back fire through carb help

ok ive had some problems with my nikki carb on my craftsman. I replaced the blown out O ring gasket that sits under the plastic fuel plate inside the carb and it didnt help. my valve lashing is spot on but the thing still back fires out the carb every 20 seconds or so....I dont know how it could have gotten leaned out or anything since the adjustment screw has that plastic anti tampering cap on it....any ideas? float needle maybe?

jaymz wrote:

ok ive had some problems with my nikki carb on my craftsman. I replaced the blown out O ring gasket that sits under the plastic fuel plate inside the carb and it didnt help. my valve lashing is spot on but the thing still back fires out the carb every 20 seconds or so....I dont know how it could have gotten leaned out or anything since the adjustment screw has that plastic anti tampering cap on it....any ideas? float needle maybe?

when you think of backfire, I think of the valves being open. as if the timing gear is not lined up, If your intake valve is slightly open when it fires, you will get backfire into a carb possibly?

may need a valve lapping or check allignment or the timing gear..also, possible push rod sticking?

well I got them both set at.003 of an inch, wich is wata reputable local mower shop said to set them at. its now running alot smoother once its warmed up. it only back fires maybe once every minute or so, now my biggest problem is at any throttle level it will be running fine then just the govenor kicks in and slows it down to almost nothing then it takes right back off working agian

jaymz wrote:

well I got them both set at.003 of an inch, wich is wata reputable local mower shop said to set them at. its now running alot smoother once its warmed up. it only back fires maybe once every minute or so, now my biggest problem is at any throttle level it will be running fine then just the govenor kicks in and slows it down to almost nothing then it takes right back off working agian

Do you think you could possibly make a quick video? because think about timing advance and then when you mention the governor, it kinda throws me off the scent.

try and post a video, I am around for quite awhile, Ill watch it for sure.

Sounds like your valves are slightly open, take the valve cover off and while its running, adjust the valves with a cresent wrench, there should be a adjusting nut on the rockers. I did this to mine and it fixed the problem.

I figure it has to do with the valves, either adjustments, or out of timing for the valves...Or, there is buildup causing them to not close all the way.

now its fighting me even more, now the valves wont stay adjusted and when its running it only runs on full choke, take choke off and it dies.....im ready to scrap this thing and just buy another atv lol

jaymz wrote:

now its fighting me even more, now the valves wont stay adjusted and when its running it only runs on full choke, take choke off and it dies.....im ready to scrap this thing and just buy another atv lol

It will run full choke, without backfire now? The key to getting the right answer is being able to explain what you have done, what it is doing, what it is, and what your skill lvl is.
I want to help you out, but, I dont know what you did to the valves..I dont know if you have things connected as they should be...There are too many variables..

are you just not able to post a video?

yeah it runs on choke on and doesnt back fire lol im not able to post any pics of videos atm sorry man....and all i did was loosen the lock nuts on the valves and then set them to 3 thounsands of an inch with the motor at TDC. as far as skill level im not intimidated by anything mechancial except carbs...they hate me for some reason and they never run right after i work on them lol

jaymz wrote:

yeah it runs on choke on and doesnt back fire lol im not able to post any pics of videos atm sorry man....and all i did was loosen the lock nuts on the valves and then set them to 3 thounsands of an inch with the motor at TDC. as far as skill level im not intimidated by anything mechancial except carbs...they hate me for some reason and they never run right after i work on them lol

My last experience with a carb needing to run full choke, I took the float bowl off and there was dirt and grime, I would imagine if it runs full choke that means without ckoke, the engine isnt getting enough fuel to run.

I think you may have fixed your backfire problem, but now sounds like you have a fuel flow to intake problem...

What I personally would do, and what I have done, Is take a carb from another tractor and mount it (a known good carb) If it runs normal, now you have a place to look for the problem. (narrows down the places to look for problems)

If you dont have an extra carb, take the whole thing off, and chem dip it. replace all the gaskets and rings.

The best I can do with out being there.

I also wanted to ask, on the carb do you have an electric solinoid right under the float bowl? these can mess up, gummed up, burn out, and lastly, if you have a weak battery, these may restrict your fuel flow. If you have the standard bolt disreguard..

Yeah those antifire solenoids are a pain in the arse - ive disabled all the ones on my motors by simply snipping the needle off and unhooking the power lead.

I have a 03 murray regular mower that constantly had running issues, due to the antifire solenoid - runs great now.

YES! excellent idea! I never thought about that dumb anti back fire solenoid! I should have known since i had the same thing happen to my Huskee's Brigg. Im going to switch carbs with the good one off the huskee and see wat happens too, if it works im ditching the nikki carb and getting walbro, ive heard nothing but bad things about these nikki carbs anyways. I'll let ya guys know what happens!

so i switched carbs out with the walbro that ahs no problems what so ever and still it only runs on choke and back fires out the carb. The valves are adjusted perfectly and im pretty sure its not a sticking valve since i have oodles of compression. The only real possibility i can think of is a vacuum leak somewhere thats interrupting my fuel flow. I should add its not a spark issue either as i have a new plug and recently put a brand new coil on it. any suggestions on where to start checkin to find out where its suckin air at?

They say you can use a propane torch that's not lit turn it on and then like move it around the air you know that general area and if it's it increases
That means you found the leak

intresting....im gonna have to try that one

Any way, use the propane to find vaccum leaks, the engine will surge when the propane finds a leak. I think there are videos on how to do it.

Carb needs to be cleaned. If its running Run some Seafoam through it. it may help clean the passages.

whats seafoam?

Haha! Sea foam. I've never used it but watch this video

Check out this video on YouTube: Redneckcomputergeak

omg thats crazy lol I wonder if the shit works or not.......

I know guys working with 40+ year old engines that swear by it. I've learned out of experience what cheap/bad fuel can do do an engine.

Decent quality gasoline begins to degrade in about 6 weeks. By the end of a winter, bad gas can be be bad enough to plug up carbs. I prefer to stabilize my fuel every fall. 2 Stroke mixed fuel is worse, and will smell syropy in the spring. Drain and replace.

That being said. Sea foam and other products are suppose to help clean old fuel deposits out of fuel systems. Fuel injector cleaner may work for you as well. These products are designed to clean the passages and jets in a fuel system while the engine is running.

If the engine won't run and you have good spark and compression, its most likely a carb problem. It pretty hard for timing to go bad on these small engines, but I have seen valve stick open after a few years.

The best thing is a complete teardown of the carb, and a thorough cleaning, making sure not to use anything that will scratch the jets or passages.. Make sure you check for the tiny little holes in the emulsion tube. They are hard to see, so hold them up to the light.

I use aerosol carb cleaner, and an air hose to clean them, I also have a set of mini drilsl for cleaning really plugged jets. The mini drills are sold for cleaning welding torch nozzles, and are also sold in hobby shops. They are frequently called a pin vise, and usually have bits down to a size in the thousands of an inch.

There are some old timers that sear bye a good boil in lemon juice, followed by a dip in fresh water to clean them. It has worked for thousands of vintage bike enthusiasts.

I'd double check your valve clearances, think .003 is too little. I had one spitting gas out of the carb, the intake valve was not closing all the way.

so yeah i totally run two stroke thru that motor more often than not lol it all burns right? I think stretch might be right im going to try.005 on the intake and .007 on the exhaust, thats what the briggs site says is the max for my motor, its not like i can make it worse at this point lol

I hope it works tho, if not im gonna have to admit defeat and shes going to the shop