My 914 is running a 1.8 (ish!) 40 Dellortos and recently recorded 111BHP and 121lbft of torque after a carb set up so yesterday I went to have a little thrash about.
A couple of times when the traffic cleared I really kept my foot flat down and pushed to over 100MPH on a slight uphill. It was still pulling strongly for a few seconds then seemed to lose power and splutter slightly. I backed off and it returned to normal. It seemed like the carbs emptied as if the fuel pump couldn't keep up. I had the heater on and the rich oily aroma changed to a hot sharp smell like it suddenly ran lean. It's running the small square facet pump mounted up front near the master cylinder.
Any ideas please
Thanks
DavidClick to view attachment

how are the carbs configured?
Is this a new issue? been fine before at this RPM?

Rich

Hi Rich
What do you mean by configured? Theyre twin 40 DRLAs. It has happened once before in a similar situation, top gear foot hard down for a prolonged period then a splutter. That time I was low on fuel so went straight to fill up thinking it was that.when running through the gears it's fine through the rev range but then you rarely have it to the floor for as long

I sugggest getting a wideband air/fuel gage to monitor your ratio. You may be running very leaner as RPMs go up and just need to increase fuel from carbs at higher RPMs.

Just looked up the wideband gauges, what's involved in installation? Presumably it won't rectify the issue just confirm it? What would be next if what I suspect is true? I'm thinking perhaps just be kinder to the car and ease off when I get to 100mph!

The Wideband O2 sensor needs to be added to your exhaust at a point after all cylinders exhausts are combined. Mine is just before the muffler but after the resonator. You have to run the wire set to the gage in the console, I run mine thru the same hole as the speedometer cable to get it in the tunnel. I also added a Vacuum meter to monitor load, but your issue is at full throttle so load is high and vacuum is very low.
If you see that the mixture gets to lean at high RPMs then a carb adjustment would be required, maybe new Jets.

Does your distributor have the rev limiting rotor?

No, it wasn't revving to the max

What model of fuel pump are others running? It seems to increase the flow, the pressure goes up too high so then I'd need to but a pressure regulator aswell

Facet pumps, while cheap, are typically viewed as inadequate/unreliable with carbs for these cars. A Carter or similar style rotary pump is preferred as they provide a constant volume of fuel at an adequate pressure. CB Performance over here in the U.S. sells one such pump: http://www.cbperformance.com/ProductDetail...roductCode=3193

This pump is self-regulated at 3 1/2 PSI, which is perfect for DRLAs or most Webers and eliminates the need for a pressure regulator. I would start there and see if that clears up your issue. From what you're describing, it does sound somewhat like fuel starvation.

That being said, go through the normal (read: FREE) checks first. Check/set your valve clearance, verify timing and check to ensure that the carbs are synched at both idle and 3,000 RPMs. Then, when you have the time and money, replace the Facet pump to eliminate variables.

Sounds like a sensible and affordable plan, Thanks

Float height is the first thing I'd go to.. If its set too low the float bowls never fill completely and therefore they run out of fuel soon, no matter what pump you have. The pump can aggravate the issue, though.

Find a dyno, you'll learn more in an hour than you will in a year of driving and tuning.

The Facet pumps are horrible and honestly 3.5 PSI is too much for these carbs. They love 2.5 PSI dynamic and anything above 3 static can bypass the needle valves. Having more pressure might help to mask a float height issue a bit, until it runs out of fuel.

I like 10 mm closed and 28mm on the drop with those carbs. Your needle valves may be too small, as well.

Don't forget, going too rich will create just as big of a power loss in the top end as going lean. Nothing kills top end power more than being overly rich. Thats why you need to find a dyno (with AFR) and quantify the condition before applying corrective action.

Thanks Jake, it was on a dyno a couple of weeks ago for a basic carb set up so I'll take it back with these ideas and see what they say.

Have any graphs? Were they plotting AFR?

If you set float height, or if they do, make sure they/you don't compress the ball-spring in the needle valve. If they/you do then your float settings are too low. Set the upper/raised height without compressing the ball.

I'd trust Jake's numbers, but the ball is marked Sf in this pic.

Compressing the ball changes it all.. I blow on the fuel inlet to know if the ball is open, or not during this setting.

I think I set mine to 5-6mm closed per the CB Performance book, but I've written down Jake's settings and will try them sometime as I'm running a non-standard air correction jet to correct my high speed enrichment.

Wow! I'm trying to keep up but fear I'm out of my depth. I'm gonna print all this out and take it with me to the shop later this week.
Thanks everyone for the input so far.

This was the only graph I got, torque and power. What's AFR?

Click to view attachment

Air to Fuel ratio.
Tom

What brand of dyno is that? Calibrated?
How is the motor built?

I've actually found the facets to be loud but last a long long time. Regulators should help smooth them out. And they don't seem to die.

I've no idea what brand of dyno, its the first and only time I've had a car on one and just dropped there in the morning and picked it up at lunchtime!
I also have no idea how the motor was built. When I bought the car a year ago I thought I was buying a 2.0 car. When it arrived here in the UK I discovered it was a 1.7 car with a 1.8 motor! The guy I bought it from says he didn't know and sent me a copy of the ad he bought it from a year before and that stated it was a 2.0.
I'm guessing its had some work internally as the dyno numbers would suggest increased bore/stroke and some cam changes but I've no idea what.
I have tried without success to get hold of the previous previous owner on here but no luck. The car is a Zambezi green '73 MY car with Tan interior from the Boston are if anyone remembers it? Was off the road for a number of years, maybe as many as 10!

Got me thinking about my own Dello conversion (done by PO). Haven't got car running yet, but I'm concerned about fuel tank venting. PO did not have a gasket on fuel tank filler cap, so plenty of venting there. I'm not satisfied with this and want to insure adequate venting, but minimize unwanted vaporization and pollution. So thinking of using the leftover small plastic line leftover from the old FI as a vent. What do you use ?
If unvented (or inadequately vented), possibly at high load vacuum built up in tank may hinder pumping capacity.

Some good comments here from folks with far more experience than I. I agree that the float settings are also a suspect, especially if the carbs were installed "out of the box." It seems that even if they are set correctly, the settings can often change during shipping/handling. So it's certainly something to check for anyone installing carbs.

That being said, I still believe that putting in a good quality rotary pump, along with fuel filter (prior to the pump) and if need be, a regulator can eliminate a lot of potential sources of frustration. Also, if the condition of the strainer sock in the bottom of the tank is unknown, this should be checked and replaced. If clogged, it can mimic symptoms of starvation, especially under situations like full throttle where the volume of fuel being delivered is important.

Regarding venting of the tank - I used the nipple off of the stock expansion tank and routed a line out to the rocker panel area. Seems to work quite well and eliminates all fumes that could potentially enter the cabin.

Ok, it's been a couple of weeks and so far I've changed the pump for a Huco rotary and after replacing the inline filter I'm getting 120 l/hr so supply to the carbs isn't the issue. I've had the chokes reduced to 30 from 34s and rejected accordingly also larger (200) needle valves.
It runs much smoother during normal use but it still does it when full throttle at higher speed for more than about 5 seconds.

If the problem occurs at a consistent RPM regardless of load you may actually have a faulty distributor RPM limiting rotor, bad points or worn distributor point contacts...

I read the title of this thread with the sun on my monitor and I thought it said:

"Fuel starvation when making out? "

My first thought was "She must be HOT if you dont even stop to eat...."

That would be my kind of woman... Might even lose a few of the winter pounds too. LOL!!

Nothing comes in the way of food!!

I'm running a new Bosch 050 without standard rotor. It will rev happily through the range in the lower gears just as it takes longer at full throttle to get towards redline the fault occurs

Good to hear that you took care of the other unknowns first. That was the simple stuff. If you have never pulled the tank out, I'm sorry to say, that might be in your future to check the condition of the strainer sock at the bottom. Might be clogged up.

Even though I get full spec flow (30 secs for a litre) from the pump when I time it pumping out a litre at the carbs?
I will pull the tank though as I've gone through everything else, it's driving me mad. Not that I need to drive it that hard but it's nice to know you can once in a while, that's the point of having it after all.

Oh and one more thing, when hot and I stop in traffic it won't idle, it splutters and pops before dying unless I heel and toe to keep the revs up.
Getting really tired of this

OK, so just incase anyone remembers or cares I was having what seemed to present as a fuel starvation issue.
Last week I took the still unwell car to an airfield track day despite knowing I should solve the problem first. Well you guessed it, I broke it

Despite the complete meltdown of the plug after much head scratching and beard stroking I borrowed a spare plug and with eyes closed turned the key. It didn't run too badly so I thought we could make it a couple of miles from the track and call the recovery truck. It made it 130 miles all the way home!!
The following day I drooped the engine and removed he damaged head. The offending plug port had a helicoil insert and now a fair bit of damage to the seat face. I had a pair of spare heads so had one cleaned and the valves reground. Yesterday I fitted it and re installed the engine.
You're ahead of me, the issue I had is gone
I can only assume the insert was bad or the fitting of it had cracked the head and when under load for a prolonged period the crack would open with the heat and cause the spluttering as if fuel had run out. By backing off the fuel supply wasn't catching up as I thought but the head was cooling sufficiently to close the crack or leak past the insert.

I've spent best part of £1000 and numerous hours trying to solve this when all I needed to do was break it a bit more!

Thanks all for your input, I've learnt a lot.

wow...
that plug is a keeper


so glad you fixed it
nasty plug...
brant