Carb adjustment 4G52 GE Siggy

[Speedy88]

Hi guys,
Got a GE Sigma, 4G52. Been running it around for a few weeks and mostly it runs fine. Noticed it is a little hesitant when I put my foot down, especially when cold. It starts and runs generally other than this so I assume it's just a problem with mixture. Also the sound of some very slight pinking/detonation can be heard when cruising although giving it more throttle makes it go away. This solidifies my theory that the mixture needs adjusting as it is too lean.

However, I've never dealt with a carb quite like this before with the auto choke and all. It seems I can't find any way to adjust. It seems it doesn't have an adjustment screw and just simply is affected by the levels of fuel in the float chamber?

How do I adjust the mixture?

Sorry if this is a noobish question, I'm new to these things. Many thanks in advance!

[75wagon]

Can you take a pic and post it up of the carb sp I can confirm exactly which carb you have, and where it's adjustments are?

Sorry if this is a noobish question, I'm new to these things. Many thanks in advance!

No one ever learnt anything without asking questions

Also the sound of some very slight pinking/detonation can be heard when cruising although giving it more throttle makes it go away.

Pinging should only happens because the timing it too far advanced. Back off the distributor timing until it stops. Your timing should be approx 8 to 10 degrees advanced (BTDC)

Mixture screws only adjust the mixture at idle.

The primary circuit and secondary circuits have jets that meter the air fuel ratio.

Solex Mukini carbs have a couple of screws to adjust (idle speed, mixture, and there should also be a screw to adjust the amount the idle increases when the choke is on), and the auto choke is also adjustable (it should have adjustment markers on the auto choke housing).

The idle speed screw will be located on the throttle lever.

The mixture adjusting screw should be located on the base of the carb on the side facing the strut of your car.

Idle speeds and mixture screws should be adjusted when the motor is at running temp. Get the idle speed as low as possible, screw the mixture screw in and out until smoothest idle is achieved, and then reset the idle speed to approx 900 to 1000 rpm.

You car should be similar to these, but obvious only 1 not 2. http://www.sigma-galant.com/viewtopic.php?f=93&t=2655
These carbs shown are 1.6 litre ones, and earlier models, but the principles are the same. Have a good look at this link, it should teach you a lot. However, these carbs don't have the automatic chokes.

As for adjusting auto choke. The auto choke housing should be retained by 3 screws and a clamp. loosen the 3 screws and rotate the choke housing until you get the cold idle speed you want, then re-tighten the screws. Adjust this when the car is cold not at running temp.

Did any of that help?

Dave...

[Speedy88]

Wow, well all of that helped I love this forum. Yes those carbs are very similar with a few different parts but the diagram I have here is almost identical (from a haynes?).

I've tinkered with a few different engines over the years but I've never seen a carb without a mixture screw. It's pretty awesome really because it means it never needs re-setting or fettling and to think they designed this back in the 70s!

I'll adjust the timing and see if it helps my hesitation problem as well and go from there. If it doesn't cure it, it's probably worth me stripping down the carb and giving it a clean anyway as I'm pretty sure it's never been done.

[geezer101]

Every carby should have some kind of A/F mixture screw so it can be tuned. If the engine feels hesitant it could be caused by either a blocked accelerator enrichment jet (pretty common problem) or the enrichment pump diaphragm is stuffed (also another common problem). I'd be tearing it down and rebuilding it anyway if it looks like it hasn't been touched for more than 10 years. Take your time with stripping and cleaning it, and it will help make the engine run far better than you'd expect. I've had some success with modding these carbies and improving their performance. Good luck Speedy

[Speedy88]

Ahh I'm getting confused there, I'll take a look at timing adjustment first to solve the pinging and then set the mixture.

Yeah I had a feeling it might be jets too, I'll try the easy stuff first as carb rebuild kits are pretty far and few between. Maybe I can get some gasket paper to make up my own ones...

It might actually be worth trying to get the engine running on a more common carb eventually but I'd rather just drive it for now. It's too nice to be sitting in my workshop!

[geezer101]

The rebuild kit for the Mikuni has a lot more in it than just gaskets. You're going to need the diaphragms, needle and seat, throttle plate spacer, 'O' rings... not much point in pulling a carby apart without replacing all the serviceable stuff - it will never work the way you want it.

[Speedy88]

Fair enough, time to wait until pay day then!

[Speedy88]

Sorted, I think she was too lean. Goes like a rocket now, thanks guys (although carb rebuild is still on the cards for next month)

[geezer101]

Got a look at the carby from your other thread. See if you can chase up another Mikuni from a Sapporo (make sure it's a 4G52 engine so the jetting won't cause you grief). There are a few minor differences to installing it - fuel cut solenoid, wax pellet choke, fuel line into the accelerator enrichment pump and the return line out of the accelerator pump. They have the same throttle butterflies but I've noticed that the throat in the primary venturi is bigger by a few mm. This will give you more mid to top end over the Sigma carby. Have a look at one if you can and compare it.

[Speedy88]

Alright I will do