Carb help needed ?
Turbo Mini Forums

I have just installed and run in my fresh 1275 engine, which differs from the previous one in that it has now got M/T turbo pistons and a gas flowed exhaust manifold and turbo elbow, as well as a new 2" exhaust with a new RC 40 single big box, up from 1.75" and an old RC 40 big box..Both this and the other engine have a TurboPhil head and a Kent Cams turbo cam.

I am using the same BDD needle and it will idle fine at an AFR of around 13 and shows AFR,s of 12.0 to 12.5 on full boost and WOT.
So far so good as its going on the RR on Wednesday to set up the MJ and carburation.(The part throttle lean off pipes are blanked off)

However, when trying to accelerate from ,say 2000rpm, the AFR goes off the gauge at the rich end and I have to dip the clutch and rev it to clear or it just stutters and stumbles and wont pick up, even on very delicate application of throttle. I get the same reaction when re-applying throttle after a few seconds on the overrun.

I have checked that the float needle seems to be ok and that the fuel pressure is not miles out(I dont have a fuel pressure gauge) by taking the vacuum chamber off the carb and switching the fuel pump on - there is no sign of fuel welling out of the jet.The needle is secure in the piston in the normal position. I have tried changing the dashpot oil with no apparent effect. The carb ran fine on the old engine.

Sorry to go on so much, but I thought I would lay out what I had already looked at before asking the combined experience on here for their views.I wouild hate to go the RR and find there was an obvious fault before we start work(and paying for it !)

have you wound two dashpot springs togeather ? i know its a frig but....... give it a wirl
keep us posted

Dave.

Had a similar issue with my van early on in the build when I was sorting out fuel and a Megasquirt ignition map.

An idle AFR of 13 does seem very rich as A/A+ engines will happily idle at 16 in most cases. I would suggest backing yours off to give you around 15 at idle which all being well should hit 13 ish on boost but give you better part throttle response. It does sound like your idle AFR is unduly affecting the large proportion of the range. I take it when you take the damper off, the jet is about 3 mm down from the surface of the bridge ? If so, this is ok for setting up purposes.

Contrary to the way you have it at the mo, I'd personally also check that the gasket between the plenum and carb has the extra hole punched through so that the plenum can pressurise the float chamber and then reinstate the part throttle lean off pipe. IMO the mod to blank it is by exception and is not needed in most cases. I tried it and whilst the idle AFR was acceptable, the rest of the range was unduly rich at any throttle except WOT and it made the car almost undriveable off boost, the wideband would stay below 9:1 until you came on boost.

Have the pistons got a different dish - could this be affecting the static CR and the efficiency of the burn with the new setup over the old one ?

Either way, it's very unlikely that the standard BDD needle will be the right profile for your new motor.

What MJ map are you running ? It could be you have too little advance at 2000 rpm which is coincident with the point at which you're having to give it some revs to clear its throat. PM or e-mail me a screen print of your MJ ignition map and I can PM you a copy of mine as a comparison.

Richard.

Edited by turbominivanman on 1st Mar, 2010.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

In my limited experience (mostly na admittedly) ive not really found that to be the case tbh

On my stage one 1275 road mini, it grumbles if i ask it to idle at 14:1, and it happily sits at 13ish:1 when warm, so thats where i leave it

On the 1380 (649 cam etc) it sits nicely at 13:1 too, any leaner and again, it starts to hunt/stutter

I did a bit of searching, reading, and 13:1 is acceptable for idle, but leaner the better for more modern engines.

Also, i thought the jet should only be around 50 thou (just over 1mm) down the bridge for a std needle?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Thanks Richard. I should re-emphasise that the carb settings and general setup are unchanged from the previous engine which ran fine, although I did not have the wideband on then.The option to reinstate the lean off pipe is not available as in the past I ran a 1/8th drill down the stub nearest to the manifold, which appeared to have a little spring in there. I did try to reinstate but it wont run anywhere near !.I expect that the needle will have to be customised in due course.
The CR is down a little but I cant believe it can have such an effect.

You are flattering me if you imagine that I could do such technical things as emailing you an ignition map !

In any case I am still on the M/T distributor pending the RR set up on Wednesday when I hope that the MJ will be mapped. I will ask for a copy of the map for future reference and we may then be able to compare notes.

Thanks too for your contribution Joey and the confirmation that my idle AFR is reasonable. I was pretty sure it was as any signiificant alteration messed up what is a reliable 900rpm idle.

Unless there are any more suggestions I guess I am going to have to let you know later how I got on -fingers crossed.

Thanks Richard. I should re-emphasise that the carb settings and general setup are unchanged from the previous engine which ran fine, although I did not have the wideband on then.The option to reinstate the lean off pipe is not available as in the past I ran a 1/8th drill down the stub nearest to the manifold, which appeared to have a little spring in there. I did try to reinstate but it wont run anywhere near !.I expect that the needle will have to be customised in due course.
The CR is down a little but I cant believe it can have such an effect.

You are flattering me if you imagine that I could do such technical things as emailing you an ignition map !

In any case I am still on the M/T distributor pending the RR set up on Wednesday when I hope that the MJ will be mapped. I will ask for a copy of the map for future reference and we may then be able to compare notes.

Thanks too for your contribution Joey and the confirmation that my idle AFR is reasonable. I was pretty sure it was as any signiificant alteration messed up what is a reliable 900rpm idle.

Unless there are any more suggestions I guess I am going to have to let you know later how I got on -fingers crossed.

sure its not icing up tadge?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I dont think so with my underbonnet temps,but will be test driving again this afternoon with revised ignitiion setting and different dashpot oil -again !