carstud

Hi everyone

I need some help/advisin on tuning a 13b that is in my sandrail. It is 4 port running a Ida 48, I run the sand rail in the oregon, california dunes. which is at see level and the avg temp of 60 to 75 deg and about 80% humidty. but will also be running it in neveda at sand mountian which is about 4500 feet elevation temp is about 90 deg and humidty is about 15%. Thce motor was rebuilt by redline performance in southern,ca but I have no idea what was done i.e. street port, bridge port etc. current set up is

main jet 180

air corrector 180

emulsion tube f11

idle jet 70f10

idle holder 120

choke tube is 42mm

accel tubes at 50

float needle valve 300

fuel pressure is 3psi

the engine will not idle below 1500rpm(maybe normal)

when driving at about 8000rpm feels like it is running out of fuel. I just took the carb appart and cleaned it. replaced all gaskets, replaced needle valve with high flow valve, opened up aux accel pump cavity.

My main question is do I need to change any of the other jets or emulsion tubes, or leave them alone. I bought 200 mains, f7 tubes, 150 and 120 air correctors but have not installed them yet. I Am trying to tune it as best as possible before i go to the dunes but cannot drive it for seat of pants feel.

Sorry it is also running a short header to a 3 inch muffler, stock distributor and coils, plus b8degv. it does backfire some times on decel which i have read is kind normal. This is my first rotary so Any help or advise would be greatly appreciated. [attachment=47104:IMG_0255.jpg][attachment=47105:IMG_0257.jpg][attachment=47106:IMG_0256.jpg]

GreyGT-C

I don't much about carb'd rotaries... so i'm no help there. But if if were me, i'd find someone with a wideband.. seat of the pants tuning(guessing) is a surefire way to blown a rotary engine up.

carstud

Thanks for the input I have few o2 sensors and I am in the process of making a new header with o2 sensor bungs for testing purposes so I can scope the cross count and my fuel ratio. The best is under load so until i get that built and put it on dyno all I have is seat of the pants. It was dynoed in 2000 and has been running the current set up since 2002, (sorry should have said that in my original post)when the motor was rebuilt so I don't think it is going to blow up with some minor adjustments. It runs pretty well but seems like it sputters at top end.

Lynn E. Hanover

Remove the brass plug above the needle seat and discard the plastic filter. Drill out the hole down to the needle seat for a 1/3 increase in diameter. Chamfer hole top and bottom.



Raise the float until the auxilery venturis just start dripping. Forget the idle. We didn't come here to idle. The choke size is big enough for 300 HP at 10,000 RPM. So there is very little signal or flow depression or vacuum, whatever terminology you like, but tuning will be more sensitive with less signal. Because the choke or main venturi is close to the carb body size.



It is more typical to use a Gene Berg Weber copy in a larger body size for 42 or 44 MM choke size. But the Weber will work. The carb is being used above its design flow rate. So the tricks are needed to keep it working. This thing is going to scream. The front hole will run over lean and the rear hole will run over rich on acceleration. At one "G" the fuel surface will be at a 45 degree angle in the carb. Add in more angle for each additional G and some more for the front end lifting a bit. So now hold the carb in your hand while full of solvent over your cleaning tank. Now tip the carb over backwards to replicate the car accelerating to about 55 degrees. Look in the bowl. The front main jet has about 1/2" of fuel to operate in, and the rear main jet is in1 3/4" of fuel, and fuel is running over the top of the air corrector and falling into the booster venturi. I would twist the float a bit so that the bottom of the float is a bit forward, and drops sooner when accelerating.



Jack up the fuel pressure until the dripping from the boosters makes it hard to keep it running.

On the line keep shutting off the pump and turning it back on after a minute or so, to keep the plugs dry. On the line turn the pump or pumps back on and take the revs up.



Keeping in mind the difference in rich and lean for the two holes I would start with your current jets in the rear hole. Put the 200 main in the front hole and the smallest air corrector you can find. If you have a number drill set solder an air jet shut and drill the solder out to make a one MM jet. If you do not have a number drill set, buy one. Start with a one air corrector.



I run 6 PSI of fuel pressure. At the end of a long straight I still have 6 PSI. Otherwise you just empty the float bowl and the main jet is then the needle seat set size. I use two Carter sliding vane pumps set at 7 PSI. Cheap and long lasting. Find at any hot rod shop. Summit racing or Jegs in the east. A big in line fuel filter just befor the carb. Fuel pressure measured right at the carb inlet. Use "T" fitting at carb in. Fuel pressure regulator after the filter. I use a Holley. Cheap and reliable. You may angle the manifold flange so that the carb is tipped foward a bunch at rest so thia helps reduce the imbalance in fluid levels in the cab under acceleration.



About 25 degrees of advance total. An MSD at least on the leading plugs. Keep the front housing wires well away from the rear housing wires.



There will be no time to look at gages, but if you can just kill the ignition at the end of the pass, keep the throttle wide open and clutch disengaged for a clean cut. You may get a plug reading. You should use racing fuel for a weekend to get good plug color. Unleaded regular is fine but you always get flat black plug color no matter what the engine was doing. I use a movie camera to watch the gages. The driver never sees much but the tach and maybe oil pressure. Oh yes. Oil pressure should be at least 100 pounds.



Sea level hot and humid is a lean setting as water displaces oxygen in the air. High and dry is the same setting the higher you go the less of all gasses in each cubic foot of air, again a lean setting. Get the car rich enough to pull hard all through the pass, then come back and tune with air corrctors only. When you run out of air jets then start changing mains. As on the dyno, make a big change, so the outcome will be a big change and easy to see. Make only one change so you know what caused the outcome.



Always run the same air horns and a big air filter. I use the biggest K&N made. Use a foward facing hose to feed the cleaner. Completely enclose the filter element.



Try that and get back to us.



Lynn E. Hanover

carstud

Wow All I can say is thank you for the wealth of information lynn. I am running the carter pump already with a adjustable mallory pressure regulator so I will adjust to 6psi. I did remove the fuel filter but had not drill the body yet. I had already ordered both coils they will be here in a few days. Also I have had to add a supertrapp muffler w/12 discs on the output of the thrush 3 inch muffler due to noise issues. I need to stay below 93db at the dunes in oregon or get a ticket. Should I leave to emulsion tubes alone f11 or use the f7's? I due have full drill sets but not sure what you mean by a number drill set. I was thinking a metric drill set ie 1mm 2mm and so on. I will start with the 120's they were the smallest available when I got them. I will order some smaller ones then solder and redrill. I am leaving wed for the dunes so I will have to play with them a little when making my test runs. Now what should I be careful about as to not damage the engine while performing these runs.

Thanks

Brian

Lynn E. Hanover

You solder shut an air corrector that is too big then drill it out with a one MM drill bit. That will make a "one" air corrector. Slightly chamfer both the top and bottom of the drilled hole.



Over rough ground, fuel injection has a big advantage over the carb, because the carb only works at 100% effective at one "G" and stationary. If you move it or bounce it, all bets are off. It starts going haywire, as you can see by the solvent exercise. The Weber reduces these problems by having a tall narrow float bowl, so has better control of the fluid level.



The down side of the rich/lean process is that when a housing runs lean it passes through its highest exhaust gas temperature. We run EGT probes 3" out from the flange for both housings.



You want to be rich enough to stay at or just below 1600 degrees of EGT. This is just rich of best power. As that housing goes lean, the EGT goes up past peak EGT of maybe 1800 to 1900 degrees, and you can hose your apex seals doing that. 1600 degrees is about 12.5 on the Air/Fuel gage.



The rotary will run just fine both way rich of best power, and way lean of best power. It will still run lean where a piston engine will shut off. The airplane people like this and run piston and rotary engines lean of Peak EGT all of the time. A lean mixture mimics a high Octane fuel.



The lean mixture has fewer clumps of hydrocarbon per cubic inch. There is much excess oxygen to burn much more of the mixture for more efficient burn. There is less energy available, certainly, but also less heat, the EGT starts down well below peak, so less stress on the pieces. The coolant temps will even come down. The throttle is still wide open for zero pumping losses. In the airplane the throttle is left wide open until you get there, and start down. You control the planes speed by changing the mixture, not changing the throttle opening. Then quickly go to full rich before landing so full power will be avaiable on landing. Saves fuel and extends engine life.



The point is that the rotary will keep running and sound fine running way lean of best power (peak EGT). So, you come out of the hole, and get maybe one gear change and the engine seems to go flat, or lay down, as though you had skipped a gear. Its out of fuel and the hole above the needle seat is the main jet now, and its too small. The bowl must be kept full for the jets to work at all. A piston engine would just shut off as though the switch had been hit accidentaly.



So you get it running too rich for the whole pass, then go back and tune it. You need EGTs on both pipes and a movie camera to watch the gages. The gages will react plenty fast enough to collect the data you need.



We had a 93 dB requirement as well. Used a big Borla stainless muffler.



Lynn E. Hanover



This is a rear iron made from an aluminum billet. And no, you cannot have one....yet.

j9fd3s

the only things i can add, follow lynns advise, he's been doing this for a long time



and i did run across a method for tuning the weber that is simple and logical. you start from the bottom up. you follow lynns advise, for the setup, fuel pressure, ignition etc etc. then start working on the mixture from the bottom up. you start with the idle/low speed jet and air bleeds, then the main jet/ emulsion tube, then the air corrector.



imo this takes some of the guesswork out of jetting the thing, as far as what jet/part to change for what part of the rev range



mike

Hugh Morris

Lynn,



With the setup that he is running what do you think would be the best muffler that would allow him to achieve the best backpressure and still be able to be under the 93 dB. requirement? Also what was the specific Borla muffler that you were using with your setup?