Azriel_Strife

hey guys,

I'm new, this is my first post, I thought this would be the best place to ask some basic carby questions.

I have an 87' 5.0 in my Mazda rx-7, it runs great and everything, great power, but I get a stumble when I give it gas too quick. It literally stops running until I let off the gas again. I have an aluminum 4 barrel intake with the ford emblem on the top, I don't know what it's off of.

I'm running a holley 1850c 600cfm carb, I thought it was the power valve giving me greif, but it didn't fix the problem when I replaced it. I tried setting my accelerator pump as well, no go.

So my last though is jetting, the car was on a stock 302 truck engine before, i never changed any jets. Would an 1850 need differnt jetting to run well on a 5.0ho? Can anyone tell me what main jets they are running on their stock 5.0 with a holley 1850?

Thanks a bunch.
Az

lxman1

Welcome aboard.

2 things, first, make sure there isn't a cheater screw in the slide part of the secondary linkage on the driver side. (in the rear linkage slot).
Second, sou may need a larger discharge nozzle. You probably have a 25. I would try a 31.

Slo5oh

What does your timing look like?

Azriel_Strife

Hey, i'll have to look into that, it's got vacume secondaries, so i'll ahve a look later.

Slo5oh: I though timing too, when i advance my timing (running it locked with no advance) I can get rid of the stumble all together. The problem is that the engine pings badly. Iv'e tried to rememdy this by putting in mid grade fuel but I still get ping, so I don't think timing is the whole problem. The engine is bone stock, and an 87' 5.0 should run happily on regullar unleaded "87" octane, at least i think it should.

Slo5oh

Why are you running it locked ? Ill bet my ballhair thats your problem. What do you have it set at anyways? Probably 16 total lol?

67mustang302

Yeah, try like 14 initial and around 34-36 total, all in by around 3,000rpm or a tad earlier. If you still have the issue try more aggressive advance curves(as long as it doesn't ping). What have you done to the pump? What cams and discharge nozzles have you tried? An what secondary spring is in it?

Azriel_Strife

I'm running it locked because i wanted to eliminate the possibility for the timing changing, if i hook up the vacum advance it runs worse, since in reality it actualy retards the timing. that and the fact that i'll be racing the car, and these engines tend to lose vacum in the top end and advance the timing in high rpm's. Boom.

I have no idea what you mean by changing how the timing is all in. i know nothing about advance curves. The carb is however it was coming off a regualr 302 truck motor. I know nothing about holleys.

I just know it;s a brand new 85' gt distributor (the only one that'll fit in the block) and that it's set however it was supposed to be from the factory, we are working with a stock engine here, so it should not require more than the stock 10 degrees BTD of advance. So i'm fairly convinced it's not all timing. If someone could fill me in a bit on the stuff about the holey cams and whatnot that would be great.

Slo5oh

Not meaning to sound harsh, but it sounds like you need a crash course in ignition timing.
Take a read, and let your curiosity further your reading.

http://www.chevyhiperformance.com/ho...178/index.html

You need to unlock that distributor and get your initial set, then your mech, then your vac (if its adjustable). One isnt dependant on the other really, but just do it like that.

Azriel_Strife

Thanks for that, and it wasn't harsh at all, I came here to learn, and you are being very helpful, thanks to everyone.

So what I have done so far:
-set the timing to the stock 10 Deg BTD, and then plugged vacum advance hose into the front of the carb under float bowl. Instead of the one to the pass side.
-Installed a 121-131 accel pump nozzle (seems to have helped a little bit)
-Shimmed the spring in the accel pump linkage

So, it still falls on it's face if I stab the carb. but it's fine if I take it semi easy on it. I'll give that link a read, but I don't see why I have to do all this fiddling with stock parts to make it run.

A stock engine should run with a stock distributor at stock timing. especially if it isn't the fuel causing it. Am I missing something? Do the brand new parts not come set up from the factory?

Slo5oh

WOW 10* is great for idle, but thats it!

unlock that thing asap. thats your ONLY problem.