Won't start when hot
 

Ahhh, yet another thread. I'm considering a new engine, lol.

Anyways, just recently my car has been getting harder to start after a drive and now it doesn't start at all until it cools down all the way. I decided to do some poking around today after I drove it home.
I turned it off and waited a couple minutes. Wouldn't start, so I checked the bowls. Full. Gas flows through the filter fine when it is cranking.
I tried checking how gas was flowing in the carb, but couldn't because a white vapor comes out from the butterflies when the pedal is floored. This is what has me worried.

I tried searching for others with this problem but I couldn't find anything with these exact symptoms.

Is this vapor an ominous sign or do I just need a carb rebuild? I'll check the plugs in a bit and try to take a look inside.

Also, the sensor or whatever that is in the passenger side of the carb has wires running across the engine bay, then down under the beehive, which has a small leak right onto the wires. I don't see any damage too them though just a bit greasy. Sorry for my lack of knowledge I'm new to all this haha, I have a lot to learn.
I'll have a video of it later, uploading it now.

There's the video, if you look closely on a bright screen you can see the vapor. There was a lot more of it when I first floored the pedal.

Update
 

Checked the plugs and they were fine, probably replace them soon anyways.

Something I forgot to mention, when I checked the carb while it was still warm there was gas above the butterflies by a few millimeters and there was gas dripping from where it is injected. The jets? I checked the vapor solenoid by unplugging it and plugging it back in, it clicked so it should be working.

I'll probably get an other carb and rebuild that and do some modifications to it and slap it on which should fix the problem. But if anyone has some ideas please share! This is really my only source of info since no one around me seems to know how rotaries work:lol:

Your gas tank vent line is plugged. This puts pressure on the fuel system and the carb siphons it down into the engine on shutdown. Usually happens when its very hot out.

Pull the skinny line off of your charcoal canister and leave it disconnected and see if it still does it.

If it does, leave the gas cap off the tank temporarily and it should not do it again if im right.

Also, the vapor is just evidence of a healthy accel pump.

You said you pulled the plugs and they were "fine", were they wet with gas?

Take a picture of the "sensor" on the passenger side. This also sounds like a FBVS issue...

I was thinking it might be pressure related. What do you mean by leave the gas cap off? While it's sitting or while I'm driving it? The plugs were not wet. I'll get a picture later today

He's talking leaving it off period. Any fuel system that is not able to breathe will vapor lock and create a bubble in the fuel system which leads to to much pressure and needs to bleed off in the easiest manner, which in your case is the carb

Well that doesn't seem very safe haha. I guess for now I can just unscrew it every time I turn off the car, unless it builds pressure while driving. I could just unclog the line right?

Try not to overthink this. I meant temporarily leave it off after a hot shutdown once or twice to see if it alleviate the issue.

Strictly for troubleshooting, not a permanent fix.

Haha that's what I thought. But thinking about it a few weeks ago when the problem started it would happen after getting gas also. It would seem flooded, but then it would start after some cranking. That was before it got bad though.

That's the "sensor" I was talking about. And that's the charcoal cannister right?

Pull the small line from that canister and leave it off

I've had this issue recently but it has stopped for some random reason. The tank would build pressure and something as a restriction caused fuel to push into my carb after shutdown. I haven't replaced or fixed anything and it stopped flooding. I even tested it out by taking it out on long, hot drives and still hasn't flooded again.

Got home from a drive today and unscrewed the gas cap right after I turned off the car. There was a lot of pressure built up, enough to blow the cap out of my hands if I wasn't holding it tightly. But even with it unscrewed the carb still flooded.

When I pull the line do I have to take the whole thing off or just take it off the canister?

pull it off the canister and try to blow through it. my bet is that its clogged.

The carb will flood on its own BECAUSE of the pressure in the tank, not just when you try to start it right after shutdown.

Please just remove your fuel cap and leave it off after a long drive. Wait 30 minutes, then try to start it.

If it still floods, youll need to go through your fuel system entirely. Carb rebuild+function checks. The whole shebang.

If it's been 30+ years since the carburetor was on the engine, it's carburetor rebuild time, no two ways around it. If your local gas station is using ethanol, then your carb has been dealt a death blow and it's definitely time for a rebuild. ;)

:cool:

Getting a carb rebuild this weekend at Mazda as well as a fuel system diagnosis. Expensive, but fastest option since it's my daily and having no previous experience I could be at it for days. Btw, is ethanol particularly bad for the carbs? Or just older carbs that need rebuilt anyways? I used to run pure gas but switched to ethanol because of the outrageous prices.

Ethanol will eat up older fuel system sealing components (rubber). The rebuild kit should have
viton or some other ethanol safe seals supplied. Rebuild carb, replace old fuel filter (figure on
doing this 2 times a year) and make sure the hoses are good under the car for the tank and
under the hood going to/from the fuel lines to the carb.

I'm surprised they have anyone at a MAZDA dealership that can rebuild a carb competently. I
hope it works out for you.

BTW, having a 30+ year old car as a DD is not going to work for you at this rate. You either
need a second beater or need to do a full on mechanical restoration on this car so you can
depend on it. If not you will be down with issues at least monthly with this car. My prediction.

Haha I hope they can do a good job at mazda, if not I'll learn the hard way. I definitely do need a newer daily but surprisingly this and the cooling are the only issues I've had with it in a year of owning it. Plus I have no money for another car :dunno:

If the guy who rebuilds your carb swaps in new seats that come in the aftermarket rebuild kits, your carb will tend to flood from now on. The new aftermarket seats are machined incorrectly.

The only correct fix is to get a genuine Mazda rebuild kit with OEM seats, which I don't know if they're still available, or leave the original seats alone.

this.

Somebody somewhere needs to start fabbing Grose jets again... I'd pay a fair amount for some!

dont leave your gas cap off while driving. terrible idea.

reading is hard. nobody told him to remove it when driving, only when the car is parked, temporarily, after a hot shutdown.


And it was only to see if it alleviated pressure in the gas tank, which we didnt even really rule out yet...

Well it did alleviate some sort of pressure, just still didn't fix the problem.

I took the car to Mazda. They didn't rebuild the carb but let me know of some problems. The starter isn't in that great of condition and doesn't crank as well when it's hot. They didn't figure out why the carb floods. But I think it may be temperature related. My car was running a bit hotter and when I finally got that sorted it doesn't happen as often, still has a hard time starting. One other thing they did was a compression test, front was 4.9--4.8--4.1 and the rear was 5.4--4.9--5.1, yikes :(

Random question that I don't want to start a new thread for, sorry: is it ok to run the oil pickup without a gasket temporarily or should I rtv it till the gasket comes in?

The numbers are low because your starter is too slow. It sounds slow in the video. I thought I mentioned that already. I guess I didn't before. Get a set of new copper battery cables and see how much faster the starter cranks. 2 gauge is a nice thickness for our cars.

You mean the oil pickup tube with the strainer on the end? Is your oil pan off for some reason? I'd say yes install a gakset. Just RTV probably isn't good enough.