Not quite. On the modded Nikki I have to manipulate the throttle for a minute or two before it will hold from a cold start (practically regardless of the ambient temperature), and even when it finally holds idle, it's only at about 500 rpm by that point, although I had set the idle low on that carb so that figures.

On the currently installed stock carb I use the choke and it will idle nicely at about 1500rpm until it warms up a bit at which point it starts to 'bump'. The choke does not auto return due to some wiring changes I made, but when I disengage it via a toggle switch, the 'bumps' decrease substantially and idle goes to about 900 rpm. The misfires are still present though at idle, and the 'choke on' misfires might be due to holding the throttle open (fast idle rod) because I can get the same effect by holding the throttle at that same rpm, or really and rpm for that matter on this stock carb.

I tune the idle mixture when up to temp so the bumps that I'm experiencing are the best I can get it with the current jetting and such.

Edit: I should add that with this stock carb, even with the choke engaged, I have to depress the throttle pedal slightly to get it to catch when cold (even on 55+ degree days). My fast idle is adjusted a little low (about 1700rpm warm) but again it's something to note.

 

Ok so on your non-stock carb or the modded one, does it have the smaller idle air bleeds at around 120? This makes a big difference for chokeless carbs and are a bit incompatible with a choke flap.

The need to push the pedal a little bit when starting a stock choked carb is due to the little horizontal tab or tang needing to be adjusted up a slight bit. This tang is what is pushed on by the long fast idle rod linkage from the top of the carb down to the throttle linkage. Study and see how it works, then grab the tang with smooth pliers and tweak it up slightly.

 

The modded carb has the 120's, the stock one is factory jetting all around ('82 year).


Ok cool. That's what I was referring to when I mentioned the fast idle rod being adjusted a little low. I seem to remember the manual stating to bend the rod, but bending the tang would work just as well - probably easier too, I've only ever adjusted the rod. I'll do that when I do the other tests.

Any additional thoughts regarding the air/fuel leak and misfire combo? Now that I've been driving with this stock carb for a couple days I'm noticing misfires across the entire rpm range, although they're only noticable when at a constant rpm - idle included but it's not as severe. I could get a couple more audio clips if that would be helpful. Thanks for the assistance.

 

I don't know that the two are related. IF the fuel system is keeping carb bowls full in all modes of operation,until proved otherwise,i would concentrate efforts elsewhere. Listening to audio clips is not same as having car in front of me,yeah throw some more clips up.Ever had a timing light on timing marks when misfire is occurring,anything visible there?
As far as carb bowls being near empty after sitting for a time and fuel pump needing to run to fill up fuel lines each time you start engine cold speaks to a loss of prime in fuel system,has to be an air leak in system somewhere. At some point will need to be addressed.

 

Ok, well here are a couple of audio clips; oh the joys of trouble shooting over the internet... The scenario is in the file name like they were last time. The lights on one isn't that important, it just shows a slightly lower idle and lessened misfire sequence. The lights off one is just a normal idle (about 900 rpm) while up to temp. The '2k and 2.8k' clip shows the bad missing when holding at a constant rpm. In that clip I start at idle, go to about 2k, and then to just under 3k. I then bring it back down to just under 2k before letting off the pedal completely. Note there is no shutter valve, ACV, or anti-afterburn valves.

Fuel is being maintained in the center of the glass so I guess I'll continue to look elsewhere for the misfire, at least for now. I'll still do those tests and investigate things when I have a free moment. The many times I've had a timing light on it I have not noticed any glitches that correspond to the misfires. I've looked for them on countless occasions, but when I get random glitches - not related to a misfire - they're most likely because my timing light is a bit worse for wear (part of the pick-up core is missing).

Anyway, here's the files.

Edit: I'll get some cold start clips tomorrow morning if I remember.

 

Here's some more audio clips I recorded a day or two back. File name is self explanatory once again. The "air in fuel system" one is a bit quiet but if you turn it up and listen carefully you can hear the air working its way through the regulator. Note that the "air" recording was taken from inside the car.

Today upon returning from a drive I decided to check my fuel pressure gauge, and after having let the car sit off for about a minute and then turning back on the pump (not the car) I noticed it was bouncing. It looks a lot like the bouncing I saw not to long ago while the car was running but this was constant compared to the previously noted erratic behaviour - and of course the car wasn't running. I've also been noticing that the air sound takes longer to go away completely and sometimes never does (before driving off at least) instead reaching only a low hum coming from the fpr. More odd things once again...

 

Have i asked you already what happens if you disconnect leading ignition when engine is warm and idling? Misfire still?
It does sound like an ignition misfire. Fuel related dropouts are a lot smoother than that,more of a rolling drop and recover.
Have you watched your fuel gauge while system is "priming"and making that noise?
Ever checked for quality of spark,color on leading,trailing?

 

I've run the car without trailing and I still get the misfire. Is that what you meant or will a rotary run on trailing only as well? If that's the case I'll gladly try it next chance I get.

I'll look at the gauge the next time I go to start my car and it makes that sound.

Leading and trailing spark color - as of a few week ago - is a strong purple, even when spinning the dizzy by hand.


I had time to check the fuel pump yesterday and the audible fluctuations do not match with any change in power draw (current or voltage) down to the tenth. The fuel filter stays mostly empty while running but once I shut off the pump it starts to fill up - from the fuel pump side. So essentially the the line is draining backwards when I shut off the pump. I checked the check valve and it seems to be fine but perhaps since there's already air in the line it's not working like it should. I was going to drop the tank yesterday too but ran out of time - should be able to do it Wednesday if it doesn't rain.

Here's a photo showing how slow the fuel enters the filter.



The filter is off the holder on purpose so you can see the effect better. Also note that I blew out the tank line with the air compressor and there was no change, so it's not likely to be a blockage issue.

 

It will run on trailing only,won’t make much power and may idle a bit lower. You can bring the idle up and see if misfire present and bring rpm up to 2-3k and hold to see if misfire present.
Do this engine warm and running, with misfire present,disconnect leading and see what happens.
You’re just trying to eliminate leading to see if problem in that part of ig system.

What check valve are you referring to?
No,gas shouldn’t be running into filter on shutdown.
It should hold what it has in it while running,which by the way should be more than empty looking. The filter should be1/2-3/4 full and stay that way indefinitely.
Is it oriented correctly in/out-some filters don’t flow same either way and have an arrow or in/.out molded on filter body stating which is which.
Try taking gas cap off,while engine running and warmed up. Any hissing,does it change anything?
Do you still have charcoal canister installed and hooked up?

I have worked on vehicles that had the pinhole problem I referred to on several cars,non Mazda vehicles also. To test fuel lines,cap one end off,spray @ 60% soap to water solution from spray bottle and apply air pressure at low psi into other end(might need 2nd person)and watch for bubbles in line-do both feed and return.
I would do this 1st before dropping tank.

Break fuel system into sections...test feed and return lines from engine compartment back to where fuel pump output hose goes to metal line that runs forward.
Disconnect pump feed hose and plug line there and test. Do same for return. You can test feed and return lines on body over rear axle same way after tank is out and you can test pickup tube in/out of tank same way.
Somewhere along the way you will find where air is getting in your system.

 

Ok, I'll try running without leading in the next day or so, maybe even tonight.

The check valve I was referencing is the silver cylinder inline with the return fuel line in the below photo. It's supposed to keep the fuel from draining back out of the feed line to help reduce the need for the system to prime each time - or at least that's the way the Hayne's manual puts it.




The filter is facing the correct direction in terms of flow.
I've tried removing the fuel cap many times before while the car is running, after it has been running, before starting, etc. to see if it affects anything. Unfortunately there's no change whatsoever. No strange sounds either.
The charcoal canister is not stock on this car but since I swapped over the vacuum rack from an FB I moved the canister as well. That said I've tried disconnecting it before and there's no suction or similar sounds that occur when I do so. And of course nothing changes in relation to misfires or general engine operation either.

I'll do the soap spray test next time I have a good lot of time for the vehicle to be in the air. Hopefully I'll find something. I have another oem check valve I could swap on too just for kicks, if I can find it that is.

 

I didn't know whether you kept oe check valve with mods you had done. Easy enough to check the valve. Blow into it in both directions,should only pass air in one direction.

Looking at pic of your filter,is that rust inside it or dirt on the outside of it?

 

Yep, I did that when I was testing the fuel pump power and such - it checks out fine.

That is indeed a small amount of rust, but that's been there ever since I recoated the tank. The tank was originally a bit crusty inside - to the point where I could clog a filter in a week - so I dropped it, cleaned it thoroughly and recoated it. The couple times I've dropped it since I haven't seen any changes for the worse. That rust was probably sitting in the pickup line after getting knocked loose from the sides of the tank during washing. Point being that no more rust has accumulated since.

I tested the car with trailing only and what do ya know, exact same misfire sequence... Just for a sanity check I tried running on leading only and I couldn't even tell a difference between it and normal running - makes sense I suppose. I guess that would mean that unless something in the dizzy that drives both systems is messed up (maybe the reluctor wheel? Just thinking out loud, not sure how it could be) or something in both systems is out of whack in the exact same way, that rules out the ignition system. I took an audio clip just for documentation sake. I didn't bother adjusting the idle screw so I just held the pedal in the same place for a little while - about 1000 rpm or just below.

So based on those findings, do any new ideas come to mind? Seems like it's got to be fueling related at this point.

 

I listened to that a couple times,you could tell it was running on trailing and idling lower,but didn't seem to misfire til you stepped on gas and brought idle speed up. Can you repeat that,take air cleaner off,duplicate the misfire as you bring idle up to around 700-750 or wherever it starts to steady skip/misfire with throttle linkage and lightly spritz some carb cleaner over the primaries. What happens,does it smooth out?

 

Yeah sure, I can do that when I get back tonight. Even at that low idle it does still misfire some (at least you tell by watching the engine rock back and forth inconsistently) even if the exhaust isn't popping. Then again the car usually does that anyway so, eh...

Did you mean ether or is carb cleaner correct?

 

Carb cleaner

 

Ok cool, just wanted to make sure.


That said I did the tests and here's the results (I took some more audio clips too). First off I took another clip of the car running on only trailing without adjusting the throttle at all so you can hear the misfire more easily. After that I raised the idle with the idle speed screw to about 800 rpm and left it there for the rest of the tests (I also took a recording of it idling at 800 rpm). When I sprayed some carb cleaner over the primaries the car would bog (as you can hear in the clip) and I'm sure I could have killed it easily if I had given it more than a burst or two at a time. It should be fairly clear in the recording when I spray the carb because there is a noticeable stumble/bog each time. Now I'm curious what the reasoning was behind doing that test. You're looking for problems with idle mixture I'm assuming?

I also took one last clip of starting the car to show the delayed idle increase which occurs about five seconds after it catches when hot (I did not touch the throttle whatsoever). I've got a feeling it has something to do with the alternator cycling on spinning up or something - not sure if that's a thing but it's an FD alternator so perhaps the newer ones have some sort of start up procedure built in.

Lastly I detached the fuel pressure gauge today and I can confirm that the bouncing needle is not due to vibrations getting transferred through the body. So that means that something in the fuel system - probably air - is causing those bounces. While I was at it I pinched the rubber line from the tank slightly by hand and I could feel intermittent pulses. I will also note that the bounces are almost never in a direction of positive pressure. Or in other words they're due to random pressure drops, once again probably air. I also tried adjusting the fuel pressure from 2 psi all the way to 4 psi and there was no tangible difference in idle quality or holding at 1500 or 2000 rpm - didn't test any higher. All that I noticed changed was the float levels which makes sense. What fuel pressure are you folks running on Nikki's, modified or not. I did some looking today and I didn't find a general consensus. Just realised that perhaps that's why I had to raising my floats to under 13mm, compared to the factory suggested 16mm or so, on my modded carb after I changed the fuel pump and set the fuel pressure at 2.5 psi.

Well that's all I have for now. Forecast shows rain for tomorrow so I doubt I'll be able to check fuel lines for leaks until later this week.

 

Reasoning is to determine if there is a possible intermittent lean condition causing this. The only constant is fuel system anomalies that appear to have been there all along with everything else that's been changed,again i don't know if this has been responsible all along,stated symptoms have to be a player somewhere along the way.
Spritzingl,not spraying carb cleaner over carb venturies is subjective,you're trying for a mist not a stream. Any near right mixture adjustment on a carb will cause an immediate overrich condition if too much carb cleaner introduced and lower idle speed/bog results.Different brands/cans yield different results.
Perhaps try this again with an unlit propane torch just cracked open to where you can hear a slight hiss. You may have to do this away from car so you can hear it and then pass it over top of carb to see what changes are. Propane is heavier than air so naturally gravitates to low areas. No change,slightly increase flow from bottle. See what happens.

Regarding alternator,it charges immediately once alternator speed reaches a minimum threshold of @ 500 engine rpm.If the dash warning light cluster is out,alternator is charging. You can eliminate the alternator as a factor by disconnecting and taping up output wire before testing/starting car. How do you have the alternator wired into the car ?
This was a test i had wanted you to do at a previous point as funky voltage regulators/rectifiers with leaky diodes can cause strange hiccups in electrical systems,especially ignition systems and ECUs. Best way to check for stray AC voltage in a DC system is with a labscope.
I'l listen to your audio clips later,too noisy where i am currently.

 

Yep, I was misting, no streams here. I tried the propane and I didn't notice much of a change, although my bottle is essentially empty so maybe later today I'll go pick up a new one and retest. Ended up that with the propane the car would intermittently run more consistent. Although I also noticed this behaviour without the propane, it was just much less common. I took another recording and as soon as you here the first smoothing out of the idle I'm feeding it propane. I continue feeding it until nearly the end of the clip, although once again, the bottle was essentially empty (enough for a flame, I checked) but not much was getting out. Best example of the behaviour I'm referring to starts at about 00:30s in the recording. I set the idle to about 800 rpm once again.

Forgot to do this. I'll go test that pretty soon here. It's wired with a new lead from the output to the positive of the battery, and then the stock alt wires are used for ground and to trigger a relay that switches a fused 'sense' line from the battery. I originally tried using the factory switched 12V as sense but the old wiring was leading to a false representation that caused an overcharging issue. Hence why I added the relay and new sense wire. The relay was also added to prevent power draw through the sense line after the car is shut off, which is apparently an issue that others have run into when not using a diode or relay. There are no idiot lights lit up on the dash. Of course the car no longer runs an ECU of any sorts, but yeah, ignition system might be getting affected. Unfortunately I still don't have access to a lab scope, but I'm continuing to look around.

Also took another clip to show the delayed idle with trailing only. I start the car twice in the clip - it did not die.

And thanks again for the help. I realise this is a rather tedious issue to help solve, particularly when you can't see and test things for yourself, so again, thanks.

 

Ok, just ran the car with the alternator's output disconnected and I can confirm two things. One, the delayed idle change is due to something with the alternator because when I disconnected the output it stopped happening, so my prediction was correct in at least some portion. And two, the misfires do not change whatsoever without the alternator connected, so if there is stray AC, it's not messing with the ignition in a noticeable way.

 

My local home depot is somehow out of propane torch canisters - even though the site says they have 50 of them... oh well. I get some more sometime here.

I inspected the fuel system today and there are some developments. For one, I found a small leak with the spray bottle test. It was on the line that connected to the fuel filter from the tank side - the only rubber fuel line I hadn't replaced. The leak was minor, but I replaced the line and everything looked great (this is after blowing through all the lines and dropping the tank, etc.). Turned on the pump, it primed, and then the filter filled nearly to the top and stayed that way. I shut off the car, turned it back on an hour later and no priming noises, filter still full. But then I go to get gas, and upon returning home I checked the filter and what do you know, it's nearly empty again. Now I'm guessing that something in the tank is floating around and clogging the pick-up tube. Maybe I'll get a chance to blow out that line again and see if it temporarily fixes it again, probably not for a few days though.

Regardless of that, when the filter was full and everything was working well in the driveway the car still misfired just as usual, so at least I can strike the fuel supply (lines, pump, tank - not carb) off the list. I'll go over the tank again when I have a free afternoon and my tank is nearly empty again.

So, I'll try and pick up that new propane canister soon but for the meantime, anything else to check over?

 

surely that's not the ONLY place that carries them. i have several places i can pick up those propane and map gas canisters.

 

Quite true, although I didn't mean it that way. I stopped by there on my way home and was surprised to see they were out of stock. Didn't have time later in the day to check other places - even on my gas run. Anyway, I'll get some next time I'm not preoccupied, hopefully Monday.

 

Ok, had some time to do a little more investigating so here's the rundown. I retested trailing only, and with it idling at about 800 rpm (I raised the idle) I added propane (no mixture changes yet) and the idle cleared up slightly. From there I decided to lower the idle back down to where it was before I adjusted it (I set the screw back to where it was when the car was running normally with leading) which ended up as about 550-600 rpm. From here I messed with the idle mixture, richening it until I got a practically perfect idle with very occasional large misfires - this is the first clip. After this I reconnected the leading and without changing anything I took the second clip (idling just under 1000 rpm). In that clip you can hear the cyclical misfire a bit. After that I lowered the idle to about 700 rpm and took another recording, again without adjusting the mixture - here you can really hear the cyclical misfire. Finally I tried adjusting the mixture (still full ignition hooked up) but I couldn't get away from either the cyclical misfire (rich) or the larger, slightly less frequent 'bump' misfire (lean). So at this point I'm fairly confident that the misfires are related to mixture issues. Any thoughts on why I can't seem to find a happy medium when the leading and trailing are hooked up? I didn't try leading only, so perhaps I could do that later today, although I doubt I'd find anything different than I did with both running.