View Full Version : another afr carb setup issue
right me five keeps leaning off to 10,s no matter what I do.
idle is 14.6 - 14.7 which is spot on but as soon as any boost comes in its leaning right off. never had this before??
a/c 0.9
120main
2nd stage 1.2
rest of the carb is standard.
running bosch 044 cossi pump and malpassi fpr
come on boys hit me with what I can do . supposed to be a brands Tuesday coming and it aint lookin good!!
Lean at 10's or rich? Your carb specs and readings suggest it's rich.
What engine spec?
1st stage size? measure it incase it's been drilled out
Lean at 10's or rich? Your carb specs and readings suggest it's rich.
What engine spec?
sorry I mean its running really rich . its idleing spot on. then I go for a drive and as soon as it starts to boost the gauge shoots down to 10.1 . so should I add more boost??
once I let off the gas it starts to lean out again back to normal 14.6-14.7.
engine spec is pretty basic
knife edge crank,standard rods and pistons(tarabusi) prima inr cam with vernier .same came which is in there hill climb gtt, ported polished head matched inlet etc uprated springs.bms downpipe,sidey , t 25 roller 0.49 rear .
When testing or setting up afr you need to do these things.
Idle (between 13.5/14.5) that you have done.
Next test is WOT (wide open throttle) You need to do this in 4th gear with the revs sat about 1k under where it starts to boost. Nice clear bit of tarmac then foot flat to the floor and take the revs up to where you planning on revving to whilst keeping an eye on the afr (and listening for knock if you can) then see what happens with the afr.
My guess is it will be down on the 10's when you first floor the gas pedal but will then lean out as the boost/revs rise. Depending on boost if your running under 14lb flat 12 is about as lean as you want it to go. If it gets leaner than this come off the gas. For anything above 14lb you really want high 11's leanest at WOT.
Once you have done this (of if you have already) tell us what happens with the afr.
If it does start to get to lean at WOT then you can increase the second stage bush by drilling I out with some micro drill bits. To max 1.4mm, once it's done it's done and unless you tap a thread down it and use an A/C jet screwed in instead ��
Your .9 ac jet is making it rich also but if your looking to run some decent boost I would leave that as it is.
You want your malpassi set at 5/6psi base pressure(when the car is idleing) again this will be for decent boost, the o.e regulator Is 4 psi base pressure. Make sure if your upping the base pressure you use an o.e needle valve. 1.7mm.
Some cars respond better than other to upped base fuel pressure, mine is fine at 6psi but I have known people who have issues with bogging down between gears with upped base pressure.
When you have all the above sorted (if you haven't already) then you can look at the 10's afr when you apply the throttle. This is usually solved like Adam says with the first stage jet o.e is 1mm to lean it of as it comes on boost you need to reduce this jet in size. .9 or .8 or .7. Be aware tho this will make WOT leaner also. So test both. Mine has a .9 first stage and it hits 10.9/11 flat when I floor it. I didn't like anything smaller if I'm honest as it was making it a little to lean.
With a .7 first stage my afr's were in the 13's when the manifold boost said 8/9psi, I didn't like it and was paronoid about high rpm gear changes and lean spots.
Once you get that on point then you want to do a test from standing start all the way to the top of fourth gear maxing the revs in every gear and watch for lean spots inbetween gears.
Det cans are a must for big boost. A mechanics stethoscope mounted on the cylinder head then piped into the cabin with 6mm nylon hard pipe making sure it doesn't touch or rattle on things under the bonnet. If you flush however there are some dedicated knock detection devices that can be bought and are far superior to a stethoscope.
Detonation is an engine killer and sometimes even just a second of it is enough to destroy headgaskets or damage pistons or the head/valves.
It's hard work tuining on the road not to mention dangerous and I don't recommend it, a rolling road is best with some heavy load on the rollers. :agree: So it's like trying to go slightly up hill. That will build in a bit of safety with the tune.
Hope this helps and I'm sure I have missed a few things out so anyone else can feel free to add or question if they like. :)
francob80
21-08-2015, 11:15
Just to add from my recent experience.
I changed my 1st stage a few days ago from 1mm to 0.8 and then 0.9 so I can make the off boost low gear driving a little leaner as I was getting some flat 10 flat spots bogging me down when pulling off. This drastically changed my AFRs at WOT to leaning off way over 12, even saw 14 for a brief second in 4th at 6k, basically shit myself. It might of been a bit of crap that had gotten in and was blocking but I decided to put the 1st stage back to 1mm and gave the carb a good blast with carb cleaner.
No back to mid 11 at WOT at 6.5k.
Current set up;
285 cam
GT2560r
22psi
Tubular manifold
2.5 inc down pipe
2.5 sidey
Front mount
Malpassi set at just under 6psi
Current carb;
1.2main
0.9 AC
1mm 1st stage
1.3 2nd stage
0.46 idle
1.7mm needle valve
As Phil mentioned above, I am one of the people suffering with severe bogging down between gear changes, mainly noticeable between 3rd & 4th gear change, changing up at 6k plus and the car just bogs for a second or two but it's enough to make a difference. I'm not sure how to resolve so going to try a few different carbs with similar specs to see if the actual carb is the issue.
right well im following the stages but im getting no where fast. iv fitted a freshly built standard carb now. one of mikes specials. im no getting 16.5 at idle and 13s on boost. im looking to run 16psi but having issues.
is there anyone available to help me try and attempt to set the carb up?? im getting no where on my own. im in southend on sea and have now taken the day off work tomorrow to try sort it.
if anyone can help please drop me a pm. im happy to drive to meet someone etc as it runs on 14,s at 40mph.
iv tried getting booked in at atspeed and a few other places with no luck.....
francob80
21-08-2015, 21:55
So what is your current carb set at now ? What is your malpassi set to ?
running the malpassi fpr009 - im getting 6psi
I belive the regulator allows its own flowand it isn't adjustable??
im trying 2 carbs as im getting nowhere.
so I have a standard carb fully rebuilt with standard jets from mike aka gtturbospares.
I cant get that on to idle anywhere near 14,s its currently running at 16.6-17,s .no matter how I adjust the mixture screw or idle it has no effect.....
the carb is like new and in perfect order.
the second I was trying is a home rebuilt carb.
again standard base but 120main,0.9a/c,2nd stage 1.2mm
idles perfect at 14.7 afr drives at 30-40mph at 14,s but when on boost runs really rich at 10,s ....
im running 16psi ....on a t25 rollerbearing with 0.49 rear
francob80
21-08-2015, 22:16
Have you not considered running more boost? Perhaps 18/19 ? Will potentially get your on boost 10s to more like mid 11s which is where you want to be. Using the second carb you mention.
What is your 1stage on the second carb ?
francob80
21-08-2015, 22:17
Also you could reduce your malpassi slightly, perhaps down to 5psi. My understanding of the purpose of a malpassi is for high boost applications where the carb bowl is emptying. Logically if you are only running 16psi you may not need to run as high as 6psi which is why it's showing too rich at WOT.
francob80
21-08-2015, 22:22
[QUOTE=Milky;396982]running the malpassi fpr009 - im getting 6psi
I belive the regulator allows its own flowand it isn't adjustable??
FPR009 IS adjustable.
I will have a play in the morning . I really didn't want to run 18psi but makes sense to if its going to fuel better. I will also tweak the malpassi a touch 1psi at a time.
thanks for the help:agree:
been a long day.
francob80
21-08-2015, 22:38
To be honest it doesn't sound like you are too far off. Either reduce fuel pressure down a bit and keep 16psi or run a bit more boost.
Let me know how you get on.
Worth adding that on mine malpassi didn't need much lowering, I'd do 1/2 psi at a time.
Good luck.
To be honest it doesn't sound like you are too far off. Either reduce fuel pressure down a bit and keep 16psi or run a bit more boost.
Let me know how you get on.
Worth adding that on mine malpassi didn't need much lowering, I'd do 1/2 psi at a time.
Good luck.
will post up tomorrow the outcome:D
cheers pal:agree:
iv ran the carb at 15psi and 22psi with the same outcome. would seem it runs at its best at 22psi but at 5k it bottles out regardless of boost pressure. has now started to hunt at idle too :cry:
trying to upload the video with no luck
so malpassi is set to 4 1/2 psi ,idle afr stil 14.1-14.7 . as said boosted at 15 and 22psi .
from watching the video .it seems to boost all the way to 5k at 11.2afr then appears to cut out and lean right off??
you say bosch 044 pump, what about filter? new or old, cheap or quality?
you say bosch 044 pump, what about filter? new or old, cheap or quality?
yeah 044 pump sytec 30 micron filter plus inline filter. all new and not cheap.getting 7psi before fpr and 4 1/2psi to the carb.
I personally wouldn't run any type of filter other than the o.e one in the fuel system, I even binned the small filter in the carb fuel hose union. The bowl emptying at 5k is way way to early the extra filters might be the cause.
I run a cheapy sytec efi pump with o.e filter my bowl stays full @ 22psi (manifold) beyond 7k rpm in fourth with 6psi base pressure.
I would up the malpassi to 5psi, get rid of any extra filters and for what it's worth for 22psi I would use this carb spec
120 main
1.4mm second stage
.9 a/c
1mm first stage
1.7mm needle valve
For 16psi I would leave the base pressure at 4.5psi
120 main
1.3mm second stage
1mm a/c
2mm needle valve
Trouble with banding carb specs about is that every engine is different and may require different carb specs.
Keep going with it :agree: Once its sorted it's well worth the effort.
francob80
23-08-2015, 15:45
Phil,
That little filter in the carb union, not required then ? Potentially restrictive ?
With the fresh standard carb and dodgy looking AFRs, I'm wondering if there are other maybe issues causing the problems?? Maybe if an OE fuel pressure reg could be hooked up, if the AFRs were still out, maybe there is another problem with air/fuel that's not carb related?
next thing to check is your drill bit sizes match the box.
Vernier caliper or micrometer the drill bits confirm a 1.3 is actaully 1.3 and not 1.4 or higher
Phil,
That little filter in the carb union, not required then ? Potentially restrictive ?
Some like to keep it but I binned mine years ago in a bid to try and eliminate every potential restriction in the fuel supply to the carb. I have never had any issues.
francob80
24-08-2015, 16:46
Some like to keep it but I binned mine years ago in a bid to try and eliminate every potential restriction in the fuel supply to the carb. I have never had any issues.
Good to know, I will try also.
minor update!
been to an old pal. we done a fuel pressure check and turns out 30 - 60 micron race filters do cause an issue!i was getting 4.5psi to the carb but when under load (16psi boost)the pressure was downing to 3psi...... we removed the filter and fitted a regular inline filter and as if by magic pressures were back up!
a lesson well learnt and a massive thanks to everyone that's helped. I was very stressed out as iv tweaked fives before and never had this issue. iv always understood that setting them up isn't overly easy without a rolling road.
so now back onto my 2nd rebuilt carb with the drilled 2nd stage - results now are
14.2 -14.6 afr at idle
on boost at 20psi - 10.8 afr
4.8psi fuel pressure
this is at wot, 4th gear to 6,800rpm
and pleased to say no carb emptying that we feel or can detect :agree:
no idea what power im running but I will have it properly setup on a rolling road soon and report back!
been a headache but as I was told was worth the work.
thanks again
Good stuff, room for a few more psi with the fuel and rr would be the best shout by far, one that can monitor for DET.
Or if this is with the .9 ac you could up that to 1mm to lean it off a little if your happy with the boost. It will make more power at 11.8 than 10.8 ;)
Nice one Milky :) Always a relief to find the cause of a sneaky problem like this one :agree:
thanks boys:agree:
cant belive that a fuel filter would cause such an issue!!! but there you go. always learning :D
bloody expensive filters too.
Good stuff, room for a few more psi with the fuel and rr would be the best shout by far, one that can monitor for DET.
Or if this is with the .9 ac you could up that to 1mm to lean it off a little if your happy with the boost. It will make more power at 11.8 than 10.8 ;)
have fitted 1mm a/c today :agree:
cheers pal
Matt Cole
01-09-2015, 10:01
A nice rolling road graph would be good now!:D
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