1. You can pull the plugs and compare them to get an idea if that is the case. The fuel pump is a holley black, and it's getting good fuel pressure to the carb on the other side of the regulator 6.5psi. Well, I don't have a clue what is going on. 1) restricted exhaust, which you seem to have not found an issue. I rebuilt the Walbro carb and that didn't help. Backfiring during acceleration typically signifies air in the intake system of a Harley Davidson. Check fuel filter. You have to know what "normal" is to identify if this is the cause, but what you're looking for is two nice strong streams of fuel spraying into the carburetor under the choke plate when you work the throttle by hand. 10 min read. TOOLS. Ideally, it should not pop thru the carbs at all (even when cold). Backfiring through the exhaust is a result of problems arising out of rich fuel mixture and out-of-turn sparking of spark plugs. 3. Not leaking, as I've replaced the intake/exhaust gaskets & that had no effect. S&S e carb by the way completely set for primary tuning. - Throttle is not wide open or - Air Valve is partially closed. Mar 29, 2006 Back firing is the result of a lean air/fuel mixture, check the accelerator pump. Troubleshooting - backfire through carburetor. The ratio of air to fuel in the mixture gets skewed in favour of fuel i.e. Faulty ignition module, switch, CKP, MAP, CMP, sensor and or any connector in the ignition circuit could have corroded, loose, or broken pins/sockets. To get a starting point the jets on both carbs should be screwed up so they are both level with the bridge. Timing; just a simple test would be to loosen the clamp bolt at the base of the distributor and rotate the distributor body a few degrees one way or the other, retighten and go for a drive to see if there is any difference; mark your original position first so you can come back to it if needs be. Story continues below . Answer (1 of 7): Because you left the fuel in it all year long and the gas left a varnish on the needle of the carburetor. Here is the tricky . When I crank it over, it wont start up, but . grizzlyhunter660. R Resq302 Registered Poor cranking may be due to a weak battery or loose/corroded connections. Nov 27, 2017 There's several things that can cause a cough out of a carburetor, but the most common is a lean condition. Heavy, lumpy running. Virtually always, the issue will either be a defective valve (burned, bent, out of time) or ignition (carbon tracks in distributor, crossed wires . I herd that a worn cam or a torn intake boot . If it blows back out the intake there is something wrong in the engine. 2. If you tip a lawnmower greater than 15 degrees with its carburetor pointing downward, then oil can leak from the crankcase and into the breather tube. First check you carburetor manifolds for intake leak warm the engine up and spray WD40 all around the where the manifold connects to the heads if the rpms change when you do thins you have leak replace the gaskets. 20, poor cylinder seal, wether it be bad rings, poor piston fit or wear. When the cilinder was in its working stroke and the ignition did not come because of lack of contact at the coil, and it comes a little later and the exhaustvalve has openend already, you hear it bark in the exhaust. Only show this user. #5 bertsmobile1 said: A bad cam, loose valve seat, bent pushrod , broken timing key , lean carb. A stumble on acceleration is often caused by a worn or inoperative accelerator pump. Personally, I would check for a vacuum leak. The problem can become so severe that the carburetor will not deliver any fuel to the engine. Hannans machine shop in hayward did the work. Try another carb or put the fuel injection back on the 6.0, but not replace it with the 5.3. The head was redone but I don't know if valves were replaced. Backfiring during acceleration can also be caused by internal carburetor problems, low compression, leaks in the fuel tank, lean engine conditions, and weak or broken valve springs. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. Remove the carb and spray carb cleaner into the small hole on the intake side of the closed throttle plate to clear the idle circuit. And if the valve on the tank discharge is a vacuum one, change out that hose. This can occur on any model, any carburetor, but seems to happen most often with the stock CV Keihin carburetors used on the newer (90 up) Big Twins and . Sometimes (not often), it'll cough so violently through the carb on decel pulling up to a light, it kills the engine. When that happens the needle gets stuck in the seat and stays open allowing the fuel to pour freely from the carburetor. Sep 30, 2018 / Backfire through the carburetor. Car backfires through the carburetor are sometimes caused by a lean air/fuel mixture. Problem cold starting may also be caused by ignition components that are past their best. If it is, on an older bike the first thing I'd do is to check for an intake manifold seal air leak. 2. vacuum advance what is the easiest what to check? The valve train will be my next effort. Loose or "dropped" needle. Backfiring is a loud bang or explosive sound that occurs while the engine is idling down or shortly after the engine has been shut off. When this cilinder is in its stroke with the inletvalve open, you hear it bark in the carburettor. Spitting back in carburetter. Cam design: Long duration cams with early opening intake valves can contribute to backfiring. Erratic slow running Four strokes, eight-stroking. The carb has 2 small holes in the bell mouth, the one that is in the middle goes through to the needle area. Took it home and shut it down. TOOLS1 said: If there is air and gas blowing out the rear of the carb, it means that you have a problem with the intake valve, or the cam timing has been retarded, like the chain jumped a tooth. Then turn the screw back in slightly to achieve about a 20 rpm drop, or a slight drop in vacuum. 400-grit works well. If its sheared or partially sheared, it will cause your timing to be off. Intake manifold air leak: A lean condition due to an intake manifold air leak can cause backfiring. 5. Two strokes, four-stroking. There are several reasons why a motorcycle sputters. This condition is primarily caused by dirty air filters, but it could also result from the incorrect fitting of after-market accessories such as exhaust systems, air filter systems, or replacement carburetors of a different type or size. Since this pressure needs to go somewhere, it leaves as soon as the valve opens for the next stroke. Burnt exhaust valve or air leak in the exhaust system. If your motorcycle carburetor spits out gas, it can be caused by a bad float needle valve. Alright I just fully rebuilt the top end on my 72 74" cone shovel. Still does it same as always. Share. Start it up and watch what happens. I cleaned up the motor before the top end rebuild . Chicago is well digger butt cold at the moment. Don't know the cure for sure, but the carb sounds like the issue. Lets check your flywheel key. 2 reasons for spitting out the intake on a 2 stroke. An engine backfire is an explosion produced by an internal combustion . 8. Spitting back normally means the mixture is too weak and/or the timing is . It seems to do it worse when its cold. Thanks for the . I got the same popping noise through carb. One of the most common problems that customers complain about is the spit-cough-pop from the carburetor as a Harley goes from idle to throttle. The saw runs fine with the aircleaner cover off but when it's put on there is enough excess fuel spitting inside that causes an over rich mixture to evently stop the saw. Whatever the cause, backfiring happens as a small . Re: Spitting through HS4 carb. I took the valve covers off to check the firing order. Increase the size of the main jet." . Acceleration poor. I did a search and found a comment stating "If the engine backfires through the carburetor, misses, cuts out or quits running, the main jet is lean. Each jet is then lowered by 2 1/2 turns on the adjuster. It could either just be stuck or it could be worn so badly that it no longer works right. With the engine idling, spray a SMALL amount around the area between the intake and the heads, and at the base of the carburetor, and on all vacuum hoses going to the carburetor. Sep 28, 2015. Spitting gas out of the carb can mean a lean mixture. Make sure your firing order and camshaft match.Even if your distributor cap is numbered wrong you can still use it,just place the wires in the right order. After priming the carb. Other causes are exhaust valve not opening, so the hot exhaust has nowhere to go except back through the intake on the next intake stroke. A lean air or fuel mixture from the carburetor of a Harley Davidson results from drastic changes in the pressure. Jump to . If you put a new coil on it, then you are familiar with removing the blower housing already, so I won't run through that part with you. Recently my grizz has been popping/backfiring back through the carb at low rpms. Moisture and condensation around the plug wires can cause induction fire of multiple cylinders. 6. 5. It doesn't do after I am going faster, only about 10 mph and under. The timing and cam have never been touched so I wouldn't think there should be a problem there. With a micrometer, measure exactly on those marks and record the diameters on a sketch of the needle. I have a Craftsman chainsaw that is spitting excess fuel out the carb while running. That is a pretty good list. Moisture in the distributor cap (condensation) can cause cross fire/ misfire until the cap warms up and evaporates the moisture. Process of elimination. Everytime I get it started it pops really bad out of the carb and I can see flames through the throttle plate and its idleing kind of high when it does idle. I can only wonder if the reason my 350 had previously seen off four owners in only 3,000 miles was the ongoing carburettor problem causing the bike to cut out - mine had a fuel flow restriction problem at the top end; a similar problem to this one, but with the metal casting/drilling at the fuel inlet at the top of the float chamber. Of course there could be lots of other reason for backfiring- bad ignition, bad timing, low fuel pressure, you could have installed a cam to radical to run in your engine or one that opened . . Backfiring caused by internal carburetor problems is a result of a defective accelerator pump. Apr 1, 2011. When the engine is at fast tick over fuel is almost running out of this hole. I will start with the lean carb just because I am an optimistic sort. I can let go of the throttle and it'll settle back to idling.