What happens with my heating when my foot is on the floor?

[JezWest]

I run a 1972 1200 with a 1776cc motor with Dellorto DRLA 40s. I have CSP heater boxes and a Python exhaust.

All is well, apart from the nagging feeling that I need an 82mm crank in there!

Now the weather has just cooled off in the UK, I'm using the heating again. I've noticed that when I get my foot flat on the floor, when only pulling low RPMs, that I smell fuel in the car. Not exhaust, fuel. Once I back off the throttle, it clears quickly. I never notice this on small throttle openings. I've taken to shutting the heat off on the one big hill I regularly drive. Mostly it's not an issue: I only get my foot on the floor ( in winter ) on that hill and if I'm being an idiot in traffic.

But why? I've checked all the fuel lines rigorously and there are no leaks.

I figure the basic issue is having a carburettor throats right next to the fan. Maybe when I have my foot down at low RPMs, I generate a lot of fuel stand off and the fan draws it into the heating air?

I don't think I'm doing myself much harm: I have so much heat that I always have a window open an inch even in the brutal English winter (!). I guess a vented decklid, lighter right foot, some ducting around the carbs might help. I suppose not having dual carbs would fix it, but that isn't happening as I'm not really a turbo guy.

[Fastbrit]

Yes, fuel stand-off, mixed with accelerator pumps dumping extra fuel – foot to the floor at low rpm will do it every time. Not enough rpm (vacuum) to pull fuel vapour through.

[Zach Gomulka]

Yes, fuel stand-off, mixed with accelerator pumps dumping extra fuel – foot to the floor at low rpm will do it every time. Not enough rpm (vacuum) to pull fuel vapour through.

I agree. Never experienced that on a type one though.

Open stacks or filters?

[JezWest]

I have filters. Maybe I'll run that hill in third.

[JezWest]

The standoff is there because there is fuel/air mix travelling down the manifold and that flow gets interrupted by the valve shutting and the mix 'bounces' off the valve? If I have that right, do fuel injected cars have stand off? I guess that if you inject fuel into the cylinder, then no; but if you inject fuel above the valve, then yes. Does that make any sense?

Amazes me how many of these things I've never wondered about before.