dirty carb?

[pishta]

My carbed mazda started running like crap, I thought it was ignition so I rebuilt the distributor with new pickup and integrated ecu. Still runs very rough at times, but smooth at others. Im leaning toward a dirty carb now. I looked at opaque filter and its still white, no crap in it. This motor has a recirculating fuel system where the little facet style electric fuel pump pumps through filter, then carb, then most of it recirculates back to tank. It keeps the tank very clean as it always filters the fuel and its always moving so it doesnt stagnate. What would a dirty carb symptom be? It seems to idle fine but at speed, it feels like it has a terrible random miss, then like that, it goes away and then comes back again, totally random. When I come to a stop, sometimes Ill stall, but it always starts right back up and settles to a smooth idle. Im pissed the distributor was not the issue, as I waited 5 days for parts. New plugs, 4 month old cap and rotor, wires OHM out ok, under 6 a piece and this was out of the blue, no repair or anything done to start it or cause it. could my main jets (2) be clogged/clogging or what could cause the truck to drive like this? 10 hour work days and 3 hours of school a night didnt allow me to look at it closer.

 

[KitCarlson]

I can give you some possible ideas based on experience, but they may not apply to your car.

I found a facet pump will not pump with water in the gas. It happened shortly after a huge rain of several inches in an hour on my kitcar. Tank was in a well, water may have got in at fill cap vent.

Dirt in carb often finds two places, the idle mixture screw seat, or in the main jet.

Not sure about the fuel recirculation. I worked on an old land cruiser, with asin carb, it recirculated on overflow. It had a sight glass, and level was above that. I replaced fuel logged float, and fixed that. It ran like a rich pig before that.

If the carb has electronic feed back with main jet solenoids and O2 sensor there can be a multitude of problems. O2 sendor check would my first check. Use propane torch, blue flame on sensor end, check for near 0.5v.

 

[pishta]

Thanks, this carb is new only 8 months old. No o2 feedback, just an 1982 asin style jap carb with nice big site glass, fuel is right at line. I'm now looking at a possible egr issue. Maybe that thing is not working or getting stuck open causing a huge leanout/vacuum leak? Sunday I'll bypass egr and plug all ports eccept vacuum advance. We'll see what happens. Main jets unscrew from outside carb so it should not be difficult to pop them and shoot carb cleaner into the wells/jet passages..

 

[KitCarlson]

Egr is a good possibility. They had a bunch in controls at that time including thermal vacuum switches. Also if the evaporative canister is purging at idle, that can be a problem. Typically it is controlled by ported carb vacuum, and more. Bunch of vacuum lines and stuff on that system too.

 

[Darter6]

pishta, I too am going thru this with my slant six. Just put the car together with mostly used parts, thinking that the problem miss/engine breaking up under load had to be electrical. I replaced each part one by one with known good components.Rechecked all the wiring, only to still have the problem. On to the fuel side, "new" tank,pickup,fuel,pump,filter,carb. If I slowly run the rpms up (under load) to 4000 and then nail it not a miss till about 5200 rpm. If I nail it at 2800 rpm it will start to miss around 3200. So now it's on to fuel delivery, low float level,jetting, fuel pump not keeping up. Our problem sounds very similar. :banghead: Just a thought.

 

[pishta]

WEll, if its similar, I got the solution today. the carb was loose on its intake! Somehow the carb nuts backed off about a full turn each, and the carb was literally rocking on the intake. I found it out when I took the air cleaner off looking for vacuum lines to test. SOB was loose for a week of down time and all it took was for me to tighten the freaking nuts! My symptoms were breaking up randomly (perfect description) at speed but mostly on deceleration and then acceleration again, and also coming back down to idle, it would just keep going down until it died, blipping would keep it alive. I found another vacuum leak down there so it wasnt a totally misdiagnoses, well the last leanout theory anyway. Check for loose carb,intake or gaskets. I was convinced it was ignition so much as to buy mail order new electronics for my stock distributor. Missed that one completely.

 

[Darter6]

Ha ! I had a 69 Nova that the 1 barrel 230 six cylinder would do that every few months.Course that was 30+ years ago. Thanks for the memory !!