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Xv535 backfiring on 1 cylinder ar half throttle. Why

Posted by Peter Tolw on


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Usually burnt valve seats run leak down test on affected cylinder, check Exhaust valve clearances not too tight.

Posted on Jun 03, 2019


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Roland W VanLue

  • 486 Answers

SOURCE: i have a 24 hp briggs & stratton els 725 motor

The engine ignition can be interupted by a safety switch (seat) out of place or adjustment, or a carburetor fuel solenoid that is loosing it's supply of voltage.
1) Check the wiring at the starter area, looking for a main engine wiring harness plug-in.
Check for connections that are burnt or loose.
2) If you can locate the 'kill' wire connection at the main harness, disconnect it, and retry the engine.
3) If the engine continues to fail to run properly: you might replace the plugs first, then I have listed a few things to check. They may not all aply, but this may help with an idea or two to try.

1) Determine that there is spark?
2) Have you used a type of spark tester?
3) What is the condition of the plug. Brown or dark brown is OK. Black or silver is NOT Ok.
*If you do not have a spark tester,
a) remove the plug, and with it connected to the wire,
b) find a portion of metal around the cylinder that you can ground it on, and then pull the rope.
c) If the plug is black, you may see spark, but you should replace the plug.

*** PLEASE NOTE ; if there is excess fuel in the cylinder or on spark plug,
it can catch fire, so be carefull to cover the hole with a heavy rag so that any fuel
cannot be exposed to spark plug durning test !!!!
Get back with me on how this issue works out.
thanks, rwvanlue

Fuel Related issues that take a certain amount of time to appear
Depending on make and model of mowers:
a) Fuel tank outlet plugged (some have a screen filter,
some are 90' angle and plug with rust and debris inside the corner of fitting)
b) Fuel lines collapse when they are routed thru fasteners and between frame and seat decks
c) Fuel cap vent clogged
d) Fuel filter clogged
e) any fitting that has an orifice that can trap debris or rust will eventually become clogged
f) fitting on the side of the carburetor
g) some systems have a filter inside the line at the opening of the carb inlet
h) fuel pump
i) vacuum hoses to fuel pump
j) debris under inlet needle/seat on carb
Fuel Starvation - Float Bowl Carburetor
1) remove air filter assembly
*be cautious of tearing the mounting gasket. If it does tear, you HAVE to replace it. It is part of the priming system
2) remove the float bowl fastener. This is the main jet
3) carefully remove the float bowl, the rubber o-ring/gasket will not be able to be used if it is removed, you WILL have to replace it
4) using a spray 'carb cleaner'
spray up thru the center of the carburetor
spray and clean the main jet with cleaner and 'tag' wire
(tag wire is very thin, and can be used to clean the hole in the center of the main jet)
5) clean any debris from inside the bowl or carb body
6) re-install bowl and center bolt, air filter assembly

*if you need gaskets, your Briggs dealer can supply. The kit is cheaper than individual gaskets, and all the parts needed to finish the above repair are in the kit.

I’m happy to assist further over the phone at

Posted on Nov 23, 2009


Rene Rossouw

  • 642 Answers

SOURCE: I have a 24 hp

What is your engine model number? It will be in the form of xxxxxx-xxxx-xx.
As far as I know the 725 ELS plug gap is 0.030"
Intake and exhaust valve clearance must be .004"-.006"
Incorrect valve clearance is the most likely culprit for backfiring. This can be caused by normal wear and tear.

Posted on Aug 30, 2010

Andrew White

  • 2239 Answers

SOURCE: i have a 350 husqvarna,

This is classic fuel starvation, start by removing the fuel hose from the tank and replace the filter on the end, if no better, it may be a tank breather issue, when the saw starts to die slacken the fuel cap, if the saw picks up you need to replace the breather, if no better you can make a small adjustment to the H screw on the carb, unscrew ( counter clockwise ) the H screw this will richen the mixture, you will need to pull the anti tamper sleeves back on the screws, this can be done by gently screwing a suitable self tapping screw into the sleeve, when it hits the screw head under neath the sleeve will start to pull back, once pulled half way off you can enter a 2mm screw driver through the centre if the sleeve and intp the slot in the adjuster screw underneath.

Posted on Mar 01, 2011

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The carb on my 350 chevey engaine is one i never seen it got wires running to the jets it started to pop and catch fire what can i do

Rick may have placed his question in the wrong category but I'll give it a shot... First, Rick, I'm going to have to presume the 'carb' is actually a throttle body and the wires are going to the injector spray nozzles on the top of the 'carb' throttle body.
If your engine is backfiring through the throttle body it can mean one of three things,
!.) First if it runs, or even won't run, double check the spark plug wires to make sure #1 wire goes to the #1 cylinder and the rest are to the correct cylinders too. Just two wires crossed will backfire through the intake with flames. For referencing which is where, The #1 cylinder on 350 small block Chevy is the forward most cylinder on the drivers side of the engine. The cylinder behind #1 is the #3 cylinder the #5 and #7 on the drivers side. The #2 cylinder is the forward most cylinder on the passenger side with #4 behind it then #6 and #8 in the rear. The firing order for all Chevy V-8's is as follows; 1-8-4-3-6-5-7-2. Looking at the engine from the front of the car the #1 cylinder tower on the distributor cap is usually at the 5 o'clock position or pretty close to it. The distributor rotates in a clockwise direction.
2.) The second condition could easily be the distributor timing is off. If you haven't turned the distributor any then that isn't the problem. If it runs double check the ignition timing for accuracy.It should read between 8 - 12 degrees advanced.
3.) Lastly, and this may be difficult to swallow if it's true but here goes. You could have either a sticking intake valve or a flat cam lobe on one of your cylinders. To check this pull the wire off the distributor cap and put it back on one by one to see if the engine runs differently with it off. If no change if found that is your failing cylinder to investigate. By that I mean to check the compression reading on that cylinder.
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One cylinder is getting hot and other isn't and backfires when I throttle up changed plugs no change

At an educated guess one cylinder is working (getting hot) and the other has a valve problem allowing the backfiring. Check valve settings or remove the head and check for burnt valve.

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My 87 savage will start fine, idle and rev at low rpm. but when I hit throttle it will backfire, pop, ****, etc?1 any ideas?

could be a bad valve intake side of headdoa compression test to make sure cylinders or reading above 100 lbs per cylinder

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My S50 backfires when I close the trottle.

The motor is running too lean on the popping cylinder. A best (but most expensive) solution would be re jetting both carbs. However you can cheat this problem by setting the air screws richer (further out). Try 1 turn out at first. More than two should not be necessary. Adjust both carburetor needles to better balance the cylinders. The needles may have a plug covering them. Remove and discard this. These needles are located below the throttle cable attachment point on both carburetors.
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Replace throttle cable 1986 yamaha virago

Hi, Anonymous for this scenario you will need your service/owners manual if you can't find the first and best tool you ever bought for your Yamaha, despair not, for a mere zero $0 you can download another one.
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My Virago XV535 was in winter storage and now the front cylinder only fires up on a higher rev than idle. With choke on, it contunues to run, but without it stalls. Back cylinder operates normal....

sounds like a pilot jet problem. Pilot jet runs first 1/4 of throttle opening, main jet the other 3/4. Take out pilot jet (usually the smaller one next to the bigger main jet) and leave it in a cup of neat petrol overnight. By morning it should be ok.

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88 Yamaha Virago750: backfiring during idle; uphill ride has no 'guts'. new plugs, carbs & fuel lines clean, air filter ok. what should I look for next?

Hi, Bedofroses49 and the usual suspects are:
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2. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
3. Faulty main circuit breaker and or connections.
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6. Faulty spark plug cables, leaking or broken, internal damage check for spark leakage in the dark.
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have you tried removing the idle speed motor and cleaning it with throttle body cleaner, as well as port it is removed from?

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