5 replies to this topic

[iwatkins]

Hi All,

Changed suspect HS4 on our Stage 1 modded 1275 (circa 1991) to a reconditioned unit.

New unit is very clean and smooth. And added all new gaskets to manifold. Red spring, AAA needle, stub stack and K&N cone, all new.

Set mixture nut to 12 flats from bridge and fired straight up. Choke cable not attached at this point so needed throttle to warm up.

Once warmed, idled smoothly at 850rpm +-30rpm.

Ran through setup as Haynes. Got it just on the lean side of the plateau (MoT today).

Final stage in Haynes says set the fast idle. Turn choke cam around until the jet just starts to move downwards and then set the fast idle screw to this point.

Did that and then attached choke cable with a 1/4" of slack.

This morning she fired straight up from cold with the choke out but was running really lumpy, maybe slightly missing too. Pushed the choke fully in and she stalled. Fired straight back up but needed to give some throttle to fast idle until warmed up a bit only for a couple of minutes.

Drove fine and been dropped off for MoT.

Obviously something isn't right with either the choke or my setup of it. Any ideas please?

I've fixed all the air leaks, so at least that is progress.

Cheers

Ian

[Dan]

  The choke isn't either fully on or fully off.  The first 1/2" or so of choke travel raises the idle speed but it does nothing to the fuelling.  That's what you should be using in conditions like this, when you just need a tickle of throttle to keep it running.  A series engines rarely need to run on full choke.

[iwatkins]

Thanks Dan.

 

Maybe with all the problems with the old carb and air leaks (that have been like it since we owned it), guess I may have just bad habits now, i.e. pull the choke handle almost all the way out, no throttle pedal, turn it over, starts, wait a few seconds push the choke back in until just about 1/2" of travel left and then push it all the way in once car has run for a couple of minutes at idle or a couple of hundred yards of driving.

 

Are you suggesting that now, i should just give it a 1/2" or so of choke to start it and then as normal? Obviously will probably need a bit more in winter.

 

On the plus side, taking it down for it's MoT this morning, I made a wrong turn and "accidentally" had to drive on the bypass for a couple of miles before being able to turn around back to the MoT centre. She is running like a dream now. No stutters, no holding back, no bangs or pops and revs easily around the clock to 80mph before I bottled it. Never had is above 60mph, or more accurately, never been able to get it there. Progress is being made.

 

Once the MoT is out of the way, it'll get dyno'ed as I don't have a timing light and that's the one thing I haven't been able to check myself.

 

Cheers

 

Ian

[Dan]

  Start it with some choke, but once it's settled back then push it right back to about 1/4" - 1/2" or choke.  Or push it right home and then just pull it back out slowly until it idles nicely.  It's an analogue control, and you can use it as a control it doesn't just have to be on or off.

[iwatkins]

Thanks Dan.

 

Understood. I think I have just got into a bad habit of all on or all off because of the other problems with the car. And this is my first car with a manual choke, so I guess I'm not used to it.

 

I'll try as you suggest in the morning once cold and see if I can give it a bit more revs. on the choke only without lobbing in loads of fuel (which I assume was the lumpy running). 

 

I'll get the hang of this in the end. 

 

Cheers

 

Ian

[midridge2]

A properley set up carb should in this temp start without any choke, most people have never used a choke and dont know how to use them.

 a choke should only be used to start a car on cold days and pushed 1/2 way back in straight away and right back in after a couple of mins.