PaulFitzwarryne

I have a 1984 with 12a, good header and modified carb. Above about 5,000rpm the engine appears to suffer fuel starvation just when I need the power for acceleration. At that rev I would expect to be getting about 130-135 hp. Any ideas as to the cause?

Based on information in previous threads it could be due to problems with the pump or lack of good spark. Has the carb been modified too much for road going use when the temperature is 42C

If this is correct should I get a Carter pump and/or a MSD ignition and coils.

Are they obtainable in Australia, if so where and roughly how much?

At present I am working out of Broken Hill which is 400 miles from civilisations, that is if the criterion for civilisation is the nearest Mazda dealer! The sudden loss of power is a worry when you are trying to overtake a 3 trailer road train which is doing 70mph on a 2 lane road.

rotorhead

first and foremost, check to make sure the fuel filter is clean. its cheap and easy insurance. then go for the higher flow fuel pump. lots of folks use carter AFB's , or holley blue(or red) pumps. just make sure you put a pressure regulator on there. if that's not enough THEN look into upgrading the ignition system. make sure all the little stuff is in good order too, like the spark plugs, dizzy cap and rotor, ignition wires,etc..

guru

Before you do anything get the manual out and check the primary and sceondary winding resistance of your coils, then look at accelerator pump, fuel pump and did you have this problem to carb modds??

guru

peejay

If the fuel filter hasn't been changed in the last few weeks, that's the likely culprit.

PaulFitzwarryne

Thanks for the ideas.

Fuel Filter, Air Filter and dizzy cap replaced 2,000 miles ago.

Did not notice the problem prior to carb modification, but then I have been pushing the car more since then to get advantage at medium revs.

FuLLsMoKe

I think I might be having fuel starvation problems... Around higher RPMs my RPMs will climb alot slower than how it used to. All i have installed is a RB street port system.
How could you tell if your car is being fuel starved?

madaz07

Ive got exactly the same problem i didnt notice it until i got my nikki card moded as well. I bought a carter pump and put it on and it didnt make any difference since then i have swaped my coils, ignighters, cap and button, leads, spark plugs and also putt an new fuel filter on and its still there. Its starts running a little funny at about 5,000rpm but when it hits 6,500 to 7,000 it almost like its hitting a rev limiter and it wont rev past it, if it was a fuel problem you could adjust the throttle and go past it.

Only thing that hasnt been swaped is my dizzy, can the magnetic pickups in the dizzy play up at high rpms????

I should be taking it to get fixed this week then ill let everyone know what the problem was.

RotorMotorDriver

iTrader: (1)

Well, Just my two cents, but the only thing I have READ (not experianced) about fuel starvation problems even with a stock engine is the fuel pump not pumping enough fuel to the engine. And, as we all know, a modified engine would use more fuel that a stock engine, so if the stock fuel pump even had a remote chance of not supplying enough fuel with a stock carb setup (which I have read about), then the engine may be using more fuel than the pump can deliver with the modified carb setup. So, personally if it were me, I would be checking everything from the tank to the carb, and if I cant solve anything that way, id just spring for the high flow pump. Good Luck!

~T.J.

RotorMotorDriver

iTrader: (1)

I just had another thought since you describe the same problems as person who first started this thread with the exception that you have replaced your fuel pump (along with many other things)...As for the lower RPM problems I dont know, but the higher ones I was thinking, (this may be way out of the ballpark), but what if the computer cant handle the ignition at those higher RPMs? I would assume that would feel like a rev limiter? I dunno, I just thought Id mention it, you never know. Good Luck

~T.J.

FuLLsMoKe

Anyway... Thanx for suggestions, I may just go ahead and get a holly pump and regulator... I'll be needing it in the future anyway... Any suggestions of types of holly pumps or regulators?

madaz07

my car is now fixed it wasnt the ignition it was the secondary jets they were too big. now ive got smaller jets and the air bleeds are one size bigger and ajusted the timing to 20 degrees advanced.

RXcetera

Jetting must be a lost art... it took 10 posts before jetting was even mentioned!!! There isnt a carb in the world that you can just bolt up to your engine and expect it to give you its full potential. Things like elevation, temperature etc all play a BIG role in how a carb will perform. Here are some rules...

If you get your Nikki modified or buy an aftermarket carb, BUY A NEW FUEL PUMP and regulator!!! Why do people not get this?? There's no way that little stock pump can keep up to anything bigger than that little Nikki carb. Whatever modified or aftermarket carb you have needs to maintain a certain PSI at high RPM for the carb to function properly... that's where the stock pump doesnt cut it. The regulator is also VERY IMPORTANT!!! You wouldnt want 60psi in your tires would you? Then how come people use 6 psi in a carb made for 4psi? It just doesnt work.

If you've got all the right amounts and pressures of fuel, next you HAVE to jet it!. Bad jetting will choke the life out of your carb. I think most people look at this as "fine tunning" the carb... they couldnt be more wrong... jetting is probably the most important step in getting your carb to actually perform... increases in HP form jetting can be huge! I've been in so many cars with aftermarket carb setups that where actually slower than the stock Nikki's... in fact, most are. All it takes is a little time and a little research and everyone can become a jetting expert.

Sorry, just had to get that off my chest .

jmseven

Okay, since you had already done the carb upgrade...did you add a fuel pressure regulator. You can purchase and inexpecsive Puraltor "dial" type. I had the same problem w/ my '79 13b Deloto set up from RB. Pressure is the key.

mar3

iTrader: (8)

Does it actually work for you? I was thinking about that one as a quick fix until I can dig out my Mallory stuff from my "moving" boxes. Somewhere else on this forum, the Purolater was flamed for being useless. As and asides----> Paul F., when you step up to the fuel pump purchase, consider the Mallory Comp 110 as opposed to the mainstream reply of "Carter or Holley!". You'll have the power without the noise...

RXcetera

I've used the purolator regulator without problems. Not the most precise thing in the world, but it's fine until you can shell out some $ for a "real" regulator.

peejay

That's probably because you have to remove and partially disassemble a Nikki just to get to the plugs in the bottom of the fuel bowls that you remove the access the jets... and if you lose one in the bowl then you have to tear the top of the carb off Not to mention if people are balking at $70 for a fuel pump, how likely do you think they'll be to buy jets? Jets are VERY expensive... it's not like you can go to Mom n Pop Speed Shop and buy a set of 30 pairs of jets for $29.95.... Nikki jets are, what, $5-6 APIECE? Times two for each size, and how many sizes are you going to buy to start experimenting?

Fuel pressure is easier to adjust. It's not IDEAL, not by far, but it's cheap and will get the job 70% of the way done... after that you start buying jets, and after that you send your carb off to Paul Yaw and have him modify it for changeable screw-in air bleeds.

RXcetera

Mazdatrix sells the jets you're "supposed" to replace in the Nikki when you loose the cats and headers... Paul Yaw is also a good source for jets if they are needed for a particular application.

Like I said in my post peejay, and you're repeating and I'm repeating again... Fuel is key! Get a decent pump and regulate it! That's the first step after any carb modification. Many people on here seem to stubornly stick with the stock pump, why? I dont get it .

peejay

Well, it's good enough for a couple seconds of WOT before the bowls run out of fuel and you lose power...

I've heard of people completely REMOVING the secondary jets because "no matter what I do it runs lean"... and they're running a tiny fuel pump and a turbo and a non-boost-referenced regulator... GEE why is it running lean?

FuLLsMoKe

Some ppl lack common sense... Like my friend who believes that there is a fan inside his muffler... Or my other friend who thought that his car could go 0 to 60 in 3 seconds... It only makes sense--modified to take more gas=more power, now more gas needed=need to upgrade pump

most ppl just look at the things in the front--not realizing the importance of the rear things like pump, etc...

RXcetera

If the floats get that low, you're not just running lean, you're running dry lol. I think the problem is that as long as the car starts and accelerates (wether fast or not) then people think the stock pump is ok. The stock pump might be good at idle and low rpm where it's giving ~3.5 - 4psi, but as soon as you ask more of it, it's pressure can drop down to almost zero. What that means is, in many cases, the car still runs, but the carb is not receiving the proper amount of fuel. The floats drop very low, the emulsion tube opens up, the carb starts sucking in even more air and you're stuck with SLOW acceleration AND a potentialy damaging lean condition. It's amazing the difference a good aftermarket fuel pump can make on a stock Nikki... Many problems people associate with timing are usualy just the carb running out of fuel .

crankit

Had the same problem with my 84 accelerate to about 5k then just like the fuel was cut off. Didn't die but lost alot of power. Anyways turns out it was the anti-afterburn valve hose. It was probably colasping inder high rpms. $25 item at Mazdatrix #13-7560-n201. Sure cured it for me.