What he's saying is the passage from the front, (small rectangle opening at bottom) as well as the coolant passages in the manifold, should be filled with quiksteel or equivalent when coolant passages from the block are plugged. Failure to do so will superheat the manifold.

Posting this merely because it seems to this reader that the question is unanswered.

The hole in the block needs to be filled in is what their saying. The solonoid you wired in is probally causing the car not to start. If its not wired in to the factory harness then unhook it and cut the plunger out. The pic shows what im talking about. Then you can put a bolt, the old solenoid, or those screw cap thingys in there.

Ah... So these things:

Attachment 756619

Do I need to seal it on the engine block or the manifold?


As for what I did today... I figured I would cut some new gaskets for the Mikuni manifold (both between the manifold and engine and the carb and manifold). Got it put back together and I put it on the car (easy at this point to hot swap them). Figured if I could get it started then something was wrong with the Nikki, but I can't get the Mikuni to run anymore either so I don't know what's wrong at this point.

I disconnected the fuel input and made sure I had fuel coming out, no problem there, and 3lbs through the regulator. I had to block off the return line, it does do too well on the mikuni since it doesn't have to run through the carb to return, it's just a T line and the pump can't put out more than 2 lbs with the return hooked up.


EDIT: Went back and looked at the videos I have of the Mikuni running. One of the ports was open when it was working and I had it blocked off. Opened it up and it started and idled, worked the throttle a bit and it started running lumpy and the engine was shaking badly, worked the throttle a little more and got backfire in the carb. Going to re-read the tuning manual I was reading earlier today.

Man this is frustrating... Everything appears to be correct. I checked the float level and reset it to 12-12.5mm it was like 1mm off or so, and I checked the seal on the starter system, no problem there... I even stretched the spring a bit to give it a little more pushing power to seal.

No clue what is wrong... It's getting fuel for sure and when I use the starter it wants to start up so bad it's almost like it's idling at 100-200rpm when I am trying to start it.

Yes fill in that port that it matches to on the block.

Yes, fill the "block" side.

Gotcha, I'll do that next then. The manifold on the mikuni has no coolant ports and no acv port actually. Should I still fill it?

Gotta ask about the roll cage, was it pre-installed I'm assuming? I really like the look of it and it appears to be removable which would be an awesome feature. Something like 6 point?

Anyways, awesome carb work and cool build!

Yeah, the cage was in it when I bought it. It is bolt-in only because spec Rx-7 does not allow for weld-in cages.

Nice! Looks well-constructed and nicely done. If you have any more pics feel free to share, I like the bolt-in idea..:nod:

You should. Aluminum transfers heat far easier than iron so filling the ACV port will keep your manifold that much cooler.

I guess if you were running the Mikuni you'd have to fill the port then since there is no coolant ports on the manifold and the ACV is blocked off as well.

The manifold on the mikuni actually runs cool near the carb, cold almost, but I think this is just the fuel cooling it off.

So if you are using a manifold like this:

http://atkinsrotary.com/store/images/P/16460.jpg

It's basically mandatory to fill the acv port on the block?

Spark plug tips are black and there is fuel vapor coming out the exhaust. I think I am flooding with the Mikuni, I just don't know why.

Forum... y u no hab edit for me!?

Only forum I use that locks me out of editing after a certain amount of time.

Attachment 756599

Attachment 756600

Attachment 756601


Are these still good? My guess would be no, but again, I'm no car expert. This is my first project car.

Attachment 756602

I've been looking for tuning info to get me started. I read the process in the Mikuni manual and it's extremely straight forward. Get the car running, test drive, based on conditions re-jet. Problem is step 1 for me right now. Getting it running.

Step two would be re-jetting and I have no clue where to start. What size inner/outer venturi should I be running in hot Louisina weather for a 12a with no porting work done, same for the main jet, pilot jet, and main air jet.

I can source the parts from Wolf Creek Racing it seems... They are expensive though...

After reading the "End all for my Rx-7 won't start" thread... I took the plugs out and turned over the engine. There are "clouds of fuel" coming out, not sure if this means flooding as it didn't say that. It just said "observe if clouds of fuel are coming out". Based on the description of the sound it's supposed to make I would have to say the seals are still good.

Thats exactly what flooding is. Its flooded. The Carb is tuned way rich.

So I shouldn't see the fuel coming out the engine then? The mix should be lean enough to be clear and still smell of fuel?

I found this page on mikunipower.com that has jetting info for the 12a apparently.

Attachment 756598

Gonna check the jetting around lunch time and see what I got inside.

Also, something that got me thinking was the solution to a flooded engine was to add oil where the spark plug goes to restore compression... I believe this engine has had the oil metering pump removed. Does that require me to run a heavier premix of oil than the Idemitsu premix recommends (1/2 oz per gallon). Once I figure the jetting out, what would be my next step? Clean or get new spark plugs and put a small amount of oil in the plug holes to restore compression (as stated in the guide)?

Dude your all over the place man, and don't have a lot of correct information.
The engine is flooding either due to low compression or the carb is tuned too rich. If its flooding out at low rpm and idle I would lean out the idle/low speed jets and go from there.

To deflood yeah a couple teaspoons of oil will help to restore compression. With all the plugs out disable spark and fuel and crank the engine until no more fuel comes out the exhaust ports. Replace the spark plugs...theyre inexpensive..might want to get FC plugs as they are a better design.

And the premix ratio is proper for OMP disabled..you don't premix with a functioning omp..

Yeah I am a bit all over the place, kinda, but due to going from modding the nikki to swapping to the mikuni. I changed my mind partly due to the time I am spending on this project. I figure if I am going to put a lot of time into tuning this thing properly I may as well do it with something that is for one easier to work on and two should perform better.

My next step is to check the jetting on the carb and compare it with the mikuni recommendations above to figure out where to start. Pilot jet is what I need to start with, I believe, to get the car running at least (if jetting is the problem). The pilot jet is used to regulate the fuel from fully closed to 20% throttle so if I am flooding while cranking that's the jet I need to change, right? And is compression is the problem.. well.. that's a bigger problem, but I don't think it's that. As for what jets to get, based on the available sizes and the recommended jets for the 12a, I'd have to imagine I should just get smaller jets than what I have. For instance, 210 is the largest main jet they make and 200 is the recommended jet for the 12a and they are in increments of 5.

The recommended jets according to Mikuni are:

Main Jet: 200
Main Air Jet: 240
Pilot Jet: 62.5
Pump Nozzle: 0.90

What is inside the Mikuni right now:

Main Jet: 200
Main Air Jet: 190
Pilot Jet: 62.5
Pump Nozzle: 0.90

So I have the "recommended" pilot jet in there right now but the Main Air Jet is too small. This regulates the supply of air and should affect the flow of fuel at medium to high speed driving so it shouldn't be the flooding problem (I am guessing, correct me if I am wrong please. I am still learning). Looking for guidance.

yep, main air jet is a bleed for the main air jet, so it isn't really doing anything under 2000rpm.

have you tried the float level? fuel pressure? idle mixture?

The idle mixture (I think this is the Pilot Screw, right?) is set to 1 1/8 turn as per the Mikuni guidelines. Everything I have read says if it's not within 1/2 turn of 1 1/8 turns then the jetting is wrong.

I checked the float level. It needs to be between 12-12.5mm. It appeared to be within spec based on a tape measure conversion from mm to in (0.4822" = 12.25mm) but I will double check this with a set of calipers.

As I understand the procedure to be:

You take the float system out of the carb and leave it attached to the upper mounting plate. You put it on a very slight angle so the float arm just comes in contact with the needle valve but DOES NOT compress the needle valve spring. Measure the distance between the float and the upper mounting plate and make changes with the set screw, 1 turn = 2mm.

http://www.mikunipower.com/PHHCarbs/PHHservice18.jpg

On top of this I checked to make sure the floats weren't sticking. The pin that holds them in is in great condition and there is no resistance when actuating the float.

Fuel pressure is recommended from 2.84 PSI to 4.98 PSI. I am currently running 3 PSI to the carb (with the return line hooked up).

I re-checked the float level, it was around 13.5mm, so a little low, I rest it to 12.28mm, right between 12 and 12.5.

I also removed the jets and made sure there was no blockage. The pilot screws look slightly malformed on the tips. As if they are shrunk in. Like someone tightened the ever living fudge out of them. Should I replace?

Also, how should I go about filling the ACV port on the block? Just leave the engine in the car and clean it out then fill it with quicksilver?

New plugs will be in tomorrow morning.

One thing I didn't use were the silicon spacer/gasket, I had made a paper gasket, I am gonna put the silicone ones back on... The o-rings looked a little flat, I may order some new ones.

I put a little oil in the bottom spark plug hole of each rotor housing and carefully re-assembled the carb and put it back on. I double checked where the pilot screws bottom out at without the spring (4.5mm) and made sure they went down that far before backing them off 1 1/8 turn. I used the starter system and the car really wanted to start. I didn't try to start it but twice because it was getting late and the car is ridiculously loud. I need to figure out a way to work on the car without annoying the neighbors as much.

Just got done talking with Todd over at Wolf Creek Racing. I ordered a few main fuel and air jets to have when I get it running so I can tune it. Gonna try to start it up with the new plugs today and see how it idles and determine if I need smaller pilot jets.

I told him how the Mikuni likes to bog down at low RPM and he said it could be either a lean or rich problem and I needed the proper equipment to determine what the issue was. Gonna do some more research but I think this is basically solved by checking the plugs after letting the car idle a bit. Maybe I should get some type of monitor? Not sure what that would be though.

Google is neat.

So I need to install a wideband O2 sensor. Shouldn't be too hard, I can cut and weld.

Anyone recommend me a good brand?

I was looking at this one: MTX-L Wideband O2 Digital Air/fuel Ratio Gauge

I called Todd back and told him to also order me two smaller pilot jets. He said they step down by 2.5 so that would be 60 and 57.5, he said he didn't have the 60's but he had the 57.5 and 55's so I've got that coming as well.

Heyooo, got her running. She doesn't idle below 1300 or so though. I got to start her up with some good sunlight, boy is it running rich. White smoke coming out the exhaust, not heavy, but visible in the sun. That plus a strong smell of fuel.

Gotta wait till the new jets come in to play arouund with it. I have been reading reviews of the wideband I posted above and a lot of people use them with great success apparently.

Even with the recommended jets being apparently on the rich side, I don't think they are so large as to cause a flooding problem, I think that was the float level. Now my question is why can't I get the car to idle? It runs fine at 1400 or so RPM and up but dies as soon as I dip the throttle to idle speeds.

Everything I read points back to a vacuum leak and solutions to that are on the order of dry ice and water or a fog machine and letting the vapors get sucked into the intake and see if anything blows it out.

Should I have used silicone or something to help the intake manifold gasket I cut seal? All the other gaskets on the carb have been replaced recently and are in good condition.

All the ports have been capped with brand new vacuum caps and I have the dist advance hooked up.

Yeah vacuum leak could be the cause of the high idle.. don't put silicone on gaskets basically the same as double gasketing. You can sometimes put a light coating on intake gaskets to reuse..I would replace all the intake gaskets and make sure you have no open ports sucking in air. Btw don't make the gaskets buy um from Mazda..I know they're kind of expensive but you won't have to worry about the quality. Also don't clean any gasket surfaces with any rotary tool..try to do it with gasket scrapers. If you absolutely cant get um off soak them in carb cleaner that should take any gasket residue off. Or use Kerosene.

I meant a light coating of grease like wheel bearing grease.

I made a gasket because there are ports that aren't used on the Mikuni intake (coolant ports and ACV port). Also the holes on the Mikuni intake are slightly larger than on the stock Nikki intake so I made the gasket to the size of the Mikuni intake manifold holes rather than modifying a Nikki gasket.

I used a dremel with a wire brush attachment (doesn't alter the surface) and went lightly over where the old gasket material was, then cleaned it all with carb cleaner. All the mating surfaces were smooth and I checked for any defects before using the new gasket.

Here is why I made my own gasket. The one on top matches the Mikuni intake perfectly, the one on bottom is one from Mazda I believe.

Attachment 756592

Attachment 756593

Attachment 756594

These are the only ports I vacuum capped. the only other port open is on top and I connected it to the vacuum advance on the distributor.

There is a small screw hole that looks like it accesses the innards of the carb, I plugged it but it changed nothing so I have to guess it wasn't leaking.

I've been over this thing front and back about 5 times now. How do I check for a vacuum leak to rule it out?

I've read methods of propane, fog machines, and dry ice. What's the safest and most effective?

Use a can of Brake Cleaner man. Have the car running with someone watching the tach and spray brake clean over the intake in the areas you think it might be leaking. If its leaking vacuum it'll suck the Brake clean in and make the rpms rise. Dont douse it in brake clean though slowly go over the areas you think it might be leaking. Don't worry it wont just catch fire it needs a good ignition source. Definitely safer than propane or ether. Safest way would be to use a smoke machine but you probably don't have access to one and they're definitely not cheap.

Would carb cleaner work? The kind in the can, not the paint jug.

Also, I think I can get some dry ice to make CO2 vapor, just not sure how to apply that method. Spread the vapor around and see if it gets sucked in at points it shouldn't be? If that's so it shouldn't be hard to fill a mason jar with a little water and dry ice then have a small port in the top with a tube to direct it.

Weber 48 ida

Buy me one, I'll put it on as soon as it gets here.

You're planning on spending 300.00+ for a wideband, which is a good idea, but you want to skimp on the carb. I don't get it? Sell the Nikki and Mikuni and buy a used 48 IDA.

Just because you think Weber IDAs are the best doesn't mean everyone else does..sure they're the most tunable but Webers are the most expensive carbs. I would take a Holley over an expensive Weber any day.

$200+, the kit I am looking at now is $199 and it's got good reviews over the internet. And I can swap it to another car whenever if need be.

Just ordered a MTX-L Wideband O2 Digital Air/fuel Ratio Gauge. Talked to my cousin that works where I work. He said spray can ether is a good solution and won't affect anything whereas brake cleaner might. He said carburetor cleaner would work but ether would be more noticeable.

I also asked him about this:


The hissing sound when the engine shuts off. This was with the nikki, but it does the same with the mikuni. Sound comes from around the brake booster area. He said it's not normal, but I have read forum posts on here saying it is.

There are two 84-85 cars here with the hiss after shutdown. It might be normal. I hope it is.

Just spent 15-20 minutes going over every inch of the car with starting fluid. I can't detect a vacuum leak anywhere.

New jets came in today. Wideband will be here Friday.

Went and picked up a compression test kit as well.

pull the a hose off the booster and see if the booster holds vacuum, if it doesn't its bad...

In dummy terms please.

Pull the "a" hose, or "pull a hose" and see if it holds vacuum (what's the test for that?).

the brake booster has one vacuum line, remove that line from the booster, and apply vacuum to the booster, if the booster does not hold vacuum, then it is bad.

sometimes a bad booster will make weird noises

Sounds like it would require a vacuum pump.

Hrmm... Could I just remove the hose from the hard line to the intake manifold (the one that comes from the brake booster) and cap the port on the intake? That way I am not so much testing the booster but ruling out that as the cause of not idling.

Also, can I perform a compression test without the intake manifold and carb installed since you don't need fuel and just air?

I was planning on taking the carb back off and completely taking it down, ordering a seal kit and rebuilding it. A master rebuild kit is only $75 and includes pilot needles/seats and accel pump diaphragms as well as gaskets.