+4 apparent fuel starvation/pressure problems

Technical queries or suggestions

+4 apparent fuel starvation/pressure problems

Postby Sean Horwood » Sat Jul 17, 2010 1:12 pm


Another one in my quest to put my +4 on track (TR engined)!!

My car appears to be suffering from fuel startvation or pressurisation problems. On anything less than half a tank the fuel pump will just run for ever trying to pressurise the system. I can sometime force the issue a bit by removing the fuel pipe, where it enters the engines bay, and covering it with my finger - pressure then builds quickley and it kind of sorts itself out.

I've dismatled the pressure regulator and checked the spring is still 'springy' and all seems fine.

Next stop was to have the carbs re-built as I suspect the needles are not seating correctly and realeasing fuel through into the body of the carb and thus de-pressurising the system.

I tired two fuel pumps and am happy that the fuel is being pulled through.

Does anyone have thoughts on this?

Many thanks

Sean Horwood
Posts: 55
Joined: Mon Jun 29, 2009 12:15 pm

Re: +4 apparent fuel starvation/pressure problems

Postby Philip Tisdall » Sat Jul 17, 2010 9:05 pm

Just a thought, if the fuel pick enters the tank from the top have a look at the pipe that goes into the tank it might be sucking in air. This would, I think, cause a strarvation problem if the car works fine untill the tank is 1/2 full
User avatar
Philip Tisdall
Posts: 366
Joined: Thu Dec 15, 2005 6:10 pm
Location: Warwickshire

Re: +4 apparent fuel starvation/pressure problems

Postby keith morris » Mon Jul 19, 2010 11:31 am

Also check the baffles in the fuel tank are all present and correct. My 2 str +4 flat rad has a "high mounted" fuel tank and unless the baffles do their job the pump picks up air due to fuel surge in the tank (just like oil in your sump) - esp under braking or hard cornering - this lead to very annoying fuel starvation until the air has been pumped thorugh - and then it all works fine. Took me ages to spot this - changed pumps, regulator etc. etc just like you! regards
keith morris
Posts: 30
Joined: Mon Aug 04, 2008 8:56 am

Re: +4 apparent fuel starvation/pressure problems

Postby Sean Horwood » Mon Jul 19, 2010 5:51 pm

Thanks Guys,

I think we're on the right track I also discussed the problem over the weekend and discovered the tank is foam filled (I didn't realise that because the foam is on either side of the baffles) and it is quite possible that the foam has broken down as it's more than a few years old.

Anyway the tanks coming out, straight after the Silverstone Classic, and all will be revealed!!

Sean Horwood
Posts: 55
Joined: Mon Jun 29, 2009 12:15 pm

Re: +4 apparent fuel starvation/pressure problems

Postby Lorne Goldman » Thu Jul 22, 2010 8:29 pm

In NA, racing requires a fuel cell, or a foam filled deformable bladder held in an aluminum tank shaped container. (Foam alone will not prevent puncture and leakage and pre-1993 Morgan fuel tanks are prone to puncture.)

I run with such a cell. Of course, there are no baffles because of the bladder and foam. BUT, foam does not completely stop fuel from sloshing and does slow its return. When the fuel lowers, fuel starvation becomes possible when the the fuel being forced form one side or t'other. This also happens to a degree with baffled tanks and no foam.)

The solution is a "collector". This is a small box placed where you want in the tank (mine is at the rear). It is filled with fuel through one-way valves where the fuel can slosh in but not out. It is attached to the tank outlet with fuel-submersible fuel line (normal fuel line dissolves when immersed in fuel.)

The collector collects and holds fuel within it and reliably delivers it to the supply hose as long as there is fuel left. Fuel delivery is no longer effected by the foam and the baffles are unnecessary. There is no stumbling with lower fuel and sharper and/or longer turns. However, when you are out of fuel..you are REALLY out of fuel.

They are an easy and inexpensive way to cure many fuel supply problems. I had mine custom made by FuelSafe in the US. http://www.fuelsafe.com/

They come in any shape, hard or flexible materiel, in-tank fuel pump optional for EFI. Click

Lorne Goldman
Posts: 20
Joined: Thu Mar 10, 2005 12:42 pm
Location: Canada

Return to How do I ?

Who is online

Users browsing this forum: No registered users and 1 guest