vipernicus42

iTrader: (4)

Hey Guys,

Well I worked my *** off today and got the rest of the engine bay assembled. Confidant that everything was set to go, I cranked the car. It caught, then died.

And after about an hour, I now know I have a carb problem! ME, one of the guys who people come to for carb problems (after Rx7Carl and Sterling), has a carb problem!

Well the main problem stems from the fact that its a loaner Nikki until I get mine back. It ran a few days go before I took it off, so I thought I'd share some info and pics with you guys and try to see if you can help me. Maybe I'm missing something obvious and my brain is fried today.

Okay ... Symptoms:

With the fuel pump jumpered direct on the battery (it's an '84, I wanted the fuel pump to be on constant so that I knew the carb bowls were full), I can only start it after pumping the pedal a few times. Then it starts for a few seconds and stalls out, making a kind of coughing gasp as it stalls.

This tells me that a) the accelerator pump works (I looked down the primaries while working the throttle too) and b) once the car has burned off the gas I gave it by pumping the accel pump a few times, it dies!

So after the accel pump, no other gas is getting past the carb into the intake.


Things I'm Unsure Of:

As per usual, I removed all the extra crap off this nikki, to simplify things. I've included two carb pics below

Carb Pic #1

In pic 1 you can see the two spots I capped off. One went to the choke (which I have disabled on many cars sans problem) and the other went to a little tube jutting out from the carb top just above the alt compensator.

Now since most of the carbs I've worked on have been 83 or earlier, they didn't have these things on top of the alt compensator (which you can see both capped in pic2)

The other thing about pic1 that I wanted to know is the plunger. Silly me removed the connector for it when I trimmed my wiring harness because my Sterling carb doesn't have one. Of course, the loaner carb does, so I'd have done well to keep it. Should this just see 12v all the time? When I apply voltage, the plunger inside pulls back (I can actually hear it). Would this cause this problem?

I left the alt. compensator hooked up because it's too much of a pain in the *** to remove and cap properly.

Carb Pic #2

In this pic you can see the two spots at the bottom I capped off. As before, the one on the right I usually cap off with no problems, but the one on the left connected to one of the spots at the top above the alt compensator. It had a one-way check valve in it. Originally I had left this connected, but I tried taking the check valve out and plugging both ends to see if that would remedy the problem.


Third, non-carb pic

And lastly, I removed the tube that went from here to the main cat, because I'm no longer running an air pump and will be chaning the exhaust shortly. Now as I recall, this should supply air to the cat, which means that it should be an air out, rather than a source of vacuum. The thing that surprised me most was that it only had a little pinprick of a hole in it, and it seemed to be wet with a fluid. Anyway, I haven't capped it, because I was doubting that it would cause a vacuum leak of any sort, but could this, too, contribute to problems once I solve the fuel delivery thing?


Final Questions/Summary

So should all the things I've capped BE capped? (the two bottom ones on the driver's side, the two bottom ones on the passenger side, and the two above the alt comp?) Or should I hook something back up? And should I just run a straight 12v wire from my fuse box to the plunger? And is that thing on the manifold gonna cause a vac leak if left like that ('cause I'll JBWeld it otherwise)?


Thanks guys

Jon

vipernicus42

iTrader: (4)

Oh.. I thought I'd mention that since (to me anyway) the capped off things seem fine and the 12v to the plunger is just a wire, I'm thinking the problem is INSIDE the carb.

So if my thoughts are right, I'm just gonna tear this sucker apart tomorrow and rebuild it. But I thought I'd run it by you guys first to see if you could catch anything I missed before I go ripping the carb apart.

Jon

blwfly

iTrader: (4)

iv capped everything except the dizzy vaccum source and the cat one also the other tube to the back off the mannifold and also i had the alt thing on so one vaccum line

flight_of_pain

you maybe getting enough fuel to fill the floats but not to keep it going, pull the banjo bolts that drop fuel into the float jets and check the screen filters there. ive seen that particular problem many times.

isaac

vipernicus42

iTrader: (4)

Cool. That'll be one of the first things when I tear it apart tomorrow, so I'll keep an eye out for that.

I also didn't install my replacement Mallory (I burnt the other one out late last year) so I'm still running a loaner stock pump. I figured stock pump on stock carb should do it, but one of the things I'm gonna do tomorrow anyway is install my mallory. Maybe the extra flow will help.

What gets me is that the carb was working last week when I drove the car home from Merrickville... But I took the carb off, and so it got moved around... Maybe something's stuck. Like the floats. I know, Sterling will be the first to point out that I should leave the floats the hell alone, but I'm gonna check their free movement at least! (don't worry, I won't adjust their drop height unless I notice something MEGA wrong with 'em)

Jon

vipernicus42

iTrader: (4)

Okay, so I went and read up on the plunger (known as the "float bowl vent solenoid" , I remembered reading about it in one of Sterling's threads in the archive and did a search on it).

Not hooking it up is associated with Flooding problems. That's the exact opposite of the problems I'm having, so I'll just wire it to a switched 12v source for now, that should simulate normal operation.

And I'm still pretty darned sure that the 6 things I've got capped off are supposed to be.

Which leaves me with a problem inside the carb. Lovely. (Or maybe a huge vacuum leak... When you put the intake on with a new gasket, do you need any sealant, or is the gasket enough?).

Someone confirm the six blocked-off things?

Jon

Tranquil

iTrader: (1)

That I know of the ONLY thing that doesn't require a gasket sealer is the Carb to Spacer. Because the phenolic spacer acts as the gasket and the seal.

You should've used some sealant, IMO. Maybe I'm wrong on this one, but I've always seen it that way, and Peejay told me about the carb thing (which I asked him about and then did, because I had knowledge of gaskets = sealant).

rOtAryIsbEttEr

in your third pic, the place where the "elbow" used to be, if thats not sealed or capped off (i cant tell if it is in the pic) you will have a pretty good vacum leak that may explain why your car is behaving like it is.
although i am no expert, i could be wrong
-jason

Tranquil

iTrader: (1)

Hmm new intake, right? Did you seal off all of the ACV and Airpump components?

vipernicus42

iTrader: (4)

Not new intake, old intake.

ACV is sealed off fine. The other elbow is pic 3 which isn't sealed off, but I'll JBWeld it tomorrow to be sure. I figured it was an "out" and not an "in" so it wouldn't be a vacuum leak, but rather it would blow air out into nothing. Which I know sounds silly, but since it just had an elbow to an empty pipe, I'd figure it wouldn't be a vacuum source because you wouldn't suck all the air out of your cats, it would never be held at vacuum pressure.

The other thing (which used to lead to AAB#2) has been sealed off with part of a hose and a bolt for over a year.

So the intake mani is fine, despite it still being old faithful of mine.

So I should take it off again and use what... red high-heat silicon on the gasket?

Jon

Tranquil

iTrader: (1)

I don't know what your gasket is made out of, but find a sealant that is compatible with it and that should solve that problem. Just make sure it won't hamper you taking the intake back off again, just it case it wasn't the problem.

But yeah, the elbow is a weird one. I had mine crushed in a vice, but it looks out of place in the engine bay and I'm JB Welding over it myself tomorrow, too

Oh and BTW! I've been using the JB Quick Stik for a while now, I always keep a spare tube of the putty in the center consol in the FB. I prefer it over the goup, but it takes a bit more effort to set it, and it isn't as temp. resistant. If you try it out you'll know what I mean by effort. Its just tacky and sticks to your fingers so when you place it you'll accidentally take it off when it sticks to you.

Whanrow

Jon, I'll have to start by saying I have no experience with the Nikki. However, I have had something over 25 carbed cars, and there are certain comonalities to any carb.

Your symptoms obviously sound like fuel starvation (you know that already). So the question becomes why? There are only a couple of possiblities.
No fuel pressure (pump circuit works so not likely)
float needles stuck (possible because it ran before)
the electric component you mention (no idea on that one)
vacum ports (the ones on the bottom of any carb I've ever seen are various ported vacums as opposed to manifold vacums. capping them SHOULD do nothing bad)
piece of dirt in the idle passages (maybe, but theroretically fuel filter should have got it)

Personally, based on over 30 yrs working on cars, I would be looking at the floats being stuck, or some kind of vacum that is litterally not allowing the bowls to fill with gas. The float bowl must be vented to ambient atmospheric pressure. If you have the float bowl vent capped, it would be like shaking a pop bottle and blocking the top off. No way the bowl could fill with gas, or at most, only a little until the air pressure stopped more from coming in.

The other thing I'd do is diconnect the fuel line and put it in a can and turn on the ignition and visually see what the fuel flow looks like.

Since this is essentially a spare carb, I don't think I'd go to the expense of a full rebuild, I'd just look for the problem.

Just trying to offer you some options that are easiest to try out.

Now Sterling or Carl can blow me away when they get online. Hopefully at least they'll be nice about it lol.

Rob

Stevan

iTrader: (17)

One the things you mentioned, the plunger, it's called the air vent solenoid in the FSM and Haynes, and I think it's bowl vent sol in the carb rebuild kits diagram.
Anyhow, with ignition on, it closes the vent from the fuel bowl to the charcoal can, ignition off it's open to vent fumes(and pressure, "I think").
So if fuel pressure in the bowls is required for it to run( I don't really know if it is ), there wouldn't be any with that open.

In the third pic, that shouldn't be a leak if you have a plate where the acv was, if the acv is still there, I'm not sure if it would be.
I have the 2 ports above the alt comp capped also.

Whanrow

Darn you buggers with highspeed. 6 posts in the time it took me to submit ONE.

Cowboyfun

ok,
so youre sealed up. youre torn apart, and put back together...we think.
now this will sound very simple, but did you check your idle set screw, i had the same problem and it just required tweaking the idle screw and the rich/lean mix screw.
And yes make sure that plunger is plugged in...mine needed to be plugged in, something to regulate fuel flow out of the bowls into the jets i believe. this is all trying to remember when i rebuilt my nikki 6 months ago.

vipernicus42

iTrader: (4)

Oh, I forgot to mention. I did do that. I thought at first the pump wasn't pumping, so I took the fuel line and put it in a container. Good flow. Then I thought maybe I had put the return line's check valve in the wrong way, so I checked flow through that, still good.

So no problems there. Flow seems fine, and can get in and out of the carb (despite me having an FPR on a stock pump right now)

Yeah, the reason I made this thread was so that I could try to locate the problem without having to rebuild it.

Sounds like tomorrow the first things I'm trying are

1. Scavange the connector for the float bowl vent solonoid from the mess of wires in the corner (done) and connect it to a switched source

2. JBQuick Weld that potential vacuum leak spot

3. Take the top off the carb and check the floats (and the rest of the innards while I'm in there)

and 4. Take the intake mani off to add sealant to the gasket (if really necessary).

I'll also make sure those things I've blocked off are sufficiently blocked.

Jon

Edit: no, the idle mixture screw is at 3 turns out and the idle speed screw is the same as it was a few days ago when it last ran, for an idle of about 1,000. I'm usually the guy setting everybody else's nikki screws, so it certainly isn't those

slashdawg00110

Silly question, maybe, but what about the float bowl levels? You must be getting sufficient fuel to the rear bowl. If you weren't, you wouldn't see a shot from the AP since that's the bowl that feeds the AP circuit. What about the front bowl?

If the levels are OK, I'd look for blockages in the air bleeds and emulsion tubes. Maybe when you removed the carb from the other car something got dislodged and got cught somewhere.

vipernicus42

iTrader: (4)

Unfortunately the carb has 20yrs of crap on it and it was getting dark. I tried cleaning the glass off with my finger and looking in but saw nothing.

I'll check them again today.

Jon

vipernicus42

iTrader: (4)

Well, #1 and #2 above are done.

No real change. For the first time, I kept it running more than 5 seconds, but I was feathering the gas the whole time, so I'm sure it was accel pump shots keeping it going. When I had it up around 4k rpm I started to hear a bit of a squeal.... sounds like a vac leak. Could be another source of problems. I've basically decided that I'm (at the very least) taking the manifold off again so that I can apply some kind of sealer to the gasket.

Once I'm satisfied that the manifold is on without any leaks, I'll try one more time before tearing the carb apart.

Part of me wonders if maybe capping the return for a bit might force through any blockage that's there. It's a crazy idea, but since I know that these nikkis *can* run with a capped return under the right circumstances, I figure I'll just flip the check valve in the return and see what it does.

Jon

vipernicus42

iTrader: (4)

Okay, here's the update.

Innards seem fine. I convinced a friend to lend me his carb, so that I could try another "known good" carb on it.

And I get the same problem!

Yes this is a good thing. It means the problem isn't an internal carb problem, and narrows the scope of this quite a lot.


So here's my working theory:


Since I can keep the car running upwards of 30 seconds by feathering the gas and using accel-pump shots to keep it alive, I originally figured that there was a problem with the gas not getting to the little tubes in the middle of the venturies to be sucked out.

NOW, I realize what the problem more probably is. Since it's highly unlikely that two carbs would have the same type of blockage or problem I started thinking of other things that could make the fuel not want to be sucked out.

So I look at the venturies and ask myself to remind me how they work. Air travelling through them gets accelerated (due to the funneling effect of the venturies.. it's like putting your thumb over a garden hose. Smaller orifice, speeds up), and the higher velocity causes a negative pressure which "sucks" the gas from the nozzles and vaporizes it.

If I had a big honkin' vacuum leak where the manifold bolts to the carb, then half the engine's air supply would come from there, leaving barely any being pulled through the carb.

So basically, by giving the engine (which is just a giant pump) another, easier air supply, my carburetor doesn't get a strong enough pull to get the gas out.

So tomorrow I re-seal my intake manifold to the block.

What do you guys suggest for a sealant? I'm going to be removing the intake again next week, so preferably I want something that isn't going to permanantly affix my gasket to the engine and the manifold and require me to buy a new gasket in a week.

Jon

Whanrow

You don't happen to have a vacum guage eh Jon? Would certainly give you a definitive answer. If you don't, they're pretty cheap. with the amount of problems I see with RX for vacum leaks of one sort or another, it might be a wise investment.

I've never had to put any gasket sealer on any carb base gasket, but always on the intake gaskets. I've used anything from the Permatex black goo, to RTV, and they all seem to work.

I can't help but wonder if you've got a manifold or some other surface that isn't flush, or a gasket that got pinched or pushed out of align when you installed it.

Another clue to a vacum leak that I never see mentioned, is that a car will often miss/misfire with a leak.

I was just thinking about it, and a huge vacum source is used for the power brake booster. A) do the brakes feel normal (full boost) when you can keep it running, and B) any chance that a line is split or you disconnected it somehow? Its such a huge possible source, and easy to check, I'd have a quick look before taking stuff apart - it can't hurt.

hanman

I would second that suggestion about the brake booster line.
Also, just as an FYI, if you have an O2 sensor hooked up in your exhaust, don't use any kind of sealer with silicone in it. Detrimental to the sensor.
Can you keep it running long enough to search for a leak?

LokiRx7.1

iTrader: (1)

RTV, anything PERMATEX, If you are removing the gasket in a week, then you should buy a new one in a week. The sealing properties of any gasket are acheived when the gasket is smashed down when you tighten the parts together. It forms to the irregularities between the surfaces. When you release that pressure the gasket wont return to its original shape, it is permantly flattened. And even if you install it in the same place between the same to parts you wont get the proper seal that is desired.

I doubt that a new gasket would even require a sealer, if so it probably would have been provided or recommeded somewhere. Generally I use VERY little of any kind of sealant, they tend to cause more trouble than they are worth.

Not going for a lecture, just helpful hints that I hope you use. Saves you headaches in the long run.... however it doesnt help your wallet

Chris

vipernicus42

iTrader: (4)

This is all very good info and suggestions.

Yes, the brake booster could be a possibility. I cannot for the life of me find a source for the two rubber brake booster lines (from the booster to the tube, then from the tube to the manifold). If I had, I would have ordered them along with my rad hoses. I'll check it tomorrow. Can I just replace it with appropriately sized fuel line?

Alright, I'll bite and buy another gasket. I just can't find 'em locally, so I usually have to order through Mazda or Mazdatrix. That's why I got one when I ordered my big Mazdatrix order. Should have gotten two.

Unfortunately I don't have a vacuum gauge, and I can't keep it running for more than a few seconds (and for that I have to be sitting in the car).

I, too, try to use as little sealant as possible, but in this case I think it would be warranted for the ability to completely eliminate that as a source for vacuum leak, since I've eliminated almost every other option.

So.... brake booster hoses and intake manifold (with gasket and sealant, checking for any pinched or mis-aligned things).

The fun continues early in the morning when I get up. Hopefully I can get it running in time to take off for Toronto, they're holding an Rx7/Rx8 meet there tomorrow.

Jon

vipernicus42

iTrader: (4)

GAH!!!!!

I give up! (for a while)

I have absolutely no idea what's causing the problem.

I took the intake manifold off. It only has 3 vacuum sources on it, so I figured I'd be able to troubleshoot if I blocked off all three of them (I wouldn't drive it like that, since I need the brake booster, I'm just trying to get it running)

So I use some brand new Fuel/Emissions hose, two big bolts and clamps to block off the brake booster vacuum source and the #2AAB source. I've never driven the car with an AAB before, so that's always been capped, but I re-capped it just to be sure.

The other vacuum source usually runs my PCV valve, but again, just for the sake of troubleshooting, I blocked it off.

The spot with the elbow that went to the cat was sufficiently JBWelded and the ACV blockoff plate I installed last year isn't going anywhere.

Satisifed that there was absolutely NO possibility of vacuum leak on the manifold itself, I turned to the mating surface between the manifold and the car.

At first I tried a bluish purple "gasket making and dressing" compound. I used a putty knife to make sure that both the manifold and the engine block were as smooth as I could get them, applied the compound to both surfaces, sandwiched the gasket between them and bolted it up.

I also checked the carb spacer. All but one port had been blocked off (the one left open for my vac advance) so I checked all the connections, and blocked off the one for my vac advance.

So from the engine up, I'm *damn* sure there are no leaks.

Then I tried two different carburetors (one that I picked up late last night from a known-working car that belongs to a friend of mine) and got basically the same result.

The car starts with no problems. Two shots of the gas and she fires up, but I have to feather the gas and keep it above 4k or it will die. On some rare occasions I've managed to stop the "feathering" and just hold the pedal and keep it in place for a few seconds, but it slowly drops. If it drops below 2.5k it chokes out and dies. Pulling the choke has absolutely no effect.

Classic signs of a vacuum leak, but I can't for the life of me figure out wherethefuck it is!

I repeated all the above THREE TIMES this morning. I even changed compounds to something called "Ultimate Grey" which is supposed to be for sealing surfaces of "frequently dissasembled engines" and was the only compound there that didn't require 24hrs to set.

Same problem all around.

I tried switching the check valve in the return line and didn't even see a difference in the way it acted. I think I *heard* a difference, but that doesn't really make sense, and that could just be my head. Man it aches.

I'm totally, completely, and utterly stumped. I missed the Toronto meet, which wasn't all that important, but if I can't fix this by next weekend, my trip to see Sterling is going to be in jeopardy.

And I'm out of ideas.

Anyone?

I can provide pics of anything you want, I have quite a few in my camera, and I even took a vid watching the tach while I started it , revved it and let it die, if someone can host it for me.

Jon