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I've seen several threads on this but nothing that actually has a fix.   My speedster is relatively new and came with a completely new engine build with dual carbs.  Cold start is always perfect, but after my engine is warm, I have to crank it for probably 10+ seconds or so until the fuel/carbs sort themselves out and the engine starts.  Pretty embarrassing when everyone is looking at your cool car and it barely starts.

I've tried the various recommendations on pedal to the floor, crank it until it catches a spark and then feather the gas...  Still nothing that gets me a clean start when the engine is warm and it has been this way since it was new.  To be fair, its never not started for me, but always takes alot of cranking when warm.

Here a picture of my setup with the fuel regulator while the engine is idling.  Let me know if anyone has ideas on an actual fix I can do.   BTW, my engine is a thing of beauty isn't it!!!



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Last edited by MarylandGuy
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Perfectly normal on aircooleds; sometimes you might have vapor lock but that's a totally different issue. ALL the aircooleds I've had are a little harder to start when hot after a moderately short stop; longer than a fueling stop. Funny how if you shut it off and need to restart it immediately it goes but if you let it cool off just a tad but it's still warm it'll be harder to start. And, if the stop is long enough where it cools off sufficiently it'll start easily. They're very quirky.

Last edited by Impala

It looks like the fuel comes from the firewall on the driver's side of the engine, goes across the hot tins above the head and over to the (mechanical) fuel pump.  It then goes back across the hot head tin and up to the regulator, then to a "T" at the driver's side carb and continues across the back of the engine to the passenger side carb.

So I see two or three places where the fuel hose is sitting on something very hot.  When the engine is up to temp (hot) and then shut down and sits, everything heat soaks from engine heat and the fuel in the rubber gas hose percolates from the heat and gets bubbles in it.  When you then try to start the engine, it first has to get all of those bubbles out of the line, followed by new fuel and that takes a few seconds of cranking and THAT is why it is hard to start when hot.

There are two fixes; (1.) easy/maybe effective and (2.) harder/much more effective

  1. insulate your rubber gas hoses from heat soak by getting them up off the head tins and engine case where-ever possible.  This will make it harder for the liquid gasoline to percolate and make bubbles.  This, alone may cure it, but if it doesn't clear it up, then;
  2. Abandon the mechanical fuel pump and install an electric, rotary, "pusher" fuel pump and gas filter in the front of the car right under the fuel tank (there is even a convenient shelf to mount it on).   Wire it in to your ignition circuit so it starts pumping with key on.  Using that means that the pump will push the air bubbles out to the carbs and get liquid gas to the carbs in a couple of seconds after "key on" and the engine will start much easier.

    Here's a popular pump from CB Performance:

An electric fuel pump will help enormously, but even with perfectly routed fuel lines and an electric pump, it's going to be harder to start after a shut-down.

I've long suspected that it's because the car is hot and the fuel in the bowls boils off when it isn't being kept cool by means of running into and out of the carbs. The bowls have to refill before the engine will "catch", which takes time regardless of whether the pump is electric or mechanical (although a mechanical pump will take longer).

@MarylandGuy posted:

I have to crank it for probably 10+ seconds or so until the fuel/carbs sort themselves out and the engine starts.  Pretty embarrassing when everyone is looking at your cool car and it barely starts.

With a mechanical pump, the action of turning the engine over is what fills the carbs back up. With an electric pump, you just turn the ignition to have the pump fill the carbs before you start cranking. This gives you time to smile at the onlookers, giving them a head nod, while reaching for the exhaust cutout all while listening to the gurgle coming from the carbs. When the gurgling stops, THEN you crank it to start the beast that lives under your deck lid.

Paul,  Since that's my build and installation I'll chime in. Is this a recent issue that has developed?  If it has been ongoing since new perhaps isolating the hoses further from the shroud etc. Aircooled is notorious for having to crank the engine when at operating temps. Another possibility is one or both carb bowls bleeding off and having to refill by cranking the engine but then you need to figure out why that issue decided to start happening. BTW Stans and Gordon nailed it ... Alan

Last edited by Alan Merklin

So I have a solution. It may not work, but it costs absolutely NOTHING to try.

I have a customer with a sandrail. 1835cc, mechanical pump, dual 35 PDSIT Solexes, with electric chokes. I installed this kit from, pre-jetted for the engine by John Connelly. Mechanical pump has several gaskets under it to drop the fuel pressure to 1.5 psi UNDER full load while driving. Yes, I hooked up a gauge and a long hose and drove it. The pressure is around 1.75 pounds at idle or revving the engine.

Anyway, he was having a warm start problem. Not catching, spitting, sputtering. He was turning the key and expecting it to catch like a fuel-injected motor.

Try just very slightly cracking the throttle open as you turn the key. It might work, it completely did work for my customer. Don't stab it as that will pour a shot of accelerator pump in there. Just slightly open the throttle plate.



Like most folks, I had this too when my car was new, so I insulated the gas lines (that run near the top of the fan shroud), but that didn't help at all.

I've found the most effective thing has been the simplest. If it's hot out and the engine is hot when I park it, and I know I'll be trying a restart in 10-15 minutes, I just open the deck lid to vent as much of the heat as possible. It doesn't fix the problem, but it seems to help a lot.

My own theory (and we all have one) is that gas is 'percolating' in the float bowls and inside some of the narrow channels in the carbs themselves. Gordon and Stan are right — the engine compartment is hottest about 5-10 minutes after you shut down. All the metal is just as hot as when the engine was running, but there's now no airflow through there to stabilize temperatures.

Try opening the lid when you park. It may or may not help, but it's a cheap experiment. I've also found feeding as little gas as possible helps the restart.

If you're not old enough to remember, this was just another foible of driving back in the '50s and '60s (for both air- and water-cooled cars) before computers made cars, uh, completely trouble-free.


As always, you guys are the best and I so appreciate this forum.   My problem is exactly what all of you are describing and it has been happening since new.  If I run it a long time, really hot, go into a store or something for 15-20 minutes, that is the worst scenario.   Gas stop, takes a little cranking but catches faster.   Its managable or I wouldn't have waited a year to look into it, but still annoying and I assumed there was a fix. 

I'm going to start with seeing how I can insulate the fuel lines and go from there.   Hoping I can get a break from work to try it out today.   I'd really rather not go through the trouble of installing an electric pump, so hopefully I can improve it some with the simpler options.   I also like Sacto Mitch's point about openning up the engine to let it cool.  My engine compartment is sealed super tight, so it is crazy hot after I've been on a long drive.  I can just pretent I'm at a car show everywhere I park and open up so everyone can see this beautiful engine that Alan built!   

@edsnova when are we going for a drive again?   I want to get out before you actually sell the spyder.  This weekend is open for me. 

Another thing about the decklid; some of us have installed the 4 decklid rubber snubs used on real 356s to try and prop it up enough to have some sort of additional airflow between the decklid and body apart from the grille itself and in my case I cannot tell the difference so I’m not sure if I wasted my money and effort on that. Some here have reported vastly improved engine compartment termperatures by propping the decklid slightly; (as with a tennis ball or something similar). Some have even more elaborate McGiver like contraptions. Maybe  this could help?

Last edited by Impala

ok, I just got into the engine and as we would all expect Alan had everything very neatly laid out.  The only adjustment I can see is if I lift the lines going to/from the mechanical fuel pump by zip tying them to the big hose that goes from the fan to the heater box, which will look ugly but get those lines about an inch above the tins.  20220803_07590820220803_07593520220803_075955


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When my car was about 3 years old, the motor started making funky carb and ignition noises at cold and warm startups.  Car came with a mechanical fuel pump, Webers & magnaspark.  I did everything I knew but could not eliminate the funk.

I went to an electric fuel pump, fuel pressure regulator with gauge and braided lines.  Motor now behaves at it should. 

When safe, I like to leave my engine lid up, I think it helps cooling.

Alan and I talked earlier today.   What I'm going to try is adding vents on the upper wheel wells in the engine compartment to allow some airflow when the engine is off and still hot.  I'm also going to try raising up the regulator on the driver side wall a couple inches in order to elevate the lines to/from the fuel pump... or maybe just shorten the hoses a little.  Need to think through that. 

These are the vent covers I'm thinking about getting and going with 4 inch holes.

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