hksthor

hey guys i just built my first pp motor its a 12a its got the high comp rotors balanced rotating assembly carbon seals



but when i put it on dyno to jet the ida it got too 7g and trailing spark goes strange and it developes a miss



it has elec dizzy



have tried new cap leads plugs rotor coils rewired coils without msd and back too the msd could it be a port problem ? any ideas





thanks steve

Lynn E. Hanover

There is more data to collect on this problem for a real helpfull answer. What was the EGT just as the problem started?

What was the F/A ratio (wideband)? Did you have a well built air cleaner installed? What timing? What does going strange mean?



https://www.nopistons.com/forums/Jet-13b-Br...ort-t75026.html



This string is for a Bridgeported 12A, but the carb mods are the same.



With the P (Peripheral) port engine there may be some interesting thing going on that are not common to side port engines.



The connection between intake and exhaust is shorter time wise, but much stronger than the bridgeported engine. The amount of exhaust back pressure has a much more profound affect than on a side port engine.



My racer has a 4" giant Borla and tail pipe. And the system is short. Exit is just in front of the right rear tire. Too loud for the street. About 100Db. at 50 feet. Enough to turn a ground hogs brain to mush.



Another intersting feature of the Weber on a Pport is recarburettion. Right when it gets to running real strong you will notice that a cloud of fuel vapor forming above the carb air horns. The engine is loosing fuel to the cloud and then it sucks the mixture back through the carb and mixes more fuel with it. So, the engine runs lean and rich from second to second. A well built (stiff) air cleaner box is required to maintain a common local air pressure above the carb.



The Pport is about 15% better than 100% on intake performance. So the 48 Weber is on the small side for a street rotary. It is very small for a Pport. So you are well above the maximum flow rate of the 48 that came stock with 36 MM chokes.



On the Pport we ran 44MM chokes, and it becomes dribble fuel injection rather than a carb. So side loads and braking had a big effect on performance. We ran 6 PSI of fuel pressure just to keep up with it.



Still it shout do 270 HP at 9,600 RPM. If you have the high rev mods in place.



Lynn E. Hanover

hksthor

the engine has all the right mods for high rpm use

when i say strange it starts going all over the place like a random miss but cant be as its all been checked

timing is locked at 16 deg until we get mix right then we can put some more in without detonation

afr was was around 13/1

carb has full radius ram tubes as well but is using a k and n no air box but these are used widley like this

its going back on dyno today so ill let you know how it goes

Lynn E. Hanover

Try 210 to 220 mains 100 air 25 degees of advance. Trigger both leading and trailing from the leading pickup. No split.



Raise the float until the boosters drip. Try for under 13 A/F. Above 8,500 the carb cannot hold rich enough and the F/A will be into the low 13s. Keep the EGTs below 1600. That should get into the ball park.



Ice cold conventional gap plugs with the gaps at .015". NGK 11.5 25 bucks each. MSD on the leading at least. I run MSD-6AL on both.



Lynn E. Hanover

Judge Ito

are you using the factory timing pulley? or after market?

Lynn E. Hanover

Good point Judge,



Mazda moved timing marks every few weeks, and many times just leave off everything but the idle timing mark for that engine /controller combination. Using really high octane fuel in a NA rotary is a waste of money, and costs a bit of power.

87 octane for the street is fine. 93 for racing is fine. The rotor face moves slowly and spends a long time in front of the plugs.

(Dwell its called), so there is no need for a bunch of advance. We raced on 20 degrees total for years, and you get great power up to 9,000 RPM with just 20 degrees.



Find TDC. Mark it on the pulley, then measure the pulley diameter and then C=3.1416 X D. Then find degrees per inch.



Mark the pulley (file a notch in it next to the engine) for TDC, 20, 24, and 27 degrees. Paint the grooves different colors, and record the data on the core support.



Dyno and race at 27 degrees. Drive around on the street at 20 to 24 degrees. This is total advance at redline RPM. It should be out of curve by 4,000 RPM if timing a screaming engine is of no interest to you.



Unless you bog down the engine by starting out in too tall a gear, it is nearly impossible to detonate an NA engine.

(Although my driver pulled it off a few times) So we just started towing the car to the false grid to eliminate the problem.



Drill out the hole leading to the needle assembly and throw away the plastic filter under the brass nut.



If your manifold is not rigid, provide a strut to support the carb to keep it from vibrating. Protect the inlet air and manifold from header heat.



Lean mixtures are hard to light, so most missing is caused by overlean mixtures and, or, ignition problems. You need no split at all. Trigger both MSDs from the leading pickup.



Lynn E. Hanover

hksthor

hey guys just a update the guy tuning the motor has turned out not to be as good as he is cracked up to be the miss is from poor fueling i pulled carb down and this is what i found 42mm chokes not fitted correctly sliding down and hittong butterlfys 175 main f16 emulsion and the air corector soldered up no hole the fuel bowl mod not done and larger needle and seat fitted poorly he is off my chistmas mailing list

j9fd3s

wow... mine doesnt run all that hot either, but the needle and seat are screwed in...

hksthor

finally got the motor running sweet making good power and with smooth power curve most of the trouble has turned out to be the exhaust which was found to be too large off the block and too short mmm guess the so called rotory expert was not all that