What revs is good condition 12a safe to - standard motor no porting thx

 

I don't know on a 12A, but you are probably fine revving the **** out of it - when it stops pulling, that's time to shift - eg, if redline is indicated at 7K, as I believe it is, you're probably fine going past - it will run out of breath before you rev fast enough to damage it. Stock, my S5 wasn't really worth running past 8K - the buzzer at 7800 came just before where it ran out of breath and stopped accelerating right around 8. With a RB downpipe and resonator and minor intake mods, it pulled to 8700, then just stopped. With a high-flow cat in place of the resonator, it pulls to 8500, then hits the wall. I've been doing that for 15 years now at autocrosses and track days - still on the original engine.

 

I ran my SA up to 7k nearly everyday took it out for 6 years, but only after it was nice and warmed up. Before I put a full exhaust on it leveled out before 6k, after it would pull beyond 7k sometimes I took it to 8k but not all that often. I think I remember something about the earlier 12A's experiencing seal chatter above 6.5K so i tried to keep that in mind when pushing it hard and tried to limit the time spent above 7K. I also had rebuilt the carb and was running a carter pump at the time.

 

Many thx - have just put 45 dcoe webber on it plus header and straight thru system so was just concerned that i would run out of engine before it ran out of breath....:-) will carefully explore above 7000 revs - thx Chris

 

Again, my experience is S5 13B, but I've kind of understood that if they would breath that far, stock-internal NA's are good to 9000 - at which point the stock seals might chatter and wear the housings. S4s were limited to 7k instead of 8K, due to heavier rotors, but it's probably safe to assume you can run to 8k if it will pull that far.

 

Whats really scary is that my S4 TII 1/2 Bridge S5 Internal (whew) motor will easily pull to well over 9500 rpm if I want it too. There is no limit to the breathing on the motor, but I have a hard limiter in there at 8500 rpm just to keep me sane in competition. If I were you I limit myself to 8,000 rpm and feel safe.

Compression is still good, power is still good, thanks Joe, and its been beat on pretty hard.

Eric

 

I thought the buzzer comes on at like 4k... I drove an fb for the first time this summer and the buzzer kept going off at 4k. Stock, I noticed that it would pull to the 6k range and then sorta become "light". But I am sure with a updated carb and free flow exhaust, 8k should be no problem hold.

 

thx all - will let u know what happens when I get to 8000.....:-)

 

Weber 45 DCOE, nice..

Do you get any sputter in 1st gear? I've got mine tuned decently, but it seems to me that 1st being such a short gear, the carb has trouble fuelling consistently thru first up to 7k.. A bit of a few hiccups between 5k and 7k.. 2nd and 3rd pull to 7k without skipping a beat..

Did you mess around with jets at all or just out of the box and you're good?

 

Hi at suggestion of Buggy (who have gave lots of good advice) fitted an AEM wide band air fuel meter and used this to tune the carb adjusting mains and air correction jets till car ran well to red line and mixture was okay - also went with a carter fuel pump as carb needs high volume lowish pressure fuel supply

 

Took lots of adjustment to get it smooth in all gears without any stuttering still have a flat spot just as you give it gas in low gears if you are too gentle on the throttle - a good excuse not to be :-)

 

Cool, thanks man.

I'm much more familiar with connecting a computer and adjusting settings and pressing enter.

I couldn't find a USB port on that DCOE Weber, so after making a few phonecalls I quickly realized I needed to lower my expectations on what I could achieve with my nose and a screwdriver.

I used a vacuum gauge and a timing light to set my timing at roughly 21 degrees advanced, which seemed to pull the most vacuum and run the nicest.. Smoothed my idle out quite a bit. Noticed a bit more pull when I went for a drive too. Spent alot of time messing with the idle mixture screws too, very difficult to tune without looking at an AFR gauge. I may try that out in the spring...

 

Tuning a carb is real tricky without an afr setup, especially a weber because they have an endless amount of adjustment. You should be able to get it to run perfectly, but it will take a lot of fine tuning. I've had my rx4 on the road for 3 years now and I still have some small adjustments to make. Last summer I actually tore the whole carb right apart and started tuning it from scratch all over again. My rx4 pulls strong to 9k but I've updated all the internals of that engine. Still builds over 100psi of oil pressure over 3k rpm.

 

Your flat spot is probably an accelerator pump adjustment issue. I'm not familiar with the dcoe accelerator pumps but there should be a way to adjust the linkage that activates the pump. It could be in the way you have your main system adjusted too but I would start with the accelerator pump. It's usually an easy adjustment.

 

I read about the "transition" from idle to part throttle.. It dumps raw fuel in from that one section of the body at part throttle (like say, 5 percent).

Mine bucks like a bastard. Either stay off throttle, or go 10 percent and no issues.

Buggy, Do you have a way to tune that out too? Seems like a carb characteristic that I'm not sure can be fixed without a more accurate means..

 

Thx will investigate further have previously run webers on minis back in the UK and even when set up on a rolling road always ended up with a flat spot somewhere when tuned for max power

 

Again, I'm not too familiar with the DCOE carbs, but in the IDA and IDF downdraft carbs there are progression holes in the throttle bore just above the throttle plates. They are responsible for adding fuel throttle opening. On rotaries it is common to add another progression hole because as we all know, rotaries need their fuel! The thing I found with my car though is you really have to get your idle set up properly. Don't turn in the throttle stop to adjust your idle. When you do that the car starts idling on the fuel from those progression holes and then when you open the throttle you get a flat spot. Make sure your throttle plates are below those progression holes at idle and then adjust your idle mixture and speed properly.

 

Crap Buggy you're smart. I can't remember the last time someone below my age knew how to tune a carb setup. Especially someone who understands how a carb works. Way to go and for those who are interested, it is also the same basic logic used in tuning a Holley, Quadrabog, Thermoquad (Edelbrock), etc.....

Start with a good idle setting and then work your way upwards in the RPM range. Everyone wants to do it the other way and wonders why they get all kinds of flat spots.

Eric

 

Good call, that may be exactly what's happening. That explains some of my difficulty setting the idle mixture properly.

Thanks!

 

At my work I get all the old weird cars to work on so I've become quite good at tuning and rebuilding pretty much any carburetor. A lot of my knowledge did come from tuning my rx4. I've basically maxed that poor 48 Idf of mine to flow as much air and fuel as it can and I still get it to run smooth and idle under 1000rpm. Pretty good for a carb half bridge 13B.