Fuel Fuel Starvation

[Guest peter2b2002]

years ago I had a mini van that I fitted a 1100 cc stage 2 head twin carbs, use to go like a rocket, one day I was going down the A2 racing a MG got him up to just over 100mph when my engine cut out, fuel starving i could hear the fuel pump rattling like mad as it tried to keep up with the fuel demand and failing ,this only lasted a few seconds before she fired up again and off we went again shooting past the MG much to his suprise, poor thing as the fuel pump was the original one fitted for a 850cc engine

peter2b

[Guest Roy P]

many thanks to you all for trying to help me, sorry for the delay in replying but only got back from holiday on Sunday, at present trying out what I can, would love to come to the next club night at Stonebridge, what time, would love to chat to like minded people, although I am a bit long in the tooth I am still a young idiot behind the wheel, the older you get the bigger the toys. P.S. can the in line filter from the bottom of the tank be cleaned or is it better to replace it?

[kevin the chicken]

If you use the plastic and paper ones you can just throw them away. It's worth changing them as a matter of routine yearly even if you don't have problems. They are really cheap and I buy them in packs of ten and use them on everything from lawnmowers to tractors and cars. Use the larger ones if you can and then if they become partially clogged they should still supply enough fuel until changed.

[Guest ollie chapman]

Check the plumbing of your fuel system. Swirl pots need four pipes with the return from the fuel rail going back to it and a return to the tank going from the pot top back to the tank to bleed air and vapour from the pot and keep it full of fuel. Should look something like the diagram below.

 

Nigel

Hi Nigel, just to put my oar in - I'm fitting a swirl pot to my zetec with bike carbs on. Would this great little diagram do for carbs too please? Cheers Andy.

[Grim]

why? you don't need a swirl pot with carbs, unless you know something i don't

[richardm6994]

why? you don't need a swirl pot with carbs, unless you know something i don't

 

the only benfiit I can see with a swirlpot carb setup would be when you've got low fuel level and on a track.

 

Other than that, I see no real point in a swirl pot as the carb's float bowls serve the same puropse.

[Guest ollie chapman]

Yes it's the low fuel level that causes the problem, especially on a long left-hander. All the fuel surges to the right, the fuel line is on the left, hence fuel starvation. It always seems to happen on the left-handers. Keep the tank to almost full all the time, never a problem. I'll let you know if the swirl pot solves it.

[Longboarder]

To a large extent carbs don't need a swirlpot as they have a mini one built in in the form of a float chamber. However as has also been pointed out a long fast corner and the level in the float chamber drops and at the very least the mixture goes weak. Geometry of the outlets from the float chamber can also have an effect as the fuel will slosh around and climb the walls under the effect of G forces. Some carbs are better than others with the main feed to the jets to the rear when mounted. They will go rich under acceleration and cornering left or right will have minimum effect. If mounted on the other side of the engine, outlet to the front, they may go weak on acceleration! Similar problems if the feed to the jets is to one side, corner one way and they go lean, the other way and they go rich, blah, blah. So it might be worth checking if the jet feed holes are in a good place for your application. What works on a pinto may not be so good on a zetec.

Ensuring a constant feed to carbs or fuel injection is always going to be sensible but because of the small safety margin built in to a float chamber, not so critical on carbs. Pumping from the bottom of a tall, narrow bottomed, baffled swirlpot is the way to go. It can be gravity fed for carbs if the tank is mounted high enough or pump fed if you want the tank low. It should be vented at the top back to the tank This is however getting a bit anal about it unless you spend a lot of time competitively on track and don't want to lose fractions of a second.

But yes. If your bike carbs like to have a return the diagram will work just fine. Probably don't bother with an injection microfilter after the second pump(low pressure in the case of carbs).

 

Nigel

[Snapperpaul]

Fitted a swirl pot to my bike carbed Pinto S3 as on exiting roundabouts as you switch from left G to right it could stutter with a low tank

Also when one fuel pump failed I could plumb the other direct to the tank by the side of the road and get home