Hot Start Problem

Hi guys, this one is really for the early car owners! I've got a 69T (webber carbs)which I've owned since Christmas and which has always had a hot start problem. I've serviced it with recommended plugs, oil, new filters, set the carbs, and adjusted timing. However when ever I try to start my car once it is hot, I have lots of trouble getting it to fire up. The best method I've found is to gently depress the accelerator pedal to the floor and hold it there whilst cranking it up to 20 times before it fires. It's annoying and it ****s me when people look at the "porsche wanker" trying to start his car! I'm hoping that one of you early car gurus might be able to help me out, thanks guys!

PS. The car is running quite well, with a small flat spot between 3 and 4 thousand. The plugs have a nice colour, and the pipe colour looks good too (I can still get real leaded fuel in Australia).

OK, I am not an early car's guru, but I had a similar problem.

I think it's a fuel pressure problem. I suspect the
1) fuel pump
2) fuel pressure accumulator (do you have with carb's?)
3) fuel line (bending, clogging)
4) fuel filter - you have checked that.

What about using the hand throttle for starting?

Just my 0.02
Jens

This brings back memories! My first was a T with the webers. I found out later that the only thing T about it was the engine case. It had the innards of an S...long story.
Anyway, learning the quirks of the webers was lots of fun.
It's been a long time, but I remember that there may be small filter sleeves in the banjo fittings that serve the two fuel inlets at the float bowls. These ( if they are still present) may be clogged. You have to loosen the large fittings that hold the banjos to the carb. The filters are in there.
I'd suggest that you remove an air filter just prior to trying to restart, move the throttle lever and while peering into the carb stacks, see if the accelerator pump forces a supply of gas as the throttle moves. There should be a strong stream..enough to almost flood the carbs. If not, the pump may be shot.
It all sounds like a fuel supply problem....or..if it's an extremely hot day..you may experience vapor lock. But that's something to worry about this summer.
Good Luck.

Fishcop,

My feeling is that it is a fuel percolation problem in the Webers, and there are two possible solutions, one temporary, and the other permanent.

First, I am assuming that you have the OEM Bosch rotary fuel pump! If so, when you are about to restart when hot, allow the fuel pump to run for one minute before turning the engine over -- to allow the float bowls to fill back up.

Second, there are 'heat isolators/insulators' available, made of Bakelite plastic that fit between two gaskets immediately below the carbs. You could make some by tracing a gasket pattern onto some (1/4" or 6 mm) plastic, or perhaps Masonite like pegboard is made of. Good luck!

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Warren Hall
1973 911S Targa

I am not an early car expert, either. Things you could check include:
1. Is there a check valve in the fuel line that keeps fuel from draining back to the tank and is it working properly?
2. What is your fuel pressure when cranking?
3. Are you getting vapor lock in hot fuel lines? (A different brand of fuel may help this.)
4. Is the fuel boiling out of the carbuerator bowls when hot? (Again, a different brand of fuel may help.)
5. Are you getting adequate spark when cranking (i.e. - is some ignition component breaking down when hot)?

Good luck!

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Bob Thayer
1971 911T
rthayer@hdrinc.com

Thanks guys, the consensus is a fuel problem, so starting this weekend I have a new project! The average temperature where I live is currently around 31 oC, so I suspect too much heat is the problem. Thanks for your help.

webers don't like to start well hot if you pump the throttle. just open it 1/2 way or more and crank it. no pumping. cold needs a pump or two, of course. PMO sells a drill jig to vent the carb tops to relieve vapor pressure in the float bowl so they don't perk as much. the insulators are a must! see if your spark is blue and nasty or yellow and weak. good spark makes a lot of difference.

[This message has been edited by john walker's workshop (edited 03-22-2001).]

Hi Fishcop

Have the same car and same problem in the same country (Melbourne). This problem seems common amongst many carb'd cars as I have the same issues with past "hotted" MG's which have SU's.

If it’s any help the entire fuel system, including the fuel pump, has been replaced on my car - and it still does it. I now start my car on hot days by pumping the throttle once and then crank the car over with it depressed about 1/2 way. Usually starts after cranking over 6 times.

Hope this helps, good luck.


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Paul
911T'69

[This message has been edited by Paul W (edited 03-22-2001).]

Thanks for your info Paul, out of interest have you got the "insulators" that the others have mentioned, and what is your usual hot start routine? Thanks maaaate, RHD rules!

I have the same problem with my 912 and my dad aso had the problem with both of his early 911's. Holding down the accelerator and cranking the engine is the only way my car will start when hot. Plus, who cares if every one stares at you, after 10 or so seconds the car starts and everyone hears the wounderous sound of your flat 4, opps sorry flat 6 and then they stand there starring in aww. What a great life!

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Joshua Harrison
1968 912 Coupe

Hi Fishcop, sorry about the delay in getting back but I haven’t been near a computer for a couple of days.

I don’t know whether I have the insulators or not, I have just reread Warrens post so I’ll have a look under the hood of my car tonight and see if I have them.

When restarting once the car is warm I usually give the throttle one pump and then keep it depressed about half way. Usually then starts without too much fuss.

Warren, what is a fuel peculation and is this only particular to carb’d engines?

Regards,


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Paul
911T'69

Paul,

'Percolation' is the actual boiling off of the fuel in the float bowls of a carbureted engine ... and it sounds just like an 'old-fashioned' coffee pot, which is where the term comes from! You can hear it happen and smell the fumes 5-10 minutes after shutdown on a hot summer day ... and last summer I seem to remember telling a board member to sit and watch/listen/smell the engine, and he did, and actually found that happening!

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Warren Hall
1973 911S Targa

Hi Warren, thanks for the explanation, sort of makes a lot of sense and I have noticed a fuel smell from my car after parking it in my garage on a hot day.

A further question (sorry to get off topic) I find my idle drops after a quick stop, especially from high revs – most noticeably in hot whether. Could this be explained by the same phenomena?


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Paul
911T'69

I'd be interested to know what is the best material to use to insulate the carbs.

It seems to me that it would be difficult to make sure that it fits perfectly so that intake venturi is perfectly smooth.

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Allan Broadribb
'70-911E, 2.2l with Webers

What about some kind of perspex product for the insulators? The stuff is fuel proof and with a die-grinder it should be easy to get smooth and well matched to the manifold.

I tried turning on the ignition and letting the pump run for a minute like Warren suggested, and this seems to work quite well with half throttle as I crank it over. I'm quite sure now that what I'm experienceing is perculating fuel (it's been real hot here lately).

Has anyone else tried John Walker's PMO jig and drilled the webbers? Is this worth the expense....how much is a jig like this, and can it be used over and over, do you want to rent it to me!!

Thanks everyone