If you can find Paul Yaw's website, there is some pretty interesting information on fuel pressures. He found that even a 1/10th change in fuel pressure can yield enormous changes in hp. He also talks a lot about fuel pressure gauges, and the need for high accuracy because of that.... Most gauges are only accurate to +/_ 10%, so if you're using a gauge that's 1-15 psi, that's a 1.5 psi margin of error. Not nearly accurate enough for tuning a 3psi target...


Ah, I see that Vipernicus posted the link to that site up above.

 

According to the Marshall website the gauges are ANSI accurate within 2% in the middle of the scale, but we could try another gauge just to be sure.

 

Thanks for chatting with me on the phone yesterday.

We are trying to finish decorating tonight and do a small shakedown on Friday. Then it is pack up time and leave on Wednesday night for Houston.

 

I see the manual and Yaw say the float bowl fuel level should be basically in the middle of the glass. Ours is pretty close to the top. I know Sterling says don't mess with the floats. Is there any concern there?

We cracked that giant flywheel nut loose the other night. I may open up the blown housing tonight.

 

The first question is, why is the fuel level high? Float adjustment might be the cause, but before you mess with them make sure that it is not high fuel pressure forcing fuel past the float needles...

If you are not sure if the floats have already been messed with, then it moves up a spot on the suspect list. Easy enough to pull the top of the carb off and verify the measurement.

I think Sterling's comment was mainly intended for people rebuilding carbs. These settings don't usually change, if ever, unless someone who doesn't really know what they're doing tampers with them.

 

Nobody has touched the carb internals but Sterling.

We played around again tonight with it. Tried to adjust idle mixture to no avail. Took the fuel pressure down to 3psi. She is running so rich, 10.3 AFR under acceleration and tons of raw fuel making it pour smoke out the tailpipe on deceleration. I guess we will find out more tomorrow, but I am way less worried about a lean condition now.

This thing is killing me. Less than a week till the race.

 

I know you can pull it off, I will have your spot for the car, if you have a CB radio bring it if you want to hear the are car communications.

 

I'm a bit confused about who's who in this thread!
(Who bought the carb from me?)
Someone should have contacted me personally about any of these problems earlier- I could've helped while there was still a reasonable amount of time to troubleshoot the carb.

Stock Nikkis run in the 3.75 - 4.25 psi range. Going too high will keep the emulsions system from working in the top end, and you'll run pig rich (like you are). I send the carbs out running at about 12:1 at sea level. You can kick that pressure right down to 2.25 with a good pump, and still not go lean up top. Over about 5 psi and you're asking for trouble with these floats as they just aren't as buoyant as soldered brass floats in other carbs. Over 5 psi and the needles will bounce out a bit here & there on the track and you'll be flooding. There's a really fine line in fuel over-pressure between that condition and the carb being downright overwhelmed and staying flooded.

Fresh rebuilds can sometimes have sticky needles & seats. This is a common problem that usually fixes it's self, but until then an ocassion a tap on the banjo bolt above the offending float bowl may be necessary. You should be able to spot this problem at idle, and also just by observing the fuel level in the sight glasses.
The fuel level MUST be in the center of the sight glass. If it's not, then there's a problem.

Please do the following:
Remove the airhorn. Drain the carb. Unscrew the four emulsion tubes, the four fuel jet access bolts, and the four fuel jets. (Be careful to hold the boosters steady as you unscrew the emulsion tubes because they are only pressed in.) Blow a short shot of compressed air directly into where the emulsion tubes were. This will blow any debris down & out into the fuel bowl. Irrigate the bowls with fuel and suck it out with a turkey baster (or something) to remove any debris. Please write down the fuel jet sizes. I need to know if I installed the incorrect ones.

Hold the air horn upside down to check that the floats are at even levels. Hold the air horn right side up to check that the drop level is the same. Now push upward on each float and observe the needle to be sure it's moving closed & then opening as you drop the float back down.
Reassemble the carb.

Set the throttle cable by having someone step on the pedal while you hook the cable to the carb. At full pedal down the primary throttle valves should be straight up & down. At throttle release, there should be some slack in the cable.

Tune the idle using the instructions on my website.
If you can't get it to idle as low as 750 RPM, there's a vacuum leak.

What year is the manifold?
What year is the carb?
What have you done to the manifold as far as emissions removal?
How did you plug everything?
What gaskets, if any, do you have in between the vacuum port plate and the carb / manifold?
Are you running a rturn line?
There is an in-line check valve in the return line, often referred to as the "restrictor" due to a mistranslation in the Mazda WSM. This lets fuel flow only one way. If it was removed and reinstalled backwards, you would effectively be dead-heading the carb. You need the FPR set up correctly for that, and in your case, there's nothing to be gained from not running a return line.
Is the tank venting properly? If you hear a "whoosh" ever when you remove the fuel cap, it's not. Can you physically blow into the carb return line, or is it plugged?
What is your timing set at? Has the dizzy ever been removed?
Performance tuning should be 24 btc for leading and 16 btc for trailing, according to Rotary Master Paul Yaw. I do NOT know a great deal about timing, so if someone has a better, "safer" setting you should use until you get the fuel delivery issues sorted, then change the ignition after it's all set.

I need you to do all of these things and gather the answers to all of these questions so that I'm better prepared to help you. Then I think we'll have to talk on the phone at some point due to the impending deadline.
Email me with all of these details, and I'll do my best to get you up & running so you can win this race.

 

Thanks Sterling. I am the one who bought the carb from you. Allen Stewat. We have talked via email a few times.

I will print off your above post, do the things mentioned and get back to you. We are heading out to the track today for some shakedown time after we go through your list.

 

We just got the wideband installed last week so we really haven't been aware of the problems. We also have little to no expierence with rotarys so it was hard to tell what was going on without any sort of AFR gauge. I didn't contact you because I thought it was something we had done, not something with your carb set-up. Sorry if I implied somewhere that there was a problem with your rebuild.

I will double check our pressure with a different gauge today. We have a Carter pump installed and a Holley FPR. We had it previously set at 3.25psi, then bumped it to 4psi before we blew the rear rotor. We turned it down to 3psi last night when trying to get it leaner. We will try 2.25psi and see if that works.


Ok, I know we have noticed high sight glass levels previously. We will investigate that further.

I'll print this and we will go through it today.

Done.

Will do.

1980

Whatever year you sent me. I didn't send you a core.

Everything is removed and blocked off per the numerous threads around here.

Vac caps on the port plate except for one for the dizzy. (I know, we probably should be running locked timing, but we aren't) Blockoff plates installed on the air control valve thingy, and the flex tube that runs to the exhaust.

I bought a stock gasket kit from Mazdatrix and replaced the carb/manifold gasket and the intake manifold gasket.

Yes we are running a return line, not plugged, this is one of the first things I checked. I will double check today. No whoosh sound or pressurization of the fuel tank as far as we can tell.


We set the timing at 24btc and 16btc. We will double check this as well. Running a smaller Mazdatrix main pulley to help water pump cavitation.

Thank you Sterling. Top notch customer service, right on par with what everyone else here has said.

 

OK, great. Check the floats, clean out the carb to be sure as per the instructions above, & give it another whirl. Email me with details of what you find at gorealfast@sterlingmetalworks.
We'll work out a phone time when you can yack with me & work on the carb at the same time.

 

If you reduce your fuel pressure (like, way down), and the fuel starts sitting at the proper level in the float bowls, would that not indicate that the float levels are good? Would that save you having to pull the top of the carb off?

Sterling usually stops in to check on the carb threads (Sterling carb or stock), but I think the title of this thread was a bit misleading. I would have let him know about this thread sooner if I had realized that you were dealing with a Sterling carb. You mentioned that it was modified, but never really stated what it was.

I totally agree with you on the customer service...

 

Thanks guys! I'll get some results today and hopefully figure some things out.

This thread kind of turned into a carb thread, when it was started just to find out why our rear rotor went bad.

 

I think iceman may have sent an email with dimensions by now. We opened it up for inspection and cleaning. No debris. With the pressure at a minimum of ~2.9, the float bowl fuel levels looked just right. I got the idle tuned pretty smooth, but left it a little high, ~1400.

It ran the best yet during the short shakedown. Smooth transition, part throttle, and almost no backfire after lifting. 10.3 a/f under any load. The puff of white/blue smoke during shifts is a little concerning. Bad oil control rings?

 

All the plugs looked uniform and rich. Also, I think a turn out on the accel pump helped.

 

Glad to hear it. If you've got oil getting by the control rings, try running a quart of Lucas heavy duty oil stabilizer in place of a quart of oil. Unless you're leaving smoke trails to make James Bond jealous, that will keep it from being a problem for you.

Don't be afraid to play around with your fuel pressures even more. You'll have to sort of believe the car instead of the gauge and see what feels right. Best of luck!

 

I have sent the results of our track side carb disassemble to Sterling. With his permission I will repost that email on here.

 

did you get a new motor?

 

No luck yet, chuck. One ok lead on one that has sat forever. Would you sell or make available your 12a? We can put a 5spd flywheel on it. See you Friday.

 

^^ I just tried to call you, I am willing to talk about a price for my 12a. It will need a 84-85 12a 5speed flywheel, and you will need to move you oil pedastool onto this motor because this motor has the beehive oil cooler.

 

Edit: Hold Please.

 

Bummer. Our flywheel is an '80. What's the difference?

I'll try to call you back this evening.

The local 12a seller guy is not moving too quickly.

 

A flywheel from a 2nd gen 13b is different? Is it beacuse of the counterweights?

I have a TII motor sitting at my house. Do you think I will be able to put it in a bag and call it carry-on for my trip to Houston?

Hell, I could just bring Julie's car and we could run that! Already has a cage and everything! I think I would have to check that (I hate waiting at baggage claim!)

 

It's the rear counterweight that's different. It appears the dimension of the lip at the bottom of the front face is ~.085" shorter on the 83-85.

http://www.mazdatrix.com/flywheel.htm
http://www.mazdatrix.com/faq/Rcounterweights.htm

Anyone have an 83-85 5spd rear counterweight they can send to Texas?

 

Since nobody brought it up and you stated that your new to rotarys, what fuel are you running? You want to be running as low an octane as possible. Regular old 87 octane pump gas runs the best in a rotary. Someone told me that the factory team from years back actually ran 78(!) octane in the race cars. They brought their own fuel to the track. Good luck.