Can't Identify my Nikki Carb, Searched A Lot!
04-24-14, 06:06 PM
#1
Can't Identify my Nikki Carb, Searched A Lot!
Hi guys,
Still going over the FB I picked up a few days ago. Expect a build thread very soon, haven't had time. The car really is mint, my only disappointment has been the shoddy emissions delete and now mystery carb!
But.. I knew from when I first saw it that there was something funny with the carb. I could see it had a bit of an emissions delete hack job, but didn't notice the carb wasn't a factory Rx-7 Nikki until I read more about them.
Please see attached pics. I am nearly certain this is from some sort of Mazda Rotary application, but haven't been able to figure it out.
Note that the one stock OMP line has been modified to connect to what I assume is the other fuel bowl.
My biggest concern at this point is proper OMP supply. Everything appears to be working fine, is whatever going on here an acceptable install as far as getting enough oil to the intake? I assume the oil is supplied into the float bowls, where it mixes with the fuel before delivery.
The OMP linkage is hooked up to the throttle shaft, and the linkage starts to move once the throttle has opened a bit.
Thanks again, this forum is has been amazing. I read it for two years before getting my own FB
Still going over the FB I picked up a few days ago. Expect a build thread very soon, haven't had time. The car really is mint, my only disappointment has been the shoddy emissions delete and now mystery carb!
But.. I knew from when I first saw it that there was something funny with the carb. I could see it had a bit of an emissions delete hack job, but didn't notice the carb wasn't a factory Rx-7 Nikki until I read more about them.
Please see attached pics. I am nearly certain this is from some sort of Mazda Rotary application, but haven't been able to figure it out.
Note that the one stock OMP line has been modified to connect to what I assume is the other fuel bowl.
My biggest concern at this point is proper OMP supply. Everything appears to be working fine, is whatever going on here an acceptable install as far as getting enough oil to the intake? I assume the oil is supplied into the float bowls, where it mixes with the fuel before delivery.
The OMP linkage is hooked up to the throttle shaft, and the linkage starts to move once the throttle has opened a bit.
Thanks again, this forum is has been amazing. I read it for two years before getting my own FB
04-24-14, 07:23 PM
#2
carb whisperer
Based on the chokehorn and fuel bowl vents, id say def an early nikki, probably not RX7 equipment. I have a 78 carb here that is very similar, probably uses the same rebuild kit.
I really like the early design, and nearly all of the early ones I rebuilt for people ran very very well with little tuning needed.
I really like the early design, and nearly all of the early ones I rebuilt for people ran very very well with little tuning needed.
04-24-14, 10:55 PM
#3
With the OMP pumping oil to the bowls you won't get the oil delivered when its needed. The stock connections dribble metered oil into the carb bores when you move the throttle. With them going into the bowls the oil will dilute into fuel and will be delayed or too late. Like if you do a quick acceleration and then cruise the oil won't have been there for the accel, then more than enough for cruise.
Hook them back to the stock nipples/ports. If the nipples have been trimmed off in the bores for some reason(more air flow) then you should premix and delete the OMP, which is what I do anyway.
Hook them back to the stock nipples/ports. If the nipples have been trimmed off in the bores for some reason(more air flow) then you should premix and delete the OMP, which is what I do anyway.
04-25-14, 08:37 AM
#5
carb whisperer
1/2 oz per gallon for regular driving, I recommend 1 oz per gallon for prolonged use above 8500 rpm...
Premix at Idemitsu Lubricants America Corporation
Block off plates are available through mazdatrix,
https://www.mazdatrix.com/getprice.a...m=10-6020-3997
There, I did your homework for you.
Short of finding a Idemitsu vendor in canada...
04-25-14, 09:11 AM
#6
You have an early carb. Possibly 71-73 from a twin dizzy 12A, or early 74 from a single dizzy 12A. The oil nipples above the float bowls gives it away. Does it have a 5/16" fuel return fitting? Early carbs had that, then they went down to 1/4" return.
Do you have the matching high flow intake manifold? If you do, you're awesome.
Do you have the matching high flow intake manifold? If you do, you're awesome.
04-25-14, 08:45 PM
#7
carb whisperer
You have an early carb. Possibly 71-73 from a twin dizzy 12A, or early 74 from a single dizzy 12A. The oil nipples above the float bowls gives it away. Does it have a 5/16" fuel return fitting? Early carbs had that, then they went down to 1/4" return.
Do you have the matching high flow intake manifold? If you do, you're awesome.
Do you have the matching high flow intake manifold? If you do, you're awesome.
Trending Topics
04-26-14, 01:58 AM
#8
Big plastic spacer? Don't you mean the small phenolic spacer? This early carb will have an angled spacer (wedge shaped) to correct the tilt of the carb to make it more or less level in the bay. The studs go through slightly angled but it didn't cause any problems.
Oh and there is no large heat shield moulded as part of the spacer like you'd find in a 1st gen spacer. Old schools were just a small square with holes in it, and about 1/4" thick depending on year (and whether it's the early angled variety).
Oh and there is no large heat shield moulded as part of the spacer like you'd find in a 1st gen spacer. Old schools were just a small square with holes in it, and about 1/4" thick depending on year (and whether it's the early angled variety).
04-26-14, 08:34 AM
#9
carb whisperer
Big plastic spacer? Don't you mean the small phenolic spacer? This early carb will have an angled spacer (wedge shaped) to correct the tilt of the carb to make it more or less level in the bay. The studs go through slightly angled but it didn't cause any problems.
Oh and there is no large heat shield moulded as part of the spacer like you'd find in a 1st gen spacer. Old schools were just a small square with holes in it, and about 1/4" thick depending on year (and whether it's the early angled variety).
Oh and there is no large heat shield moulded as part of the spacer like you'd find in a 1st gen spacer. Old schools were just a small square with holes in it, and about 1/4" thick depending on year (and whether it's the early angled variety).
I found a pic of the ones I bought:
https://www.mazdatrix.com/c-3.htm
Its the 2nd pic down. Do these go on the angled spacer like whats under his carb?
04-26-14, 11:51 AM
#11
Thanks for all the feedback guys.
I have been doing a lot of tinkering on the FB lately. I have installed and gotten the hot start assist motor working properly (no more foot on the gas and me worrying about flooding it!).
I also fixed to be what I thought was one or two vacuum leaks. I put a vacuum cap over the nipple in the pic below. Capping this made the engine run AWFUL. Not long into the warm up (with a bit of choke), the second cat started glowing red and smoking. I took it for a quick drive, and it simply would not idle well. Like 100 RPM, almost wanting to die.
I removed the vacuum cap and sure enough it was back to running great as usual. Took it for a spin and it was awesome. Idled at 750 RPM smooth and steady. At idle, this nipples is sucking in a ton of air. My gut feeling is idle speed will need to be adjusted if I fix this vacuum leak?
EDIT- After more research, maybe this nipple has something to do with the idle circuit to supply air to it??
The other odd thing, at idle, there doesn't seem to be a lot (or any) vacuum at the two ports on the other side (see pic) I removed the vacuum advance hose and couldn't feel anything. Is this ported vacuum and only kicks in at higher RPM?
I am quite overwhelmed with all of this, thanks again guys.
I have been doing a lot of tinkering on the FB lately. I have installed and gotten the hot start assist motor working properly (no more foot on the gas and me worrying about flooding it!).
I also fixed to be what I thought was one or two vacuum leaks. I put a vacuum cap over the nipple in the pic below. Capping this made the engine run AWFUL. Not long into the warm up (with a bit of choke), the second cat started glowing red and smoking. I took it for a quick drive, and it simply would not idle well. Like 100 RPM, almost wanting to die.
I removed the vacuum cap and sure enough it was back to running great as usual. Took it for a spin and it was awesome. Idled at 750 RPM smooth and steady. At idle, this nipples is sucking in a ton of air. My gut feeling is idle speed will need to be adjusted if I fix this vacuum leak?
EDIT- After more research, maybe this nipple has something to do with the idle circuit to supply air to it??
The other odd thing, at idle, there doesn't seem to be a lot (or any) vacuum at the two ports on the other side (see pic) I removed the vacuum advance hose and couldn't feel anything. Is this ported vacuum and only kicks in at higher RPM?
I am quite overwhelmed with all of this, thanks again guys.
05-03-14, 02:07 PM
#13
A member local to me is shipping a Nikki from an 85 FB. I will rebuild it.
Now, what I never considered, was that my intake manifold is not from an FB, and may have issues bolting up a Rx-7 Nikki and spacer/gasket.
Here is a photo of several early 12A Mani's:
http://www.rxforyour7.com/4sale/general/_EBY3032.JPG
I found this photo of several years of FB mani's:
http://www.rxforyour7.com/4sale/general/_EBY3031.JPG
Looking at these pics, I doubt that my manifold is from an 1982 FB.
It looks closest to the 1974.. which my carb seems to agree with.
So, I assume an Rx-7 nikki simply won't bolt up to my manifold.
05-03-14, 02:35 PM
#14
The RX-7 spacer may need to be trimmed. It has a big heat shield or whatever it's supposed to be that might hit the old style manifold. Just trim it off.
Whatever you do, keep the older manifold. They flow much better than new. But it might not have channels. The RX-7 carbs need channels in the manifold for the idle circuit to work correctly. Otherwise the RX-7 carb will idle pig rich. That's been my finding with 13B hitachi carbs from a channeled manifold installed on non channeled manifolds.
Whatever you do, keep the older manifold. They flow much better than new. But it might not have channels. The RX-7 carbs need channels in the manifold for the idle circuit to work correctly. Otherwise the RX-7 carb will idle pig rich. That's been my finding with 13B hitachi carbs from a channeled manifold installed on non channeled manifolds.
05-03-14, 02:59 PM
#15
Ok Jeff that sounds like a good idea.
If the older Mani does indeed flow better I may not be so eager to get rid of this carb/mani. I have found rebuild kits for it on Ebay and a few other places.
I could potentially just take it (and the manifold off), clean everything up, rebuild the carb (if necessary) and continue to use it.
My only hesitation with this setup was the OMP supply, but I am thinking that supplying oil to the float bowls may still be OK, except for the dilution/delay that was mentioned. Hence, I may run a bit of pre-mix to compensate.
If the older Mani does indeed flow better I may not be so eager to get rid of this carb/mani. I have found rebuild kits for it on Ebay and a few other places.
I could potentially just take it (and the manifold off), clean everything up, rebuild the carb (if necessary) and continue to use it.
My only hesitation with this setup was the OMP supply, but I am thinking that supplying oil to the float bowls may still be OK, except for the dilution/delay that was mentioned. Hence, I may run a bit of pre-mix to compensate.
05-06-14, 03:13 PM
#18
carb whisperer
01-21-18, 11:52 PM
#19
The RX-7 spacer may need to be trimmed. It has a big heat shield or whatever it's supposed to be that might hit the old style manifold. Just trim it off.
Whatever you do, keep the older manifold. They flow much better than new. But it might not have channels. The RX-7 carbs need channels in the manifold for the idle circuit to work correctly. Otherwise the RX-7 carb will idle pig rich. That's been my finding with 13B hitachi carbs from a channeled manifold installed on non channeled manifolds.
Whatever you do, keep the older manifold. They flow much better than new. But it might not have channels. The RX-7 carbs need channels in the manifold for the idle circuit to work correctly. Otherwise the RX-7 carb will idle pig rich. That's been my finding with 13B hitachi carbs from a channeled manifold installed on non channeled manifolds.
Hey Jeff, rather than cut channels into an old manifold that doesn't have it, would these 1/2 inch spacers do the trick? They connect the primaries to the secondaries be separate rotor 1 from rotor 2. What do you you think the hp/tq effects would be with or without vs an 81-85 mani with an 85 nikki? Thx.
Mazda Rotary RX3 RX4 RX7 performance
01-22-18, 01:13 PM
#20
That looks like it could work. But you have to understand the height these will add will cut into your hood clearance. Old school manifolds are already pretty tall, and the Nikki is a tall carb. Mazda made the manifolds shorter beginning with the 79 and kept them at that height through 85. They also changed the tilt by a few degrees to better match the engine tilt which was changed for the 1st gen. Old schools seem to be more tilted down toward the rear.
The following users liked this post:
David Chan (01-22-18)
01-22-18, 02:08 PM
#21
That looks like it could work. But you have to understand the height these will add will cut into your hood clearance. Old school manifolds are already pretty tall, and the Nikki is a tall carb. Mazda made the manifolds shorter beginning with the 79 and kept them at that height through 85. They also changed the tilt by a few degrees to better match the engine tilt which was changed for the 1st gen. Old schools seem to be more tilted down toward the rear.