"dead spot" in throttle? - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 5 (permalink) Old 07-30-2018, 10:22 AM Thread Starter
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Question "dead spot" in throttle?

2004 650A Classic.
Needs a long time on choke to warm up. Even when warm, throttle has a "zone" in it where it will cut out (as if not enough gas). If course, this is only noticeable in first gear, but it's making a smooth rollout from a complete stop impossible. Have to tweak the throttle every time, which isn't good in turning from a stop.
Any ideas on what this is, how to fix?
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post #2 of 5 (permalink) Old 07-30-2018, 10:51 AM
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are you leaving the choke fully engaged when you ride off on the bike, pushing it in half way, part way? ...

If the bike has been sitting a while it would not hurt to run some SeaFoam thru on a full tank of gas.

does the bike run normally when its warmed up?

Do you have a way to measure the idle speed? It should be 1200 rpm which is really fast compared to what a V twin like a harley sounds like.

If you are going to adjust the idle you need to ride the bike a good 5 miles to get the engine up to operating temp before you change it.

Last edited by KCW; 07-30-2018 at 12:12 PM.
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post #3 of 5 (permalink) Old 07-30-2018, 01:10 PM Thread Starter
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It's always warmed up and ready to go by the time I ride, but I'd love to know what it is before removing the tank to clean the carb (in the hopes that will fix it).
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post #4 of 5 (permalink) Old 07-30-2018, 01:22 PM
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If you are letting the bike idle with the choke on, even part way, you could have carboned up your plugs.

You dont need to let the bike warm up anymore than the time it takes to check your lights and adjust your mirrors. Push the choke in till its running at a normal idle speed and ride off.

About half a mile down the road push it in all the way.

When you are riding the bike the choke is only giving it a slight bit more gas for that first half mile. But when the bike is idling with the choke on, its a very fine balance between flooding the engine and stalling it out.

With a manual choke its nearly impossible to let the bike sit and idle for a few minutes while keeping the mixture right. You would have to keep nudging the choke in a bit every ten seconds as the heads warm up.

As long as you are not getting on the throttle hard for the first couple miles, the bike will warm up just fine as you ride it.

If you think the carbs need to be cleaned, goto walmart and get a bottle of SeaFoam from the auto department fluids shelf. Its about $10. Put 5 ounces in a full tank of gas and let that run thru the carbs.

As long as the bike is running (gas is flowing thru the jets) the seafoam will do its job - google seafoam on this forum - there are literally hundreds of bikes every year that are brought back to top form running a tank of the stuff thru. People cant believe it works so well, but it does.

Then if you still feel like you need to clean your carbs, have at it. But normally you should not have to tear carbs apart unless the bike wont run at all, or its leaned out so bad you cant ride it.

Last edited by KCW; 07-30-2018 at 01:27 PM.
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post #5 of 5 (permalink) Old 07-30-2018, 05:25 PM
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I have to admit, I'm old school... if something is amiss with carburetion then take the carbs off and clean them. Dislodging deposits or restrictions with a gas additive can only clean an obstruction to a certain extent and then pass the foreign particles through to the pistons, rings and valves during combustion to hopefully expel it through the exhaust. My inclination would be to remove the carbs and clean all circuits thoroughly and reinstall the carbs. If the problem still exists then set your idle mixture screws and lastly raise your needles one notch higher if your needles are adjustable or install a thin shim or two (the thickness of a beverage can) to see how that fares. Granted that's assuming that you're running lean just off idle but that's pretty typical given that modern carbs are set on the lean side.

Is your bike stock or do you have aftermarket exhaust and/or intake?

My 650 was running a little rich due to the (believe it or not) restrictive aftermarket mufflers fitted thanks to the previous owner. I installed freer flowing pipes with baffles and ended up having to shim the needles to compensate for the resultant lean mixtures just off idle through the middle of the rev-range. My completely stock 883 Sportster had the same problems you are experiencing (mj48) and the fix was turning the idle mixture screw 1/4 turn open and shimming the needle.
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Last edited by Diogenes415; 07-30-2018 at 05:31 PM.
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