i have a 48ida on a 12a street port and its stumbling out at 3000rpm on a regular basis its only good past half throttle let me know if you guys know anything


Thanks

 

List your current settings.

The stumble is caused by incorrect emulsion tube and idle jet combinations. Read this thread:
https://www.rx7club.com/1st-generation-specific-1979-1985-18/weber-emulsion-tubes-805950/

 

fuel jet 170
air jet 150
f11 emulsion tubes
250 needle valve

Exactley what racing beat says and thanks for the thread but i was running the f7's and it had the same stumble

my idle jets are

60/120 on the top

70 f10 ew

i feel like my idles could be the problem but the cut is unbelible when slowly increasing on the throttle

 

Forget what Racing Beat says, or anyone else for that matter. They can only give you a guestimate for what might work on your car. With a carburetor things like barometric pressure, altitude, air quality, temprature, port size, and compression all come into effict when tuning. For example I tuned my car at 65*F ambiant the other night and at idle it's almost exactly 13.8:1 AFR's, but in the heat of the day today it was 93*F It was idleing at 11.5-12:1 AFR's because of the thinning of the air with the heat.
First thing is get rid of the 120 idle jet holder and use a 100 jet holder. That should help a little. The problem is that a 48 IDA really is kind of small for a rotary and they like to be rich in the midrange. The ida gets really lean on transition from the idle circut to the main curcut which happenes right at 2500-3500 RPM. What you're experiancing is a lean surge. There isn't enough fuel put out at 3000 RPM by the idle circut to keep the engine running, and the e-tube is too restrictive making the main circut not come on until 3050 rpm, so the engine stumbles falls to 2950 then drives fine until it gets just past the limits of the idle circut and the main isn't on yet so it falls again and so on. From my tests and tuning throughout the years even with the 3rd progression hole the f-11 e-tube is way too lean on the transition and the lean stumble will never go away. Try f-3 or f-8 etubes and a 100 idle jet holder and it should go away. With the 120a/c I had to run 65idles and I would get about 14 MPG. When I switched to 100 a/c i could run 60 idles and I can get ablmost 17mpg if I stay out of it. Keep in mind I made 190 rwhp on this engine and it's my daily driver.

 

Also, You need to check and make sure your float is set correctly. If it's off by 1mm it can screw things up BAD. The general rule is for every 1mm of adjustment you change when the main circut comes on for 1000RPM

 

im just going to pm you its easyer

 

I don't respond to technical PM's. Post it here for others to learn from.

 

This was his PM
F8's are really rich. More suited to a bridgeported 13b that gets street driven. Like I said before get f2's or f3's. You can get them at http://www.webercarbsdirect.com/ for $7 each...
The idle screws only effect idle. If you have them turned out more than 1.5 turns your idle circut is too lean.

 

the idle screws will make the car run lean if turned out past 1.5 from bottuming out?

ive noticed my car bucking at low throttle at a cruise its before 3000 rpm have you ever encounters a problem like this before beacuse of the f11 e tubes?

thanks once again

 

Turning out the idle mixture screws makes the idle richer. Turning them in leans it out. What Hyper is saying is that you shouldn't have to turn them out more than 1.5 turns to get it to idle well. If you do, it means your idle circuit is too lean for your engine.

The bucking is probably a lean surge, also indicating that your idle circuit is too lean.

 

It also indicates that his main circut is coming on too late. F-11's suck... I have answered all your questions. Reread the thread man! The whole thing not just the parts you like and you'll get your car running well. read the Link %7C posted as well. The WHOLE THREAD!

 

I'll try some f2s and post how it works out

 

that depends on the size. larger idle jet are less than 1 full turn.

 

Put a bigger main jet and should fix the problem, it stumbles because there is a lean spot...good luck

 

sir,
you're making it too easy for them. Give them a hard time so they wont forget

 

The lower the F# the richer the tube. F2 Emulsion tubes are used for alcohol, so the F8 emulsion tube would not be richer.

 

did you read my prior post??? I said, give them a hard time. I feel evil tonight

 

Oh, sorry Wacky... ok, throw the f11's in then.

 

my bad, In that case put some sugar in the tank and it will fix all problems

 

WARNING RANT IN PROGRESS!!


that's not exactly true. Go read my e-tube thread. The placement and the size of the holes in the tube decide how rich/lean the tube is. There is almost no rhyme or reason to webers e-tube numbering system. The f-3 etube is drilled exactly the same as the f-11. the only difference is it is thinner and therefore has a larger fuel well inside the main circut chamber allowing less of a pressure drop across the aux venturi before the main circut starts. in other words the car will run almost the same AFR's as an f-11but the main circut will start lower in the rpm band. look at weber's charts listed here: https://www.rx7club.com/showpost.php...4&postcount=24
These are the exact specifications on which the e-tubes are made.
Not at all true. If you put a larger main jet in you will fatten up the bottom end opf the main circut, but it doesn't change anything about where the main circut starts, and you will still have the same stumble, and you'll get shitier gas mileage. I have done thousnads of experiaments and testing on this. In direct compairison the f-7 tubes I will cruise at 10.8: afrs where as with the f-3's my wideband says I'm at a healthy 13.5:1. In fact the f7 & f8 tubes are much richer than the f2 or f3 based on the arrangement and size of the holes in the tube. Remember the 48 IDA was designed to work with 36mm Chokes. Once you go any bigger than that you are out flowing the design of the IDA. Realistically 2 48IDA's with 36mm chokes would out flow a 58IDA once properly tuned, and drive as well as the stock nikki. That's why we have to go way out of the tuning norm for using just one on a rotary.

Remember as air flows across the aux venturi the vacuum in the main circut fuel well grows exponentially. That's why there is an air bleed and a e-tube. They act as nothing more than a brake for the fuel flow. without them the fuel drawn into the engine would also increase exponentially as rpm's rose. The air bleed, or air jet meters, how much air is allowed into the main circut and drawn into the carburetor leaning out the fuel mixture. The emulsion tube emusifies the air and fuel together. Where the holes are drilled into the tube decide on what RPM the amount of emulsification accure. The lower the holes are in the e-tube the higher in the RPM band the mixture is effected.

As i said before his problem is that the idle circut is running at it's maximum capasity and the engine is demanding more fuel at say 2500 rpm. if the main circut doesn't start adding fuel until 3000 rpm like the f-11 do then he will have a lean stumbe from 2500-3000 rpm. so if you just add a bigger main jet you're not solving your problem all you're doing is adding more fuel at 3000 RPm and not solving the issue of the lack of fuel that the engine is demanding at 2500 rpm. There are two ways around this either extend the idle circuts ability to supply fuel by running a smaller air bleed or bigger idle jet. the smaller air bleed is a great idea as it will only efect the top end of the idle circut. so he puts in the 100 idle jet holder and now his car can run to 2700 rpm before the idle circut tops out. there's still a lean spot from 2700-3000 rpm. So you could add a larger idle jet, but that's only going to richen up the bottom of the idle circut from idle to 2000 rpm or so. so much so that it'll idle like **** and smell terrible and waste a **** ton of gas. And, as I said before if he just plugs in a larger main jet he's only making 3000 rpm to 5500 rpm richer, not at all solving the lean area from 2500-3000 rpm, so he needs to change his e-tube to get the main circut started sooner.

 

You sure know allot about the way webers work with that a/f meter of yours, How fast is your car in the 1/4 mile. I use to run a ida back in the days, just want to compare how much faster you are than i was.

 

oh god, just give us a summary. too much reading is not good for our health and you make life too complicated

and yes, I agree with Jose, we want to see your time slip.

 

No time slip as the last time I went to the track I snapped my out put shaft in half and I'm tired of swapping trannies. Gsl-SE 13b with a very small street port.
here is the 1st dyno sheets. I had to back up my 189whp cause a bunch of internet race car drivers didn't believe my numbers. so %7c came out and taped the runs. I backed up 189.6 with 190.5

I'm an autoXer not a drag racer. Why pay $40 for 3 14 second runs when you can pay $25 for 5 50-70 second runs with turns. Plus last time we got about an hour of fun runs. fawk drag racing...

http://www.youtube.com/watch?v=U0vbPTuvCzs

 

If you run 14 seconds in the 1/4 mile, sounds like you need some tuning. Dont get caught up on dyno numbers. I ran slicks for many years running my best e.t. of 12.78 @105mph with an early street port engine and never broke a output shaft. I think you been reading too many "how to modified a weber" books. to the original poster my advise still stands put a bigger main jet and let us know how it works out.

 

I ran a 14.2 when I was making 140whp. i haven't completed a run at the drag strip since... last time I went the output shaft broke on the first run. that was about a year ago and the time I went drag racing before that was 2001 maybe. I'm not some kid preending I know what I'm talking about. I come from a family of rotards, I'm ******* Puerto Rican for gods sake. what else do we do, and I'm 27 y/o and I've been building these cars with my family my whole life. Get the **** over yourself. FYI half those "how to tune a weber" books give the shitty advise you have been giving. p.s. **** off for questioning my integrity. there are at least 20 people on this forum who have had my output shaft in thier hand I keep it in the glove box.