Cannot run my pinto less rich

**Aranckashi** · 29-01-2021, 23:16

Hi everyone,
I've got one last issue on my 2.0 pinto and it comes from the mixture on the carb. The engine runs smooth at idle and revs almost perfect but it's so rich.
The pinto is from a sierra 88 with a weber 30/34 DFTH carburetor which was tired. I replaced this original carb for a new 32/34 DMTL from Fastroadcar. I've been in touch with them and they said it replaces the 30/34 DFTH with good settings, no problem.

Indeed it fits pretty good but I can't set it less rich. I did a CO content test and it indicates 8% while I must have around 1% recommended in Haynes book. Turning the mixture screw all the way in I manage to get 7% but not less..
Do you guys already faced this issue on carbs and solved it ?

**Graham** · 30-01-2021, 09:02

what are you using for a co meter? 8% at idle on a warm engine usually results in fairly rough running, are you sure its that rich? if its a diy type meter its reading could be way off. another possibility is you have an intake air leak somewhere, which means the idle speed screw needs to be screwed so far in to make it idles, the carb is actually drawing fuel through the main jets, if its idling on the main jets if you look down the carb with the engine running you will see fuel dribbling from one of the aux vents

**Aranckashi** · 30-01-2021, 09:47

Originally Posted by Graham

what are you using for a co meter? 8% at idle on a warm engine usually results in fairly rough running, are you sure its that rich? if its a diy type meter its reading could be way off. another possibility is you have an intake air leak somewhere, which means the idle speed screw needs to be screwed so far in to make it idles, the carb is actually drawing fuel through the main jets, if its idling on the main jets if you look down the carb with the engine running you will see fuel dribbling from one of the aux vents

I did only one test for the moment and I probably need to do some others to confirm that. I'm using the gas-tester from Gunson, I used to test on different cars and it works quite well. Yeah that's why I don't understand the 7-8 % while it idles great.

Idle settings on the weber is how it needs to be, I'm 1 turn in after contact. But the mixture screw doesn't do anything when moving.
Carb is brand new but I will check the aux vents if I see somthing.

**Graham** · 30-01-2021, 10:13

i wouldn't trust a Gunson co meter as far as i could throw it. Even our mega expensive £5000 mot testing gas analyzers need checking and calibrating to ensure sure they are totally accurate, a diy machine stands no chance of being accurate

**Miniliteman** · 30-01-2021, 15:25

What were the old and what are the new idle jets?
Did you set the ignition timing (static), as a retarded ignition timing will give a rich mixture.

**Aranckashi** · 31-01-2021, 09:21

Originally Posted by Graham

i wouldn't trust a Gunson co meter as far as i could throw it. Even our mega expensive £5000 mot testing gas analyzers need checking and calibrating to ensure sure they are totally accurate, a diy machine stands no chance of being accurate

You are certainly right. No more auto garage are able to do this test for carburetor sadly. Checking sparkplugs is probably the only way but can we say this is accuracy..
What is your most efficient way to set it right nowadays ?

**Graham** · 31-01-2021, 09:41

Originally Posted by Aranckashi

You are certainly right. No more auto garage are able to do this test for carburetor sadly. Checking sparkplugs is probably the only way but can we say this is accuracy..
What is your most efficient way to set it right nowadays ?

it all depends on what your trying to achieve. if you dont have to pass an idle emission test all you need do is adjust the idle screw to get the best and smoothest idle. this adjustment doesnt effect the mixture when you are actually driving

**Aranckashi** · 31-01-2021, 09:49

Originally Posted by Miniliteman

What were the old and what are the new idle jets?
Did you set the ignition timing (static), as a retarded ignition timing will give a rich mixture.

On previous carb (original) it's 45/45. The new one it's 55/60. I tried to use them on the new carb and it was a complete mess.
And yes ignition timing is set (6-8 degrees).

**Aranckashi** · 31-01-2021, 09:56

Originally Posted by Graham

it all depends on what your trying to achieve. if you dont have to pass an idle emission test all you need do is adjust the idle screw to get the best and smoothest idle. this adjustment doesnt effect the mixture when you are actually driving

Idle adjustment is very well, on 850-900 rpms engine is smooth no problem. I'm just trying to have a good air/fuel mixture ratio for fuel economy.

**Graham** · 31-01-2021, 10:30

Originally Posted by Aranckashi

Idle adjustment is very well, on 850-900 rpms engine is smooth no problem. I'm just trying to have a good air/fuel mixture ratio for fuel economy.

unless you spend a lot a lot of time with the engine idling, the adjustment will have no real effect on economy as thats controlled by the main jets and ignition timing

**Aranckashi** · 01-02-2021, 17:28

Originally Posted by Graham

unless you spend a lot a lot of time with the engine idling, the adjustment will have no real effect on economy as thats controlled by the main jets and ignition timing

Ok I see. Don't wanna mess with jets so I'll leave it like that.
Thanks for the help !