Fuel evaporation problems :(

[Tj]

That time of year again. I'm guessing you guys get this question from noobs a lot when summer comes around.

My poor old zed is suffering in the heat a little.

 

First off, I'm running a stock (and tired) L26 with round top, four screw SU's that are a little on the knackered side (one of the needles doesn't seat properly making it idle funny  :-\ )

I'm not too concerned with the condition of the carbs, I have a new motor and webers waiting patiently for me to swap into the car but I'd like to make it a little more reliable at the moment.

I'm pretty certain it's fuel starvation caused by the heat as it never does it in the mornings and it starts playing up in the same spot every arvo on the way home from work (if you see a red 2+2 conked out at the intersection of Reservoir Rd and the Great Western HWY Blacktown at about 3:30 to 4:30 in the arvo, give us a wave )

The best way I can describe what's happening is that it starts to sound "fluffy". I should note at this stage that the car doesn't overheat. The temp gauge might move a tiny tiny bit but that's it.

And after that, if I get caught at a set of lights for a while the revs will start "dipping" even when I'm holding the throttle a little open (which is pretty common for me because of the aforementioned carby problem ) it'll idle for a second or two, then cut out for a sec, then idle for a second or two then cut out so on and so on.

Trying to accelerate way from stop it'll stammer and misfire (doesn't spit back through the carby though) and if i'm lucky it'll start to clear as it presumably sucks more cool air into the engine bay.

If it gets really bad it'll just stall and wont start for a few minutes.

 

In my attempts to remedy this I discovered it had a second fuel filter in front of the fuel pump that I didn't know was there. Turned out it was stuffed and disintegrating inside so I temporarily bypassed it (still running one in the engine bay before the carbs tho)

The pump seems to be running OK, it is an aftermarket one and I do have the original that was given to me when I bought the car but I don't know if it's working.

I might pilfer the pump out of our sometimes-race car and switch em over to see if it helps before I spring for a new one.

 

The old man also fiddled around re-routing the fuel lines away from the engine as they were still wrapping around the front of the head but none of this seems to have helped (except for getting rid of the knackered filter, that made a BIG difference  )

 

Are there any other causes for not only fuel evap that I haven't mentioned? or is there a completely different reason for this behaviour?

 

Should I just bolt the Webers onto this motor in the mean time? They're 45mm running 135 mains and 36mm chokes and are set up for an L28 with a fat cam, high compression, is this going to be ok on the stock L26? or is it too much for it?

 

Any pointers would be great.

 

Thanks guys

[260Coupe]

Do you have the original heat shield still fitted between the carbs and exhaust manifold?

 

From my experience fuel does not vapourise in the lines (as it is a return system that constantly circulates fuel)..........and vapour lock issues will usually be in the carbs due to radiant heat coming up from the exhaust manifold.

 

The age old method to prove this was tie a rag around the fuel bowls and pour water over the rag, as the water evapourates it will cool the float bowls and "should" remedy the problem...............all be it temporarily. This may help identify where the problem is.

 

I have also had fael vapourise in after market electric pumps (those square diapragm pumps are the worst).........maybe check that as well

 

Alan

[luvemfast]

+1 for heat shields.

They are def under rated.

I had issues also with my triple Mikuni's. Put a heat shield on and the issue went away. Easiest fix ever!

[260Coupe]

Roger that - the factory put heat shields on for a purpose ...........so if it's missing.........put one on

[Tj]

Yeah its definitely missing one.

I might try to track down a nice Chrome tray type one to go under the webers. Any ideas where to get em?

Otherwise, antique have a spare heatshield they don't need? 

 

[Tj]

Shortly after posting last night I remembered I still had a bit of that ACL heatshield left over from a project on another car. It's a bit on the expensive side but it's really good stuff, same as what's used by a lot of manufacturers and can be shaped and moulded how you need.

 

Not wanting to destroy a nice flat sheet I've temporarily jammed it in between the carbies and the exhaust making sure that it wont fall out and whatdyaknow! it fixed it!

It still runs like a heap of shite but that's got nothing to do with vapour locking.

 

Thanks guys!