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Hi All,
So I have been starting to sort out my Covid project. It's a 1969 Triumph GT6 with a '79 or '80 RX7 12A and 4speed transplanted into it. Picked it up a few months ago and been having fun figuring it out and dealing with a few issues. I now have it running pretty good but I know it can be better. At idle the AFR is usually between 12.5 and 13 (any leaner and its hard starting... there's no choke.) Part throttle and WOT it's usually between 10 and 11. Hopefully I can post a jpg of a street run. Super rich. Seems like I want to be closer to 13? What's the best way to get better AFR's on accel? I have almost no carb experience...
To start here's what I know (or think I know) about the car. Builder was a racer and ran a race shop and built car approx 20 years ago (now deceased). Has had at least 3 or 4 owners since. One I picked it up from knew very little mechanical history on the car. Best guess is that the 12A motor interior is stock. As is the 4spd trans. Has a later Dizzy ('83 maybe?) not hooked up to vacuum. The Nikki has been completely stripped. No smog, no choke etc. Mechanical secondaries. No air injection pump. Header (originally collecting to 2" and going through 2 glass packs that were dead and loud.) When I got it it was kinda rough running. Very hard starting. Sometimes would run to redline, sometimes completely bog when I hit the secondaries. Especially in 1st gear (though that seems strange to me that gear would have anything to do with it...) Ran Seafoam through the tank, cleaned the carb as good as I could without taking it apart (spray cleaner) and replaced the inline fuel filter. Adjusted the throttle linkage and secondary connection to make sure that they both hit completely open right at the end of pedal travel. New exhaust going to 2.25" at the collector and all the way back to a small flowmaster (biggest I could fit.) It sounds glorious. Also between the collector and muffler added a wideband O2 going to an old Innovate LM-1 to log RPM (barely...) and AFR for tuning. Also did new plugs and 2 MSD blaster coils. Much easier to start these days and rips to 8K. every once in a while there is a slight hesitation if I mash the throttle from low RPM's but I'm surprised it is so rare and so slight from the complaints I'd heard. Idle is great (about 950) and smooth under acceleration but part throttle cruising has a little stumble. With the plot below, red is AFR and black is RPM and is not quite calibrated (thinks I can do 10K) and is a pretty noisy signal but hopefully that helps.
i'm sure other people will chime in with hardware tips, but here are some AFR targets
Idle- setup like any other carbed engine, the Rotary likes to be rich due to exhaust gas dilution (internal EGR), 12.2-13.0
1200-3250rpm steady cruising - a stock car will be 14.7:1 here, and give or take its about right. a ported engine will have a narrower window where its happy, and a stock engine doesn't care much.
WOT: 12.5-13:1, i find once you get in this range you're in the sweet spot. richer is ok, you start to loose a little power. leaner is ok too, but your margin for error goes down, and power doesn't really change, so when you're done tuning its usually best to be high 12's low 13's
So I feel like I'm 1-1.5 too rich across the board except at idle. I assume its better to add air (if possible) instead of remove fuel. Is there an easy way to do that? If not what's the hard way?
Also if I book dyno time what's realistic to be able to play with on the carb in an hour with runs?
Thanks,
Jay
So I'm hoping I will still get someone to chime in with additional guidance on my original question but here's another thought/question. I do have the OMP and it seems to be functioning (though I have not tested to see if the output is actually in spec...) I have been adding an additional .5 oz 2 cycle oil per gallon in the tank. just curious if anyone knows if that can affect AFR?
I have always tuned to run as lean as the engine likes to run under idle and part throttle, and somewhere between 12 and 13:1 at WOT. Rotaries are really insensitive to fuel mixture with respect to power output or detonation.
I know some people run 14:1 or leaner at WOT for max power, but the increase in EGTs is huge and the power gain is negligible.
so, it's never been a case of shooting for a number, it's tuning to what the engine likes.
OK, I'm sure I'm opening a can of worms here.... since I seem to be getting enough (too much) fuel.... If I hogged out the venturi's keeping everything else the same would that get more air in there to balance it out?
So I got my car on a dyno today. 99.01 whp so that’s good. Confirmed my readings about how pig rich it is. Less than 10:1 (as rich as the machine read) under 3.5k and still not quite 12:1 between 5k and 6.5k. anyone sell modified Nikki carbs? (Would love to purchase and keep this one as it does still run well...
Hmm 99 is a bit low. My 12A setup like in my signature except for the nikki (had a Dellorto on it when I did the dyno run) put down about 134hp to the wheels (oh and I get 24mpg @80mph highway cruising). With the nikki its pretty much the same but easier to drive and gets better gas mileage and has more grunt down low in the rpms and screams to redline. Note the ignition is weak and you may also want to look at modifying that once you have the carb dialed in. You can definitely tune the Nikki on you car for better flow and more fuel, its called a hogged out Nikki. Search on threads started by Jeff20B in here to get educated on how to do this. I also did a thread on what I did as well.
It's not rocket science and given what you have shown so far I think you should be able to handle it.
That car sounds sweet. I think I may have heard of it before or seen it on here before but not sure.
So I just got most of the interior in Friday... been working on it a bunch the last month. Had to trim some new carpet to fit around the roll cage. Was bare interior with aluminum Kirkeys when I got it so I designed some panels and had my wife show me how to use a sewing machine and I made them with diamond stitch vinyl. Gotta finish the carpet on the passenger side and fab up some brackets so I can get that seat in and I plan to make some vinyl sleeves for the door bars and the cross brace behind my head. Once that’s all done I plan to replace the wood dash with one painted white like the other interior accents.
As Mr Farrell (I assume I got that right) 99 HP is low. Even a little bit low with a stock 12A, fully stock Nikki and stock exhaust manifold. With a header you should be in the 125-135HP range. What are the jets in your carb now? I found for my ITA RX7, with stock port 12A, Racing Beat collected header, and stock Nikki, worked best with primary jets = 110 and secondary jets = 170 generally gave the best HP (135) and air fuel was pretty much 12.5-13.0 through the "racing range". I don't really know what was going on at cruise or mid-rpm. There were generally no drivability issues with putting around the paddock or under double yellow flag conditions on track though.
Nice interior. Also where did you get the switch protectors? Or did you make them? I foolishly put my fuel pump switch closest to the driver, which has resulted in turning it off twice during "stressful driving" at my last two races. Pretty dumb on my part. Can also just move the switch.
This is the switch panel I bought... https://www.ebay.com/itm/Light-Weigh...2-f696a613267f
I plan on using one for the fuel pump and one for some aux driving lights. It’s a simple piece with U bolts with 2 nuts on each side as the toggle switch protectors. You might be able to install something similar for just a couple bucks spent at Home Depot... they look good and are simple and cheap. Adds to the period look of the car imho. I have no idea what jets are in the carb. I’ve yet to open it up. Only thing I know is it already had mechanical secondaries done to it.
09-28-20, 11:17 AM
