Mi16 twin Dellorto fueling issues

[Wallby 39]

Hi all, 

 

I managed to get my new 205 out at Llandow last weekend for my first track day with it. I've had it running on the road for a short while and put it in for a tuning/carb check the week before the track day. They had a few issues with the pump jets leaking, but once that was sorted it was dynoed at 170bhp.

 

The main issue at the track day was that every time I came off the last corner, a long right hander, there was no power.

 

My immediate thought was fuel surge, but I'm not sure how that works with the bowls in the carbs holding an amount of fuel. The current setup is a facet cylinder type pump on the inner wing, feeding a fuel regulator set at 3psi and then on to the carbs. The fuel pick up is also non standard, just an alloy tube into the tank with no return. 

 

I haven't had the car that long so still trying to work through all the things that need attention. Any suggestions/ideas on how to sort it before I start fiddling? 

[Tom Fenton 1,541]

Easiest way to see if it’s surge is fill the tank right to the top. If that makes it better the chances are it is fuel surge/starvation.

[Wallby 39]

The tank was between 3/4 and full which I thought would have been plenty. I can't get it to do the same on the road either. Maybe it's an issue with the pump not keeping up? I'll have to check if the pump is OK. 

 

I did try hooking up a fuel pressure gauge yesterday on the regulator outlet, and the pressure did drop when accelerating, not sure if that is normal or not 

[Richie-Van-GTi 71 2 Cars]

is the Facet having to lift from the tank? It seems like a long lift from the tank to inner wing. If it gets even a small amount of air in a line that long it will take a while to recover. Try modifying the pick up so its still in a complete housing as it will retain a small amount of fuel around the pick up a little bit longer. If you intend to track it a lot I would suggest a swirl pot and a low pressure in tank pump to keep it full.

Edited April 18, 2019 by Richie-Van-GTi

[Reebmit 51 4 Cars]

I had same but now run a swirl pot and all good now..... you don’t want too much pressure with carbs.....

Edited April 19, 2019 by Reebmit
Additional info

[Wallby 39]

Thanks guys. I've ordered a fuel pump housing so hoping that will make a difference. If it doesn't then I'll be getting a swirl pot.

 

I've also just bought and fitted some 'anti-surge' top cover gaskets for the DHLA's, anyone know anything about those? Described as 'for motorsport use', but can't find much info about them.

 

Reebmit - Do you run a return line from the swirl pot to the tank?

[Reebmit 51 4 Cars]

Hi Rhys, yes I do run one, I retain tank injection pump which feeds swirl pot, out of swirl pot to Facet red top pump into regulator filter then to carbs. Run about 2.5-3.0 psi under load.. the return line comes from near top of swirl pot to tank... never had any fuelling issues since... obviously this suits me and others may have other solutions... each to their own... hope you sort out okay.... cheers

[boldy205 75]

Hi Rhys, just a thought, are the float levels in the carbs set right? This can cause a bogging down mid corner.

 

Regarding the fuel pump, there are two types of those available,  a 'pull' and a 'push' type. Most are pull types, so this is what you would need for your set up.

 

Matt

[SootySport 23]

I would increase the pressure to 5psi and/or adjust the float level a little higher, about 1mm.

 If the tank is the problem only a swirl pot will solve the problem. You don’t need a return pipe unless a swirl pot is fitted.  Also check there is no vacuum in the tank.

[SootySport 23]

This will help

 

[SootySport 23]

[Wallby 39]

Thanks guys. I have that book and did set the float last week when I changed the top gaskets for the anti-surge ones.

 

I then took it out for a blast and the bogging down /missing wasn't there. Time will tell when I go to Anglesey next month. If I have time before it I will fit a swirl pot, but given I'm currently fitting our new kitchen, time on the car is limited to say the least!

[SootySport 23]

My Westfield did the same with Dellortos, but only with sustained full throttle on the track. They also hesitated in the progression phase.  On the road it was ok at full throttle.  

That was last year but this year fitted R1 carbs and with a slight increase in float height over factory level, I can give it full beans all the time with smooth acceleration.

R1 carbs also make the car more driveable at slower speeds, don’t smell of fuel parked in the garage and no constant tweaking the balance screws.   Suggest you try them out.

[Wallby 39]

Coming back to this, I did another track day just over a week ago at Anglesey, and the issue was still there. Better than it was, but definitely still there. This time, it was happening coming off the last corner, sorting itself out after a few seconds, having a big backfire a few seconds later, before accelerating ok up to the next corner and doing the same again! These were both left hand corners, where the issue was on the last right hand corner at Llandow.

 

I had the tank full at the start and ran it down to around 1/3rd full and there was no difference, so I don't think it is a fuel starvation issue.

 

The way that it was bogging down and then having a big backfire a few seconds later would make me think that fuel is there and getting sent down the exhaust, so could it be more of an ignition issue I have. Spark plugs and rotor cap are new so maybe time to try a new coil and ignition leads.

 

Its great/strange how it happens on the part of the track where most people are watching!

[boldy205 75]

Maybe its something shifting over during cornering forces, could be something rubbing through the loom and shorting out temporarily? 

Is the battery in the front still? Is it moving about?

Is the engine moving over and touching wiring?

[Wallby 39]

Possibly, I'm not ruling anything out at the minute! The battery is in the back and securely mounted.

 

It could be a vibration causing it or something like that. The trouble is that I'm struggling to replicate it on the road, and its not doing on every corner on a trackday!

 

[jackherer 543]

1 hour ago, Wallby said:

I'm not ruling anything out at the minute!

OK If you're looking for unusual possibilities I have a story; I was in my mates 205 on track once and under heavy braking going into some corners the horn was sounding. The marshalls thought we were crazy. I assumed some wiring had got caught or something but it turned out the expansion tank had a pinhole leak and a tiny jet of coolant was spraying at the horn relay and shorting it out,  for some reason it cleared up after the corner. It didn't do it on the road at all. How well waterproofed is your ignition related wiring...?

[Tom Fenton 1,541]

I'd consider fitting a wideband lambda, at least then when it cuts out you can see if its leaning out through lack of fuel supply whatever the cause.

[Wallby 39]

Wideband lambda is a good idea and would help to point me down which direction to start investigating. Can you recommend any?

[Tom Fenton 1,541]

I've always used AEM and never had an issue with them.