Hard warm starting issue (Weber 38s)

[Paul Wegweiser]

I exhaustively searched for all variations of this topic with no success... so here goes:

Freshly installed new 38s on a 3.0.

***Choke and jetting is finally where I want it, but warm starts (after sitting 15 min or so) require full throttle.

Thinking the obvious "fuel boiling / seeping into the manifolds" issue, but there's gotta be some solution that will keep me from rinsing my cylinders w raw fuel every time.

car has stock new mechanical fuel pump. Hot starts are great, cold starts are instant..but warm starts are embarrassing.

have 1/4" phenolic spacer under each carb. Weather here has never been above 75 degrees.

Anyone experienced this and have a reliable fix? Float levels seem good. Timing is dialed in, etc...

Many Thanks in advance! Photo for air cleaner style reference.

 

[Stevehose]

I have a similar issue with my sidedrafts, instant cold start, instant hot restart if not sitting. If it sits for about 10min or so it takes an open throttle to start. I just figured it was a quirk of the technology. But yes, probably related to some sort of heat soak in the carb and/or manifolds.

 

[Paul Wegweiser]

I have a similar issue with my sidedrafts, instant cold start, instant hot restart if not sitting. If it sits for about 10min or so it takes an open throttle to start. I just figured it was a quirk of the technology. But yes, probably related to some sort of heat soak in the carb and/or manifolds.

I'm used to cracking the throttle open a wee little bit with side drafts...but this requires FULL throttle opening...and that's become tiresome.

 

[Thomas76]

If your cold start is good it suggests the bowls are maintaining fuel and not draining into manifold.
The type of choke might impact troubleshooting (water, electric, none)

 

[Paul Wegweiser]

If your cold start is good it suggests the bowls are maintaining fuel and not draining into manifold.
The type of choke might impact troubleshooting (water, electric, none)

You make a very good point!

Electric choke. I may need to work on very SMALL, incremental changes to choke adjustment to get this just right.

 

[Dan Wood]

Could the float needle valves be leaking and filling the bowls after shut down?

 

[Honolulu]

If the theory is that fuel is boiling out of the carb (into the engine or not), check the temp of the carb(s) under various circumstances.

If you don't want dirty hands, there are any number of infrared non-contact "guns" that will read temps. Alternatively you can get a contact thermocouple which, plugged and calibrated into a DVOM, will tell you the temp of the surface it's touching. Either of those should address whether fuel is boiling out. We await hearing furher. That is all.

 

[Paul Wegweiser]

I'm currently dialing back the spring pressure applied to the choke plates (electric chokes on the 38s) and will let y'all know if it helps. I haven't been driving the car regularly enough to allow frequent 15-25 minute heat soaks - and doing this in my garage just to test things is costing me precious fuel money!

I suspect choke adjustment (making the choke less aggressive - esp with warmer weather temps) will be my answer.

 

[Ohmess]

Like Steve, I have this issue with my sidedrafts. No chokes, so choke adjustment is not the issue.

I don't have phenolic spacers, so in theory I may get more heat transfer to the carbs. I like Honolulu's idea of measuring temperature; I may try that.

 

[TedS]

I put 1/2" phenolic spacers under my 38s and don't have any problems. Although it's a B35 engine.