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08-06-2020, 09:20 PM | #1 |
Getting Wild
Join Date: Jul 2011
Location: Farmington, MN
Posts: 83
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High Idle Issue After Driving
Hi All,
I'm in the process of trying to tune my new VC 625 carb, but running into a consistent issue. Total novice at this, learned alot reading posts here, but i'm stumped and welcome any advice. Issue: I start the warmed up engine and let it idle. I adjust the black plastic idle screw to bring it down to about 1100-1200 RPM. Idles great. After i take it out of the garage and give it a bit of gas, when I let off the pedal it idles right at 2000RPM. Only way i can get it down is if i restart the engine, or flick the choke on for a second. I have the following installed:
Screw settings:
The throttle is seated back against the screw, so it's not like its getting stuck open. If i turn the idle screw out, it takes a few turns, then the engine dies after a few seconds. Wondering if this is caused by the pilot jet being too large? The one which came with my kit visually has a larger hole then the one which came with the carb. Is too much gas getting into the carb? When i restart after this issue, i get a loud backfire everytime. I've read several posts which mention gas pouring out of the carb. I have not taken my air filter off, but am i experiencing symptoms related to this? I'm happy to add the gas overflow line if needed. Thanks! Gilby |
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08-07-2020, 07:26 AM | #2 |
Searching for The Way
Join Date: Oct 2009
Location: Medina, Ohio (NEOHIO)
Posts: 11,421
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Re: High Idle Issue After Driving
Sounds like the butterfly is sticking. I took mine apart and deburred the edges and polished the shaft, and installed a stronger return spring. That did the trick for me.
With your jet settings, it sounds adjusted correctly. What air filter are you using? I have found when using a K&N oiled filter the carbs run funny because they can suck in oil. I recently have found red oil in the throat of my carb. That can lean a fuel mix out and introduce oil into the fuel. |
08-07-2020, 08:28 AM | #3 |
Getting Wild
Join Date: Jul 2011
Location: Farmington, MN
Posts: 83
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Re: High Idle Issue After Driving
I'll take it appart this evening and try the deburring/polish method. I assume using some 1000 grit sandpaper will do the trick.
The return spring is the one attached to the throttle arm assembly which pulls it back closed on the top of the engine, correct? I have a duromax 16hp sitting around i can canniblize from, maybe i'll add that one as well to it. Air filter - i'm using that K&N one which comes with the VC 625. I'll run it a bit and wipe a white paper towel in the throat to see if there is any red residue. I'll report back with the outcome. Thanks! I do have two questions regarding two adjustable screws. The air screw, does that only factor in for the idle circuit? And the main jet screw, I would open that up some more if i'm backfiring when i lay on the pedal, correct? |
08-07-2020, 09:46 AM | #4 |
Crazy Ole Man
Join Date: Jan 2016
Location: Owego NY
Posts: 2,758
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Re: High Idle Issue After Driving
https://buggiesgonewild.com/showthread.php?t=141306
Please read this - it will help you understand how to setup an adjustable carburetor. |
08-08-2020, 03:13 PM | #5 |
Getting Wild
Join Date: Jul 2011
Location: Farmington, MN
Posts: 83
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Re: High Idle Issue After Driving
Okay, think I have it "good enough" for now.
Idles around 1400, but it sounds healthy. Can shift just fine, and it doesn't sputter too low to quit. Acceleration is solid with some very slight backfires on deceleration. But, after fighting this thing for a few hours I'm just going to leave it as is. On another note, I think I need to adjust my brakes a bit. Was backing up too fast and ended up going through my cedar privacy fence...couldn't stop fast enough. Hahaha! |
08-08-2020, 03:47 PM | #6 | |
Crazy Ole Man
Join Date: Jan 2016
Location: Owego NY
Posts: 2,758
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Re: High Idle Issue After Driving
Quote:
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08-08-2020, 03:50 PM | #7 |
Getting Wild
Join Date: Jul 2011
Location: Farmington, MN
Posts: 83
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Re: High Idle Issue After Driving
Shepard - edited my post. Things are good for now. I appreciate you linking that write up, definitely helped zero things in.
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08-14-2020, 01:52 PM | #8 |
Vegas modded 420
Join Date: Jun 2009
Location: West MI
Posts: 15,433
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Re: High Idle Issue After Driving
I always set the mix then idle it lower, reset the mix and repeat until I get the low idle I want. Then I open the idle mix a little more and its all good. The main should not affect idle mix that is for like 10-20% throttle opening and more. Setting the idle mix a little rich will make it start in the morning without a choke in summer, and usually keeps it from backfiring when you let off.
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