its an Auto-hobby shop. believe me. i'm trippin over camaros, mustangs, and dodge trucks whenever i work on my car there. Even saw a chevy LUV in there the other day. nice little pickup. Flat black. Chromed out V8 with double pump carbs. Fiberglass hood wih a big scoop on it. fuel cell. full autometer gauge cluster. all on a pickup truck the size of, if not smaller than, the datsun pickup.

Back to the backfiring tho. It didn't start backfiring until i removed the exhaust system. but i will get back on those a/f mixture screws. they're turned all the way in one direction. my bet is its on the really rich side too.
thats what i get for tuning the carbs with the engine cold.

 

make exhausts and stuff. and etc. make that stuff for friends to. itll be very useful... make a lil money off it.

 

When is it "backfiring" ? When you let off the throttle? At full throttle? Is it backfiring out the intake or exhaust?

 

What do the plugs look like?

 

It'll backfire whenever i let off the throttle and just coast. It'll also backfire some when i'm at cruising speed (60-70mph). And every now and again at idle but not nearly as much as when i let off the throttle and coast. and its on the exhaust side. It backfired once through the carbs when i changed the manifold (just kinda when Pop and sprayed gas back out thru the intake) but that was because my dumbass self put the throttle linkage back on wrong and it was being given throttle when i didn't want it to be. I've fixed that already. i haven't looked at the plugs yet. I'll do that tomorrow when i get back into the hobby shop and grab my exhaust pipe. Still haven't figured out why its missing sometimes. possibly out of time, or maybe bad plug wires. Not sure. Trouble-shooting it as i go and with what little daylight i have left each day. As always, Technical information is welcome.

 

exhaust manifold question.
does the n36 exhaust manifold have the same bolt pattern as the f54 manifold on the exhaust pipe side?

(will my old exhaust pipe bolt right on, or do i have to go have an exhaust shop weld it to the little bit of existing pipe left on the F54 mani?)

 

The cracked manifold and the rust damage.

 

looks like the same bolt patter as my car.

 

haha, if you think that has rust damage, you havent been around enough s30's. People would kill to have that little rust.

Why dont you just get a header?

 

Sheesh! Something like that goes to the crusher around here. Think I'll start buying them up to sell to you guys. That's all fixable but what about the underside? If it's bad it might not even be safe to drive. If you can't do the work yourself you might consider another donor car. Put a floor jack under the front cross member and raise the car. If she creeks and growns and the door or fender gaps go away you are in for some major work.
All the L6 manifolds bolt right up to the head. The difference is where the down pipe bolts on.

 

passenger floorpan has two fist sized holes in it. driver side floor pan has only a little bit of rust. Shes structurally sound. i've had her up on jacks, jack stands, lifts, etc... no bending. aside from the floor pans, the underside is solid as a rock. And shes safe to drive. Cept when the lights quit on ya. Lol. And if the downpipe pattern is different then i'm a bit screwed. I'll have to track down someone with a welding machine.

 

sorry for the ingnorance but what kind of carbs are on this again? all the s30's used SU's right?

 

Yeah but the late '73 and '74 used a "flat top" SU for smog and they aren't very good for high perf.

 

yeah. I got a set of bell top SU's from a 240 though.

 

ok. so your major mixture adjustments are needles and jets. i believe you turn the jet screw in clockwise to lean it out. 1 flat at a time. if you get it good at idle but not at WOT, i think you change the needle shape. or your needle may be worn and you just need a new one of the same. rich running can cause a symptom much like cylinder miss.

 

just ordered a 3 into 2 header and the exhaust package from the z-store.

And thanks for the tip on the carbs.

 

good stuff! sure is fun putting new parts on.

and i don't know how much you already know on them, so i hope i wasn't telling you stuff you already knew.

 

what exhaust? twice pipes? lol.

 

no. just a standard 2.5" performance exhaust.
http://www.thezstore.com/page/TZS/PROD/PEC06/15-6021
it was a tie between this and twice pipes. so i flipped a coin and ended up with the performance exhaust.

And no. you're not telling me stuff i didn't already know. I KNOW carbs, and i know carb concept. But I know carb stuff for Motorcycles. Not too much for cars. And i've never worked with SU's before. So i'm not really relearning so much as adapting what i already know. I've never worked on a six cylinder bike, so, yeah..

Edit: I leaned out the mixture on the carbs and upped the idle a little. She sounds much better, but could use a much Finer tune. I had to do it quick cuz i was running outta light. As for the my old exhaust pipe, it will not bolt to the new(used) manifold. The N36 downpipe bolt patter is different than the F54 Bolt pattern. The F54 is a larger bolt and larger bolt pattern. So No Joy. I'll just have a noisy car till the Header and pipes get here.

 

oh ok sorry. i hate it when people do that to me lol. glad you're getting them tuned up now though!

 

Wow. did i ever speak too soon. Had to use Lady to go to the tax office and she sounds like porky pig now. ya know. pu pupupuh puuu puhpuh puuuuuuuh. I have F-ed up the syncronization something fierce. Oh well. will Tune again tomorrow. But on the upside, she didn't backfire.

 

well, once again i've retuned the carbs. leaned out the mixture a bit and synced them up. She runs wonderfully. Even with no pipe she sounds great. No more stuttering and the exhaust fumes aren't as bad anymore. Though i have a bit of a question.

The big screw on the bottom of the carbs, on the forward carb i can back that screw out(clockwise) several turns, but the rear one will only back out 2.5 turns. so i backed them both out to 2.5 turns from the richest setting (counter clockwise until it stopped), but is the rear carb's a/f mixture screw supposed to back out more?

 

it just stops? they should be close to the same i think

 

The flat top carbs are not meant to be rebuilt. They have a power valve with a diaphram. You can remove and inspect it and replace it. Not sure about that thumb wheel but if it runs good leave them alone.

 

Yeah, it just stops.

I've got the belltop SU's off of a 240. but since they're working good right now, i'm not gonna mess with them.