Hi guys.

I have a very interesting situation.

My nikki is overly rich. The plugs are pitch black.
When it idles,the is a constant petrol smoke ,and when flooring it i can see a cloud of fuel fumes in my rear view mirror.

I havent done any jet changes ,the only changes have been some air flow improvements.

My fuel pressure is 2.1 psi and was adjusted using a trusted Glycerine filled pressure gauge.My float level is according to factory specs,and the needles are sealing properly.The amount of fuel being sucked into the primary circuit is equal on both chokes.

Any ideas ?

 

Hows your idle mixture set?

 

The idle mixture screw is the one in the middle of the carby on the drivers side. you will have to get a thin (preferrably long) screwdriver to adjust it. Turn it right to reduce the fuel, and vice versa.

Good luck!!



Carl- you have pics for him, I'm sure, right?

 

-What sort of changes?

 

ha ha, you took the words right out of my mouth.

 

Dennis (Sterling): Well,i did all the mods that you suggested ,when we spoke on the e-mail ,some time ago.

Rx7Carl : Its spot on in the middle of rich and lean. If i make it any leaner,it doesnt start by turning the key when hot. You have to then press the accelerator.(i`am fussy about this !)

*Please refer to the attached pic*
The supports have been removed (circeled in red).The remaining supoport have been smoothed,for better airflow.(circeled in yellow)

Secondary throttle shaft size was halved,with short,flathead screws fitted to the butterflies

Venturies have not been machined,seeing that i dont know the size to machine them to,but they have been polished by hand
Mechanical secondaries are also part of the list that was done

There is also no choke on the carb ,to aid in flow improvement.I will be refitting one in the near future ,only the flap, cable and linkage.


Thanks for the replies !

 

Are your air bleeds/emulsion tubes clean? Have you removed them and checked them?

 

Yip,i have removed them Monday night,and they are clean.All the passages as well.There are no air leaks.

My engine is a Bridge Port

 

So your A/F meter is telling you your good at idle, but you can smell that its rich? And what does the meter tell you when your driving?

A weak ignition can also cause it to run rich cause your not getting a full burn. And hows your timing set?

 

I dont have a A/F meter ,yet.I`am still busy laying out the circuitry for it.

Are you referring to the fuel pressure gauge ? I`am not sure about the timing,i know its very far from of standard. It was set at 5500rpm(total advance method)

I feel like a idiot...have built many successfull engines,and my one one is the tuffy! :-)

 

OMP linkage out of whack?

 

Ok, then how did you set your idle mixture? And if yur timing is too late you could just be throwing unburnt gas out the tailpipe.

 

let me get this straight, you have it set up so that it will start from cold without using the accelerator pedal, but you removed the choke?

Can anyone else see the slight flaw here?

You have it running FAR too rich, you need the choke so that the fuel mixture is at optimum for when the engine is warm. It would be like driving with the choke fully out all the time!!

Also, contrary to belief, polishing the inlet is actually bad - the lumpy/grainy texture helps keep the fuel/air mixture suspended, if you polish it, the fuel will try to stick to the walls, which can lead to backfiring through the carb and a sluggish response. But polishing the exhaust is fine - since there isn't a mixture to keep together, you just want it out of there as quickly as possible!!

just my 2p (I'm in the UK)

 

He said it starts without using the accelerator when HOT, not cold.

 

chairchild :The intake manifold is ported to match the intake port on the engine,but i didnt polish it,it still has the rough surface .Only the carb venturies were polished.

Rx7Carl : I set the idle mixture,using my dads ear (sounds funny).He has tuned Webers for the last 35 years,and is very good with determining when the mixture is right.

The idle at this stage is a crisp,smooth brap-brap.no 4 stroking or anything,it sounds quite happy .Is also very rev happy.

Any idea what i could set the timing at ? I think i`ll have to start looking at it,seeing that i cant really find fault with the carb.

Thanks for all the replies ! Please do reply if you have any suggestions

Karis

 

Ok, well just as an FYI, the starting point is 3 turns out. On the timing, start back with the stock setting.

 

Thanks!
I`am on my way to my engine builder after work,to here what timing he set it to.

I decided that he should also build a intake manifold for me for 2 40 DCOE Webers. I need more hp!!!

Stuped question : I have never set the timing to normal specs on a Bridge Port.Will it be difficult to start if i do so ?

I`ll update you guys tomorrow.

 

Hi.
So i went to my enginebuilder last night (Lazerspeed Developements) He said that he set the timing to 20 deg at 5500.

He suggested that i should mark my dizzy and turn it.To see if it makes any difference.

I`am quite excited about the manifold for the 40`s.I`am sure its going to run great.

Almost forgot ; i put a choke on the nikki ,working with the cable,and no electrical stuff. The result : It flooded it horribly,and didnt aid in the cold starting at all.

Luckilly one fo these days,i`ll be running Webers.No more Nikki!

Karis