Triple Webers Won't Start When Engine Is Hot

[Ownallday]

Hey guys, back with another question. Recently switched over to Triple Webers back in December. Loving the setup so far, still in the process of tuning them as they don't like open throttle in lower rpms. I am currently having an issue with starting the car after driving for a couple minutes. The car starts up pretty good for three carbs when cold, usually starts right up on the second crank. However she will not start after driving for a while and hot.

Example, I drove the car recently for about 20 minutes, pulled up to a gas station to fill up the tank which took approx 2 minutes to do, then I try an start my car right after and the car wont turn on, doesn't matter if I open the throttle a little or all the way open it just struggles to start. I had to sit and wait about 10 to 15 minutes to finally get the car to start again.

Is the gas evaporating in the webers and I just need to prime a little longer to refill? I currently do not have a heatshield in between my webers and headers but my headers are wrapped.

My first consideration is to make a heatshield for the webers and add heat reflective tape at the bottom of each weber also. Should this be enough or are there other things at play here?

 

[siteunseen]

I had a set of 40s but sold them because I read too much.

Here's some of the stuff I read.

https://www.google.com/search?client=ms-android-americamovil-us-revc&ei=OGwgYPvzCK2g5wLT463wBw&q=webers+won't+start+whaen+hot+classiczcars.com&oq=webers+won't+start+whaen+hot+classiczcars.com&gs_lcp=ChNtb2JpbGUtZ3dzLXdpei1zZXJwEAMyBAgeEApQz9MBWL_eAWDv7wFoAHAAeACAAdQBiAGxCJIBBTAuNi4xmAEAoAEBwAEB&sclient=mobile-gws-wiz-serp#scso=_WGwgYJrrFIar5wKm87KYCg36:0

[240260280]

Heat soak.  The proximity of the exhaust manifold causes the fuel to evaporate.  Add a heat shield and also change your fuel routing so that the fuel recirculates rather than dead-heads and you should notice an improvement.

[jitenshakun]

I haven't had this issue with my unshielded triples over wrapped headers so I'd look elsewhere.

Are you able to mount an inline fuel pressure gauge to monitor pressure? Have you popped the inspection lids to check bowl fuel level with vernier calipers cold and hot?

If fuel never differs and is always good it's not the fuel.

To your comment about throttle at low RPM, would that be at 1,700-2,000? Say, every time you come around a corner in regular traffic?

[LeonV]

If you open the throttle fully and crank, will it eventually start? Say after 5 seconds of cranking with the pedal all the way down. If you open the hood before the hot restart, do you notice fuel dripping from the air horns? This sounds like a flooding issue either due to fuel siphoning, too rich of a mixture, or both. If the car restarts with the throttle floored, then we can look deeper into why it might be flooding.

[Ownallday]

On 2/7/2021 at 4:17 PM, 240260280 said:

Heat soak.  The proximity of the exhaust manifold causes the fuel to evaporate.  Add a heat shield and also change your fuel routing so that the fuel recirculates rather than dead-heads and you should notice an improvement.

I have a custom heatshield in the works as we speak. I figured heat must have some part take with this issue. I have three friends with triples, none of them run a return line but they don't experience the heat soak issue I do. All three of them however have a heat shield and an msd ignition. This week I should be installing the custom heat shield and msd ignition.

 

On 2/7/2021 at 4:27 PM, jitenshakun said:

I haven't had this issue with my unshielded triples over wrapped headers so I'd look elsewhere.

Are you able to mount an inline fuel pressure gauge to monitor pressure? Have you popped the inspection lids to check bowl fuel level with vernier calipers cold and hot?

If fuel never differs and is always good it's not the fuel.

To your comment about throttle at low RPM, would that be at 1,700-2,000? Say, every time you come around a corner in regular traffic?


 

I have seen people run no heat shield or even wrapped headers and still run their cars fine without issues. I can mount a fuel pressure gauge. I will order one sometime this week. I have not checked the fuel level. I am still pretty new to webers so still learning the ins and outs.

And its pretty much any rpm below 2500 but this issue was resolved after my friend put some new jets in and retuned the webers

On 2/7/2021 at 4:36 PM, LeonV said:

If you open the throttle fully and crank, will it eventually start? Say after 5 seconds of cranking with the pedal all the way down. If you open the hood before the hot restart, do you notice fuel dripping from the air horns? This sounds like a flooding issue either due to fuel siphoning, too rich of a mixture, or both. If the car restarts with the throttle floored, then we can look deeper into why it might be flooding.

It starts after about 15 to 20 seconds of cranking sometimes. Other times no luck. Doesn't matter if my foot is fully to the floor or not, it struggles to start. I have not noticed fuel dripping but I did in the past when I first got my weber

[LeonV]

So you have tried cranking with foot-to-floor for 5-10 seconds?

You should first check your fuel level. This is best done by removing one of the main jet stacks and measuring from the shelf down to the fuel. It should be no less than 25mm. When you do that, also record your main jet/etube/air jet as well as idle jet. What's your displacement and cam?

My Z has no heat shield and no header wrap of any kind, I have no issues with hot starts although I typically crack the pedal a bit. This is typical of a carburetted car.

[jitenshakun]

Popping out the floats and measuring their distance to contact with the needle is a good measure too.

For the bog at acelleration from low RPM I had to step outside the online gospel of jet selection on L-engines.

Post up your jetting and we can chime in.

[Ownallday]

On 2/9/2021 at 9:36 PM, LeonV said:

So you have tried cranking with foot-to-floor for 5-10 seconds?

You should first check your fuel level. This is best done by removing one of the main jet stacks and measuring from the shelf down to the fuel. It should be no less than 25mm. When you do that, also record your main jet/etube/air jet as well as idle jet. What's your displacement and cam?

My Z has no heat shield and no header wrap of any kind, I have no issues with hot starts although I typically crack the pedal a bit. This is typical of a carburetted car.

Next time I get to driving the car I will leave the throttle open for 10 seconds flat and test the results of that again. If anything I think the fuel level is fine because the car starts right back up when cold without me even priming the the fuel pump. I will check however when I get to drive the car again. It's an L28 with a stock E88 head cam.

 

On 2/9/2021 at 9:58 PM, jitenshakun said:

Popping out the floats and measuring their distance to contact with the needle is a good measure too.

For the bog at acelleration from low RPM I had to step outside the online gospel of jet selection on L-engines.

Post up your jetting and we can chime in.

I will do that once I get around to driving the car again. The bogging is no longer and issue, my friend popped in some bigger jets and retuned the webers and now the car runs near perfect in the lower rpms. If he remembers what size jets he put I will post back here

[jitenshakun]

I will do that once I get around to driving the car again. The bogging is no longer and issue, my friend popped in some bigger jets and retuned the webers and now the car runs near perfect in the lower rpms. If he remembers what size jets he put I will post back here

I'd appreciate hearing what you jet selection is.

[Ownallday]

I can confirm that before upgrading to the MSD, holding the throttle wide open and cranking for about 10 to 15 seconds would get the car to start. However I completely solved the issue by upgrading to an MSD Ignition 6AL. Now the car only takes about 2 to 3 seconds to start when hot which seems pretty normal for me with triple weber. A lot smother acceleration now at top end especially and also noticed less fumes in the car. Definitely a worthy upgrade.

On 2/11/2021 at 7:54 AM, jitenshakun said:

On 2/11/2021 at 7:20 AM, Ownallday said:

I will do that once I get around to driving the car again. The bogging is no longer and issue, my friend popped in some bigger jets and retuned the webers and now the car runs near perfect in the lower rpms. If he remembers what size jets he put I will post back here

I'd appreciate hearing what you jet selection is.

Here is my setup, this is what my friend who tuned them remembers off the top of his head so may not the 100% I believe the idle jet and Emulsion Tubes are different.

Main Venturi - 30

Aux Venturi - 4.5

Main Jet - 120

Emulsion Tube - F11

Air Corr Jet - 200

Idle Jet - 45F9

Pump Jet - 50

Pump Exh - 50

Needle Valve - 1.75

[jitenshakun]

That's an interestingly lean combination with F11 emulsion and 45f9 idles.