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Engine flat at top end

malcolm

malcolm

& Clementine the Cat
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Location
Bedford UK
I think I'm having a similar problem to ggcton. My Gordini is a bit flat at full throttle.

Previously I was having trouble with the distributor. I've replaced the smaller of the two advance springs with one from a spare R5G distributor and that's cured the problem with advancing at idle speeds which was making the idle speed difficult to control and requiring a great deal of advance to make the car work.

Now the advance can be set at factory settings, the idle is smoother, and advancing it a bit further will cause pinking, so it feels about right.

Now this full throttle thing - It's flat on full throttle regardless of whether I stamp my foot down or try to bring it in gently, and reducing the throttle slightly seems to improve things. The problem is much less severe now the distributor has been sorted, but it's still there.

I've had the carb off to blow out the jets several times. I'm thinking not enough advance or not enough fuel. But the car must have worked in the past so I'm not keen on just bodging it with a jet. Equally I feel I'm missing something. Ideas much appreciated.
 
Just spoken to an engine development guy. First thing he suggested was it's not advanced enough. True enough the problem does reduce if the advance is increased, but I'm on to pinking.

Second suggestion was trying some higher octane fuel. Fuel doesn't seem to last very long so I'll give that a try in the next tank.
 
We have 95 octane unleaded petrol as standard and an option of 98 octane which is a lot more expensive.
 
Do things improve a little (or a lot) if you pull the choke out. For example, if you put your foot to the floor and it plateaus out try playing with the choke, and if there is a surge of power as you pull the choke out then it points to not enough juice going through the carb.
 
I've got unleaded valves in there so no additive.

Will try the choke at the weekend - having can't be bothered moments in the evenings these days, but I didn't think of trying that. There's not a lot I can find on the R5Gordini website so likely a fault to find just on mine.
 
In our country you can buy 95, 98 ,100 octane fuel.
The price gap is not that big.
I was thinking to poor in 98 because the R4 was originally fueled with 98 leaded fuel.

But lets came back to you problem. If my R4 isn't fully warm and I press the pedal to the metal. Then it's going nowhere, my solutions were pull the choke out or release the pedal just for a bit. But when the engine is hot, the problem is gone.
 
About ignition advance-the best way to set it on any high performance engine is not at idle, but at the point of the maximum advance. On virtually all distributors of that age the first spring (soft) will have been stretched, and allow more ignition advance at idle rpm. That will make you to retard the whole curve, just to achieve the correct idle advance.

There is really little difference, if an engine idles with 8 or 14 degrees ignition advance, but a huge one if these 6 degrees are taken off the maximum torque rpm point.

So I guess it would be better to have the engine set up on a rolling road (both fuelling and ignition timing). As a first try, set the ignition to the maximum advance given in the manual and see how it behaves.

There is also a far easier solution to your problem, simply drive Ornella continuously for one week...when you drive the Gordini again you will not notice any top-end flatness :-D
 
I think you are right angel. The old spring I had removed seemed soft, but the new one may have stretched (it was from another distributor).

I've advanced it a bit. It's pinking a little on heavy throttle at low engine speed so probably as far as I can go. That has made a difference - it isn't loosing power on full throttle, but it doesn't seem to add much power.

Tried pulling the choke out a little and it might make a small improvement, though it was difficult to judge. Rolling road might be an idea.

How do you get hold of new springs to try for the distributor? I have an idea of retaining the current spring stiffness but reducing any slack. Some cotton thread to tie the spring to the supports might work for that but it would be easier to fit a new spring.
 
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