Idle Mixture Screws does nothing..
- Bill Lawless
- 356 Fan
- Posts: 951
- Joined: Mon Oct 25, 2010 10:17 pm
- Location: Northern Vermont
Idle Mixture Screws does nothing..
Hi All,
I was out for a drive yesterday and my engine has a fluttering sound when idling: The right Weber Carbs seam to act normal when I turn in the Idle Mixture screw, RPM's drop off and I back it up till it run faster.. When I turn in the Left Idle Mixture Screws, on Cylinder 3 & 4 they do nothing, even going all the way in??
Weber 40IDF Carbs,
Valves adjusted,
I have a Pertronix ignition. I remember reading that the distributor is the culprit when the Idle Mix screw doesn't react, Is this true with Pertronix?
Thanks Much,
-Bill
I was out for a drive yesterday and my engine has a fluttering sound when idling: The right Weber Carbs seam to act normal when I turn in the Idle Mixture screw, RPM's drop off and I back it up till it run faster.. When I turn in the Left Idle Mixture Screws, on Cylinder 3 & 4 they do nothing, even going all the way in??
Weber 40IDF Carbs,
Valves adjusted,
I have a Pertronix ignition. I remember reading that the distributor is the culprit when the Idle Mix screw doesn't react, Is this true with Pertronix?
Thanks Much,
-Bill
Thanks,
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
- Martin Benade
- 356 Fan
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- Joined: Wed Nov 23, 2011 10:52 am
- Location: Cleveland, Ohio
Re: Idle Mixture Screws does nothing..
Off idle it runs perfectly? Maybe try turning the left idle speed screw in a half turn to see if that gets the mixture screws responding. If not maybe you have a pair of plugged idle jets, although I’m not sure how likely it is for them both to be the same.
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna
62 Cabriolet
56 VW
02 IS 300
04 Sienna
- Bill Lawless
- 356 Fan
- Posts: 951
- Joined: Mon Oct 25, 2010 10:17 pm
- Location: Northern Vermont
Re: Idle Mixture Screws does nothing..
Thanks Martin, It drives good, but at a low RPM cruise I still hear a faint fluttering, or not 100% smooth..
I have adjusted the idle speed screw.. When I increase the RPM's it's less noticeable but there.
I have checked the float level, but not in a while, maybe I'll pop the cover and check it again..
-Bill
I have adjusted the idle speed screw.. When I increase the RPM's it's less noticeable but there.
I have checked the float level, but not in a while, maybe I'll pop the cover and check it again..
-Bill
Thanks,
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
- Bruce Smith
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- Wes Bender
- 356 Fan
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- Joined: Wed Aug 27, 2008 10:54 am
- Location: Somewhere in the Gadsden Purchase, USA
Re: Idle Mixture Screws does nothing..
+1 on Bruce's suggestion. If one side idle screw adjusts and the other side doesn't, it shouldn't be an ignition issue.
Some days it's just not worth chewing through the restraints.....
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Re: Idle Mixture Screws does nothing..
Butterflies are higher than the first idle progression hole. By this way, fuel is coming out by the first progression hole and the idle mixture screw has near no effect.
On the drawing below, "A" shows the butterfly at the right position.
"B" shows a totally wrong position at idle.
On the drawing below, "A" shows the butterfly at the right position.
"B" shows a totally wrong position at idle.
- Martin Benade
- 356 Fan
- Posts: 12194
- Joined: Wed Nov 23, 2011 10:52 am
- Location: Cleveland, Ohio
Re: Idle Mixture Screws does nothing..
Or the same symptoms with the plates in the right place and no fuel to adjust
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna
62 Cabriolet
56 VW
02 IS 300
04 Sienna
-
- 356 Fan
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Re: Idle Mixture Screws does nothing..
2 plugged jets..... it's not impossible but probability rules push me to think that butterflies are not at the right position: both are at the same level because they are on the same shaft.Martin Benade wrote: ↑Sun May 28, 2023 2:49 pm Or the same symptoms with the plates in the right place and no fuel to adjust
We are gambling on the same table and Bill is the croupier: we just need to wait and he'll tell us what playing card will pop up!
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Re: Idle Mixture Screws does nothing..
You did not mention anything about using a unisyn (or equivalent). If one side is pulling harder than the other, then the idle screws on the other side will have little effect.
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Re: Idle Mixture Screws does nothing..
Weber are coming with air bypass screws: left carburetor can be with "open" butterflies & closed bypass screws / right carburetor can be with "closed" butterflies & open bypass screws.Dave Erickson wrote: ↑Sun May 28, 2023 7:45 pm You did not mention anything about using a unisyn (or equivalent). If one side is pulling harder than the other, then the idle screws on the other side will have little effect.
In this case, you can obtain the same result on the unisyn.
Last edited by Olivier Auvray on Mon May 29, 2023 2:47 am, edited 1 time in total.
- Martin Benade
- 356 Fan
- Posts: 12194
- Joined: Wed Nov 23, 2011 10:52 am
- Location: Cleveland, Ohio
Re: Idle Mixture Screws does nothing..
I suppose that only happens with a twisted throttle shaft, which is unlikely since I think it idled well recently
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna
62 Cabriolet
56 VW
02 IS 300
04 Sienna
- Bill Lawless
- 356 Fan
- Posts: 951
- Joined: Mon Oct 25, 2010 10:17 pm
- Location: Northern Vermont
Re: Idle Mixture Screws does nothing..
Just getting back on here....... Thanks everybody for all the info, I got a few things to look at....
But we are in the middle of moving and my unisyn gauge has already made the move so it will be a while before I try that, it was good last year
But we are in the middle of moving and my unisyn gauge has already made the move so it will be a while before I try that, it was good last year
Thanks,
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
- Bill Lawless
- 356 Fan
- Posts: 951
- Joined: Mon Oct 25, 2010 10:17 pm
- Location: Northern Vermont
Re: Idle Mixture Screws does nothing..
FYI, I got it, all 4 Idle Mix Screws do their thing properly now!!! Sounds Good.,
Now to figure out the Idle on my 911 SC, “That’s a horse of a different Color “ to quote the Great And Powerful Oz “
Thanks Everybody..
-Bill
Now to figure out the Idle on my 911 SC, “That’s a horse of a different Color “ to quote the Great And Powerful Oz “
Thanks Everybody..
-Bill
Thanks,
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
- Wes Bender
- 356 Fan
- Posts: 4861
- Joined: Wed Aug 27, 2008 10:54 am
- Location: Somewhere in the Gadsden Purchase, USA
Re: Idle Mixture Screws does nothing..
Don't leave us in suspense. What fixed it?
Some days it's just not worth chewing through the restraints.....
- Bill Lawless
- 356 Fan
- Posts: 951
- Joined: Mon Oct 25, 2010 10:17 pm
- Location: Northern Vermont
Re: Idle Mixture Screws does nothing..
Well, I did a few things:
Checked the Float Lever and that was right on.
I cleaned the Idle Jet's but don't think that was it, I also blew out the ports from the jets to the Mix Screw and I think that was plugged.. I sprayed WD40 in the jet hole and didn't see anything on the Idle Mix port till I hit it with the compressor..
Checked the Float Lever and that was right on.
I cleaned the Idle Jet's but don't think that was it, I also blew out the ports from the jets to the Mix Screw and I think that was plugged.. I sprayed WD40 in the jet hole and didn't see anything on the Idle Mix port till I hit it with the compressor..
Thanks,
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350
Bill
65' 356 SC Cab Irish Green
82' SC Targa
81 VW Westfalia with 2015 Forester Engine
BMW 64'-R50/2, 75'-BMW R90/6, 74' BMW R90/6, Yamaha BW350