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post #1 of 17 (permalink) Old 06-17-2017, 10:45 PM Thread Starter
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Idle issue with 2008 carbed Thruxton

When starting cold engine with full choke, engine fires up and idles at about 2000 rpms but doesn't hold. Idle drops to 1000 or less and engine struggles to not cut off. If I push in the choke marginally, idle speed drops and engine does cut off.

I've adjusted idle speed to the recommended 1000 after bringing the engine to operating temp. No operating issues once warm.

Any ideas regarding why not holding idle with full choke? I know I need to replace the battery soon as it's discharging faster than it should. I'm having to keep it on a tender most of the time now. And I'll replace the original rectifier at the same time. Could a bad battery and / or rectifier be the culprit?
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post #2 of 17 (permalink) Old 06-18-2017, 02:28 AM
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My experiance with carb bikes, is that the idle speed vairies quite a lot between hot and cold. It's a bit of a balancing act but I normally set the idle so it will hold a reasonably steedy idle when cold and live with a highish idle (1100-1200) when hot. My tach also over reads on my carb bike so don't take your tach reading as gospell.

A slightly high idle is preferable to a low idle which can have low oil pressure.

According to my tach the rev limiter (Piemans ignitor map 8500) cuts in at 9000 so it's 500 high at redline and I suspect around 100-200 at idle.

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post #3 of 17 (permalink) Old 06-18-2017, 08:37 AM
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I have the same issue with my 07 Thrux too Chazz. Looking forward to any responses. I bought some Sea Foam in the hopes that the problem lies in gummed up jets. We'll see.

My choke has never been the same since I did an AI removal and reject according to the Jenks guide btw but it's never been this bad.

Changed my rectifier and have a new battery...still have idle issues.

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Last edited by WhiteStripe; 06-18-2017 at 08:50 AM.
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post #4 of 17 (permalink) Old 06-18-2017, 09:17 AM Thread Starter
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Quote:
Originally Posted by WhiteStripe View Post
I have the same issue with my 07 Thrux too Chazz. Looking forward to any responses. I bought some Sea Foam in the hopes that the problem lies in gummed up jets. We'll see.

My choke has never been the same since I did an AI removal and reject according to the Jenks guide btw but it's never been this bad.

Changed my rectifier and have a new battery...still have idle issues.
Deja vu, I added Sea Foam yesterday. I don't think it's a carb issue but can't hurt.

I'm going to marginally bump the idle speed today and see if this helps.
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post #5 of 17 (permalink) Old 06-18-2017, 09:29 AM
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Before starting, you could operate the choke lever in and out several times instead of just pulling out and see if that produces a different result. Sounds like too much extra fuel is being added with the choke. Might need a cleaning of the choke circuit and as such, an overall carb cleaning.
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post #6 of 17 (permalink) Old 06-18-2017, 10:15 AM
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Yeah, I have a couple of buddies at work who know carbs. One is saying dirty carbs the other is saying too much fuel like Felony was suggesting. I'm trying to avoid a carb cleaning if I can. I'll run the sea foam through a few tanks and see what happens first and then look for alternatives if that doesn't work out.

I also have problems starting the bike sometimes. On a few occasions I try to start it but it doesn't turn over..no clicks...nuthin'. All the correct lights are on but it's like I have the kill switch on. I'll turn it off, move the gears around and try again. Sure enough it'll start. Ah...the joys of an old bike.

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post #7 of 17 (permalink) Old 06-18-2017, 10:35 AM
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Is your neutral lamp lit when it doesn't want to start? You may need a cleanup at the neutral switch wiring?
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post #8 of 17 (permalink) Old 06-18-2017, 11:52 AM
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I also need to keep the idle a tad high and since owning the bike .. 03 .. have had to let it warm up with the choke open longer than a friends 04. Since its been like that from day one I've always assumed it just the vagaries of the carbed engines ..
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post #9 of 17 (permalink) Old 06-18-2017, 12:53 PM
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Is your neutral lamp lit when it doesn't want to start? You may need a cleanup at the neutral switch wiring?
Yep, all proper lighting are on...neutral and oil.

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post #10 of 17 (permalink) Old 06-18-2017, 01:44 PM
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I had a '05 Thruxton with none of these cold start issues or idling. Not necessarily a common feature of an engine with carbs. If the carbs are clean and well tuned, should not be an issue.
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