I need help trying to figure out what's going on with my stock Nikki carb. A couple days ago, it started flooding really bad when the fuel pump is on, and I can't find the problem. I have to admit, I am a carb noob, but like to learn to fix my own things.

I have tried searching on the club for solutions, and have tried a few things with no results. I've tried reducing my fuel pressure at the regulator, I have taken the air horn off of the carb to clean it (cleaned the bowls, floats, and needles). The bowls were dirty with what looked like residue from my old rubber fuel lines. Here is a pic, you can see there's gas sitting on top of the primary and secondary venturies, and in the cavity next to the primaries (what is that cavity for anyway?). With the pump on, that cavity fills to the point that it overflows.



A little background that might be important: after having fuel delivery problems and clogged fuel filters, a couple weeks ago I got my gas tanked cleaned/sealed, I changed all of my rubber lines, changed my fuel filter, installed a new carter 4594 fuel pump, new fuel pressure reg with gauge. Everything was working really well until two days ago.

Anyway what should be my next step? I'm getting tired of taking the spark plugs out to blow gas out of the holes.

 

usually the reason that the carb will overflow with gas are misadjusted or stuck floats. no matter how you look at it, its time for a carb rebuild my friend.

 

Lap your needles and seats after your rebuild. After mine my floats would stick and flood out than one day it stopped (needle and seats wore eachother smooth my guess)

 

mine is doing the exact same thing. i have gotten to the point where i think my needles need replaced and or my floats. the tricks they say to tap the top of the carb work and make it run fine again. what is happening though is the bowl that is operating the secondaries is filling up completely for some reason and just constantly pouring gas on top of them. i believe the front bowl operates the secondaries. i am not sure on that at all.

 

just replace the needles and seats with new parts included in the rebuild kit. the rebuild kits do not come with new floats. those are usually fine, just in need of a cleaning.

 

you may also have a problem with the bowl air vent solenoid.
you need to be sure this is getting 12 V with ignition on .

PS
very common in some parts of the world for wasps to get into the charcoal / evap system pipes and cause all sorts of dramas ,, some of them like this. unlikely as it seems

 

That's the connection between the bowls and the vent solenoid. Fuel there means you're not just flooding but are completely filling the float bowls.

Once fuel gets that high, it can overflow from one bowl to the other, too.

IF you are sure your fuel pressure is correct (testing with a good pressure gauge is the only way to be sure), then you either have:

1) a blockage in your fuel inlet spider or the tank return line that's preventing fuel from bypassing & returning to the tank when the needles close

2) a needle that's not closing properly

3) a float that's stuck or fuel saturated & not lifting the needle to close it.

Since you said it started suddenly, odds are it's not a float. More likely a return path blockage (esp. if you had line debris in the bowls) or a needle that's worn/sticking & won't close.

 

I've checked it and it's fine. I'm getting 12V and can hear it click when I turn the ignition on.

DD:
- I have a Professional Products regulator with an Autometer gauge. I know all my other autometer gauges work well and are very accurate, so I'm assuming my fuel pressure gauge is fine too. I had the pressure at just a tad over 4psi. I have since readjusted to just under 3.5psi.
- I will start with making sure my return line from the carb to the tank isn't clogged. If this doesn't get me anywhere, I'll take the air horn off again and check the fuel inlet spider for clogs.
- My car only has 60,000 miles on it, not sure if this matters or not, and my needles looked really nice when I took them out to clean them. Like I said though, I'm a carb noob, so what do I know.

 

The needles can be finicky even when they are new. If the flooding started suddenly, ITS NOT THE ADJUSTMENT!!!!!! There could be debris keeping it open as was mentioned. Sometimes the tap on the top of the banjo bolts does fix it. You might just need new needles. A bad float could flood it, but only one bowl, not both as yours looks like. Your fuel pressure may be too high. I can't remember offhand where it should be. Definitely check the return line for a clog. That's a good place to look.

Ok then the solenoid is working correctly,good.

One tip for everyone. When you install the needles, new or used, put a dab of Vaseline on the rubber tips. It helps them to seat and seal. Those here who now and remember me know that I've built dozens of these carbs.

 

gonna be providing a Nikki modding service?

 

Stock fuel pressure spec is 3.7 - 4.7 PSI static on a capped line (1980)

 

Jibaro, probably not anytime soon.

DD, you have to account for the return line. That drops the pressure down further.

 

make sure your fuel bowl vent is not capped off, my secondaries used to flood like that. if not just rebuild it, best way to learn, before i learned, i took mine apart 28 times until i finally figured out all the bugs including flooding secondaries. good luck

 

Try dropping the pressure to 2.5 but keep in mind that most guages are not going to be accurate at those low ranges, so you'll have to kind of "play it by ear". The only guage I know of that is accurate at the ranges we run is the one from Respeed.

Good luck.

P.S. Holy Cow! Carl, where the hell have you been man? Glad to see you're still around.





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Which is why I stated it the way I did - - Mazda AFAICT never published a spec for in-line pressure for the Nikki. Only for a capped-line test.

Which means of course the only way to be sure it's in-spec is to do a capped-line test with a known-accurate gauge.

 

Hey Ken, long story, thanks man. I'm gonna hang around for a while. Maybe you guys will get me fired up enough to get one of my cars back on the road.

DD- good point and I believe you are correct about the specs. Thanks for the clarification.

 

hoping you get fired up enough to get one of your cars back on the road Carl! one you get the bug to do so, it'll sting you like a swarm of yellow jackets to the eye! what 7 do you currently have that's on the back burner?

sa7, were you able to make any progress on the overflowing carb?

 

No I still haven't found the problem, but I haven't had much time in the last week to work on it. I've checked the fuel return line from the carb to the tank, and it seems to be fine, no clogs. Now I need to check the fuel inlet spider on the carb to make sure the return isn't clogged there.

 

Here's some reading material for you. The flooding section may apply to your situation, or it might not.

First Gen Rx-7 Tech

 

I finally got a chance to take the air horn off again. The fuel inlet spider is clear, I took it all apart, and see no debris or clogs. Now I'm trying to find a carb rebuild kit so I can try replacing the needles and seats. We'll see what happens, hopefully this will solve it.

 

Be sure to gently burnish the corners of the new needles before installing - -greatly helps prevent flooding while they seat in. A Stirling idea and one that really works.

 

I have been purchasing my rebuild kits from Autozone. I think they are like $30 and are very complete.

 

I just got mine done and fixed over the weekend. my problem was the needles were not fulling closing for some reason. Maybe your problem too.

 

So I finally got my car started. I haven't bought a carb rebuild kit yet. But I tried reducing the fuel pressure to 3psi, and used rx7carl's idea and put some vaseline on the needle tips. No flooding.

So if it's the vaseline that helped, I don't know how long it'll last. so I better still order a rebuild kit to get the seats and needles replaced at least.

Thanks for all your help

 

SA7, you could confirm if it was the Vaseline that fixed it by raising the fuel pressure again.

Many times the wear factor on the needles is a combination of wear in the viton tip (with a magnifying glass, you'll see a groove around the tip where it has been contacting the seat) and age compression of the spring inside the needle body that the float-contact pin rides on. Both make the needle effectively 'shorter' than it should be, so normal float position doesn't close it. Enough wear at the tip, and it just doesn't seal any more.

The Vaseline might soften and swell the viton slightly, allowing for a better seal until it wears more.