82streetracer

iTrader: (1)

My car is leaning out bad at high RPM and anything past 1st with my exhaust. (white spark plugs.

I got a carter pump and Holley regulator and a huge fuel filter.

What pressure do I need to set the Reg at (I dont actually have a press guage but Ill figure something out)

do I need to rejet my carb
I heard to go 1 bigger on the primary and 2 bigger on the secondarys.

What do you think?

REVHED

Fuel pressure should be about 3-4psi.

How do you know for sure you're leaning out? To get an accurate plug colour reading you'd need to drive the car hard and then shut the engine and pull the car over. If you let the car idle it won't be a true indication of your fuel mixtures under load.

If it is definately lean they yeah, it may need slight rejetting. But make sure you have the correct fuel pressure first.

mperformance

get a fuel pressure gauge...set it at 2 psi.

you must have something wrong with the carb because with exhaust only you should not be going lean.

I went lean now that I ported my 79 intake...and it's still drivable and the a/f ratio gauge reads stoich from a richer condition presented before. I still haven't jetted...

SilverRocket

Naw, don't rely on a guage to set your fuel pressure - every aftermarket automotive low-pressure fuel guage I've ever seen has been hopelessly innacurate. If you just buy any guage and set it to 2psi you're gonna be way off. You have to set your fuel pressure either with a good guage, which if you can find one let me know what it is, or by experimentation. The way I set mine on my Dellorto was through experimentation and road-testing different settings. To make a long story short, I turned it up in small increments, driving it and observing any differences. I stopped when it started to flood a little bit at idle. Then I turned it down a bit until it was all good. Seemed to work well for me.

And yeah, you must have another problem, I think it's pretty unlikely that you could be going lean at high rpm with a stock Nikki.

REVHED

Pual Yaw specifies 2psi for his carbs. Fuel pressure has to work in conjuction with your float level and jetting. That's probably why you're running lean. As a matter of fact I ran 4psi on my modded Nikki without any problems.

Silverocket, have you tried the VDO gauge? I've got one and it's very accurate.

Sterling

Something must be impeding the flow. But it's not because you're running a pound or two too low. The volume of fuel is being stopped.

Guys, all fuel pressure dictates in a carburetor is at what point RPM wise that the holes in the emulsion tubes become uncovered, leaning out the mixture. If it were'nt for that feature of the carb, running it at 2psi or 6 psi would make no difference.
Increasing the pressure makes the carb lean out later in the band. Just how much it leans out is governed by the diameter of the air bleeds.
It's just another "tool" to tune the curve.
Too little pressure, and the rate of fuel delivery won't be up to the task of feeding the engine at hi rpm - But that's REALLY LOW pressure!
Too hi, and the needles will allow the fuel to push past them. They are'nt very strong when you concider the fact that there is a return circuit in our carbs. However the orifice for the return is quite small.

If you're running all stock, then rejetting can compensate for the problem, but your carb won't be at its full potential until the problem is solved.

Test the volume of fuel coming out.

theNeanderthol

iTrader: (1)

I used a drill press to drill out my secondary jets from #165 to about #177. I noticed a difference, but I'm still leaning out. Rob at pineapple racing told me to use #180 secondary jets as a starting point. Think its time to take sterlings advice and check my fuel flow. Good luck.

peejay

First you must make sure that you are not having a fuel delivery problem!!!

Leaning out at top end means one of two things - insufficient fuel flow (does it lean out only in higher gears but 1st maybe 2nd are okay?) or air bleeds are too large.

Is your intake manifold modified in any way? I found that if you cut open the manifold so that all four ports are open to each other, it will run really lean the higher you rev it.

Normally the problem with stock Nikki is too MUCH fueling at top end - they run overrich and lose power.

What I did was, since I had no jets at my disposal (drilling jets is not recommended as the fuel flow is EASILY upset - even though you go larger you may actually lose flow!) I went to the dragstrip and kept changing fuel pressure and watching top end MPH. This actually ended up being far too rich at the top end and at the low end but it made for fastest times. Through the muffler my best power was at something like 1.75 on my gauge (inaccurate but it's accurate enough to judge from one setting to the next - this is meatball tuning, not a science) and through open headers I had to crank pressure up to 5-6 psi, whatever my fuel pump could put out max - I bypassed the reg entirely. Probably could have gone a bit faster with better tuning, but hey, they don't call me Shallow Pockets for nothin'.

mperformance

I keep flooding my carb. I'll do the test driving and regulating bit since the gauge is not accurate...

Neanderthol do you have a pic of which jets you drilled? thanks man

Sterlin you mentioned that the return orifice is small, can this be removed/altered someway that is beneficial?

82streetracer

iTrader: (1)

No. no. no.

Sorry, my post was kind of deceptive.

I have the carter and holley BUT have yet to install them.
(probably tommorow)

I am pretty sure that they will fix my problem but I was still wondering about rejetting.


Thanks though

82streetracer

iTrader: (1)

What is the stock fuel pressure for a nikki.
Some of you said 2 some said 3-4.

What is it?

mar3

iTrader: (8)

Run it at 3.5 and go from there. 2 is for a YawPower carb. Had my bone stock Nikki on a streetport taken to a dyno for some chassis numbers. At 3.5, it rev'd to 7800 rpm and kicked out 113 HP at the rear wheels. Just for grins, I turned the regulator up to 4.5 lbs (or was it 4?...it's all in an old thread "An Interesting firstgen Adventure....) and she was breaking up bad at just 6500 rpm, so much so, the guy got out of the pedal and aborted the run. We dropped it to 3 and it posted a 112...with numbers that close, it's hard to tell what's optimum, but I'd rather be rich than lean...

theNeanderthol

iTrader: (1)

I drilled out the secondary main jets slightly. (sorry i dont have a digital cam)If you look at the sides of the float bowls there are two bolts on it. Take them off but be careful not to lose the washers. Look inside the float bowls and you can see the main jets. You can take them out with a screw. It is WAY easier with the carburator off. I would suggest a rebuild. It is pretty easy to do, and a rebuild kit is $20 from victoria british. Our 17+ yr old carbs need rebuilding.

Sterling

NO! Don't go messing with that! If the carb needs to be in the 3.5-4.5 psi range, and you go and open that hole up, then suddenly your carb might require 8-10 psi to run the same way as it did!
(I've overdramatized a bit, but you see how it'll just add another variable to your list with nothing at all to gain.)

If you're flooding the carb, then your pressure is too high, or your needle is stuck (or there's the usual "crap in yer carb" checklist).

My Yaw is essentially a stock Nikki. There's no change to the needle seats. IE, they are stock and so fuel flow is the same; and the return orifice is un modded. The point is that I don't have any different pressure requirements to make the carb run. I have run my carb at as low as 1.5 psi, with hellacious fuel jets, and leaning out at over 6K.

So with this, I say you should be able to get your car running with very little pressure, everything being fine, and the problem being Hi RPM leaning due to fuel starvation. (Often halfa lb'll do ya. Make changes in 1/8 psi differences with each test run. You might be suprised how close you really are to "just right").

Once again, fuel pressure needs to be adequate to feed the engine at it's highest RPM. That's the "low pressure limit". The "high pressure limit" is just before it's so high it blows the needles out of the seats, and the carb is awash with fuel.
Somewhere in between is that perfect pressure where the emulsion tubes are uncovered just enough at just the right RPMs to give you the perfect mixture to power out of your curves, cruise superfast on the highway, get great mileage, or whatever you've got the carb set up for.

Is yer float bowl solenoid hooked up? (I always ask that. It's the Devils creation, that ****** thing! )

mperformance

sterlin you know yer stuff...

Man I went really really low pressure (cured it seems) Yeap it's the damn pressure regulator it has a mind of it's own. I noticed that the pressure varies with temperature when the regulator gets really hot from engine heat.

I kind of stopped the flooding.
Remember I ported my intake also...so I am going to play with the main jets now to richen it a bit, but so far so good. I really wish there was a pictorial on where the jets and the airbleeds are located. I do know now where everything is located after I looked into the microfiche slides in www.iluvmyrx7.com site...


BTW I left the orifice intact I was just asking
Float bowl solenoid <---WTF is that LOL!!!

thanks

82streetracer

iTrader: (1)

I just got my pump and reg hooked up. I cant see any fuel in the the window on the float bowl. the car runs and I can drive it. but it is still leaning out.

THe regulator goes on the pressure side right.
or does it go on the return line.

I have it on the inlet side.

REVHED

Regulator goes on the inlet side.

Have you tried cranking the screw all the way down so it's at the max. setting?

mperformance

inlet side...yeap it's correct either pressure is too low and you don't see any fuel or too high that it's completely filled...

82racer...shake the car that's what I do...YES you read right grab the car and move it up and down side to side and see if the gas splashes inside the carb thru the sight glass. You'll know where the meniscus is..

mperformance

here are some pictures I have been using.


sorry no pic

mperformance

this one for the air bleeds.



Current configuration (probably way off)

1=60
2=stock ?
3=140
4=70
5=46
6=150

mperformance

main fuel jets...




this is the location I needed to know hope this helps somebody else.