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Car consumes way too much petrol

Messages
34
Location
Kenya
#1
Hello everyone,

I have a 1970 r4, which runs on a zenith 28IF carb. I restored the car myself and the engine runs smoothly. However, I have only managed to keep the fuel consumption to a maximum of 12 Kpl (28mpg), which I think is horrible. I have new spark plugs and the distributor gap is properly set. What else can I check? Someone suggested that I fit a return pipe after the fuel pump back to the tank. I, however, doubt this would change anything, because in my little knowledge, even if the pump was to overwork, I suppose no extra fuel will drive past the float tap in the carb. Am I wrong? Should I try fitting a return pipe? Any help will be really appreciated.
 

mojobaby

Enthusiast
Messages
1,109
#2
Hi Brian
I had the same problem until I reset the choke flap on the carb. I was running with the flap half closed which meant less air and more petrol was being used.
A good indicator will be black spark plugs.

To test, make sure that your choke button in the cab is pushed all the way in. Then loosen the screw on the carb that holds the choke cable. Now make sure that the choke flap is in a completely upright or vertical position. In other words open it as far as it will go.

You can read how I fixed my carb here:
http://www.renault4.co.uk/forum/threads/zenith-28if-problem-solving.8248/
 

seedc

Enthusiast
Messages
23
Location
spain CLM
#3
hi!
Maybe the valve clearance.
You have said have restored the engine?

I know one case, the owner of a R4 told me doesn't work very good...
I asked him for the valve clearance and he told me"what the hell is that"???

I made the valve clearance and after work perfect.
the spark plugs were black too because the combustion was working bad.

Sorry for me English.
I don't know if you know what I mean...
 
Messages
34
Location
Kenya
#4
Thanks Mojobaby and seedc. I will go through the carb flap opening again and also check the valve clearance then report end of week. I appreciate your advice.
 
Messages
34
Location
Kenya
#5
Hi Mojobaby, Seedc, I confirmed the flap opening was all way out and valve clearance was as required, but the car still drinks like a sailor. Anything else you think I should check?
 
Messages
238
#6
Might I suggest a carburettor rebuild? I've just had a carb rebuilt for a Daf 33 and the result has been spectacular! It runs like a new car, with quicker acceleration, happier cruising and better economy. I don't know if such facilities exist in Kenya and they're pretty limited in England, but a company in Leighton Buzzard, Buckinghamshire were helpful in sorting mine out. Details available if you PM me.
 

seedc

Enthusiast
Messages
23
Location
spain CLM
#7
Hi Mojobaby, Seedc, I confirmed the flap opening was all way out and valve clearance was as required, but the car still drinks like a sailor. Anything else you think I should check?
ok.
I don't know if you have check the angle and the advance of ignition.
If the advance don't works well could makes the engine drink like a pirate.
Could you post some pictures of the spark plugs?


Also check what Andrew say.
A rebuild carb can be a good idea.
Before rebuild the carburetor you can regulate the CO and the mix.
 

mojobaby

Enthusiast
Messages
1,109
#8
hi Brian, I was really hoping that it was the choke flap because I had that issue and went from 30mpg up to about 40mpg immediately. The condition of the plugs is the key to whether you are running too rich. mine were always black, but not any more.

Anyway, a carb rebuild as Andrew suggests is probably a good move.

I made the mistake of opening my carb without a spare gasket on hand and the existing gasket broke into a 1000 pieces and I had to wait a week for a new one to arrive.

I suppose that you've already inspected the carb with the engine running to make sure you have no visible leaks.

Of course it might be possible that someone has changed your main jet to a bigger size and that's why you're using more petrol. Your main jet should have 91A printed on it. You don't have to dismantle the whole carb to check this. Have a look at my post.

In 2010 Angel also suggested using thin copper wire as in my picture below to reduce the amount of petrol in the main jet. Never tried it myself though.
16416-258d5d3e26d7ab5bdeaf038de703d898.jpg
 
Messages
34
Location
Kenya
#9
Great news guys!

Finally, after lots of frustration, I decided to try the return pipe suggestion. Put a 't' splitter immediately after the fuel pump, one outlet heading back to the tank and other to the carb. This fix allowed me to do an astonishing 47mpg. I have no idea why this would work, because I used to imagine that the float tap in the carb, would not allow more fuel once the chamber was full. The car drives smoothly, and the smell of unburnt fuel that was creeping into the cabin has vanished. I will take a few photos of the car tomorrow as well and share with all. Good evening and good night, from Nairobi, Kenya.
 

seedc

Enthusiast
Messages
23
Location
spain CLM
#11
Great news guys!

Finally, after lots of frustration, I decided to try the return pipe suggestion. Put a 't' splitter immediately after the fuel pump, one outlet heading back to the tank and other to the carb. This fix allowed me to do an astonishing 47mpg. I have no idea why this would work, because I used to imagine that the float tap in the carb, would not allow more fuel once the chamber was full. The car drives smoothly, and the smell of unburnt fuel that was creeping into the cabin has vanished. I will take a few photos of the car tomorrow as well and share with all. Good evening and good night, from Nairobi, Kenya.
I glad you fixed it!!!
 

petak

Enthusiast
Messages
1,239
Location
Vodice, Croatia
#12
Great you have sort it out but still do not get it how it works.

My thinking was renewing carb and cleaning from inside.

First time i hear about return line on Zenith28IF

Pictures please.....maybe others can reduce consumption in same way.
 
Messages
238
#13
I'm guessing (only guessing, mind you!) that the float chamber ballcock wasn't working properly and was allowing too much fuel through the carb. What your actions have done is to reduce the fuel pressure AT THE CARB and divert the excess pressure back into the tank-a sort of petroleum merry-go-round! Although you now have a correct MPG figure (in fact a pretty good one!) and the correct pressure at the carb, I would be inclined to carry on investigating why the fuel pressure at the carb was so high. The pump pressure can be altered by changing the number of gaskets in between the pump body and the engine.
 

mojobaby

Enthusiast
Messages
1,109
#14
Good for you Brian!!

But like Andrew and Petak have said, it would be nice to know the reason for the poor fuel consumption.

Andrew makes an interesting point about changing the number of gaskets, I had no idea that you could do that. It might be worth checking that you've actually got that 8mm spacer gasket in place between the engine and the pump. It's function is to protect the fuel pump from the heat from the engine but will also obviously have an effect on the pump pressure as well.
 

JdeW

Enthusiast
Messages
328
Location
Laarbeek, The Netherlands
#15
Great you have sort it out but still do not get it how it works.

My thinking was renewing carb and cleaning from inside.

First time i hear about return line on Zenith28IF

Pictures please.....maybe others can reduce consumption in same way.
According to the book of Haynes, chapter 12, section 8 describes a return line only according to Zenith 28if (or 281f?) carbs.
I'm considering going for this option with a fuelpump with calibrated return.
See enclosed picture and sorry for the Dutch descriptions I haven't an English Haynes book...
Zenith 28IF modificatie_2.jpeg.jpeg
 
Messages
34
Location
Kenya
#17
Here is how the restoration happened
 

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