still carb problems

[Fizzy]

been trying to set my carbs up the last couple of days. after setting them up using a guide, and getting them to what i think is right according to the guide, its running pretty badly.

its very lumpy, and when you put your foot down, instead of accelerating, i just trundle along at the same speed while the exhaust/engine sounds like its burbling and spluttering/choking, absolutely no response on the accelerator pedal. its hard to describe. im now going to go and check the plugs and clean them up.

the only thing i was having trouble with the carbs was it was telling me to push the little plunger thing up that pushes the piston up, and the revs 'should rise momentarily then stay at a level'. i got the front carb to do this, but couldnt get the back one to do it, the revs always just dropping.

any ideas as to why the lumpy, unresponsive acceleration ? the problems only arise under acceleration.

[neilnaz]

Fizzy sounds like it is running lean. What are you using to set the mixture? One alternative method to using colourtune (if that is what you are using) is to drive check the spark plugs by cutting ignition and rolling to a halt and whipping out spark plug 1 and 4. Check colour and adjust front and rear accordingly. What you are looking for is biscuit coloured spark plugs. Your mixture sounds lean. Drive along with the revs at 3000RPM, look behind you and if it is safe to do so, cut the ignition and roll to a halt in a lay-by or similar and check the spark plugs. Keep doing this and check that you end up with biscuit-coloured spark-plugs and a car that pullslike a train

I would richen up 3 or 4 flats and take the car for a spin. If it is still behaving the same and does improve when you pull the choke out whilst driving then richen up some more.

The only real way of tuning a Spit is by the seat of the pants.

Best of luck, Neil

[Fizzy]

cheers, thats a point to start at at least. ive been looking at which needles im supposed to have, and the more i look into it, the more i think my carbs are a hodgepodge of bits. but reading about all the different types is confusing me.

Ferny has told me the needles should be matched to the engine, not the carbs. ive got an early mkIV engine, so i think im looking for AAN needles. i not sure the carbs are the original ones from teh engine though. but then i started seeing 'fixed metering' and 'swing bias' needles for mkIV's.

then reading about the springs in the dashpots that i thought were just srpings - turns out they're all different and should really make sure ive got the right ones.

having some lunch now, but then i'll go and turn the mixture up and see what happens

cheers

[BarryH]

Hi Fizzy

The question of needles and springs for SU's crops up frequently and is dependant on what modifications you have made to the engine.

For most its S & N filters and a free flowing exhaust system and the consensus for that is Yellow springs and AAQ needles.

You can also tamper with the damping oil in the carbs, the thicker the oil the greater the damping effect which keeps mixture richer for longer as you depress throttle.

Anything more radical you need a good rolling road with a wide selection of needles to find what is most effective for your stage of modification.

Setting up the balance, idle etc is well dealt with on James Carruthers's Minty Lamb web site and he has a very good needle comparison section as well if you want to see how different needles compare.

You could also try a search on this forum to see what has been said in the past.

[Fizzy]

far as i know my engine is standard, the breathing is standard and the exhaust is an unknown quantity, but probably not good. ;D. ive got ep90 in the dashpots at the moment. i need to order from rimmers soon (canley's dont have a mk3 hardtop headlining :() and at the same time i'll order some AAN needles and blue springs - i think those are the standard ones.

ive just been out after richening the mixture a few flats, and its a lot more responsive. my plugs looked lean before i made any changes, which is the first time i've ever seen them like that ??)

another question though. heres a pic from an SU manual Ferny kindly emailed me :



i've read differing terminology describing screws 4 and 5. which one do you adjust for the idle speed, and what does the other one do ? im assuming screw 4 is the idle adjustment due to its name. or is that for the choke adjustment? i dunno.

cheers Neil, seems like you managed to diagnose my problems and hopefully ive sorted it now, nice one.

[Royboy66]

No5 is idle adjustment,

if you pull the choke out you should see screw No4  come into contact with the choke cam,thus giving increased throttle opening at idle ;)

get someone to operate the choke, and it will become clear ;)

engine oil for the dashpots I'd say :)

Roy 8)

[Fizzy]

ahh right. now you mention it it all makes sense. its running infinitely better than it was this morning, which is good. looking at the plugs, its a little bit rich, so im backing it off in tiny increments and re-checking the plugs each time i come back off a run.

now i've got to decide whether to risk messing everything up putting the plasma plugs back in ;D. im convinced they work better than normal plugs, but ive been trying to set a standard to get the carbs right, figured it would be best to try get this standard on standard plugs.

as for the dashpot oil, i've seen the debates on here, though to be honest i didnt really read them much.

so whats the score ? am i right in basically thinking ep90 will give a faster response but engine oil, as BarryH mentioned, keeps the needle at optimum position a bit longer ?

[Pete Lewis]

ep90 is going a bit far  it should be  engine oil like 20/50 as barry said it is in effect the accelerator pump, and gives a rich mix for accelerating, so you dont want goo or cats pee .
stick to wahts in the manual .

on lifting pins you need to lift the pin lightly till you just 'feel 'it contact the piston base, then lift it 1 to 2 mm max   if the revs rise its rich if it falters its lean if nothing  its about right
the rev change is only short and maybe only 50rpm up or down  not big changes just a sensation   Pete

[Fizzy]

ahh right cheers. i'll swap the oil over tomorrow, see whats kicking about in the garage. its running as well as it has done since ive had it now. i put the plasma plugs in, and was able to lean the mixture a tad more with no adverse effect.

cheers

[bob dunn]

i have auto transmission fluid in .canly recon pack says sae 20 .or maybe some of this stuff.