AFR on light throttle

[FSP]

Hello,

my AFR is round 11 on boost, 13,5 whan standing still and on light throttle it gets up to 17, when going downhill with no throttle it gets over 18 in to the ---. Is that right? :ashamed:

The car is standard.

Thanks,
Martin

[Brigsy]

If it drives ok dont worry about it. If you have a slight leak on the exhaust it will appear leaner than it is.

[FSP]

Its like crousing round at 50-60mph and its red all the time and its annoying...
The carb was rebuild and maybe I can fix this..?

Thanks,
Martin

[FSP]

After a bit longer trip this are the afr readings...

On idle 13,3
Cruising in 5th gear at 70-80mph 16-18
Full boost 11

Should I be worried about the crusing readings? :ashamed:

Thanks,
Martin

[LeeR5GTT]

After a bit longer trip this are the afr readings...

On idle 13,3
Cruising in 5th gear at 70-80mph 16-18
Full boost 11

Should I be worried about the crusing readings? :ashamed:

Thanks,
Martin

If the engine likes 16-18 at cruising speed then just enjoy the extra mpg dude, although if it feels hesitant then you have an issue :agree:

[FSP]

There is some hesetation. How can i lower this afr?
Thanks,
Martin

[FSP]

Really, no one? :(

[James5]

What size jet's have you got in the carb?? main, air corrector, 1st stage, 2nd stage, needle jet?? , what boost pressure are you running? is the boost pressure at carb top or carb base? When was the carb last rebuilt

What you have I wouldn't really worry about, I take it your on boost driving was done in 4th or 5th gear it's a little rich you want to be aiming for a max of 12.1 @ WOT

Some Tips for each jet

Needle jet - this can be increased in an attempt to stop the carb fuel bowl from emptying normally when running higher boost than standard (Dependant on setup) and normally only required when a high lift cam is in use that allows higher rpm's. Standard size is 1.7 peeps increase to 2.0.

The 1st stage (the removable screw in jet that is inside the triangle enricher section) is only 1mm - if this has been increased then it'll get too rich when you give it alot of throttle, before boost comes on. Some tuners used to swap this jet around with the a/c! cheap skates, it made the fuel curve bloody horrible. standard size 1.0

The 2nd stage only comes alive after a few psi of positive boost (This is where jetting is required for on boost driving). Standard size 1.0

Normal driving is a real pig, that NEEDS a smaller main jet (so stay standard as long as you can)! Standard size 120

The air corrector does't make a huge difference at normal driving rpm's, it has more effect on boost and higher up the range (Normally reduced to around .9). Standard size 1.25

[Wallace]

Ive had problems from not setting the acclerator jet properly, have a look here on how to set it corretly.......

http://www.rtoc.org/boards/showthread.php?t=27381

Also, i run a 125main jet - as i generally just cruise (about 2k rpm) and it still gives me afr's around 16 but the car drives and feels much better........

Lets us know what you find??:agree:

[FSP]

Hello,

carb and the rest of the car is standard and carb was racently rebuild. Also boost is standard and I have no separate boost gauge, so only boost gauge at clocks. Boost gets 2nd mark from the end of marks that are wide apart.

Ill be going on a long (600 miles) trip and it will be round 400 miles highroads and thats why Im a bit :ashamed:

If the car will be ok my back wont :)

question; idle mixture screw only adjust AFR at idle?

Thanks!
Martin

[Alex]

question; idle mixture screw only adjust AFR at idle?


Yes.

[Woznaldo]

I've had a similar problem for a while now. Rebuilt my carb, fuel pump is only 4 years old and is a genuine Bosch 070. It's really frustrating as the car the stutters around cruise. The only thing that hasn't been changed in the last 8 years (including fuel lines) is the OE FPR. I'm even running my MegaSquirt 1 Extra for ignition only and still can't get past this!

[juha5gtt]

I got couple years ago lean cruise 17-18 afr.
Problem was one missing restrictor inside short
breather pipe that went behind carb.

[Woznaldo]

I got couple years ago lean cruise 17-18 afr.
Problem was one missing restrictor inside short
breather pipe that went behind carb.

Interesting? I'll check the restrictor.

[juha5gtt]

That missing restrictor can also cause "hollow breath noise"
coming from o.e airbox. Not sure about freeflow airfilter.

[Brigsy]

My gtt had a slight stutter/mis when cruising yesterday. Turned out that breather pipe from inlet had a small split on the underside. I would always check for air leaks first.

You could try changing the aei as a ign fault could cause a false lean reading/hesitation.

Sometimes its easier to up the jetting a bit where it needs more fuel and forget, instead of trying ten different fixes and nothing else works. Some engines just appear to need more fuel

[FSP]

I got couple years ago lean cruise 17-18 afr.
Problem was one missing restrictor inside short
breather pipe that went behind carb.

There are somany pipes round carb, anyone got picture wich pipe should I check? :agree:

Thanks,
Martin

[FSP]

Hello,

heres some pictures from my car, if anyone see there something wrong...

http://i156.photobucket.com/albums/t15/mrph_block/CAM007392_zps906b6abf.jpg (http://s156.photobucket.com/user/mrph_block/media/CAM007392_zps906b6abf.jpg.html)

http://i156.photobucket.com/albums/t15/mrph_block/CAM007401_zpsad5b7849.jpg (http://s156.photobucket.com/user/mrph_block/media/CAM007401_zpsad5b7849.jpg.html)

Thanks,
Martin

[juha5gtt]

That lower picture. Lower "L" shaped pipe
take it off and check any splits there should be
also small restricter inside that pipe somewhere.
Mine was near bend area. That Should be (i quess)
near " T" section of three pipes. Check also splits that pipe
that goes to turbo this one have also restricter near
plastic t-piece.

[FSP]

Thaks thanks thanks! :agree::)

[Woznaldo]

My car has been running quite lean during cruise but it has been coping ok with it until very recently. To this end I decided to check the breather pipe with the restrictor and was surprised that the hose just at slipped of the manifold!

I cleaned up the hose and put a zip tie around the restrictor to keep it in place. The hose went back on, hose clamp done up nice and tight and hey presto, the lean area is all but gone!

[FSP]

So, I changed the hose with restrictor and its still lean on crusing.
I have noticed that telephon hose got crack and hose, that conect to telephon hose alo cracked and leaking. Could this couse the lean crusing?

thanks,
M



30314

[Alex]

No that wont cause any issues.

[FSP]

In the next days ill replace all those hose. Bougt them some time ago. I did broke the T peace that goes to the hose with restrictor. :sad2:
Then Ill try mess round the acc pump thing.

[Alex]

You can do away with most of the breathers and just run a pipe to a catch tank.

[FSP]

I kind of like all those spageti under the bonet :)
I dont really understand how to adjust acc pump. Do I need to take the carb off the car or can I adjust it with a nut?

[Alex]

You need to take it off. Get yourself a 5mm drill bit and flip the carb upside down. Rest the drill bit between the throttle plate and the side of the carb and adjust the nut on the end of the pump arm until the its at the end of its travel. Once you're doing it it becomes quite obvious :)

[FSP]

Taking carb off sounds like a lot of work... :sad2:

[Trevhib]

But in practice it's not really :agree:

[Alex]

Literally a few minutes work. Carb top off, disconnect choke and throttle cables, remove the 2 coolant hosed at the base and a few boost/vacuum lines. The carb itself is held onto the manifold by 2 nuts.

[FSP]

So, I changed the hose with restrictor and its still lean on crusing.
I have noticed that telephon hose got crack and hose, that conect to telephon hose alo cracked and leaking. Could this couse the lean crusing?

thanks,
M



30314

Changed the telephone hose and no diference, just to let you know :)