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#9
Re: stock 1200 dyno'd
D
Posted on: 2011/6/23 17:44
Umm they match up well in size. For packaging reasons and price
the Hitachi seems a perfect choice but for a bit more maybe a 1.75 su will be a good compromise of power and economy if the runners could be made longer and of suitable sizing.  
#8
Re: stock 1200 dyno'd
ddgonzal
Posted on: 2011/6/23 17:36
More about the heat range:
Quote: It was equipped with Hitachi L 46 PW plugs which are extremely hot ... two were blistered, one showed a heat-shock chip in the porcelain insulator and one had glaze and beginning blisters. Mileage on the clock was just over 5000. We exchanged the plugs for Autolite AG 42s
#7
Re: stock 1200 dyno'd
racer135
Posted on: 2011/6/23 9:38
Quote:
What was the supposed 'correct' heat range they chose? Quote:
What size secondary main jet did they use? Swap or remove the spring? What strength spring did they replace it with?
#6
Re: stock 1200 dyno'd
ddgonzal
Posted on: 2011/6/23 6:36
Don't need to change the carby, that's the beauty. First, unlock the power that's in the A12. They gained 13 HP.
bakat, there are two weights in the dizzy, and they said the lighter one controls the high-RPM part. That's the one they changed. They didn't change the curve for low-RPM, so fuel economy did not change. D, could a single 1.5 inch [38mm] SU improve over a Hitachi? Well, the hitachi is a 26/30. Area 26+30: 4951 square mm 38: 4536 square mm That's the bore. It would be more accurate to use venturi sizes. The DCG-306 is 20/26. I do not know what the HJE38W venturi size is.
#5
Re: stock 1200 dyno'd
D
Posted on: 2011/6/23 5:30
whats 50% power increase on an a12? 5 hp :)
I can only imagine what a longer inlet manifold length might add to an A12 for economy and performance. If you can improve the low and midrange further then there is better energy use and engine effort. Could a single 1.5inch SU improve over a Hitachi? I often think about making a long equal length inlet manifold with separate runners curving over the rocker cover to the sparkplug side with a single su on the end.
#4
Re: stock 1200 dyno'd
bakat
Posted on: 2011/6/23 5:13
one 'crude' way to alter the advance curve, is to use only one spring instead of two. that way, the spring strength is practically halved. sometimes i used a spring and lighten the counterweight a little bit by filing it.
#3
Re: stock 1200 dyno'd
ddgonzal
Posted on: 2011/6/23 5:00
Here is what they did to boost power by 50%:
* Replace secondary main jet with larger item * Set dwell to 51 degrees * Swap distributor mechanical advance secondary spring Quote: in all cases of this sort, the points should be set by dwell rather than by guess or feeler gauge since improper point setting can negate much of the effect Of course if you have Electronic Ignition you don't have to worry about points and dwell. Quote: Back on the street, the added power at the bottom end wasn't especially noticeable until 3500 rpm, though it made itself apparent by a smoother take-off. It was the secondary tip-in in the lower gears that gave the clue that something was different. The conjunction of the quickened advance and the air/fuel curve now matched better, giving a more efficent burn and the difference was one that could be felt and even seen. Getting onto freeways was no problem...Mileage suffered not at all expect in the top end
#2
Re: stock 1200 dyno'd
bakat
Posted on: 2011/6/23 4:31
champion of economy. unbeatable since half a century ago lol.
i tuned a friend's mazda 323 that used hitachi carb (mazda and datsun shared the same carb), and his mazda could rev as high as 8k rpm at first and second without loosing power. the engine is stock, only the flywheel had been lightened a couple of kilo's. FC is still good!
#1
stock 1200 dyno'd
ddgonzal
Posted on: 2011/6/23 2:08
Motor Trend dyno'd a stock 1200 and found:
* Plugs were the wrong heat range, and had blistered After putting the correct ones in:Quote: The checks showed that the primary throttle functions of the [Hitachi] carburetion were right on. Idle on this car gave an air/fuel ratio of 14.1/1... Primary cruise...gave an air/fuel ratio of 14.3/1 ... The power phase, as expected, shot the air/fuel ratio 12.9 So far so good. Yet while the 1200 drove well, power was down above 4,500 RPM. By adjusting the carburetor and distributor they increased power by 50%!!! without fitting extractors nor a larger carburetor.
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