and the pipes literally start to glow red under that wrap and eventually melt or crack or bend to where they don't seal good at the head and you get a leak there.
I don't know what this would do to a stock cast iron exhaust manifold on a spridget. It might be ok, or it might crack or something. I just know it will get a lot hotter under that wrap.
 
Back
Top