Boost+Carb+FPR Fuel issue.
11-11-14, 03:27 PM
#1
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Boost+Carb+FPR Fuel issue.
Hi guys, I'm having a problem on going dry (lean) at sustained high RPM's after 3rd gear (1/4mi pass). I have a Boost referenced FPR, it is set atmospheric and at 6.5 psi.
I 'THINK' the bowls might be going dry, and want to try raising the fuel pressure in less than 1:1 ratio.
Explanation: I'm running 10psi boost, if i go 1:1 it will raise fuel pressure 20psi+.
I'm getting the boost signal from the charge pipe, because if its taken from after the throttle the vacuum makes the FPR go 0psi
can I use a boost controller to lower that 1:1 ratio? maybe 2boost:1fuel?
I know the jetting is OK, because the A/FR is on the 11.5-12 on 1st-2nd-3rd @ 10psi + H2O/Meth
any other thing i might not be thinking of?
maybe take signal from manifold + check valve (to avoid vacuum) + boost controller to go 2psi boost : 1 psi fuel ??
Thanks in advance
I 'THINK' the bowls might be going dry, and want to try raising the fuel pressure in less than 1:1 ratio.
Explanation: I'm running 10psi boost, if i go 1:1 it will raise fuel pressure 20psi+.
I'm getting the boost signal from the charge pipe, because if its taken from after the throttle the vacuum makes the FPR go 0psi
can I use a boost controller to lower that 1:1 ratio? maybe 2boost:1fuel?
I know the jetting is OK, because the A/FR is on the 11.5-12 on 1st-2nd-3rd @ 10psi + H2O/Meth
any other thing i might not be thinking of?
maybe take signal from manifold + check valve (to avoid vacuum) + boost controller to go 2psi boost : 1 psi fuel ??
Thanks in advance
11-12-14, 12:13 AM
#2
Hi guys, I'm having a problem on going dry (lean) at sustained high RPM's after 3rd gear (1/4mi pass). I have a Boost referenced FPR, it is set atmospheric and at 6.5 psi.
I 'THINK' the bowls might be going dry, and want to try raising the fuel pressure in less than 1:1 ratio.
Explanation: I'm running 10psi boost, if i go 1:1 it will raise fuel pressure 20psi+.
I'm getting the boost signal from the charge pipe, because if its taken from after the throttle the vacuum makes the FPR go 0psi
can I use a boost controller to lower that 1:1 ratio? maybe 2boost:1fuel?
I know the jetting is OK, because the A/FR is on the 11.5-12 on 1st-2nd-3rd @ 10psi + H2O/Meth
any other thing i might not be thinking of?
maybe take signal from manifold + check valve (to avoid vacuum) + boost controller to go 2psi boost : 1 psi fuel ??
Thanks in advance
I 'THINK' the bowls might be going dry, and want to try raising the fuel pressure in less than 1:1 ratio.
Explanation: I'm running 10psi boost, if i go 1:1 it will raise fuel pressure 20psi+.
I'm getting the boost signal from the charge pipe, because if its taken from after the throttle the vacuum makes the FPR go 0psi
can I use a boost controller to lower that 1:1 ratio? maybe 2boost:1fuel?
I know the jetting is OK, because the A/FR is on the 11.5-12 on 1st-2nd-3rd @ 10psi + H2O/Meth
any other thing i might not be thinking of?
maybe take signal from manifold + check valve (to avoid vacuum) + boost controller to go 2psi boost : 1 psi fuel ??
Thanks in advance
If your AFR's are solid through 3rd and you're leaning out in 4th, that would make me suspect the fuel pump can't keep up with the demand.
11-12-14, 10:07 AM
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That's an interesting idea. But I don't see why you would want less than a 1:1 ratio. The point of a referenced FPR is to maintain fuel pressure to the carb by compensating for boost pressure. Any less than 1:1 and you're going to lean out pretty fast.
If your AFR's are solid through 3rd and you're leaning out in 4th, that would make me suspect the fuel pump can't keep up with the demand.
If your AFR's are solid through 3rd and you're leaning out in 4th, that would make me suspect the fuel pump can't keep up with the demand.
A little about the engine, it has a .63cold / .82 hot garrett turbo with OBX external WG and Greddy BOV. Also FMIC and blowing 10psi boost.
The carburetor is a Mighty Demon DP Blow Thorough 650CFM. Engine, I believe its a Cosmos 13b. locked dizzy and premix 1oz:2gal. 50/50 water/meth injection boost activated at 5psi.
yes, i know about the Demon carbs in rotaries, but i haven't had a problem with it. I'm just concerned with it going lean on high 3rd and 4th gear.
every thought and help its greatly appreciated
11-12-14, 01:49 PM
#4
I had a problem with going way too rich on my setup so I looked into ways of correcting it. Maybe some of this info will be helpful to you. Here's my setup:
boost prepped Nikki
mallory 4309 connected to carb hat
MSD 2225 EFI fuel pump rated at 43psi or something like that
3/8" fuel send line, stock 5/16" return (I know this is wrong and will correct it soon)
Blitz BOV
AEM EUGO wideband
stock S5 turbo spaced out 7/16" to clear the intake manifold
full 3" exhaust
My carb would flood out any time I'd drive it spiritedly whether in boost or still in vacuum. Any time the turbo would spool it would cause the mallory to push too much fuel into the carb. Nikkis only want 2.5psi so you can see I have a setup that is potentially easy to flood. The wideband would read 10.0 and run all sputtery for a while until the excess fuel was used up. It really gets bad when the fresh installed needles would get slightly hung up inside the seats. They need time to "burnish" in. So some of this floodiness will improve with time, but some of it won't until the fuel lines are corrected. Mallory states in their instructions to use 5/16" send and 3/8" return. Ok I'll do that when the weather warms up again.
But maybe I can get rid of some of the annoying tendency to flood in the mean time. I searched a lot, asked a lot of questions, and tried a few things. The first thing I tried was to follow some advice I saw on this forum mentioned by Robert at Rotary Shack. If that gets censored, his shop's name sounds like Radio Shack. He was helping out a guy who bought some boost prepped weber DCO or DCOE stuff from him. He said to hook the mallory to the intake manifold so it could see vacuum AND boost. The thread is around here somewhere but I'm not going to search for it at the moment. But you can if you feel like it.
Another very good reason to hook it up to the manifold was in Mallory's instructions that come with the 4309! That's what they say to do!
So I hooked the mallory to the manifold. The floody problem was gone! And it ran so lean it would have popped the engine had I been in boost. D'oh! It ran similar to when it flooded out (sputtered, lost power) but I saw 17.8, 17.9, 18.0 and then --- on the gauge. Scary. Ok, it never did that when it was hooked to the carb hat.
I reasoned that as the pressure makes its way through the carb past the venturis etc, there is a pressure drop, therefore if I had two boost gauges; one on the carb hat and compared it to the manifold, there would be a difference. Enough of a difference that it influences the mallory a lot. But I did notice it would still go somewhat rich sometimes - just not when you needed it to driving up a steep hill. It made the fuel pump seem way too small, like back when I had a crappy Facet on the REPU. What a piece of garbage that pump was (recommended and sold by RB if you can believe it).
So what I learned is the pressure drop through the carb could be useful if I could recreate it in a more linear controllable way. Just a way to trim or delay it a little so during spirited driving still in vacuum the mallory won't flood the carb out every time, but once it spools up enough to start producing positive pressures under the carb where the boost gauge is reading from, it will provide the extra fuel necessary to keep the engine alive.
What did I come up with? A calibrated boost leak! Click to see picture. https://www.rx7club.com/attachments/...i-img_1353.jpg
I took an old damaged primary slow air bleed from a Nikki, drilled out the tiny hole at the bottom and relied on the somewhat larger hole at the top to bleed off some pressure while the engine is at low RPM but at highish load like when I'm driving it spiritedly through the gears but not getting into boost. This did the trick! I hooked it in the line between the carb hat and the mallory with a simple plastic T fitting at like 3/16 using a common Mazda vacuum line. I just ground down the threads a little and shoved it in. When you free rev the engine you can feel a healthy tiny stream of air coming out of the small end which I leave out so it can be grabbed with pliers. It's in deep enough boost pressure can't push it out.
Sorry I don't have pics of it installed in the engine bay but it's easy to imagine. Just inline with a Tee fitting. Extremely simple device but it solved almost all of my flooding problems. All that's left is to redo the fuel lines which should solve the rest of my problems.
Oh and don't worry about introducing a boost leak into your system and having it negatively affect performance or not let the mallory go as rich as it needs to, to keep the engine from exploding. This leak is so small and there is so much abundant air pressure available from a turbo, I haven't noticed anything negative (this leak is in the line leading to the mallory, not tapped from somewhere else. This seems correct to me). In fact the car has actually gotten more powerful since this mod. It can now break them loose in 3rd gear where before it could only do it in 2nd going up my "test hill". Also the carb goes so rich in boost I'm seeing 10.0 on the wideband and some of the carbs start to sputter mildly up there while others don't. I'm calling this one "secondary tuning needed now," not a problem with the mallory still getting too much boost signal as before. I think the tiny calibrated boost leak fixed that problem and now the carbs just need secondary tuning as they are still on a factory tune which is going to be different from a boost tune - I've discovered that little tidbit on the primary circuits which needed turbo tuning just so the carbs would be driveable in boost in order to get me to where I'm at now. Does that make sense? The rest is in the fuel lines, I'm sure.
I hope this was helpful. Maybe you and I are experienceing the same thing? Or maybe your setup needs a much different approach. I don't know anything about the carb you're using but the basics should be similar enough, right? They're both carbs being force fed.
boost prepped Nikki
mallory 4309 connected to carb hat
MSD 2225 EFI fuel pump rated at 43psi or something like that
3/8" fuel send line, stock 5/16" return (I know this is wrong and will correct it soon)
Blitz BOV
AEM EUGO wideband
stock S5 turbo spaced out 7/16" to clear the intake manifold
full 3" exhaust
My carb would flood out any time I'd drive it spiritedly whether in boost or still in vacuum. Any time the turbo would spool it would cause the mallory to push too much fuel into the carb. Nikkis only want 2.5psi so you can see I have a setup that is potentially easy to flood. The wideband would read 10.0 and run all sputtery for a while until the excess fuel was used up. It really gets bad when the fresh installed needles would get slightly hung up inside the seats. They need time to "burnish" in. So some of this floodiness will improve with time, but some of it won't until the fuel lines are corrected. Mallory states in their instructions to use 5/16" send and 3/8" return. Ok I'll do that when the weather warms up again.
But maybe I can get rid of some of the annoying tendency to flood in the mean time. I searched a lot, asked a lot of questions, and tried a few things. The first thing I tried was to follow some advice I saw on this forum mentioned by Robert at Rotary Shack. If that gets censored, his shop's name sounds like Radio Shack. He was helping out a guy who bought some boost prepped weber DCO or DCOE stuff from him. He said to hook the mallory to the intake manifold so it could see vacuum AND boost. The thread is around here somewhere but I'm not going to search for it at the moment. But you can if you feel like it.
Another very good reason to hook it up to the manifold was in Mallory's instructions that come with the 4309! That's what they say to do!
So I hooked the mallory to the manifold. The floody problem was gone! And it ran so lean it would have popped the engine had I been in boost. D'oh! It ran similar to when it flooded out (sputtered, lost power) but I saw 17.8, 17.9, 18.0 and then --- on the gauge. Scary. Ok, it never did that when it was hooked to the carb hat.
I reasoned that as the pressure makes its way through the carb past the venturis etc, there is a pressure drop, therefore if I had two boost gauges; one on the carb hat and compared it to the manifold, there would be a difference. Enough of a difference that it influences the mallory a lot. But I did notice it would still go somewhat rich sometimes - just not when you needed it to driving up a steep hill. It made the fuel pump seem way too small, like back when I had a crappy Facet on the REPU. What a piece of garbage that pump was (recommended and sold by RB if you can believe it).
So what I learned is the pressure drop through the carb could be useful if I could recreate it in a more linear controllable way. Just a way to trim or delay it a little so during spirited driving still in vacuum the mallory won't flood the carb out every time, but once it spools up enough to start producing positive pressures under the carb where the boost gauge is reading from, it will provide the extra fuel necessary to keep the engine alive.
What did I come up with? A calibrated boost leak! Click to see picture. https://www.rx7club.com/attachments/...i-img_1353.jpg
I took an old damaged primary slow air bleed from a Nikki, drilled out the tiny hole at the bottom and relied on the somewhat larger hole at the top to bleed off some pressure while the engine is at low RPM but at highish load like when I'm driving it spiritedly through the gears but not getting into boost. This did the trick! I hooked it in the line between the carb hat and the mallory with a simple plastic T fitting at like 3/16 using a common Mazda vacuum line. I just ground down the threads a little and shoved it in. When you free rev the engine you can feel a healthy tiny stream of air coming out of the small end which I leave out so it can be grabbed with pliers. It's in deep enough boost pressure can't push it out.
Sorry I don't have pics of it installed in the engine bay but it's easy to imagine. Just inline with a Tee fitting. Extremely simple device but it solved almost all of my flooding problems. All that's left is to redo the fuel lines which should solve the rest of my problems.
Oh and don't worry about introducing a boost leak into your system and having it negatively affect performance or not let the mallory go as rich as it needs to, to keep the engine from exploding. This leak is so small and there is so much abundant air pressure available from a turbo, I haven't noticed anything negative (this leak is in the line leading to the mallory, not tapped from somewhere else. This seems correct to me). In fact the car has actually gotten more powerful since this mod. It can now break them loose in 3rd gear where before it could only do it in 2nd going up my "test hill". Also the carb goes so rich in boost I'm seeing 10.0 on the wideband and some of the carbs start to sputter mildly up there while others don't. I'm calling this one "secondary tuning needed now," not a problem with the mallory still getting too much boost signal as before. I think the tiny calibrated boost leak fixed that problem and now the carbs just need secondary tuning as they are still on a factory tune which is going to be different from a boost tune - I've discovered that little tidbit on the primary circuits which needed turbo tuning just so the carbs would be driveable in boost in order to get me to where I'm at now. Does that make sense? The rest is in the fuel lines, I'm sure.
I hope this was helpful. Maybe you and I are experienceing the same thing? Or maybe your setup needs a much different approach. I don't know anything about the carb you're using but the basics should be similar enough, right? They're both carbs being force fed.
11-14-14, 05:18 AM
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I idle on 10.5 a/fR 8 ( and with the methanol it doesn't help while under boost... cop wise, It spits "skittles" out the back (a rainbow of flames lol)
I've thought of changing the bov to a synapse. The one that stays open while on vacuum, it might help idle tunning a lot.
Back on topic, I'll try that leak on the AFR boost line, it should bring down the pressure being registered by the fpr, before investing on a boost controller.
Tnx for the reply, its awesome to know that other people think outside of the box when it comes to something serious (boost
). I'll let know after testing.
I've thought of changing the bov to a synapse. The one that stays open while on vacuum, it might help idle tunning a lot.
Back on topic, I'll try that leak on the AFR boost line, it should bring down the pressure being registered by the fpr, before investing on a boost controller.
Tnx for the reply, its awesome to know that other people think outside of the box when it comes to something serious (boost
). I'll let know after testing.
11-14-14, 05:20 AM
#6
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Just thought about this, rising the secondaries float... would it help?
Demons have too many adjustments, that's why I'm asking before diving into it and have to reconfigure the whole thing.
Tnx
Demons have too many adjustments, that's why I'm asking before diving into it and have to reconfigure the whole thing.
Tnx
11-14-14, 07:53 AM
#7
carb whisperer
But it sounds to me like the carb is drinking all available fuel. What kind of fuel rail are you running on this? I assume dual inlet being a demon carby, but your basic fuel rail can screw you if it wasnt made to split fuel flow properly. Most of them tend to feed the primary bowl about 40% better than the secondary, which is pretty dumb. A lot of guys in the high end NoS/Boost engines run those typical rails in reverse for just that reason.
Any pictures of your setup would help us a good bit, as it could be a glaringly obvious delivery to carb issue.
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11-14-14, 09:43 AM
#8
Originally Posted by ShawnMua
before investing on a boost controller.
The three sizes I've tried so far are:
.46mm (seemed too small)
.66mm (just about right on some carbs but too small on others)
1.00mm (correct on one carb but a little big on others making them take too long to start receiving additional fuel pressure from the mallory)
If you make this calibrated boost leak adjustable, it makes life a lot easier than just one hole size fits all.
11-24-14, 12:18 PM
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Engine Bay Pictures 
a little crowded, but its ok
^^The secondaries fuel line is like that because the original line wouldn't fit, turbo too high.
also, before I get the question, the 'orange insulation looking thing wrapping the charge pipe' its aircraft grade insulation.
any more thoughts? rising the secondary floats helped.
a little crowded, but its ok
^^The secondaries fuel line is like that because the original line wouldn't fit, turbo too high.
also, before I get the question, the 'orange insulation looking thing wrapping the charge pipe' its aircraft grade insulation.
any more thoughts? rising the secondary floats helped.
11-25-14, 07:53 AM
#12
Full Member
Check this site out. They have details and pics of what it takes to make a holley/demon blow thru. Good info here. Hope it helps
http://www.hangar18fabrication.com/blowthru.html
http://www.hangar18fabrication.com/blowthru.html
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