Benjamin4456

Previously I had thought this was a problem with the AP delivering too much fuel. After some research I decided that's not possible so.... What are things that would cause the car to run worse when the float levels are at spec and better when less fuel is in the bowls? And I mean anything: jets flipped, wrong sizes, clogged something or other... The car stalls under load at low rpm even if you barely touch the pedal (accelerating). I have the carb off and disassembled again so I can check anything. Tonight I'll probably go through, clean it out again, and check all the jet sizes (just did a rebuild so I may have done something backwards). Thoughts?

t_g_farrell

iTrader: (1)

Thats a good start. Get the carb manual from foxed.ca to help id and verify placement of parts.

Benjamin4456

Thanks. Last night I actually had the pleasure of reading the entire theory of operation section in the carb FSM and also sketched a quick diagram of where each jet should go and what size. From the symptoms, would I be correct in assuming it's running way too rich/not getting enough air? At least considering that it runs better with less fuel in the bowls, ie: leaner.

t_g_farrell

iTrader: (1)

That sounds right to me. Are the jets all stock?

Benjamin4456

Yep, all the jets are stock and in the right places. I also visually compared all the jets to ones of the "same" size on one of my parts carbs. It doesn't seem that they were inlarged at all so that's a plus. Last night I also cleaned all the passages in the carb body, throttle plate, air horn, and the vacuum block/spacer thing. Anything else I should check before I put it back on the car (I did already reassemble it though).

t_g_farrell

iTrader: (1)

There are emulsion tubes that will only function correctly at the right float level. I think DivinDriver mentions this in a post somewhere else. These same tubes can also cause issues like this if they are dirty/clogged internally. These sit in the top of the carb body under the top cover. So even if the right numbered one is in the right hole it could be not working right due to dirty or a clog. The good news is you just have to remove the top to get to them. I don't have any other wisdom to give you at this point.

Benjamin4456

Hey just out of curiosity, would a clogged or restricted fuel line cause the car to die at low rpm/high load, yet allow it to run under other circumstances? Recently I've noticed the fuel pump seems to be cavitating, or a least running really rough and noisy. This happened once before in the summer and it ended up that the tank pickup line had clogged (the tank has been cleaned since but not re-coated). I replaced the filter just a week ago, and it took the pump a long time to pull the fuel up out of the tank and into the filter so maybe it's happened again? At idle the float bowls are spec but I haven't checked them at other op conditions. Is the car stalling a problem that would be caused by low fuel pressure? Lots of questions.

EDIT: Forgot to mention that the carb is back on and the problem persists.

mazdaverx713b

iTrader: (91)

If there's a fuel line restriction or the pump is failing then the needed fuel pressure would not be there under load.

Benjamin4456

Did the fuel system and all is now well there, but there has been a development. Now, even with car sitting, it will die everytime it hits just below 2k rpm if you are slowly accelerating. I just checked spark and it's all good. If you get past 2k rpm it runs just fine, it's just that small area. Any clue what would be activating at that rpm? Is the carb tranision circut under heavy use at that point? It's not the throttle sensor, I've checked that. This is a wierd one for sure.

Jeff20B

iTrader: (13)

Yes.

Benjamin4456

Well that makes sense. On a different note, my previous post apparently didn't upload, but I fixed the problem. I started messing with different vacuum and ignition stuff and ended up unplugging the line on the top of the PCV which made the car run great. I plugged both open fittings with bind caps and it still fixed the problem, so it's not that I created a vacuum leak. Any ideas on what unplugging that line would do? I know there's a diagram of the PCV in the Haynes manual but I seem to have misplaced it.

Jeff20B

iTrader: (13)

The PCV lets in some additional air to the carb. It is like a semi-controlled vacuum leak. But as I've mentioned countless times on the forum, these carbs are factory tuned to let in a lot of air in order to work with all the excessive "bulk" and accessories they come with stock. But problems arise when any of these factory add-ons begin to fail. You are suddenly getting a ton of unwanted air and it causes serious problems. That is why blocking off some or all of these sources of additional air seems to fix the problem. The actual problem really lies in the factory air bleeds themselves, in my opinion. I've had tremendous success simply reducing many of the factory air bleeds a good .50mm or so, here and there. Some more, and others less. And with reduced unwanted air, you must now retune the factory jets to something smaller as well, because you are now pig-rich. Well, not really but you get my point. It's a careful balancing act that took me a fair bit of time and effort to figure out.

To answer your specific question, the factory didn't really use a PCV, but unplugging it will cause a buildup of moisture under the oil fill cap which can lead to a rusty condition in the steel tube. Then this rust falls into your oil pan and has to go through your oil pump, and oil cooler, before eventually (hopefully) getting filtered out by your oil filter.

Benjamin4456

So if I understand correctly, you're saying that from factory they set the carbs so that when all the vacuum "accessories" were hooked up they would run with the proper a/f ratio. As I unplugged the vacuum signal for the PCV, it's no longer operating, or at least that my assumption since the car runs the same no matter if the bind caps are fitted on the signal line or not. That then will cause a buildup of moisture in the oil filler neck, etc. I'm not really in the mood to mess with re-jetting the carb since I'm trying to put as little money and time into this car until it passes smog testing (I bought it after it had sat in a field for 16 years). So in the end, is the car running better because I eliminated was essentially a vacuum controlled vacuum leak?

Other things:
1. Car wont go over 6k rpm.
2. Backfires like mad on down shifts.
3. Idle drops sometimes after driving around and then coming to a stop.

Could these be caused by my vacuum advance not working at the moment (the ECU isn't giving the solenoid any power so I just disconnected it). Perhaps I could use the vacuum signal from what was the signal line for the PCV (it looks like it's a ported vacuum signal) to control the vacuum advance?

Thanks for the help thus far.

Benjamin4456

Well here's the latest:

1. I could care less about getting over 6k right now since it just has to get to the testing station.
2. It's a rotary; so backfiring, meh (plus I have a small exhaust leak at a weld in the down pipe)...
3. This one is bothering me. After driving around at above 3k and then going to neutral (idle), the engine drops way low and then bounces around below 1k rpm for a while and then steadies itself. A couple of times it has died and that's really the only reason I care. Thoughts? I relies this could be anything so...

Sort of related to the 6k thing, the higher the rpm the more "backfires" there are at cruising. It's not really a big backfire, it's just a kinda bump every second or two. Maybe it's due to a messed up mechanical advance (vacuum advance is kaput as of now)?

t_g_farrell

iTrader: (1)

Check to make sure the advance mech in the dizzy move freely. It might need to be cleaned good and lubed to make the mech and vacuum advance work as designed.

Benjamin4456

Will do. Off the top of my head, I know that the vacuum advance "works". If you give the diaphragms vacuum they advance the ignition, the problem is that the solenoid that is supposed to control them isn't getting any power. My guess is a wiring issue since other emissions rattitude is working just fine. I'll radio trace the wire today and see if it's broken. Do you know if the vacuum solenoid should have power at idle or off idle? Also, should one of the vacuum diaphragms be more difficult to move than the other?

t_g_farrell

iTrader: (1)

Can't answer your first question, don't have rats nest anymore or emissions or even inspections. DOH! Both vaccum advance pots may move at different rates because ones for leading and the other is for trailing so I would expect the vacuum effort for one will be higher than the other but I could be wrong on that.

Benjamin4456

Well I've found something interesting and probably the reason why the car is dying when I let off the gas after cruising. If I hold the rpm at 3k for a little and then let off, the float bowls are filling all the way up and the car starts to have a low bouncing idle. As the levels lower back to normal the problem fixes itself. Now then, what the heck would be causing that to happen?

Something else is that the car is still running rougher the higher the revs. Even at 3k it's jumping and bucking. The mech advance seems to be fine.

Thoughts?

t_g_farrell

iTrader: (1)

Did you use the needles and seats from the rebuild kit? If so put the old ones back in. The new ones are all pretty poorly made.

Benjamin4456

Ironically I've already fixed the problem, and yes, I used the needles and seats from the kit as the previous ones were far gone. Now for the fix: I had thought the vent solenoid on the carb may have gone bad since that would cause vacuum at high rpms (rough running at high) and then causing a vacuum on decel (overflowing bowls). Tested it and it was bad so I swapped it for one on another carb. Works great now. Since that's all connected to the PCV I thought I'd test it and voila, it's fixed too.

Thanks for all the help (including my other threads). Inevitably something with go wrong and I'll need help yet again. I'll be off to DEQ tomorrow so wish me luck after having done so much to it, last trip permit too.

Benjamin4456

Well uh... Problems have arisen again. Not enough daylight to start investigating but here's the story. Car sat for a couple hours after I had finished working on it. Went out to do a test drive to make sure everything was still working. Started it up, choked and left to warm up, running a little rougher than "normal". Pulled out, around the block, seemed to be getting better. Up a decent hill, into a neighborhood I use to turn around in and it started sounding like a motorcycle, barely held idle. Pulled over, floats were stuck on both sides. Knocked on the carb with the trim hammer I kept with me for just that purpose. Held at 2k to get the extra fuel out of the system, but it wouldn't return to idle and kept bouncing around (still sounding rich but floats were back to normal). Limped it home and that's as far as I've gotten.

So this carb has always had sticky floats, before and after the rebuild. Just because I'm paranoid I'll probably end up swapping the seats, needles and floats from my SA carb which worked fine but is no longer in use. I might lower the float level just a little too since it seems to prefer that and if anything, they're a little high. Not sure what else to do, I'll check and see if anything else got stuck tomorrow but this is the same engine that ran just fine before so it's got to be the carb or emissions stuff. If all works out I'll still go to DEQ tomorrow but who knows what is wrong this time.

t_g_farrell

iTrader: (1)

Old carbs are fun! Sounds like a plan. Those new seats and needles don't like to work very well.

Benjamin4456

Well I readjusted the float levels and swapped needles and seats from the SA carb... Let's just say the car is running quite well. One small problem though, the front float is still getting stuck and flooding the car causing, well... problems... As of now that's the only issue so if anyone has some sort of float unsticking advice, throw it on out here.

Benjamin4456

I think I've fixed the float problem but we'll see over the next hour or so.

On a different note, what do you think the odds are of passing smog with the following setup providing everything works correctly: All emissions equipment intact or jerry-rigged, original exhaust "header", OEM FB cats have been replaced with a single high-flow cat. When I had the previous system installed (it was a full SA setup but with an FB engine so the TR didn't work), I failed with HC 12 times over the limit of 220 and carbon monoxide was also quite high. So, what are the odds, and if it does fail again what are some "fixes" to pass? Would a "bad" engine cause it to fail even it otherwise runs and drives fine?

Benjamin4456

Good news, the car made it all the way to the DEQ station and back with no problems. At idle I got the HC down to 11 over, 2.5k HC is 170 over. I ran out of time before they closed to do a couple more runs (they let you through as many times as you want and you only pay when you pass). When I arrived the HC and CO was much worse but with a few tricks I've brought it down, CO is passing now. On Saturday I'll go for another run and I should be able to pass with a little more tuning and if not, there's always alternative methods . Thanks for all the help and I'll keep y'all posted on whether or not I pass smog. There should be another SA back on the road in the near future