MazdaTed

I have a 1984 gsl. Stock as far as I know except for bonez exhaust pipe, no air pump and acv blocked off.

Anyway, under light throttle and cruise (most notable between 3000-3500 rpm) I have a mild miss/surging/hesitation. Car seems to run to redline with no problems. Starts normal also. Po installed a generic fuel pump, I can't see a fpr even though I haven't had any flooding issues.

I had checked for spark a couple weeks ago and it seemed fine then. At the same time I reset base timing.

I sprayed carb cleaner around and couldn't find any leaks.

I've replaced the fuel filter just today (though I have to do it again because the new one leaks).

I tried to find the float level sight glass but couldn't find it. Where is it?

I've read about the return check valve causing hesitation, I'll check it tomorrow.

Tomorrow I intend to spray some carb cleaner in the carb.

Should I hunt down a fuel pressure tester? Where would be the best place to check? I tried pinching the pressure line and it gave resistance.




What does it sound like to you guys? What else should I check?





Also possibly related, I've had a strange idle issue, I have two idle speeds, each about 400 rpm apart, the car seems to pick or choose them at random. I've tried adjusting the idle speed and mixture. I can get it to idle as low as 450 (its rough, but it idles) so i'd be suprised if I had a vac leak. I've often wonderd if stripping the carb and the rats nest would solve this issue.

diabolical1

iTrader: (3)

assuming all checks to pump, lines and filter are valid. i would say clean the carburetor thoroughly and adjust the mixture. may be a tad lean???

as for the sight glasses, they should be oriented front and rear with the carburetor on the car. they may be obscured by dirt.

MazdaTed

Adjust mixture with the screw? Isn't that only for idle?

MosesX605

The idle circuit is still active under light throttle, if I'm not mistaken. I'm having the exact same issue as you are: excellent power, good clean acceleration to redline and good starting but a hesitation at cruise under 4k rpm.

I haven't looked at spark or stripped the carb down yet, but I did check for leaks when I deleted the rats nest and couldn't find any (other than the ones I caused due to a leaky ACV gasket. )

Jeff20B

iTrader: (13)

I've never experienced a problem like that with modded (hogged out) Nikkis, so in my world, that's the solution. Maybe look into Nikki mods to increase air flow through the carb. It seems all the complicated mess on these carbs does more harm than good. The small stock venturis also seem to limit air flow just enough to cause problems.

I recall trying to start a couple of fresh rebuilds last year with stock off the shelf sitting for who knows how long Nikkis. It was a nightmare. Tried three in a row and after a couple hours of trying various things, got them to start. Then I finally got smart and swapped on a modded hogged out Nikki on my next rebuild. It started up in 2 seconds of cranking. Learned my lesson.

MazdaTed

Today I...

Checked the check valve, its good, with flow going away from the carb.

Sprayed the carb with carb cleaner. Cleaned it a little. No change I can notice.

Adjusted the idle mixture. I tried a lot of different adjustments, no bueno.

I watched the barrels, while not running both squirt fuel with the throttle, at idle both drip fuel a little, at higher rpms fuel moves faster.

I found the coasting valve bad, it wasn't honking or wooshing but it was pulling vac at idle, plugged with a bolt, no noticable change.

Also, I sprayed around again with carb cleaner, might have found somthing, I sprayed at the lower left of the carb near the coasting valve (I think). When I sprayed there the engine stumbled (though I thought it was supposed to run better), then I ran out of carb cleaner, so I couldn't try again. I'll try again later.

MazdaTed

Update, stumbled into can of carb cleaner, so I started the car, and sprayed in that spot, no change. Then I notice the car was running perfect, absolutoly perfect, took it for a drive, and maybe a half mile down the road it runs worse. Car can't get out of its own way. Hesitates bad below 4000, and is real sluggish ro redline.

I popped the hood and started to play, reset mixture etc. Then just for kicks I pull the trailing wire from the dist, it shuts off, put it back and start again, runs, then pull leading and nothing happens. Coil ohm checks good. Maybe a flakey igniter. I'll switch them over next week. Busy this weekend.

Stripgear

iTrader: (2)

Welcome to E10 ethanol gas. It's 90% gas, 10% inert filler. I had the same problem, changed the jets to 095 from Maza trix (.003 richer) and the problem went away.

https://www.mazdatrix.com/c-3.htm

MazdaTed

Not likely E0 is still available in my area, and I use it religiously. I'll tuck that away for future reference though.

MazdaTed

Update: I found the time to mess with it this morning. Swapped igniters, ran smoother maybe, but quickly shut off. No fuel, also no tach. After some fuel pump trouble shooting and some schematic reading, I found the trailing igniter runs the tach, and also sends a signal to the emission unit that the engine is running, if no signal it cuts fuel through the fuel cut relay.

Orderd an igniter, it'l be here sometime. I'll update then if that's the solution for anyone searchng in the future.

MazdaTed

Conclusion: replaced leading igniter, problem solved. No more funky idle. No more hesitation, lots more power. Idles smooth anywhere above 600, I chose 700.

Things I learned: 1. Trailing igniter must be functional for thr tach and the fuel pump to run. 2. Don't swap leading and trailing igniters while the engine is hot because... well... its hot...

wankel=awesome

You're still a little lean@ 95's. Although you're close. I got a Mazda handbook from J.E.M. that calls for 97.5mm primary jets when cats/emissions are removed. And that was written long before the 10% ethanol gasoline, which also plays a role im sure.

Jeff20B

iTrader: (13)

wankel=awesome, with that in mind, maybe it's time for the OP to get a wideband to see what his carb actually needs so he can get the right jets for it without guessing. 97.5 might be a hard size to get, and I doubt he would actually need a set that big on a stock carb with stock crappy 81-85 intake manifold.

I tried 95s in a setup that had a lightly modded FB manifold and RB header with a single pipe collected at 2" and it was too rich. Swapped down to 92 and it ran better. Then I hogged the venturis out to 24.5mm and threw in some custom drilled jets at 118 and it's just a tad rich right now on a different engine with a different exhaust. I'm thinking 117.5 would be the answer because it's drilled professionally.

wankel=awesome

yeah, the book I have was written with performance driving in mind, and it clearly says to "drill" the stock jet to .975 mm. It also says to "check your particular class rules", which says to me its a baseline for some racing class somewhere in northern Georgia. I run the 95's as primary's for normal driving and like them very much on the street. I still think that the 97.5's would be better though!

And im running a ported SA manifold and slightly modded nikki (acc pump, light secondary spring).