Hi guys! (and girls)

I have been having trouble with my nikki,and i`am fed-up with it

Here is my setup

Setup : 12A Bridge Port
Good Compression(only 600 miles since new seal springs installed,seals were fine)
Fuel pump : Nippon Denso 3 Psi ,18 Gph
Exhaust :2.25 " header ; 2.25 " exhaust ,straight through silencers

The fuel level is halfway in the Nikki`s floatbowl,looking through the glass.
the APC is squirting a strong,equal amount into both Primary chokes when acclerator is depressed

It doesnt want to start.I only makes promising sounds,and allmost starts.I normally pump the accelerator 2-3 times before turning the key

I have tried to pour down fuel ,the primary chokes.It starts then, after some turning.

When trying to restart after shutting down ,it *almost* starts , but doesn’t.
Sometimes it does, when I pump the accelerator 2-3 times, but only on the odd occasion

Any input will be highlly appreciated

Karis

 

Please help!!!!!

 

A Nikki on a bridge port? That doesn't sound like it would work! I can't see how a stock carb can possibly provide enough Air/Fuel for a bridgy..

Carl, Sterling... correct me if I'm wrong please?

Jon

 

vacuum leak? Does it idle normally when warmed up? Sorry, no experience with ported engines.

 

Im with vipernicus, i dont think that a stock nikki flows enough for a bridge port. whats it around 300 cfm?

 

not even 300 cfm. I have seen tests that with stock air cleaner and junk the nikki only provides around 275 ish cfm( w/ k$n). and with air cleaner totally removed only flows 350cfm

 

Karis, sounds like you may be boiling off the fuel in the float bowls after a hot shutdown. Do you have any heatsheilding between the exhaust header and the intake? So your starting off with a dry carb everytime. Then you have to wait for the carb to fill up before itll start right. Next time, before you start it, pop the hood/bonnet and look at the sight glasses to see if theres fuel in the bowls.

FYI- The stock Nikki flows approx 300 CFM. The aircleaner is a major restriction. Yes as stock its too small for a BP, but that has nothing to do with getting it started and idleing and actually driving.

 

Hey, Rx7carl and sterling are the ones to talk to, but I have a stock nikki on my bridgey and it runs sweet. The performance is crap though, but it does run fine. It sounds like you may have a manifold or carb leak. Try spaying some engine start round the carb and maniflod and see if it spikes in revs when its running. Or soapy water is ok and see if it spluters.

My bridgey never starts with out using a choke linkage I made. I just made a pull choke from the cockpit that conects to the choke linkage on the carb. Having that closed when im cranking her over gives her heaps more compression ( i think but could be wrong) but yeah starts first time every time.

Also check your timing, port overlap requires advanced timing, maybe its out.

Please correct me where im wrong tech guys. This is all a guesstimate

 

You know, you just gave me a thought. A BP also has low compression at low rpm's cause of the porting. The fuel your pouring in may be actually acting to seal the motor [like adding oil to a piston engine to bump up the compression] bumping up the compression. Karis, hows the cranking speed of the engine? With a BP youll need really good cranking speed to get her started. Maybe next time as an experiment, add oil instead of fuel into the carb to see if it starts the same.

 

let me get this straight,

it won't start when cold or hot?

If cold, the Nikki may not provide enought fuel but it would at least run and idle. It would just have problems under a heavy load.

Checking vacuum leaks is a good idea too but i would also run a fuel pressure and fuel volume test, fuel in the float bowl or not.

Let us know what fuel pressure and volume you get.

 

Tipping a bit of oil down the carb will bump up compression, cant be to good for it, but it shouldnt do it any harm. Better than tow starting it I guess :-P

 

Thank You very much for the replies!

Ok....didnt think that the cranking speed would be to slow!
If i think about it...it makes perfectly sense!

I really couldnt have broken the engine,as i dont drive it that hard..never really go above 8k in anyway.

Why a Nikki you may ask? Well,this is a tight budget project,learning along the way,and having loads of fun is the 2 most important things!

Fuel flow = 18gallon per hour
Pressure = +- 3.0 psi normally (i know the pump is a bit light in the pants,but i got it for free!)

Karis

Ps:I appreciate all the replies.Good to know people want to help!

 

Hi Karis,

Is this the Nikki you modded?

 

Hi Dennis!
How are you doing these days ?

Nope,its not the one i modded.Its a stock standard Nikki.
I think the only difference is maybe 170 second stage fuel jets,the rest are all standard.

(I`am on my 3rd Nikki at the moment ,i seems like no2 was the good one,it started most of the time,when the starter was still ok)

1.Modded nikky(constant rich running problem)
2.One i bought about 3 months ago.It starts quite easilly.Allthough not just by turning the key)
3.One i got on Tuesday evening ,to see if it works.
Worse than both my Nikki`s combined.(does sound kickass with the 2nd stage stuck open!)

I removed the starter yesterday afternoon,and took it to be overhauled.
Hopefully i will have it back by this afternoon ,or maybe the latest tomorrow morning.

I hope that the starter will do the trick,i will also be replacing the starter`s wiring

Karis

 

Karis I emailed you with a possible solution to your problem.
If it works, then I'll put it up for everyone to see.

 

Hi Everyone!

Here is the outcome of last nights doings :
Closed up the carb top,after doing what Dennis(Sterling)suggested i should.Let the fuel pump run for 30 sec or so ,pumped the throttle 4 times.

Fired right up!

Yay!! I cut just chew a rock of happiness! It sounds way different when the overhauled starter turns the engine (more quite and solid)

I kept it running a bit ,so that it warmed up

Adjusted the mixture a bit.

The idle was so much better! The Pulses were stronger, and evenly spaced. The car was rocking from one side to the other, like a BP should.

Dennis will have to post what he suggested for me to do.

Thanks for all the great suggestions!

Karis

 

The idea was that due either to blow-by gases diluting the mixture severely, or a minor vacuum leak somewhere within the carburetor, the idle circuit needed to draw in more fuel than the idle jetting would allow.
The jetting that controls how much fuel is drawn into the engine through the idle circuit consists of the "idle step jets"- the stubby jets found on the edges of the top of the carburetor. They act the same way that the emulsion tube air jet act; by "bleeding off" vacuum signal to the circuit, thus limiting the amount of fuel that will be drawn into the engine.

I told Karis to try removing the primary step jets (#150), which are luckily quite large and give us Nikki-tinkerers all kinds of tuning room to play with, and replace them with the much smaller secondary step jets (#60) from another carburetor.
This allowed more vacuum signal present to the idle circuit, and the incoming fuel is still trimable by the mixture screw.

The drawbacks to this are that there is no actual cut-off mechanism within the carburetor for the idle circuit, and even at high RPMs the idle circuit is still drawing in fuel.
Though you can control the amount of fuel that comes into the idle circuit during low idle vacuum, the circuit is subject to the same fuel siphoning problem that can happen with emulsion air jets being too small at WOT.
What all this means is that if you have a modded Nikki that you had dialed in just right but for some reason think you need to do this swap, you will have to fine tune your carb again. (Stock carburetors won't need rejetting.)

I've used this trick to temporarily fix idle problems that demonstrate a vacuum leak in my intake somewhere. It works like a charm, but I concider this a bandaid fix...a temporary solution to a vaccum leak.

-I do not know enough about BPs to say if this is an idle problem solver for that porting configuration, or if Karis simply has a leak somewhere.
He also installed a healthier starter.

I'm always learning some little thing, and as promised, I'm always going to share it with all you poor bastards that still love good ol' fashioned carburetors!

 

A big thank you to :

Sterling and Rx7Carl. ( Sorry Carl ,Dennis would kill me if i put your name first!)



chierie-chierie...brap-brap-brap-brap


Karis