650 backfires - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
  • 1 Post By Geoffrey LaGioia
  • 2 Post By KCW
  • 1 Post By Deeksvstarclassic
  • 2 Post By KCW
  • 1 Post By lesblank
  • 1 Post By Yamaha Pat
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post #1 of 7 (permalink) Old 06-10-2019, 09:49 PM Thread Starter
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Join Date: Jun 2019
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Unhappy 650 backfires

I'm having trouble with my girl's 2009 650 Classic. It backfires through both the pipes and carb at 65 mph in 5th or higher rpm's in any gear.It starts and idles great. Has good power higher rpm.

2009 Star 650 classic
20k miles
Owned and trouble free since new
Garage kept

Trouble history:
In December the bike started one day and ran fine. The next day it would only crank not run. No spark.
I Tested the ignition pick-up and it was bad. Replaced the pick-up and stator, leaking neutral switch and changed oil and filter.
The bike started right up. The first 75 miles it hesitated little ay speed. The next 75 miles it would die above idle and then not run at all. Left bike overnight and and went back with trailer next day. Started right up and pulled on trailer. Thought it might be clogging fuel filter. Drained fuel and put in fresh with sea-foam.Replaced filter. It ran but would die sometimes. Backfired at speed. Removed the carbs and rebuilt. They were clean inside But rebuilt them anyway. Used fine piano wire to verify small passages clean. Now it runs and never dies but it has a constant backfire at higher rpms and at 60 in 5th gear.
I hear fuel pump running when key is on.

Any one ever had this? Any Ideas?
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post #2 of 7 (permalink) Old 06-11-2019, 07:25 AM
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The problem started with the pickup and stator. Strictly from a cause and effect perspective the last thing you did before the trouble showed up is often the cause.

Is it possible the pickup has come loose throwing the timing a bit off? Is it possible to put the pickup in upsidedown or backwards?

I would also check the throttle position sensor on the carbs, that is the signal the ECM uses to advance the spark, so if its failed, not adjusted right, or the connector is loose, the ignition timing would also be off. That is a really easy thing to check with a volt meter just twisting the throttle.

From the top of my head Im not sure if a backfire at constant RPM is from running rich or lean - what do the spark plugs look like? The idle, PMscrew ports, and the main jets are sequential. The main jets do not even open until the throttle is near half way open, so if something is only bad at highway speeds, it points to either the main jets, or maybe the PMscrews being a bit off which makes it worse when the main jets engage.

Since you had the carbs off also make sure the choke (enrichment) is working correctly and not staying on when you push the knob in.

One other thing: if your air filter is not white like paper it needs to be replaced. My 650 started running weak at highway speeds when the odo got to 25k miles, the air filter looked grey like a nasty old teeshirt. Replaced it and the bike came back to life. That whole thing in the owners manual about blowing it off with compressed air is bullKwrap.

The other question is whether the valve clearance has been checked or adjusted recently? If the valves are getting tight they will not close all the way, and backfire. Unfortunately you need to pull the carbs loose (enough to get them out of the way) to check the intake valves.

I know this is a lot of things to check, but a lot of things can make an engine backfire.

Last edited by KCW; 06-11-2019 at 10:29 AM.
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post #3 of 7 (permalink) Old 06-11-2019, 09:50 AM
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Location: Milwaukee Wisconsin
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It has been years since i had a carb on bikes. Does my 2001 1100 vstar have a primer (enricher) or and actual choke. It seems to work like an actual choke
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post #4 of 7 (permalink) Old 06-11-2019, 10:32 AM
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Im pretty sure the Vstar carbs are all the same configuration, and have an enricher circuit instead of a choke butterfly.
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post #5 of 7 (permalink) Old 06-13-2019, 08:29 AM
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Hi Geoffrey!
Welcome from East Tennessee. KCW has given you a great insight into your issues. Hes extremely knowledgeable and helpful and has helped many of us in the past.
Were big on pics here so please share some with us, and feel free to post your questions in the Vstar section for more exposure. Glad you joined us!

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post #6 of 7 (permalink) Old 06-13-2019, 07:01 PM
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Location: Houston, Texas
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Welcome from Houston, Texas. You stated carbs were cleaned and ran better after that but still not right I would redue carbs again to double check reassembly was correct. Here's a few interesting threads to check out when you get a chance.






Ride often and safe.
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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
Loose nut "me" behind the bars
2006 Harley Electra Glide Ultra Classic

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post #7 of 7 (permalink) Old 06-13-2019, 08:03 PM
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Welcome from Sacramento, Ca.
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Cherry 2007 650 Classic
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