Well I've found an 'interesting' behaviour of my friend's GT. If I remove my foot from the gas the mixture gets reacher not leaner as it has to. (There is a wideband gauge in it)
I have taken off the carb elbow and I can see if I push the gas the accelerator is squirting, but If I remove gas it is also squirting a bit (after a second or so).
What could be wrong?
Something similar seems to be happening on my car. When I'm driving on the motorway with the car in fifth gear and engine at 3500rpm, I gently squeeze the throttle and the AFR reads 12.1-12.3 and when I gently back off again the AFR goes down to 11.7-11.9 briefly before climbing up again.
If I put in a slightly larger throttle input, to say pass a car on a dual carriageway, the AFR will climb to 13.5-14.0?
If I go WOT the AFR will climb to 13.0 for a second before settling to 12.1-12.3, so it seems like I can only cruise or go max chat? Or is this normal for these carbs?
I was going to up the 2nd stage bush to 1.1mm because the car seems to lean on the initial application of boost?
Sorry for the hi-jack Jimmy
No hi-jack at all mate.Originally Posted by Woznaldo
Something similar seems to be happening on my car. When I'm driving on the motorway with the car in fifth gear and engine at 3500rpm, I gently squeeze the throttle and the AFR reads 12.1-12.3 and when I gently back off again the AFR goes down to 11.7-11.9 briefly before climbing up again.
If I put in a slightly larger throttle input, to say pass a car on a dual carriageway, the AFR will climb to 13.5-14.0?
If I go WOT the AFR will climb to 13.0 for a second before settling to 12.1-12.3, so it seems like I can only cruise or go max chat? Or is this normal for these carbs?
I was going to up the 2nd stage bush to 1.1mm because the car seems to lean on the initial application of boost?
Sorry for the hi-jack Jimmy
No, I do not think this behaviour is normal as my car won't make it, only my friend's one.
And this car is also leaning to the 15-15,5 if I'm gently accelerating in 3rd till 4000-4500. (Not WOT)
Maybe you should also take off the carb elbow and see how the accelerator behaves.
Check that the pump lever throw is set correctly - 5mm.
And if that makes no difference, check that the ball bearing & small brass rod within the accelerator pump jet are moving freely/not caked in crud.
Is this something I can adjust and where do I measure from?
I think I'll service the whole carb while I'm at it, that way it should eliminate any secondary problems before checking AFRs again.
James 5 has written it into another thread:
So what yo do is open the throttle with the carb removed from manifold insert the 5mm drill bit between the wall of the carb (part with the straight line gap) and let the throttle butterfly rest on the 5mm drill piece then adjust the screw if necessary so it has allowed the accel pump to be compressed.
https://www.rtoc.org/files/Technical%...n/IMG_2944.JPG
also check the ball bearing in the jet that supplies the accelerator pump circuit. - the that faces upwards in the float chamber.
Thanks guys I'll check those things.
But first I'll try a spare carb.
Can soemone please measure the height of the cylinder of the accelerator membrane?
I have found 3 pieces with 3 different heights. I think it is important to get the correct one for the 5mm drill setup.
Ah crap! Just serviced the carb and forgot about this 5mm drill bit set up and I've just put everything back on the manifold!
The service article just says do the rod nut up as far as possible but, as I was doing it, it seemed like it was wound on a lot further than it was before the service?
Do you mean 'just starting to compress' or 'fully compressed' with the 5mm drill bit in place?
'Just starting' as I know.
The end of the rod should be around 3,5mm over the nut.
With the 5mm drill bit in place it should make it fully compressed at this point.
Thinking about it, it would hard to do it the other way.With the 5mm drill bit in place it should make it fully compressed at this point.
Thank you Squire.
Yes, it was a misunderstanding from me.
It should be fully compressed.
No worries Jimmy. My carb is all back together and back on the car. I'll go out tomorrow afternoon to check AFRs and report back on this thread.
I went out for a quick blast but, didn't have a decent stretch of road to get any meaningful numbers but on the whole the AFR's seem a bit richer everywhere?
I'll head out again tomorrow afternoon for another crack (very busy week).
Please also check the AFR in 3rd accelerating from 2000 till 5000 with half (or 2/3) throttle. Thanks!I went out for a quick blast but, didn't have a decent stretch of road to get any meaningful numbers but on the whole the AFR's seem a bit richer everywhere?
I'll head out again tomorrow afternoon for another crack (very busy week
OK, been out on a test drive today and things have changed but not for the better. The car won't idle at all now. If I apply a light throttle input to keep the engine running, it does so very erratically, like it's misfiring. The AFRs are also jumping about at the same throttle setting, as is the tacho.
Out on the road, the jumps about at light constant throttle settings but, when I a gradual throttle input in, the car seems to pull cleanly most of the time? The AFRs still creep up to mid 13s but come down almost instantly to low 12s. If I try accelerating off a trailing throttle where the car has been lumpy, the car hesitates before pulling hard with the occasional misfire?
The weirdest thing now is the AFRs when I back off the throttle completely. When I did this before the AFR might go as high as 18 or 19 but now, they get 20 and then jump to 65!!!!? like no fuel is getting in at all?
To this end I checked a few things:
-The idle mixture screw - It was clean (but not sure where a good starting point is for set up?)
-Security of breather hoses - No obvious signs of leakage or looseness
-Security of Vacuum hoses - No obvious signs of leakage or looseness
-Engine Loom connector (LHS of engine bay next to header tank) - All clean but gave it a good spray with WD40 anyway
-Pulled the TDC sensor plug off the AEI - didn't tell me much other than it was properly fitted
That's all I've managed so far. Any suggestions?
I've just read this thread too.
https://www.rtoc.org/boards/showthrea...t=won%27t+idle
I'll check these bits as well.
Idle screw has been set up correctly? Is it in its place?OK, been out on a test drive today and things have changed but not for the better. The car won't idle at all now
Out on the road, the jumps about at light constant throttle settings but, when I a gradual throttle input in, the car seems to pull cleanly most of the time? The AFRs still creep up to mid 13s but come down almost instantly to low 12s. If I try accelerating off a trailing throttle where the car has been lumpy, the car hesitates before pulling hard with the occasional misfire?
The weirdest thing now is the AFRs when I back off the throttle completely. When I did this before the AFR might go as high as 18 or 19 but now, they get 20 and then jump to 65!!!!? like no fuel is getting in at all?
To this end I checked a few things:
-The idle mixture screw - It was clean (but not sure where a good starting point is for set up?)
-Security of breather hoses - No obvious signs of leakage or looseness
-Security of Vacuum hoses - No obvious signs of leakage or looseness
-Engine Loom connector (LHS of engine bay next to header tank) - All clean but gave it a good spray with WD40 anyway
-Pulled the TDC sensor plug off the AEI - didn't tell me much other than it was properly fitted
That's all I've managed so far. Any suggestions?
Have you checked your accelerator pump? Is it spraying petrol in when you move the throttle?
The dodgy idle will be down to blocked idle jet or incorrect mixture adjustment, thats why you have extremely lean afr's on overrun.OK, been out on a test drive today and things have changed but not for the better. The car won't idle at all now
Out on the road, the jumps about at light constant throttle settings but, when I a gradual throttle input in, the car seems to pull cleanly most of the time? The AFRs still creep up to mid 13s but come down almost instantly to low 12s. If I try accelerating off a trailing throttle where the car has been lumpy, the car hesitates before pulling hard with the occasional misfire?
The weirdest thing now is the AFRs when I back off the throttle completely. When I did this before the AFR might go as high as 18 or 19 but now, they get 20 and then jump to 65!!!!? like no fuel is getting in at all?
To this end I checked a few things:
-The idle mixture screw - It was clean (but not sure where a good starting point is for set up?)
-Security of breather hoses - No obvious signs of leakage or looseness
-Security of Vacuum hoses - No obvious signs of leakage or looseness
-Engine Loom connector (LHS of engine bay next to header tank) - All clean but gave it a good spray with WD40 anyway
-Pulled the TDC sensor plug off the AEI - didn't tell me much other than it was properly fitted
That's all I've managed so far. Any suggestions?
Cheers Brigsy!
I've pulled the idle jet out again and given it a good clean with carb cleaner and given the body receptacle a good blast too. Haven't chucked it back in yet.
As for the mixture screw, that was pretty clean but, gave everything a good blast with carb cleaner. Is there a basic setting start point i.e screw it in until fully home then unscrew 4 turns? Or, just set to the rough mid travel position?
2 1/2 - 3 turns out after screwed all way in (don't screw all way in as you could snap the end off just merely to where it bites quiet firm - hope this makes sense)
Last edited by James5; 16-07-2010 at 15:23.
Thanks James
Does the idle jet screw normally have a washer or o-ring under it's head?
A few more things checked:
-Pulled carb off to check gaskets and plastic spacer - all in fine condition (new)
-Removed Idle Jet and cleaned - wasn't dirty but, went through the motions
-Physically checked the carb body and visible gasket edges - all looks ok
-Set the Mixture Screw to 2.5 turns out from full home - a start point
Started the car with no problems as per usual but, the idle problem remains the same. I wound out the mixture screw gradually until I was at 3.5 turns out but, it appeared to have no effect?
The strange thing is, the car was idling fine before I pulled the carb off for the service? Could I have screwed up one of the internal gaskets and if so, which one is most likely to give a poor/no idle?
I'm going to check the ignition side of things too but, hoping it isn't this as I have NIL ignition spares. Dizzy cap and Rotor Arm are relatively new, HT leads are in good condition, TDC sensor is of unknown health other than the car runs?
And there lies the problem! Not an o-ring as such but a flat rubber ring for which there is no replacement in the service kit. I have replaced said item with an o-ring of equivalent size and it appears to have done the trick.
The original seal was in place but very hard and brittle.
I'me going to put a couple of amendments in the service article up for suggestion so that others don't make the same mistake
Nice to hear you've found the problem.And there lies the problem! Not an o-ring as such but a flat rubber ring for which there is no replacement in the service kit. I have replaced said item with an o-ring of equivalent size and it appears to have done the trick.
The original seal was in place but very hard and brittle.
I'me going to put a couple of amendments in the service article up for suggestion so that others don't make the same mistake
I'll also check that O ring.
Ok, now the idle is sorted and the car able to take the road again, I carried out some evaluation of the AFRs. Things have improved in some areas but got worse in others?
Traveling in 5th at 3500-4000 rpm, cruising AFRs are low to mid 12s, if I gently squeeze the throttle to increase speed the AFRs drop to mid to high 11s? Once I back of again gently the AFRs drop to low 10s and sometimes high 9s? before settling back to low 12s when at cruise again.
If I put a lagre throttle input in (not WOT), the AFRs climb to low to mid 13s for a second before falling to mid to low 12s.
At WOT AFRs are high 11s to low 12s.
So the set up seems to be safe, if a little rich everywhere other than WOT.
Where do I go from here? Smaller main jet or up the boost to 15-16psi (currently 13-14psi)?
What is the spec of your carb?
Some tips for you:
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! Cheapskates, it made the fuel curve bloody horrible
The 2nd stage only comes alive after a few psi of positive boost (This is where jetting is required for on boost driving).
Normal driving is a real pig, which NEEDS a smaller main jet (so stay standard as long as you can)!
The air corrector doesn’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 .
Thanks for the info James!
As for carb spec, all I can say for certain is that the Main Jet is STD and 2nd stage looks untouched, pretty sure A/C is STD too but, 1st stage is unknown?
I'll have to pull it off during the week and check.
Id check the main it could have been drilled out?? If not stg one could have been swapped/enlarged?
Afr's dont sound too bad though so i wouldnt worry too much, small turbo's do trigger the 1st/2nd stg easily at mid-high rpms as they are always wanting to boost.
Do you mean stick on a disco potato, crank it up 20psi and see how she goes?
I pulled the carb off again today and checked sizes and this is what I found:
Main Jet - 120
Air Corrector - 125 (changed for a 110 as, the end of the 125 was a bit burred)
1st Stage - 100
2nd Stage - 110
Put it all back together and reset the idle mixture. Still running rich everywhere really
Light throttle - low 12s to high 11s
gentle squeeze to mid throttle - flashes briefly (less than 0.5 sec) to mid 13s then drops to low 12s to high 11s, sometimes as rich as high 10s
WOT - high 11s to low 12s initially then getting even richer with 4th gear at 6000rpm holding high 10s to v low 11s.
I checked the orifices using my micro drill bits as go/no go gauges. I think I need a smaller main jet? Boost is currently 15 psi by my el cheapo boost gauge.
I'm going to solder up on of my larger main jets and drill to 115 and go from there. Any tips for soldering?
I've decided against the above for the time being but, might have a crack at it a bit later down the track. Mainly as my micro drill set jumps from 1.0mm to 1.2mm then 1.3mm?
Any who, just wanted to check that it's ok to get AFRs of 14-15 when the boost gauge is reading between 10-14 vacuum units (the mercury things that escape me, mm Hg I think)? As soon as the boost gauge reads zero or more positive pressure I'm getting low 12s and high 11s.
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