C'mon guys walk me through this step by step. Krochus'es Carb tuning thread O doom
03-28-2014, 07:30 PM
#21
Even so though I'm at a loss as to how the bleeds would allow my to add fuel at idle if the mixture screws won't
Last edited by krochus; 03-28-2014 at 08:13 PM.
03-28-2014, 08:36 PM
#22
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Oh yes, I've got a full machine shop at my disposal. I'm just not sure this carb is worth the effort the more I learn about and experience the design's issues
Even so though I'm at a loss as to how the bleeds would allow my to add fuel at idle if the mixture screws won't
Even so though I'm at a loss as to how the bleeds would allow my to add fuel at idle if the mixture screws won't
03-28-2014, 08:47 PM
#23
I didn't have a lean idle condition before restricting my IFR's It's not like this problem has always been here I know EXACTLY what I did to cause it. But i did go ahead and go over the engine everywhere earlier with carb cleaner hunting for any errant vac leaks.
Last edited by krochus; 03-28-2014 at 08:57 PM.
03-28-2014, 09:15 PM
#24
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Guessing it didnt show any signs... hmmm. That vac secondary carb isnt like mine but im sure with tinkering you will get it to work. Its easier to give ideas of your helping hands on ya know what I mean... its odd that you cant get it to richen up at idle.... should be pretty easy to flood the engine out at idle ....
03-29-2014, 11:14 AM
#25
You need to make the idle bleeds smaller and maybe a slightly smaller wire in the IFR.
Air bleeds are the easy thing to drill out and replace. I used 10-32 set screws on the idle bleeds for my DP.
http://www.mcmaster.com/#set-screws/=rb0o67
A bottom tap helps here, MMC # 26955a82
Make sure you measure the size of the bleed with a drill bit before you drill out the press in restrictor.
you might be able to put a piece of wire in the bleed but I'm not sure how you would hold it in place. Better to use the set screws.
Air bleeds are the easy thing to drill out and replace. I used 10-32 set screws on the idle bleeds for my DP.
http://www.mcmaster.com/#set-screws/=rb0o67
A bottom tap helps here, MMC # 26955a82
Make sure you measure the size of the bleed with a drill bit before you drill out the press in restrictor.
you might be able to put a piece of wire in the bleed but I'm not sure how you would hold it in place. Better to use the set screws.
03-29-2014, 11:22 AM
#26
It's funny you should mention restricting the bleeds with wire as I'm attempting to do that right at this moment
Much patience is required to get em to go but I've managed to dog leg some .027" wire UP and back out the top of the idle bleed from the face of the main body behind the metering block.
The zig zag through the port "should" keep the wire in place. Either way I've decided that whatever I try on this carb is going to be non perminate as it's remaining time atop my motor is now limited.
Much patience is required to get em to go but I've managed to dog leg some .027" wire UP and back out the top of the idle bleed from the face of the main body behind the metering block.
The zig zag through the port "should" keep the wire in place. Either way I've decided that whatever I try on this carb is going to be non perminate as it's remaining time atop my motor is now limited.
03-29-2014, 11:54 AM
#28
Well crap! The idle bleed restriction was a success. 1.5 turns on the mixture screws = 13 AF ratio. Unfortunately I'm right back to where I started as far as part throttle low speed rich ! I guess I'll dive back in and try a slightly bigger ifr restriction wire :-(
I also took the liberty of blocking the power valve which netted me some SPECTACULAR WOT performance improvements @13 or so 1 AF
I also took the liberty of blocking the power valve which netted me some SPECTACULAR WOT performance improvements @13 or so 1 AF
03-29-2014, 02:04 PM
#29
Ain't this **** fun?
Funny, I just got back on here to say I meant you should open up the bleed.
Good idea on running that wire up from the bottom though.
You've boxed in the problem, you need to put it somewhere in between what you have tried. Get a wire slightly smaller than what you have in the IFR and open up the bleed a touch. Take good notes so you can back off when you get confused.
One other thing, Moroso makes Buna-N gaskets that I find much more durable than the blue composite ones.
Raining non-stop here. Canceled my kid's soccer games so now I have a free day to finish welding in brackets for the Recaros I got for Christmas. Can't wait for good weather, at least the rain is clearing the salt off the roads. I did get one burn out in turning the car around.
Funny, I just got back on here to say I meant you should open up the bleed.
Good idea on running that wire up from the bottom though.
You've boxed in the problem, you need to put it somewhere in between what you have tried. Get a wire slightly smaller than what you have in the IFR and open up the bleed a touch. Take good notes so you can back off when you get confused.
One other thing, Moroso makes Buna-N gaskets that I find much more durable than the blue composite ones.
Raining non-stop here. Canceled my kid's soccer games so now I have a free day to finish welding in brackets for the Recaros I got for Christmas. Can't wait for good weather, at least the rain is clearing the salt off the roads. I did get one burn out in turning the car around.
03-29-2014, 02:45 PM
#30
That's no joke! My back hurts from leaning over the fender so much!
Since my last post I've probably had the carb apart a dozen times.
What I did was stay with the big feed restriction which ultimately proved futile. But after making about four IFR wire changes I started to get a mental picture of how one effected the other and one ALWAYS affects the other.
In the end I ended up going down on the bleed wire and up slightly on the ifr with the best combination thus far being .017" wire in both.
I was |---| close to giving up but I gotta say this last test drive and this last change has got me A/F ratios well into the "OCD needed to improve" range.
It idles 13.8 in N low 13 in gear.
At low throttle very low speed it dips into the high 12's
At what I call in town speed it's high 12-13's from 35-45mph
From there up to my fastest cruise speed of 60 it pretty much holds perfect 14-1
And at WOT on up in the rpm it appears to be in the low 13's pulling EXTREMELY hard!
No hesitations, and very responsive on the throttle.
It will fall below those ranges coasting or go above em accelerating slightly but this isn't EFI so I kinda expect that.
How rich the carb remains on such low jetting bugs me and has me wondering if it's simply too small and thus leaving quite a few unused ponies on the table. But FOR NOW I'm considering this carb tuned till at a later date I either decide to upgrade my "wires" to more perminate fixes or replace it with a bigger carb.
The final configuration ended up being...
.017" wire in the ifr and idle bleed
68 primary jets
69 secondary jets
NO powervalve
35 squirter
Since my last post I've probably had the carb apart a dozen times.
What I did was stay with the big feed restriction which ultimately proved futile. But after making about four IFR wire changes I started to get a mental picture of how one effected the other and one ALWAYS affects the other.
In the end I ended up going down on the bleed wire and up slightly on the ifr with the best combination thus far being .017" wire in both.
I was |---| close to giving up but I gotta say this last test drive and this last change has got me A/F ratios well into the "OCD needed to improve" range.
It idles 13.8 in N low 13 in gear.
At low throttle very low speed it dips into the high 12's
At what I call in town speed it's high 12-13's from 35-45mph
From there up to my fastest cruise speed of 60 it pretty much holds perfect 14-1
And at WOT on up in the rpm it appears to be in the low 13's pulling EXTREMELY hard!
No hesitations, and very responsive on the throttle.
It will fall below those ranges coasting or go above em accelerating slightly but this isn't EFI so I kinda expect that.
How rich the carb remains on such low jetting bugs me and has me wondering if it's simply too small and thus leaving quite a few unused ponies on the table. But FOR NOW I'm considering this carb tuned till at a later date I either decide to upgrade my "wires" to more perminate fixes or replace it with a bigger carb.
The final configuration ended up being...
.017" wire in the ifr and idle bleed
68 primary jets
69 secondary jets
NO powervalve
35 squirter
03-29-2014, 03:00 PM
#31
Now for some more fun information. The IFR/LSB combo is just one part of the equation. You can lean out your cruise further by reducing the main jet, then to get your WOT AFR back you drill out the power valve control restrictors. Your part throttle cruise can typically go up to 15:1 without problems.
However, since you are richer in the lower rpm cruise and it cleans up as the RPMs increase, you are correct to reduce the IFR. And, as you have learned, the IFR and LSB have an important relationship. If it were mine, I would keep reducing the size of the IFR and the LSB until your part throttle AFR becomes more even. In general, to a degree, the IFR will affect the low RPM more and the LSB will affect the upper RPM cruise more.
However, if you are going to be OCD about getting it right, I would ditch the wire game and go ahead and drill and tap the metering plate and main body for replaceable jets. Or, ditch that vacuum carburetor and get a 750 quick fuel mechanical secondary carb that already has all those features. That is what should be on the car anyway.
However, since you are richer in the lower rpm cruise and it cleans up as the RPMs increase, you are correct to reduce the IFR. And, as you have learned, the IFR and LSB have an important relationship. If it were mine, I would keep reducing the size of the IFR and the LSB until your part throttle AFR becomes more even. In general, to a degree, the IFR will affect the low RPM more and the LSB will affect the upper RPM cruise more.
However, if you are going to be OCD about getting it right, I would ditch the wire game and go ahead and drill and tap the metering plate and main body for replaceable jets. Or, ditch that vacuum carburetor and get a 750 quick fuel mechanical secondary carb that already has all those features. That is what should be on the car anyway.
03-29-2014, 03:53 PM
#36
03-29-2014, 05:25 PM
#37
If you get their SS series carbs you pick up a choke and save $100.
It will be cheaper yet if you drill your own blanks. Replaceable bleeds from quick fuel will run $4 a pair, more if you buy a set with multiple sizes. You can get a bag of 50 blanks for $7 and you will never have to worry about having the right size on hand.
Quick fuel and holley ultras are nice carbs. But hitting a swap meet and building a fully adjustable one from a used double pumper works too.
It will be cheaper yet if you drill your own blanks. Replaceable bleeds from quick fuel will run $4 a pair, more if you buy a set with multiple sizes. You can get a bag of 50 blanks for $7 and you will never have to worry about having the right size on hand.
Quick fuel and holley ultras are nice carbs. But hitting a swap meet and building a fully adjustable one from a used double pumper works too.
03-29-2014, 06:07 PM
#39
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Just a helpful tip. I picked up some plastic/nylon 10/32 set screws for getting mine set. They didnt leak and were super easy to drill vs the brass. I broke many bits drilling the brass ones and never had issues with the nylon ones.