rx7learner

I am running 12.5 AFR under 5PSI boost (blowthrough mikuni) using the largest main jets wolfcreek sells and I even drilled them out slightly. I would like to get a lower AFR any suggestion?

DriveFast7

iTrader: (1)

Larger needle and seat. Smaller air jet. Can you raise the floats higher to reduce fuel drop?

rx7learner

The floats are as high as possible.

I cant recall the size of the needle and seat but I will check when I get home (it came with the master rebuild kit). I didnt know that a larger needle and seat would cause a richer mixture... I was thinking that it would just prevent the bowl from emptying... but it makes sense that the faster the fuel flows into the carb the richer it would run.... I did put in a larger fuel inlet fitting than what came with the carb.

I think I am also using the smallest main air jet that wolfcreek sells... with an OA jet block. Maybe there is a way to modify the jet block to block off some of the air passages. Wolfcreek didnt have much information on tuning for a blowthrough application.

I'll get the specific jets and post back latter.

rx7learner

I'm running 170 on the airs and 250+ what I drilled out to max on the fuel.

Wolfcreek said that 170 airs were the smallest they had... so I'm going to try to fill in and redrill my old airs smaller. That charge pipe changes too much of the dynamics.

I can see that the weber will give more flexibility but I dont think the mikuni is that far off.

rx7learner

correction 70's not 170's on the airs

DriveFast7

iTrader: (1)

Put a richer emulsion tube in there. You're at the max.

rx7learner

When you say emulsion tube do you mean jet block. Like the one attached?

I have the OA jet block.

Hyper4mance2k

iTrader: (40)

Yea that's what he's talking about. I say trash the mikuni and go to a weber or delorto and boost your worries away.

rx7learner

That's what I was afraid of. Robert if your still out there im me with a good deal.

racerlinkfc

x dellorto off the list too.. they can be boosted but float bowls run dry on 1 thru 4th pulls due to needle valve size, larger ones are not available for mikuni or dellorto

DriveFast7

iTrader: (1)

Dellorto. You can ream out the commonly found 225 seat to 300 or higher and still use the same needle since it's tapered. CB Performance.com sells the jet ream kit.

twinkletoes

iTrader: (17)

You'll have to email or call Robert to get ahold of him. Any videos of your car lately rx7learner? I'd try and go weber too, even though I have a mikuni also lol.

rx7learner

Last night I took my old air jets and filled them in with JB weld then stuck a thin nail down the center and after it got slightly firm... I pulled the nail out. I'm going to give them a shot when I get home today... It prolly wont work well... but worth a shot if just to eliminate the possibility that smaller air jets than normally made for the mikuni NA application may fix the problem for a blowthrough application.... Even if it makes me run extremely rich I would have proven that I could richen the mixture to acceptable levels and explore a more permanent option further.

I couldnt find that ream kit on the site... Is the concept to enlarge where part# 20threads into the mikuni top cover which would in turn allow me to use a larger #20(needle and seat)? Couldnt it just be drilled and tapped?

No recent videos just the old youtube one. Let me qualify I have run the mikuni jetted as is for 1+ year 12lbs boost until I cracked the rear plate right after putting fresh TII plugs in (swapping out my b9es) a few HARD pulls later... the end plate cracked and I didnt feel any detonation but it pulled like a bat out of hell and still ran well just oil all over...

Now I have my backup 12a in and running. My afrs still drop to 12.5 under 5lbs boost but I dont continue to lean out as if the bowls were emptying. I'm only going to run 5lbs boost till I get over this.

Going to see if I can find roberts number also.

twinkletoes

iTrader: (17)

(818)576-9191 is roberts number .

rx7learner

OK It looks like I am good for now. Took a test drive using the main air jets I JB welded with a small nail hole as the air passage and when I get on it the afr drops to low 10's as opposed to the 12's I was getting with 70 airs...

I'll report back tomorow after my 50 mile regular commute with her to let you know whats up... but it felt good to boost with those afrs.

Heres cheesy camera phone video that my 11 year old shot. I dont push it with her in the car but you can hear the bov go off and match it to my afrs... Also it shows where I live... the beach....

http://www.youtube.com/watch?v=bIcH_...e=channel_page

MAN I just watched that myself that's bad video.... I'll get some with a regular cam

680RWHP12A

the needle valve is not big enough in the mikuni to do wot passes through 4 gears. the float bowl goes dry, motor goes lean and bam! you crack a housing or apex seal
im glad you got her running and my turbo is treating you well

Hyper4mance2k

iTrader: (40)

OMFG Robert's back WOOT!!! lol. hey check yer MSpace sometime hoe. lol

rx7learner

Robert great to see you are around. Yes... the turbo, the carb hat, fuel pump, plus all the tips you gave me have been treating me very good. I guess I havent really had the need to pull hard WOT on 4 gears yet even when I smoked the Lotus Elise.

The drive this am was the best it has been in a while with the jb weld air jets... I noticed if I hard floored it... it would hit low 10 AFRs and get too rich... but If I stayed a bit up on the pedal the AFR's were mid to upper 10's and it pulled much harder.

What AFRs should I be looking for in terms of safe good power.

DriveFast7

iTrader: (1)

cb performance is out of stock on the jet reamer but you can buy it here:
http://www.larrysoffroad.com/item523949.ctlg

jbweld is not resistant to gas, you should use another material that is like devcon alumuminum putty.

reaming the seat - idea is to make the hole bigger to increase volume of gas going into float bowl. The hole is tapered. The needle is tapered. You have to keep the taper in the seat for it to seal properly.

Sounds like the air jet is a tad too small now.

rx7learner

Understood on the reamer, thanks for the insight...

Yes it is too small and I am going to adjust. Why did you say that JB weld is not gas resistant? I used it to plug the choke passages on this carb for 1+ years and at the JBweld site http://www.jbweld.net/faq.php it says...

"When fully cured, J-B Weld is completely resistant to water, gasoline, and about every other petroleum product or automotive chemical."

Have you had some bad experiences with it?

DriveFast7

iTrader: (1)

Yeah. I used it in a carb to hold a float pin in place. That stuff dissolved within a year.

rx7learner

I now know what you mean... pulled the jb welded jets to make the hole larger and the jbweld crumbled!!!!

Going to look for the stuff you mentioned.

broke7

iTrader: (1)

Cb performance sells a turbo book for vw's. It does get into the dellorto and weber side drafts but not the mikuni. They do discuss various ways to increase fuel flow and setting up the carbs. It may be a well spent $15. I have never tried this but a guy that was wanting to buy a set of webers that I had already sold told me to grind the middle edges of the float needle and it really increases the fuel flow. He road raced british cars and had a shop in denver. I plan on trying that on my next big vw engine if I have fuel flow problems

rx7learner

Ok this is going to sound weird but I tuned it with fish hooks!

I live on the water and have stainless fishing hooks of many different diameters so I cut the hook end off and used the straight shafts and set them into the air jet till I found the best diameter. They are too long to pop up out of the jet because of the jet cover and they dont fall into the jet because of the looped end of the hook where your fishing line ties onto.

Worked 100% and should last. Better than buying a ton of these jets (plus they dont make them as small as I need them).