Stage 2 carbs bike dies - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 44 (permalink) Old 11-01-2018, 10:47 AM Thread Starter
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Stage 2 carbs bike dies

As the title says, I just had stage 2 cobra jets installed in the carbs at the same time I did the 8k maintenance. Now once the bike gets hot it idles down and turns off.... but will start right back up no problem..... original shop says it needs a valve adjustment and quoted $1k, second opinion shop says fuel delivery and the carbs need gone through again for $390. Hiw can I test this before spending that kind of money?
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post #2 of 44 (permalink) Old 11-01-2018, 11:54 AM
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Why did you change the jets in the carbs?

Did you recently change the exhaust or intake pods and filters?

Was the bike running correctly when you took it in for maintenance?
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post #3 of 44 (permalink) Old 11-01-2018, 12:01 PM
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I just looked up your posts from last year. When you got the bike it had straight pipes on it.

Did you get a set of mufflers? How did you determine which jets to put in the carbs?

Normally the jets do not affect the idle - when the bike is idling the main jets are closed.

I doubt that a bike with only 4k miles on it needs its valves adjusted so much that it wont idle. If you have a compression tester, you can tell if the valves are not closing all the way (low compression). But if the bike was running and idling when you took it to get the jets changed, its not the valves.

Last edited by KCW; 11-01-2018 at 12:03 PM.
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post #4 of 44 (permalink) Old 11-01-2018, 12:06 PM
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By any chance has the bike been parked for the last year with the same fuel in the tank?

That is the #1 problem we see on here, old gas.
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post #5 of 44 (permalink) Old 11-01-2018, 03:13 PM Thread Starter
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I did put mufflers on it and moved down to Florida so I figured it needed the carbs reworked due to adding pipes and all. The shop saying it was valves said riding it in cold weather with shorties could damage the valves and since I rode year round through 45 degree weather at times that could have caused it.

I personally am leaning towards a fuel/air issue. I told them when I wanted the carbs done that I wanted a little more performance out of it if possible and his suggestion was a cobra jet kit. So that is what we went with.

The bike has not been sitting for any extended amount of time until this past month.
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post #6 of 44 (permalink) Old 11-01-2018, 06:16 PM
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Sounds like the carbs were not done properly. I'm with KCW, valves should be good at 4k miles. Normally a "kit" is not needed for carbs to eliminate a lean condition from opening intake or exhaust. All that's needed are two $5 jets and maybe a new gasket. If proper jets were installed you might just need to sync the carbs. Carbs MUST be synced any time you mess with them. By the way, when ever a "mechanic" suggests a carb kit he is trying to up the price, just my opinion. Here is a good read on jetting carbs.

https://sites.google.com/site/vstar1...g/carb-jetting

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2001 Vstar 1100 Classic (sold), Cobra Slash Cut full exhaust, Dropped 1 inch with lowering links, ORK, 4.5 inch handlebar risers, Ultimate passenger seat, Passenger pegs moved forward 4 inches, Handlebar clock, KN air filter, Viking saddlebags, Additional rear lighting
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post #7 of 44 (permalink) Old 11-01-2018, 06:29 PM
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maybe its only the way you worded your post but:

1. to adjust the valves would take about 2 hours. At a normal shop rate of $75 to $100 per hour that is a $150 to $200 job at the most, plus maybe $20 to replace all four O rings on the tappet covers. You can do it yourself with simple tools in maybe 3 hours if you have any experience turning a wrench.

2. If he meant maybe your valves are burned from running with straight pipes on the bike, then ok maybe a valve job might run $1,000. Before you even consider something that drastic go borrow or buy a compression tester from Advance Auto and do a compression check on your bike. If the compression is low, and putting a teaspoon of oil in the sparkplug hole does not bring it up to normal THEN you have a leaky valve. That might just need to be adjusted, or it might be a burnt valve. If you can change a spark plug you can run a compression test.

3. Running a bike with no mufflers should not push it lean enough to burn the valves, or damage the pistons, unless you put over 20,000 miles on the bike and you rev'd the hell out of the engine all the time.

Lesblank knows carbs and jets. Look up the right jets for a bike with slightly modified exhaust only, they should only be a bit larger than the stock jets that came on the bike. I dont know what a stage two kit is, that sounds like a Harley dealer mod package. If you know what size jets they put in the bike compare that to the standard jet tables for a VS 650.

Normally when a carb has new jets installed you also have to adjust the Pilot Main Screws (PMS) and balance the carbs like Les mentioned. The shop that is asking for another thousand dollars did not do a good job on the bike, if they changed the jets and now it wont idle.
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post #8 of 44 (permalink) Old 11-02-2018, 12:39 PM Thread Starter
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So the bike is at 8k now, I know not much of a difference. The jet kit came about because I bought it with no mufflers (without a rejet) and then added mufflers, I asked if they could give me a bit more power out of the jets and the stage 2 cobra jet was what was suggested, I do not know the specs.

I plan on testing the compression this weekend and testing both the sync of the carbs and the timing next week sometime after a friend loans me the tools.

My biggest thing is they immediately threw bad valves at me and until I got a second and third opinion on it I did not want to pretend I was smarter than the dealer and risk my heads.

I was an auto mechanic for a few years across different car brands but for some reason I can not seem to transfer that to bikes... it spooks me to work on a bike.
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post #9 of 44 (permalink) Old 11-02-2018, 01:31 PM
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Everything you said sounds good, but there is no reason to check the timing. With the electronic ignition the timing is controlled by a position detector on the crankshaft, and the ECU moves the timing around based on throttle position and (I think) engine rpm. There is no way to adjust the timing, its not like setting points, so there is no way someone could have set the timing wrong.

If the throttle position sensor has failed then the timing wont be advancing correctly, the bike would be sluggish as hell and maybe idle crazy fast. If you are not seeing any indication of those things then check the compression and put the vacuum gauges on and see if the carbs are out of balance.

You are on the right track.

Another thing you can do, just like with any gas engine, if the jets they put in are too big the bike will be running very rich. The exhaust will have that distinct 'old car' carbon smell, and your plugs will turn black on less than one tank of gas. Checking the condition of your plugs is a good indication of the jets being too big or too small. The caviot is you have to have clean (new) plugs in there to begin with then see if the jets are fouling them black or maybe burning them white (jets too small - wrong jets for the bike).

You will pull the plugs out for the compression test, so its a freebee

Dont know if anyone has mentioned this: I tell everyone: if you dont have a torque wrench go get one from harbor freight. Even a cheap one is better than none. A 3/8" drive is all you need.

Nearly everything on a motorcycle that you put a wrench on puts a steel bolt into an aluminum part. There is no 'feel' for tightening bolts into aluminum. It feels snug..snug..snug.. then it strips out. This is the single most important thing to know for a motorcycle, even with simple things like spark plugs (12 ft lbs).

Also if you dont have it already the Yamaha Vstar 650 factory service manual is free online in PDF format. All the torque specs are in there.

Last edited by KCW; 11-02-2018 at 01:39 PM.
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post #10 of 44 (permalink) Old 11-02-2018, 02:44 PM
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I was paranoid to work on my old bike, but after watching tons of youtube videos I have basically concluded there isn't really anything you can screw up so badly to really hurt yourself. Sure you can get things out of alignment. But really as long as you don't screw up the gear box your likely be ok, just won't have a running bike, or things will wear strangely.

Working on lawnmowers, cars to a point for most of my life. I have done a few motorcycles, but never to make street legal and never with a manual. So it is kindof new to me to dig into them. Much more enjoyable as getting to service parts on a car seems to require to know where all the special holes are, and tools to get to things. Much more straight forward on a bike, even a supersport isn't too horrible, but they are getting closer to annoying.
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