Starting from hot - dellorto carbs

[pabbage]

Hello clever people

Could someone explain why my dellorto carb sprint will not start from hot unless your foot is on the floor. If you have you foot on the floor it will start very easily. Is this normal? What mechanism is at play - what does having the carb opened fully (foot to floor) achieve when hot? Could someone explain to me in very simple english.. and explain if it is fixable?

Thanks

Paul

[trw99]

All I know is that it works!

Hot engine, open the throttle wide open, starts away.

Tim

[pabbage]

Won’t start with out it but why????

[JohnMorin]

I think it might be because when you push the accelerator to the floor the accelerator pumps in the carbs squirt some fuel into the ports, then all you need is air.

John

[pabbage]

Thanks John / I just don’t know enough about dellortos … you can open and close the throttle as many times as you like but it won’t start. Only if the throttle is full open and held open will it start .. which is also the technique for a flooded carb.. so does it actually cut fuel when fully opened?

[mbell]

When you press the throttle on DLHA/Webers the pump jets shoot fuel into the engine inlets. This only happens as you press the pedal, so as soon stop moving you foot you don't get any more fuel. You then need some air to ignite that fuel.

So pressing it once and holding open, give you shot of fuel and loads of air, so the engine will start easily.

Not sure if starting with no throttle is difficult because of lack of fuel being pulled from carbs, or not enough air for any fuel.

[alaric]

Hi.

There's no fuel shut off with the Dellortos.

While cranking the engine is it possible that the spark is not as strong, and the open throttles just gives it a better mix / quantity to allow it to fire? That's why there are ballast resistor coils - the volts are boosted while cranking. But modern coils will usually give enough spark if all the components are in good condition.

So I guess I'm suggesting you check the ignition system to make sure that it's giving a strong spark. With mine I put the spark plugs on top of the engine with them earthed, and turned out the lights. I found one of the plugs was not working. You may find yours are intermittent while cranking or just very faint.

My car now has new ignition coil, leads, cap and plugs, and rebuilt dellortos, and starts first cycle of the engine. When hot it just starts with no throttle or choke needed - I can reach in and start it while standing next to the car. It doesn't run as smoothly as I'd like because one of the barrels has a leak in it, but it certainly starts ok.

I hope that helps.

Sean.

[promotor]

My motorbike (carb) had a hot-start plunger as well as a choke lever - as you'd think, the hot-start plunger was used when the engine was hot - this plunger uncovered a hole to allow more air into the engine if the engine wouldn't start. I presume this is to overcome the engine being "gassed".
As most carb-engine vehicle users know sometimes when engines are cold (depending on how cold) they need more fuel (via choke or a couple of pumps of the throttle, depending on carb type) so it would appear the inverse is true (ie more air) when trying to start an engine from hot (depending on how hot).

Since owning this motorbike I have used the method of opening the throttles (depressing the throttle pedal to open the butterfly's to allow more air into the engine) numerous times on carb'd car engines when an engine refused to start when hot, and it's always worked. Just don't pump the throttle too much or you may foul the plugs.

[Slowtus]

Some light reading which may help...

https://www.vortex-rok.com/gestione/all ... /88_40.pdf

[pabbage]

Some great comments and links / thanks everyone

[Dellortofan]

Some cars need the phenolic spacers if the manifolds heat up.
But if it is dripping fuel when hot or stopped then it may run into manifolds etc.
Theres something called "dell drip"...