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Do I Have Vapour Lock?


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#1 ScottyB

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Posted 30 December 2016 - 07:51 PM

Hi guys.

In your experience, do I have vapour lock?

I've got the stock Twin SU L24 in my 240, but the car is running a Fujitsubo Legalis R exhaust c/with headers. There is no heat shield. Drives fine in all conditions to date bar one...

To start this car, it takes no less than 3 long cranks before it considers firing up. Once started, it's fine - but it's frustrating and would be battery draining without being on constant charge.

I believe that a heat shield will help - but I'm new to carbs and keen for advice on potential fixes.

Cheers.

#2 Brabham

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Posted 30 December 2016 - 08:31 PM

Mech fuel pump? If you don't drive it often might take a bit of cranking to get fuel to it?

#3 gav240z

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Posted 30 December 2016 - 08:33 PM

Add the heat shield back in, it's not doing you any favours not having it.

#4 ScottyB

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Posted 30 December 2016 - 08:45 PM

Yes, mechanical pump still in the bay. Should it really be that hard to start though? Gets driven every second weekend, but this is a next day issue too. Also - while warm, starts first crank.

I bought it as is unfortunately... no heat shield and a customised spring return for the throttles that would foul on a heat shield.

So, heat shield would be number 1 and if pain persists electronic fuel pump be the next best suggestion?

#5 Gareth. J.

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Posted 30 December 2016 - 09:27 PM

If it's a cold start issue only it won't be heat soak.

 

Check the choke operation, the jet nozzles should be all the way down. To test pull the choke on in the car, then in the engine bay reach under the carbs and see if you can pull the jet nozzle on each carb down any further. If you can they are sticking, you aren't getting full choke and cold starts will be hard. Try lubricating them when they are fully down, it worked for me many years ago.



#6 Cozza

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Posted 30 December 2016 - 09:28 PM

If it starts fine when warm, I wouldn't think you've got vapour lock.
Your description sounds more like cold starting issues?
What do the plugs look like?

#7 gav240z

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Posted 31 December 2016 - 11:58 AM

Check the choke operation, the jet nozzles should be all the way down. To test pull the choke on in the car, then in the engine bay reach under the carbs and see if you can pull the jet nozzle on each carb down any further. If you can they are sticking, you aren't getting full choke and cold starts will be hard. Try lubricating them when they are fully down, it worked for me many years ago.


I agree it sounds more like a cold start, choke issue. If it starts fine when warm.

Gareth what did you use to lubricate them? WD40?

#8 Gareth. J.

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Posted 31 December 2016 - 04:53 PM

I lightly smeared high temp wheel bearing grease onto them with a finger and then worked them up and down a few times. I wanted to use something that would stay on when things heated up and I thought spray grease or lubricant spray would cook or boil off due to the radiant heat in that area.

I thought I read somewhere it's a sign of the needle jet being worn and needing replacement? The fairly expensive though aren't they.

#9 gav240z

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Posted 31 December 2016 - 05:20 PM

I have a rebuild kit for the SUs but I plan to go with Triple Mikuni's anyway.

#10 ScottyB

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Posted 01 January 2017 - 07:17 AM

Thanks Gareth... this makes sense.
I'll have a look the next chance I get and see if this is the issue. Cheers.

#11 dat2kman

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Posted 02 January 2017 - 11:51 AM

If not using the crinkled waffle material as heat shield, but metal, get the metal one ceramic coated.
Not running it every two weeks, is enough to cause a bit of fuel evaporation, so that fuelpump will have to work to get enough fuel back into float bowls at high enough level, for vacuum to pull fuel mist up and through.

Considered a rear mounted electric fuel pump???
If so, fit a filter between the pump and tank, no need for second filter up front.

#12 Retro Z

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Posted 02 January 2017 - 03:33 PM

I had similar issues with hard starting on cold mornings. Installed a MSD 6al2 ignition box and MSD blaster coil. No such problem for me anymore.

#13 nizm0zed

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Posted 02 January 2017 - 05:30 PM

First thoughts about your hard starting when cold or sitting for a while, Your mechanical fuel pump diaphragm is leaking.
The fuel that sits in the pump and lines to the carbs drains out slowly, you have to reprime the whole thing before it'll start, hence the long cranking after sitting for a while.



#14 dat2kman

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Posted 02 January 2017 - 07:05 PM

I had similar issues with hard starting on cold mornings. Installed a MSD 6al2 ignition box and MSD blaster coil. No such problem for me anymore.


I got a brand new in box one of those!
Will sell!
PM me if interested!

#15 gav240z

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Posted 02 January 2017 - 07:14 PM

First thoughts about your hard starting when cold or sitting for a while, Your mechanical fuel pump diaphragm is leaking.
The fuel that sits in the pump and lines to the carbs drains out slowly, you have to reprime the whole thing before it'll start, hence the long cranking after sitting for a while.


I have to crank mine for a while also (although I think it's also the choke on the SUs), so I was looking into a rebuild kit for the original pump. Found this thread.
http://www.classiczc...ikki-fuel-pump/

Problem is my fuel pump says Atsugi not "Nikki" so I'm not sure if the components are the same. My guess is that they are.




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