Strombergs and Grosejets

[3lotus]

So my '71 S4 Coupe was running great other than hot starting, but I thought i'd try some Grose jets thinking that maybe fuel was bleeding off and causing the lame hot starts. Usually after an hour or so of sitting.
I also have the updated the floats to the new fuel proof ones as well.
Anyhow ...I do all this and it runs great just sitting there. . I'm off for a drive and 10 minutes down the road I slow down ( revs down ) and smell gas and the rough running starts.....It's dumping fuel from the front carb. Limp home and pull that carb. Interestingly as I pull the fuel line pressure is released. So the float jet was working. Weird.
I took the float bowl off and everything looks fine. Reassemble and it does it again. Though it started up and ran great sitting there , just like it did the first time round. It was only after a drive that it started to leak
For kicks I put on a fuel pressure regulator and the problem stopped....it runs great AND no leak. This car has a newish mech fuel pump. Could it be creating too much pressure at higher revs ? It didn't do this with the standard jets. Or vibration at higher revs ? I also set the floats to 18mm, they had been 16mm.
I'm just wondering if anyone else has experienced this.
Thanks, Paul

[USA64]

I've not much to add other than I had the same problem. Back in the 80's my car was a daily driver; worked great except for hot starts. It went into storage after failing emissions for high hydrocarbons and then snapping an axle on the way home. I fixed the axle promptly but the carbs were found to be flooding at idle; gas pouring out of the vent holes at the air cleaner. Gross-jets were tried to no avail, life intervened, and it sat for the next 35 years. It is not yet on the road, so I can't say if the problem is fixed, hence the opening line. However, a consultation with Joe Curto had him thinking a rebuild with new float-valves (from him) would fix the problem and I didn't need to have him rebuild them (a considerable saving for me). Perhaps you could call him.
http://joecurto.com/

[Pfreen]

A friend of mine put a new mechanical pump on his twincam Europa. Fuel leaked out of the Strombergs and in fact caught on fire. There was no damage. It turned out the fuel pump was putting out almost 10psi. A regulator was installed and the problem was fixed.
So, if you fit a new mechanical fuel pump, be careful!

[3lotus]

Thanks, that's what I was wondering.
My car seems fine now, with the regulator.

[nmauduit]

Thanks, that's what I was wondering.
My car seems fine now, with the regulator.

détails or specs (plus photo?) of the replacement fuel pump that could produce too much pressure may be of interest for future reference...

[Pfreen]

CBA1F215-32AE-4DD3-B3DA-343CDAF37A7C.jpeg (79.27 KiB) Viewed 1937 times

The attached photo shows the fuel pump type that leaked. It had a pressed in port instead of two threaded ports.