After the work on the weekend I was driving to work and noticed it starting to backfire on the downshifts. I'd only driven it around the block after tuning and it ran fine.

Exhaust backfiring on downshift without accelleration = too lean right?

So I pulled over and richened it up

(from the bonnet that means turning it clockwise right ie. pushing the jet down).

Now no matter how much I went, I couldn't get it to stop backfiring. It idles fine, under acceleration it gets through one and 2 ok, but at the high end of two going into three it's missing and then the accell cuts out completely and engine will shut off when I come to a stop. Have to wait a few mins then go again. (flooding??).

It's a stock 1.5su on a stock 998 but I do have extractors and a 2 1/2" exhaust... I've asked aobut the needle before but stopped worrying about it because I managed to get it to run fine ages ago and it was going great till last weekend.

Now that the timing and points have been done on saturday (timing first time in at least 2 years we set it to 7deg, points I last did myself last dec), is it a case of time for a bigger needle? Will that make it run better?

What it feels like now is that I can't seem to get enough fuel into it. I can make it run a bit more stable with a ridiculously high idle speed, but i;m not a fan of the car accelerating on its own in the low end as you down shift towards lights :p.

What exactly would I be upgrading too and is it a simple go get needle from repco and install and put back together and try to retune, or is it worth just going to a carburettor place and telling them what i've written here and letting them do it (price?).

Mokeys almost back on the road !

Oh, and after much swearing and punching of thin air (sputtering down punt road on a sunday night after work is not fun), I managed to get it home driving in second using the choke as accelleration. Pedal would stall it.

Choke = more fuel yeah? The fuel filter has fuel going through it ok, rises and falls as I adjust the mixture so I'm guessing pump/filter isn't the problem and it's purely a tuning issue...

Shard

Pulling the choke will make the mixture richer so if it runs better with the choke out it sounds it sounds like you have tuned it to make it leaner and not richer.

I don't know a lot about SUs but to me pushing the jet down would make it leaner ie the piston and jet inside the dashpot rise under acceleration. This link explains SUs a bit if it helps...

http://www.zparts.com/zptech/articles/mal_land/ml_sucarb2/images4/SUcarb_111601b.htm

Maybe someone better versed in tuning SUs can help

_________________
---
Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

Yeah, i was about to say, if you screwed it clockwise and it got worste then screw it the other way

_________________
Lillee - 1969 Morris Mini K

Screwed it as far as it will go anti, it idles great but im still getting backfire on down shift and then engine cutout. It runs fine accellerating until i have to hold constant or deccelerate then it sputters and accel stops responding.

Shard

Is the backfire in the exhuast or the carb?

So many things it could be, including bad fuel, bad timing, bad fuel pump...

_________________
Lillee - 1969 Morris Mini K

exhaust. we set the timing to 7 on sat. I'm kinda at a loss as to why its not happy other then now it's been timed it wont run without more fuel?

Shard

air leak?
high revs and
constant revs
are screwing up

but increasing revs is not

1. do you have a PCV
2. are the tappet covers gasketted
3. check from engine to muffler for holes gaps etc

_________________
Inconspicuously Conspicuous
Appreciation without Depreciation
forever chasing clearer skies...

Not sure what a pcv is, that the big black canister thing attached to various bits?

Cant hear or feel a leak around the exhaust, it's <1yo so i'm pretty sure it's all fine that end. Eng to muffler again is all <1yo and cant hear or seee anything dodgy.

Tappet covers haven't had anything done to them, so i'm assuming yes seeing as it was running fine before it started playing up?

As for general air leaks i'm kind of stumped. I checked the rubber boot on the top of the exhaust manifold it's still fine, dunno where else to look.

Check the gapping on the points using a dwell meter for accuracy!

Hmm, I've booked it into a carby place a suburb away. Will choke drive it down there tommorow and see what they say.

Luuuurve how nothing is ever simple in my cars.

Shard

CHeck to see if you have any gap at the points...I think you will find they have closed up or a RS
Unburn fuel is going out the Exhaust

_________________
Stop Licking the Dog...I Don't Care Who Started It

Yeah are the points all good?
What are your spark plugs like?
And the leads?
How bout the coil?

i had something like this happen to me recently. the car would stall at the lights unless i pulled the choke right out and wouldn't idle without the choke.

this is what i did that ended up fixing it:

pulled the dahpot off the top of the carbie, cleaned it out and put it back together, it was a bit gritty and was probably stopping the piston from sliding up and down freely.

i don't know why but this seemed to fix it.

it might be something to give a try.

_________________
72 Clubbie - Current project - Vauxhall C20XE 2000cc 16v 150hp.
78 Clubbie - Future project.

Y'arrr will double check the points, replace the plugs with new ones (will clean the <1 week old ones in there now for the clubbie) and have a squizz at the dashpot tommorow morning.

Hopefully I wont have to go down bell st in 2nd in afternoon traffic .

Shard