Mikuni issue, AFRs
08-08-10, 01:17 PM
#1
Mikuni issue, AFRs
I have a streetported 6pt S5 motor that is using the mikuni 44 phh style (weber dcoe style) and I just can't get the AFRS to what I want.
my idle is at a cool 1000rpm around 12.5-9:1 AFR
transitioning is flawless works great and no stumbles
WOT above 3k it pegs 10:1 but it may be richer than that since thats as rich as the AEM UEGO reads.
if you hold the RPM at 3 or 4krpm in neutral it runs about 11:1 (so basically I'm just pouring out black smoke)
cruising speeds and maintaining speeds is 10.8 to 11.4:1
Is there a way to adjust the float level on this style? or are my jets too big?
I've tried adjusting the fuel pressure from 3.5 to 4.5 and it doesnt seem to make a different (and anywhere in between)
I'm also having a hard time starting it since it doesn't have a choke, did you guys rig up one on the starter disc or what do you all do to get it to start when the engine is cold?
my idle is at a cool 1000rpm around 12.5-9:1 AFR
transitioning is flawless works great and no stumbles
WOT above 3k it pegs 10:1 but it may be richer than that since thats as rich as the AEM UEGO reads.
if you hold the RPM at 3 or 4krpm in neutral it runs about 11:1 (so basically I'm just pouring out black smoke)
cruising speeds and maintaining speeds is 10.8 to 11.4:1
Is there a way to adjust the float level on this style? or are my jets too big?
I've tried adjusting the fuel pressure from 3.5 to 4.5 and it doesnt seem to make a different (and anywhere in between)
I'm also having a hard time starting it since it doesn't have a choke, did you guys rig up one on the starter disc or what do you all do to get it to start when the engine is cold?
08-08-10, 07:47 PM
#2
I am no expert but it sounds like you are just jetted too rich to me.
Mine starts just fine with no choke using the "enriching circuit" or whatever they call it. ( I did have to learn to keep my foot off the pedal, starts fine unless you pump the gas, if you do, it floods)
I would get a manual so that you can make sure your floats and pressures are correct.
Mine starts just fine with no choke using the "enriching circuit" or whatever they call it. ( I did have to learn to keep my foot off the pedal, starts fine unless you pump the gas, if you do, it floods)
I would get a manual so that you can make sure your floats and pressures are correct.
08-09-10, 07:51 AM
#3
If you hook up the choke cable to the starter disc it works like a stock Nikki. What are you jet sizes? You should see around 10-11 afrs at idle but they should be nearer 13-13.5 once your off the idle circuit and cruising. Leave the floats alone and go for smaller jets. You should be able to get your idle down to 750.
Idle afrs are controlled by the pilot jets, main jets control afrs past 20% throttle, iirc. Wolfcreekracing.com has photocopy manuals and parts.
Idle afrs are controlled by the pilot jets, main jets control afrs past 20% throttle, iirc. Wolfcreekracing.com has photocopy manuals and parts.
08-09-10, 11:49 AM
#4
I have the mikuni PHH manual and I've read through it a few times.
see the problem is, I don't know my jet sizes. I bought this carb off someone who had it already tuned for a streetport 13b, is there a way that I can check my jet size? is it written on the jet or do I have to measure something?
I have my idle at 800-1000rpm depending on my electrical load
its an s5 streetport in an s4 2nd gen with this side draft set up actually, so there was no stock nikki, just fuel injected. I dont know if it differs from being carb to EFI for idle AFR but it is significantly richer at a carb.
right now though I think it is misfiring a bit, it could be the nappa brand spark plug wires, but I'm not sure. Its a big PITA for some reason to get plug wires that aren't total **** and will either stay on the dizzy or coils from local parts stores, they just kept popping off...
I wish cruising at 13s afr, it does 10.8 to 11.5
see the problem is, I don't know my jet sizes. I bought this carb off someone who had it already tuned for a streetport 13b, is there a way that I can check my jet size? is it written on the jet or do I have to measure something?
I have my idle at 800-1000rpm depending on my electrical load
its an s5 streetport in an s4 2nd gen with this side draft set up actually, so there was no stock nikki, just fuel injected. I dont know if it differs from being carb to EFI for idle AFR but it is significantly richer at a carb.
right now though I think it is misfiring a bit, it could be the nappa brand spark plug wires, but I'm not sure. Its a big PITA for some reason to get plug wires that aren't total **** and will either stay on the dizzy or coils from local parts stores, they just kept popping off...
I wish cruising at 13s afr, it does 10.8 to 11.5
08-09-10, 05:43 PM
#7
BS, I ran a 44 on my 12A 1/2 sp-1/2bp. Granted a 48 mm Weber would be a better carb but the 44 will do the job. Pull your mains and post the jet sizes. Post the pilot jet while you're at it. What are you running for a fuel pump and regulator?
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08-09-10, 05:55 PM
#9
I have a holley blue pump (loud as ****) and a holley 1-4psi low pressure regulator
the engine build is as follows
S4 6pt NA housings pineapple racing streetported w/ polished turbo inserts
racing beat collected exhaust (street)
S5 6pt NA irons w/ pineapple racing large streetport
RB Aluminum flywheel
S5 rotating assembly
RA soft seals
RA classic apex seals
port/gasket matched LIM
RB side draft manifold adapter
oil pan baffle (not relevant but neat)
I'm going to pull the jets tonite, I'm not very fond of the holley pump. I may switch to the mallory comp 70.
I was having some drive ability issues today on my way home from work. didn't feel like it was receiving enough fuel off the line at some lights.
the engine build is as follows
S4 6pt NA housings pineapple racing streetported w/ polished turbo inserts
racing beat collected exhaust (street)
S5 6pt NA irons w/ pineapple racing large streetport
RB Aluminum flywheel
S5 rotating assembly
RA soft seals
RA classic apex seals
port/gasket matched LIM
RB side draft manifold adapter
oil pan baffle (not relevant but neat)
I'm going to pull the jets tonite, I'm not very fond of the holley pump. I may switch to the mallory comp 70.
I was having some drive ability issues today on my way home from work. didn't feel like it was receiving enough fuel off the line at some lights.
08-09-10, 06:10 PM
#10
Im running the mallory and I am happy with it, its not the most quiet though, I have been thinking about adding some vibration isolation to the mount to make it more quiet.
However the holley blue and the pressure regulator you mentioned will do the job for you. I dont think they are your issue. (That is to say that your pressures may need to be adjusted).
However the holley blue and the pressure regulator you mentioned will do the job for you. I dont think they are your issue. (That is to say that your pressures may need to be adjusted).
08-09-10, 06:17 PM
#11
I'm not foreign to mechanic work or rotaries by any means. Its just that when you have a pump moving fluid for a specific rate it should have the same motor tone/pitch, well I keep hearing this one change its tone or pitch during driving as if it was partly sucking in air, but mine is mounted to the spare tire wheel well and the bottom of the pump inlet and out are below the gas tank entirely. I bought the pump used too so... you get what you pay for? its just acting very weird today...
08-09-10, 06:38 PM
#12
well here was my drive ability problem...
I remove my cover to see this....
I wonder if the solid trans/engine mounts helped shake that free.
main air jet is 210 (maybe 270, hard to read)
main jet is 200
pilot jet is 62.5 or 625
(hard to read)
hope the helps
I remove my cover to see this....
I wonder if the solid trans/engine mounts helped shake that free.
main air jet is 210 (maybe 270, hard to read)
main jet is 200
pilot jet is 62.5 or 625
(hard to read)
hope the helps
08-09-10, 10:10 PM
#14
No wonder it runs rich. Try this combo: Main air-240, Main jet-175, Pilot 57.5. That's the combo I had on a 44 setup for a 13B and what I ran on the 1/2sp-1/2bp. Even then it was a bit rich and the engine didn't draw a lot of vacuum due to the overlap from the 1/2 bridge.
08-09-10, 10:24 PM
#15
WOT above 3kprm is 12.1 AFRish, better but still too rich I should see 12.5-13.0:1 for optimal power and I still would like cruising speeds not be as rich.
I'm still working on it at from off line lean bogging with moderate throttle. I haven't tried adjusting the accelerator pump but I'm also wondering if it is with my fuel setup.
Do you guys run a return or returnless fuel setup on yours? And where is a good place to purchase jets? I didn't see anywhere on wolf creeks website for jetting.
08-09-10, 11:08 PM
#16
I run a return line with a small jet (cant remember the size) in the return line to restrict the return.
Wolf Racing has the jets. Call them if you dont see them in their catalogue.
You can also find them on E-bay HOWEVER you have to know what they look like as e-bay is covered up with motorcycle mikunis, so you have to pick out the ones for the phh, like I said you have to know what they look like.
Wolf Racing has the jets. Call them if you dont see them in their catalogue.
You can also find them on E-bay HOWEVER you have to know what they look like as e-bay is covered up with motorcycle mikunis, so you have to pick out the ones for the phh, like I said you have to know what they look like.
08-10-10, 03:09 PM
#20
I was using a return fed system and everything was fine but with my gas tank full and this hot of days I was only getting fuel pressure to the carb if I pinched the return line. the fuel was taking the path of least resistance, I am wondering if it is a return/feed line location on the chassis that varies from the 1st to 2nd gen causing this.
Although, I had it set up as a return way before and it was fine and viewing pressure to the carb. oh well...
So I plugged that and now it is a non return way and it seems to run much better and consistent, wot is mid-high 12s now, cruising speed afrs are still the same.
Although, I had it set up as a return way before and it was fine and viewing pressure to the carb. oh well...
So I plugged that and now it is a non return way and it seems to run much better and consistent, wot is mid-high 12s now, cruising speed afrs are still the same.
08-18-10, 05:18 PM
#24
Okay I ordered those jets and played with them a little bit.
replaced the fuel jet and kept the pilot and main air but it ran too lean, mid to high 13s AFR under WOT
so I put the 200 main fuel back in and repalced the main air with the 175 and it liked it alot better, about 12.8-13.1 AFR which is exactly where I need to be at but it hesitates at sudden acceleration because it leans out.
now I was reading the manual and its because the fuel is denser than air and the accelerator pump is used to overcome this during 0 to 30% throttle. I'm reading it and I see that I can adjust the rod but it is unclear.
turn clockwise = more fuel?
turn counterclockwise = less fuel?
can someone correct me because when I go to step on it the response got worse but when the fuel load catches up it makes great AFRs I just don't want to be WOT that lean until the fuel catches up.
fuel pressure is set to 4psi.
replaced the fuel jet and kept the pilot and main air but it ran too lean, mid to high 13s AFR under WOT
so I put the 200 main fuel back in and repalced the main air with the 175 and it liked it alot better, about 12.8-13.1 AFR which is exactly where I need to be at but it hesitates at sudden acceleration because it leans out.
now I was reading the manual and its because the fuel is denser than air and the accelerator pump is used to overcome this during 0 to 30% throttle. I'm reading it and I see that I can adjust the rod but it is unclear.
turn clockwise = more fuel?
turn counterclockwise = less fuel?
can someone correct me because when I go to step on it the response got worse but when the fuel load catches up it makes great AFRs I just don't want to be WOT that lean until the fuel catches up.
fuel pressure is set to 4psi.
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