8 replies to this topic

[mini_mad69]

Right im trying to get my 1380 running.


It runs a little rich on idle but not too bad, on cruising it is lean, and under hard acceleration it runs rich.
I have a a fuel ratio gauge inside the car which is telling me where the fueling is.


Now my question is, when adjusting the fueling does it adjust the whole fueling range, I.e Idle, cruising and acceleration.


I have a BBW needle at the moment, but I have a BFZ needle sitting here, that came with the engine, although a few things have been changed since it ran with this needle.



This graph shows that it will run about the same at idle if not a little leaner, which is what I want, it also shows running leaner at hard throttle.


SO again the question is, if I fit this needle the engine will run leaner all through the rev range. But if making the mixture richer, will it make the whole throttle range richer, theoritically it will, as it lowers the Jet making the hole bigger for more fuel and richer through the rev range.



Ben

Edited by mini_mad69, 21 July 2009 - 06:21 PM.

[Turbo Phil]

You need to set the mixture to give the correct setting at idle, then the needle needs to be the correct profile to ensure the right fuelling throughout the rest of the range. If you can't find an off the shelf needle to do the job why not profile your own if you have a wideband gauge fitted ?

[lrostoke]

Like mentioned above, profiling a needle may be the way to go.

I've never tried it, but from what I can gather the 0 - 16 on the graph corresponds to the 16 sections of a needle.
As the piston in the carb lifts and falls a different section of the needle is responsible for the fueling.

The trick is knowing which section is in use and corrisponds to the readings on your fuel ratio gauge, I believe there is an optimum ratio you should be looking for.
I saw one article where they had made a modifiction to the dashpot plunger so that a rod corrisponding to the 16 lands on the needle could be seen rising and falling

Found it

http://www.terryhunt.../picsb/pics.htm

Edited by lrostoke, 21 July 2009 - 08:40 PM.

[Ethel]

Adjusting the mixture just moves the jet up or down.

Bad step ladder analogy:

If you are on the 3rd step above the ground and you go up 2 steps you'll be on the 5th step. Now if the ladder sinks into the ground (it's boggy ), that's equivalent to leaning the mixture by moving the jet up. You'd now be on the 4th step and if you returned to the previous step it would be the 2nd. The line is the same but it's all a bit lower on the graph.

Or as Turbo Phil says, you need to alter the needle profile where it's over or under fuelling.

[mini_mad69]

Ok, thanks guys, I'll fit the BFZ needle tomorrow and see where I am, if it's out I'll go about profiling it a bit, it won't be perfect but it'll be better than it is now.

[mini7boy]

alternatively, if you need expert help or a needle customized for your engine's requirements, check out AC Dodd and his needle service
He can be reached through M&L Motorsports. See information on this website: http://www.mlmotorsp...i...=view&id=56

Edited by mini7boy, 23 July 2009 - 07:08 AM.

[Grayedout]

I have a a fuel ratio gauge inside the car which is telling me where the fueling is.

How is that working? What is it based on ?

[998dave]

I have a a fuel ratio gauge inside the car which is telling me where the fueling is.

How is that working? What is it based on ?

Would a lambda sensor work, but wired in to give AFR rather then a signal to an ECU?

[Strontium Dog]

I have a a fuel ratio gauge inside the car which is telling me where the fueling is.

How is that working? What is it based on ?

Would a lambda sensor work, but wired in to give AFR rather then a signal to an ECU?

You need a wideband lamda for monitoring AFR's. I use the VEMS unit as found here

http://www.vems.hu/w...page=AFreshTiny

It's very good unlike the cheapo fleabay offerings that attach to a narrow band lambda which are as much use as a chocolate tea pot!