(INTAKE) Nikki Carburetor Rebuilding Tips - RX7Club.com - Mazda RX7 Forum

(INTAKE) Nikki Carburetor Rebuilding Tips

 

 
 
 
Old 11-02-03, 02:57 PM
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(INTAKE) Nikki Carburetor Rebuilding Tips

This is a collection of helpful tips for rebuilding the Nikki carburetor- something that many Rx-7 owners will haver to do at some point while enjoying these fine cars.
The following is a list of things that I have found useful.
If you have rebuilt any engine component and can add from your experience, please do so.
Sterling


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CARBURETOR REBUILDING TIPS

So you're gonna rebuild it finally, huh? Good for you. It's not that difficult, but can be very intimidating at first.
First things to concider;

Do you have a workspace that's clean, uncluttered, well lit, and out of the reach of tiny, curious fingers? Can your car be laid up for a while?

You also need to understand that even if you've done everything correctly, the carburetor may still take some coaxing, soft gental caring words of encouragement, and a few smacks to get working. But when all is finished and you're back behind the wheel, you'll swear your car has at least 15 more horepower - 10 from the rebuild, and 5 because you're the one who did it!
The satisfaction is great.

Buy the kit first. Don't have the carb strewn about in bits while waiting for the rebuild kit. You'll be amazed how quickly you forget how things came apart!

Clear the table! I have a white formica workbench, and it's great. I've used news paper on a table top in the past, and the newsprint is very distracting. It makes it very easy for checkballs and weights to get lost. I suggest white meat packing or roll paper if you can get it, or a light colored sheet.
A block of 2x4 serves well to set the throttle body down on. This way the weight won't be resting on the linkages.

After removing the carb, do yourself a favor and clean the crap off it. SUPER clean it. Then clean it again. I'm talking "tooth-brush" clean! If you don't then grit will find its way into the carb and cause all kinds of problems.

I use Simple Green to clean all my carb parts, and I just rinse very well in hot water. Simple Green is great, but it contains ammonia and will eat at aluminum and zinc. It won't burn holes in like swiss cheese; just create a white oxidation here and ther if not fully rinsed off. Dry thoroughly.

A toothbrush with hard bristles is good to have. Apply heat to the neck of the brush just before the bristles, and bend the bristle side out at 45*. This makes a great tool that will even scrub the bottom of the float bowls

Remove the airhorn on the carb outdoors because of the fuel still in the bowls. I suggest allowing the carb to sit for a while and air out, but I realize most people won't be able to wait that long to get started.

Have a notebook handy, and take notes, no matter how stupid or crappy the drawings are. I believe that the effort of having drawn or written something to paper does something to my brain to cause me to better remember the process/subject later on. Often, I would not have to look at my notes afterwards. Had I not bothered to take them, I surely would've forgotten.

Put the airhorn back on with just the center stud so you can remove the plumbing lines. It's easier to work on this way, and the floats won't be damaged, ect.
First remove the plug bolt that holds the return line on.
Then undo the banjo bolts, taking care not to destroy the metal screens that surround them. They will get distorted, but if you are careful, you can reuse them with a little massaging.

Then remove the mainline tube. Note the orifice in the side. This is the return orifice where fuel flows back to the tank. Be certain this area is clean and free from rust, and reinstall it to tension.

When reassembling this plumbing, do NOT use the paper gasket washers often found in the cheaper rebuild kits. You're better off using the original aluminum crush washers.

Reinstall the double inlet tube with the banjo bolts and an aluminum washer on the top and bottom of both banjos. Then, install the plug bolt last, being certain that all aluminum washers are present at each junction.

If the reinstallation of this plumbing is not done in this order, you chance having misallignment problems, and breeching the sealing of the crushwashers. This will be a BIG headache!

There are two check *****, and three weights in the carburetor. The two smaller weights and the check ***** are for the accelerator pump circuit.

The largest weight is for under the brass screw that is part of the richer coasting/decelleration circuit, and there is no check ball under it. (This confuses people, and they fear they've lost a check ball!)
Some carburetors do not have this weight and associated jets.

The fatter of the two smaller brass weights goes over top of the check ball located under the accelerator pump nozzle. The skinniest weight goes over the check ball located under the fat brass plug over the the accelerator pump housing.

The long step emulsion jets will only fit where they are supposed to go. The tiny idle air jets on the edges of the carb are specific to the primaries and the secondaries. Those marked "60", and usually nickle plated, go into the secondary edge holes, and the others marked "150" and brass, go into the primary side.

Inspect all of these jets to be sure that the holes are clean. Do not use drill bits to clean them! They are very specifically sized to deliver precise air to your carburetor idle circuit, and you can seriously mess up the idle if you open these up.

Use a drill bit (shank end) to remove and install the needle seats by inserting through the cross-drilled holes and turning. Tighten the new ones the same way. Be certain there is an aluminum washer under both of them when reinstalling.

Do not forget to install the pins and springs that come with the kit into the needles when reinstalling the floats. The needle clips on the floats should be handled very carefully to avoid bending them, which can cause the floats to bind.

All components in the needle-seat assembly are very important. New needles have a tendency to stick a bit because the finish on them is factory matt. I use a drop of sewing machine oil (or "3 in One") to lubricate them, and when the float assembly is completed, I spend a few minutes moving the floats up and down. Do not force the floats as the tabs may bend, thus changing the fuel level.

Fuel level in the carburetor is a critical part of its operation, and it's changed by the level at which the floats rise before closing off the needles. The float level is adjusted by bending the tabs on the backs of them. Float drop is adjusted by bending the other tabs that rest against the airhorn mounting/pivot casting.

With the gasket on the airhorn, and the airhorn held up side down, the tops of the floats should be about level with the gasket. You don't have to get the vernier caliper out unless you have a modded racing carb. But they should be very close. If one is lazy-eyed, then you'll need to get it to where it needs to be by bending the float tab. be careful and go slow! A little tweaking goes a long way, and too much back and forth WILL break that tab off.

Inspection of the secondary vacuum box is easy enough without taking it apart. Most kits don't come with a new diaphragm for these, but they hardly fail. A simple test is to plug the vacuum tube ( it sticks out about 3/16ths inch and can either be metal or plastic ) with your finger, and try to operate the lever. Don't use too much force. You just want to tell if there's an appreciable leak. Truth is, even with a tiny leak, the vaccum box will still do its job.

Use fresh cotter pins supplied with the kits.

Carl and I have thus far found "Hygrade" kits to be the best. They offer aluminum sealing washers for everything.
Other kits seem to have better-cut gaskets, but the Hygrades gaskets work fine. The other kits have only paper washers which outright suck! Don't ever use these washers!
The Hygrade kits also come with new checkballs and wieghts, where other kits do not. They are also the most expensive we've tested, at $35. The cheapest I've ever paid retail was $25.

A rebuilt carburetor should last another ten years in the hands of someone who maintains their car well.
"Ten Years?!" -Sounds like so long. But chances are you are about to crack open the guts of a carburetor that has'nt seen the light of day for over twenty!
Point being, the extra money is worth it for the best rebuild you can give it.

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Old 11-04-03, 12:58 PM
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where can I get a kit?
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Old 11-04-03, 01:34 PM
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Just make some calls to local autoparts places. They can all order a kit for you. Few will actually have them in stock unless they're huge (at least here in NY). The waiting period can be 1-4 days.
If you want the best (or what Carl and I have determined so far to be the best) then ask if the place sells kit made by Hygrade.
Napa here in NY sells Beck Arnely. No good. The gaskets are cut clean and perfect, but everything else is lacking...paper washers, **** like that. No checkballs or weights in those kits, either.

BTW, you can certainly reuse the ***** and weights. If you look at the old needles they might look fine enough, but they really are shot. Not so with the ***** & weights. But it's just nice to have the new ones.
Beck Arnley = $25, Hygrade = $36.
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Old 11-04-03, 08:28 PM
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Hygrade is also sold under the Standard brand. Actually Standard is the parent company of Hygrade.
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