Question about 2004 Yamaha V Star Silverado

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I am getting pre-ingition knock when I throttle fast and front exhaust pipe is turning blue. Also backfires when letting off throttle. Only 8,000 miles

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Backfiring when slowing down is usually caused by leaking exhaust gaskets in the head, or head pipe to muffler connection. A lean condition on the front cylinder could be dirt in the carburetor. Although the bluing in the pipe could be caused by unburned fuel from a malfunctioning choke mechanism on the front carburetor or leaving the choke on too long. Often the the pinging is caused by ethanol in the fuel you are using. Your bike should be designed to run on 87 Octane regular unleaded style gas. If you have non-ethanol style fuel available in your area , I would run a tank of non-ethanol fuel with a dose of Chevron Techron fuel system cleaner in the tank. Inspect the choke mechanism is working correctly and replace your exhaust gaskets.

Posted on Nov 03, 2010


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1998 astro van runs fine at times and terrible sometimes. getting worse by the day. started as if pulling off and not getting fuel or taking turns fast. getting worse even shouting off while driving. now...

Park it and forget where you left it. Or if you have any mechanical skills or inclinations, you could do some basic tests, but avoid the dangerous driving test - do this with the engine running if it needs to be running, but stationary.
It sounds like it could be the catalytic converter is getting clogged. It blocks the exhaust from going out the tail pipe. When the car is completely cool, if you thump it pretty hard, or grasp and shake it, and hear any rattling, then it is damaged and probably blocking your exhaust. If it sounds good, you could next open the exhaust somewhere ahead of the cat converter, like pulling out an oxygen sensor temporarily, or disconnecting the exhaust somewhere. Then run the engine and see if it noticeably improves. That's a bad cat.

Last, which probably should have been first, is check for trouble codes. Most important don't let repairs bankrupt you.

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1993 bmw 318i backfires and shuts off

Several problems can lead to backfire including fuel air mixture ratio, but I suspect that you may have a blocked catalytic converter and to check this you would use a sawzall or hack saw to cut a hole in your exhaust pipe an inch or so before the catalytic converter and see if the car will run properly (although it will be very loud while testing). To reseal the pipe (assuming you don't have to remove the catalytic converter and something else is causing the issue) you would get a short pipe extension at any parts store that is pre-shaped on the ends to slip over your pipes and clamp it on each end with a muffler clamp, or pay someone about $20 to reweld the pipe.

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1 Answer

Backfires when you let off the throttle

Sometimes this is caused by excessive air leaks, usually in the exhaust or inlet. However if you have a set of aftermarket exhaust pipes on the bike or have modified the air intake. Then the engine will be running extra lean, and causing your backfiring.

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1 Answer

My 1999 Honda shadow backfires on deceleration after steady throttle what could cause this? I have tuned it and cleaned the carb but it still does it.

The most common reason for backfiring is lack of back pressure from changing the exhaust. To compensate for the flat spot you get you put in a jet kit. This leaves the possibility of more unburned gas getting into the exhaust. Honda uses Kei Hin carbs with a fuel shut off diaphragm to help limit this condition (backfiring) by turning off the fuel to the carbs during deceleration. Even stock exhaust can pop or backfire. Typically it is caused by air getting into the exhaust either past the copper o-ring gaskets in the head or leaking muffler connections from the head pipes to the mufflers. Try replacing all the exhaust gaskets and you should minimize this condition.

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My sportster backfires constantly. How can I resolve this problem? I had the carburator cleaned and adjusted, but it still backfires.

Ok, due to different terminology used by different people, I'm going to assume that by "backfire", you mean it pops through the exhaust system when you back off the throttle. On stock exhaust systems which use the "crossover" connector to connect the front and rear pipes, the backfire is usually caused by an air leak somewhere in the exhaust system.

When you back off on the throttle, the mixture is usually too rich to burn in the exhaust system. But, if you have an air leak allowing the scavenging effect of the system to **** air in, the mixture becomes combustable and is ignited by subsequent exhaust pulses.

Check your exhaust system gaskets and replace them if necessary. This should stop your problem. Rejetting the carb may be necessary as well.

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I ahve a 2003 Road King, with fuel injection, I`d always heard about true duals, so being a welder and fabricator, I took my stock exhaust and removed the cross over pipe, welded the holes, and reinstalled...

You need to get a race tuner for the bike. When you made changes to the pipes you changed the pressure that the ECM was looking for and that's why the bike is backfiring on deceleration. You need to get a race tuner (Harley's Screaming Eagle Race Tuner, Power Commander V). These tuners will allow you to adjust the ECM settings so that you can control the amount of fuel unburned in the cylinders. My suggestion is to go to and look at the power commander (since you like to play with your own stuff).
Also take a look at which has a wealth of knowledge on the HD.
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Vn800 running fast on tickover

I am not sure what you mean on the "running fast" statement. If idle speed then turn the idle screw outward to slow down the idle.

The backfire is caused by turning off the ignition key when the bike is at high revs. let it idle down THEN turn it off. The backfire is there because the carb idle circuit is active anytime the piston is in motion. Gas goes into the cylinder as the bike revs down then a hot spot in the exhaust pipe finally ignites the built up gas. There is your backfire.

Is the running fast question answered? Give me more information on the problem if it isn't.

Please rate this answer. Thanks njv6!

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Engine is poping (backfiring) when I let up throttle.

Most common cause of backfiring would be a vacuum leak....most common areas that develope leaks would be the manifold seals. I'd check there. To troubleshoot...warm up your engine and with it idling...spray some starter fluid on it and see if the engine speeds up. If it does... theres u're problem. While u're lookin around, check all your hoses for good connections and good rubber. If that doesnt do it...check your pipes for tight connection

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Televison: Toshiba Model 46L5200U1 with logo flash and then blank screen. I bought a TV LED/LCD Backlight tester, but am not 100% sure I used it correctly, or if I do have an issue or not. 1. How many LED/LCD strips does this TV have? 2. Wires from the LED/LCD's into the connector on the board. The connector (CN003)chart on the board says Pos1:black wire and says output. Pos2&3:Empty/Reserved. Pos4, 5, 6 & 7:white wires that are 151, 152, 153 and 154 respectively. It doesn't say anywhere on the board which are positive and negative. I put the Red lead into the hole of the black wire and the black lead in pos 4 for white wire. Then moved the black lead one at a time to the next 3 positions. Results: Pos4: 78.6 Pos5: 88.1 Pos6: 87.9 Pos7: 87.9 A. Is the above the correct test to do? I put the leads in the open holes of the disconnected wires to touch them as they would be if they were connected to the board. B. If this test is correct. Is Pos4 showing I have an issue with one or more of the LED/LCD's in a strip since it is below the others? All of them lite up the lights in the test for reference to this question. 3. If I didn't test question 2 correctly, I also did two other tests with the leads even though I had no idea which was positive and negative. Test 2: Pos4: Black lead and Pos5: Red lead with 92.4 reading Pos6: Black lead and Pos7: Red lead with 101 reading Test 3: Pos4: Red lead and Pos5: Black lead with 101 reading Pos6: Red lead and Pos7: Black lead with 101 reading Please let me know what you think and which test might be correct. I did watch a video and read the directions for the test, but I want to be certain before buying an LED/LCD strip or two. Or, if you think the results are within the correct limit and if I might have a different issue, what that issue might be? and, how to test that issue? I have a good multi-meter as well. I haven't used it much though, but with directions and I can do the testing with no problem. Thank you for your time.

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