Lowering idle su 67

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legit_chicken
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Lowering idle su 67

Post by legit_chicken » Mon Feb 04, 2019 2:37 pm

I have a 1967.5 1600 and I’m having trouble adjusting my carburetors. I adjusted the mixture knob to spec with digital measuring calipers and then I had someone help me with the airflow adjusting screw to get the mixture right and the carbs balanced but now the engine is idling at a really high rpm. The guy that helped me said to lengthen the dog bone linkage but It doesn’t seem to be helping. I think they may be extended as far as they can be. Is there something I’m missing or am I not understanding the process? Any help will be appreciated as I’m really new to adjusting carburetors. Thanks.
Lincoln. Age 16
1967.5 SPL 311-11442 (1st Car!)

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Linda
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Re: Lowering idle su 67

Post by Linda » Mon Feb 04, 2019 3:36 pm

Check to see if the choke cables are stuck. I would suggest you take the cables out at the carbs, be sure linkage is not stuck, then reattach the choke cables, being sure they are long enough and not too short. Also the throttle cable in the middle, could be short or stuck, it needs some slack. Lastly be sure the throttle adjust screw, in the middle , is off.
Otherwise the idle screws, on top of each carb, can be adjusted, just a hair each time, till perfect.
Just a dab of silicone spray on the nozzles from below, can aid movement.
If you don’t have the correct hoses on each carb they can drag on the nozzles. I like Tygon 4040 gas, ethanol resistant, for the tiny hoses, with tiny wire clamps, must be checked every 3 months to be sure not getting stiff. Used on gas powered blowers etc. See archives for discussion. Found on eBay or mower shops, get correct size.
15493130242450.jpg
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notoptoy
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Re: Lowering idle su 67

Post by notoptoy » Mon Feb 04, 2019 4:11 pm

Lincoln, follow these instructions to the letter. If after doing this, it doesn't idle properly, you may have worn throttle shafts.
http://www.311s.org/pmwiki-311/pmwiki.p ... sNewSuTech
"When all else fails, force prevails!" Ummm, we're gonna need a bigger hammer here.

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65 Impala Convertible
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legit_chicken
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Re: Lowering idle su 67

Post by legit_chicken » Mon Feb 04, 2019 4:30 pm

Thanks for the response. I actually don’t have my choke cables connected and the linkage doesn’t seem to be stuck. Also my throttle cable has a fair amount of slack. And my throttle adjust screw is backed all the way. The problem is that when I adjust the idle screws down to the right rpm, it runs really rich but the mixture knob is set to spec 0.087 in like it says in the wiki.
Lincoln. Age 16
1967.5 SPL 311-11442 (1st Car!)

greydog
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Re: Lowering idle su 67

Post by greydog » Mon Feb 04, 2019 4:39 pm

You're getting air in somewhere.
Try this....spray a carb cleaner on the carb where the throttle shaft goes into the carb body. Try it on both sides of both carbs.
If the engine changes speed when the carb cleaner is sprayed on, you know that's where air is leaking in. You can try the same thing at the carb spacers on the intake.
Careful tho, don't want to start a fire.
If you're lucky, you have a leak at the isolator blocks between the carbs and the manifold. That's easy and pretty cheap to fix/replace. If the throttle shafts are leaking, that's a tougher, more costly fix.
Dan
.68 SRL311 aka "Skortch". On the road again.
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Gregs672000
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Re: Lowering idle su 67

Post by Gregs672000 » Mon Feb 04, 2019 4:57 pm

If the problem is dog bone related: If you disconnect the dog bones, that should eliminate any influence from them. You should be able to adjust the idle or throttle plate for each carb with a screw right next to the position of the throttle plate, and the carbs should flow equally when tested. Then, if you snap the dog bones back on and the idle is wrong, you know they need adjustment until they are neutral. Check the flow on each carb to see which or if both changed when you snapped on the dog bones (you really need a flow tester to do this right). The dog bones have set nuts that will allow you to loosen and then rotate the socket end itself to extend or shorten the length of the rod. Once they are set so that they don't change idle when you snap them back on, there should be a common "idle screw" on the linkage to set idle rpm and effects both carbs. It may be necessary to fiddle a bit with dog bone shaft length to make sure you have some adjustment available to you... for example so that the common idle screw has some travel so you can increase or decrease the overall idle with this screw only.

Do look over all the linkage first so you understand what does what, and check the choke system as recommended as they often bind up. That system drops the fuel nozzle AND opens the throttle plate slightly to increase rpm. Binding there will be a problem.

Regarding your most recent post... spec means little, so adjust the fuel mix to what the car desires. When you push up the carbs push pin (on the side of the carb, has a spring, pushes up the carb piston) it turns off THAT CARB and tells you what the OTHER carb is doing (to be clear, start with the rear carb, push up the pin, you are now checking the settings on the front carb). Roughly, the engine should increase in idle speed initially when you first push up the pin, then drop down and run on 2 cylinders but not die. If it does not respond initially with an increase in idle for a second, then try leaning the front carb a set amount and keep trying, noting how many 1/4 turns you are doing. If that does not work, try going the other way to richen it (but you're saying it's rich, so...). When that one carb does as described, do the same to the rear carb. Note if they are different and try to find a happy medium. Rev it up and make sure it doesn't lean out etc.

Hope that helps!

Specs are starting points, each engine is different! Also, make sure you have a decent set of plugs and wires, good state of tune or you're wasting your TIME!
Greg Burrows
'67 2000 #588
Tacoma, WA

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notoptoy
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Re: Lowering idle su 67

Post by notoptoy » Mon Feb 04, 2019 5:30 pm

I hate to be a nudge, but, follow the link I posted above, and follow it to the letter - it takes care of every suggestion here in a methodical approach. I could never get my SU's right, then I read "the bible" above. Once doing that I both understood it better, and was able to do it reliably. Even so, when I do go to adjust them, I start by printing off those instructions and following them to the letter - perfect results every time. The only exception is when the throttle shafts leak - which is easily detected as GreyDog described.
"When all else fails, force prevails!" Ummm, we're gonna need a bigger hammer here.

67.5 SPL311 H20 w/5 speed
65 Impala Convertible
2017 C43 AMG

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legit_chicken
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Re: Lowering idle su 67

Post by legit_chicken » Mon Feb 04, 2019 5:39 pm

Ok thanks so much
Lincoln. Age 16
1967.5 SPL 311-11442 (1st Car!)

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Linda
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Re: Lowering idle su 67

Post by Linda » Mon Feb 04, 2019 6:23 pm

Sometimes the float level and/or the float valve inside the fuel bowl lid is shot. Nice to check or just rebuild. And you can have a sinker float not helping if it is brass....get the plastic floats.
Linda
68 1600
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Re: Lowering idle su 67

Post by vinechoy » Mon Feb 04, 2019 10:41 pm

Similar, maybe same problem

Recently, I readjusted my carbs because my rear carb was pulling more air.
I turned up the idle set screw on the front carb and then the car would idle high sometimes until I closed off some air to the front carb.
It turns out my front dogbone was then loose but the rear dogbone was tight. After adjusting both ( high speed sychronization ), idle is back to normal everytime

Viney

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Gregs672000
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Re: Lowering idle su 67

Post by Gregs672000 » Mon Feb 04, 2019 11:40 pm

notoptoy wrote:
Mon Feb 04, 2019 5:30 pm
I hate to be a nudge, but, follow the link I posted above, and follow it to the letter - it takes care of every suggestion here in a methodical approach. I could never get my SU's right, then I read "the bible" above. Once doing that I both understood it better, and was able to do it reliably. Even so, when I do go to adjust them, I start by printing off those instructions and following them to the letter - perfect results every time. The only exception is when the throttle shafts leak - which is easily detected as GreyDog described.
He's Right! Step by step is always best!
Greg Burrows
'67 2000 #588
Tacoma, WA