# Surging with a bit of backfire.



## z28man (Apr 4, 2017)

Hey guys. I was here a few months ago and well, I'm back again lol. I recently replaced my carb with this one https://www.amazon.com/gp/product/B00U1RZN5Y/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1
As well as adjusted my valves. I've checked the valves 3 different times now and they're adjusted properly. I've mowed a few times and while under load with the blades going everything seems fine but otherwise I get surging as in throttle going up and down. There's also a tiny bit of backfire through the carb. I say tiny bit because it's not constant and it's never a full POW it's just a little puff. I decided to start from scratch on the carb adjustments so per what I found online I screwed in the idle screw all the way then backed out 1 1/2 turns, same thing with the air/fuel and have tried adjusting from there. The thing is, I can't get it to stop surging. At one point while adjusting the air/fuel it will kinda start to seem like it's smoothing out as I add fuel but then it will start to backfire. As I take fuel away it backfires less but surges more. Also if I it with full choke it's almost completely smooth but just like with adjustments, will start to backfire. Before I replaced the carb and adjusted the valves it ran smooth but was really hard to start because the valves needed adjusted. Now it turns over and fires right up so easy but it's running rough. I could probably take a video showing how it's running and what now if you wanted. I feel I'm at the end of my rope with this darn thing trying to get it to run right. I also reverted back to a 150 micron fuel filter for more flow since that's what it had on it before. Initially I went to a 75 so I thought maybe I was restricting flow. I am adjusting it with the air filter removed and like I said, as soon as I think I'm getting close to running good then I get backfires so I back the screw back out.
Edit: I might also mention it has a brand new spark plug.
Also if it makes a difference this is my engine model - briggs and stratton 313777


----------



## AVB (Nov 28, 2014)

I could say something about these clones but won't. The mixture adjustment is only an idle mixture and not a mid range to full setting. 

I first verify the static governor is set correctly. If this solve the problem and with being a 310000 series I would do leak down test as these engine are bad about blowing head gaskets. If it pass this test. then most like the main jet is under sized for the engine causing a lean surge as these tend to run the low speed circuit with little from main feed so as governor opens the throttle it leans and the governor over condensates by opening the throttle even more and then drops back. This becomes a never ending cycle until loaded.

Here I would simply resize the main jet but with it being a Nikki clone I don't know if the Nikki jets will even fit.


----------



## z28man (Apr 4, 2017)

So could I adjust the governor instead? I haven't touched the governor ever. It ran once this year on the old carb before the float got stuck and filled the block with gas. However when it ran, it ran smooth though it did smoke some I assume because of too much fuel. It doesn't smoke now at least. So giving it more fuel through the adjustment isn't the same as installing a bigger jet I guess?

Also since you say the adjustment is just an idle mixture adjustment, should I be adjusting this carb at idle or full throttle? Or does it matter? Does it also matter if the motor is warmed up or not? Most guides say to have it warmed up. The first time I had it running on this carb it ran great. After I let it sit for an hour or two I came back and it started surging. (that's just more info lol) I'm also curious why it seems to run great under load?

I've been looking around and it looks like you can buy parts for a nikki but I really don't want to since it's a brand new carb :/ Guess in the end I may have to. I'll probably have someone else look at it before I do though just to make sure it's not something I'm doing.


----------



## AVB (Nov 28, 2014)

Yes adjusting the governor is advisable as you're are now running a clone and the positioning of the governor linkage to carburetor can be slightly different.

Sorry I don't see why you change the carburetor what possibly was just a bad float bowl gasket but those Chinese prices can suck you in for the inexperience repairman. I know the repair kits that Briggs sells are around $50 but I seldom spend over $10 cleaning and repairing these carburetors as my UC unit allows me to re use the paper gaskets most times.

As the mixture adjustment it is at idle with a warmed engine. You can't adjust the high speed mixture except though main jet mods.

As for buying the Auto Express carburetor you brought most likely OEM Nikki carburetor will not work. THe clone is made in China and normally they don't provide spare parts.


----------



## z28man (Apr 4, 2017)

The video I found on youtube of a guy taking apart a nikki looks just like mine. I may be different but it does look the same. I bought the new carb cause I had never repaired one before and the kits for the same or more $$ for a new carb so I figured the new carb would be easier. I may look into adjusting the governor. I just mowed with my most recent adjustment and it mowed great. No surging under load. When I was done and disengaged the blades and turned the throttle down to probably half it was hardly surging, just a little compared to earlier. It did give me one little puff through what sounded like the carb but then it seemed to smooth out for the last little ride I had. I'll keep fiddling with it and I'll probably have someone who deals with this stuff all the time look at it. If it comes down to it, $40-$50 isn't really that much money and maybe I'll just rebuild the old carb. Either way I go, thanks for the advice. If it comes to anyone else I'll recommend they go ahead and rebuild the one they've got.


----------



## z28man (Apr 4, 2017)

Update question. I haven't actually tried screwing the mixture screw all the way in (should be more gas?) I don't know why but I feel like I should ask before trying it. Is that an option? Since it smooths out under choke or load.


----------



## AVB (Nov 28, 2014)

In (CW) leans, OUT (CCW) enriches. As I said it is an idle (low speed) mixture adjustment and the high speed mixture is non adjustable. It can affect the off load mixture some as these engine tend off the low speed circuit when not loaded.


----------



## z28man (Apr 4, 2017)

Thanks. I'll give it one last go on adjusting then I'll probably leave it and maybe later just rebuild my old carb. Since I got it on amazon I'll only be out about $40. I was going off what someone else said that IN was more fuel, guess I should have checked on here at first with my other questions. Thanks for all the tips. I'll check back in with an update whether it fixes it or not.


----------



## z28man (Apr 4, 2017)

So I've got it running pretty good but still surges some at high rpm, guess that's the nature of this carb as you've been saying . I'm also still getting a bit of backfire which it never did with the old carb. Maybe I need to revisit the valves again for that I dunno. If I were to go ahead and try to fix my old walbro (the one that filled the block with gas) Should I just need a new float needle, seat, and bowl gasket or should I go for a whole kit? I can get those few things pretty cheap on their own but the kits are more than I want to spend right now, at least what I've seen. Also, do you think the slight backfire out of the carb could simply be related to this carb?


----------



## AVB (Nov 28, 2014)

I found a CSB 1006 dated July 2012 bulletin that might help a little as it might be erratic ignition.

Quoted Text from the bulletin as follows:



> We have received limited reports of unstable/erratic performance on some subject engines when run at top no-load speeds under certain operating conditions. After the engine warms up or when load is applied, the engine will perform smoothly. If encountered, be sure to perform standard ignition, carburetor and governor checks as follows:
> • Check the quality of the fuel and ensure proper fuel flow to the carburetor.
> • Check the condition of the air filter (and pre-cleaner, if equipped). Replace as necessary.
> • Check for any binding in the throttle linkage and ensure the equipment throttle cable is adjusted properly. Also
> ...


And yes just the needle and seat along with the bowl gasket should it as long you haven't damage the other paper gaskets.


----------



## z28man (Apr 4, 2017)

Thanks. Most of that stuff I've done. The spark plug is new but I can go ahead and check it. I'll also double check the vent tube. Looks like I can get those parts for about $20 though so that's not bad. Really I could probably oput up with the surging if I could just figure out this backfiring issue. It's annoying because it's not even a full POW, just more or a poof from time to time. Thanks again for the info.


----------



## z28man (Apr 4, 2017)

Another thing of note maybe, When the assembly is back together and the air cleaner and housing is on, it seems to backfire less. I hardly ever hear it when driving it and never when mowing but when sitting there idling that's when it seems to do it the most. I may revisit the valves one last time just to make sure I've adjusted them properly. I think my biggest mistake was replacing the carb and adjusting the valves and doing it all at once. I probably should have done the carb first and when I knew that was tuned right, then do the valves so I wouldn't be searching as much for a cause. I wasn't thinking about it like that when I first started but hey, live and learn.

Edit: I just read something interesting, here's the quote. "It sounds like while this machine was stored all this time carbon deposits on the head-piston and valves dried out. The first time this dried carbon got wet from fuel it popped loose and is now stuck under the exhaust valve seat, The exhaust valve not seating fully will cause backfiring and poor run." Since My block was full of gas from the old carb, I wonder if any deposites got cleaned off/broke loose, and are now messing with the valves on the inside. I really don't want to take the head apart lol but I guess if I rule everything else out, eventually. Later on they suggest seafoam before taking the head apart. Think that's worth a shot? Maybe something got in the new carb or is in the engine that seafoam might help? By the way, I really do appreciate you letting me bounce questions off you left and right.


----------



## AVB (Nov 28, 2014)

I hear Seafoam works but personally I have never tried it so can't say one way or the other on that. 

If you happen to figure out what's going kindly let me know as I am interested in the problem as I know my luck it will happen to either one of my customers or me.

This is about as far as I can go without putting my hands on it here. Best of luck resolving the problem.


----------



## z28man (Apr 4, 2017)

If you live in mid MO, you're welcome to come take a look lol. I may try the seafoam. I've used it in vehicles before but never small engines. It would be a cheap/easy try before tearing it back apart.


----------



## z28man (Apr 4, 2017)

Back again. Question about adjusting the governor. I followed the steps in this video, 



 Seemed simple enough. Thing is, now I don't seem to have full throttle. How do you think I should go about adjusting the governor from here if turning it all the way to the right takes away full throttle. By that I mean, when I turn the throttle all the way up, engine speed is only probably half or so of what it normally is at full throttle. Should do the same thing, just turn the governor screw back to the left a touch? By the way, this is exactly how my linkage setup looks, same as the video.


----------



## z28man (Apr 4, 2017)

I just read where the governor should always be adjusted the same way, no in between like I was wondering about. But I read where you can change which hole the governor linkage is in on the throttle to make it less sensitive? Is that something I should try if I adjust it back and don't seem to have full throttle. Also, does it matter what my throttle is set at when I adjust it? I had it set to idle last time.


----------



## z28man (Apr 4, 2017)

Or should I set it back to where I set it first where I didn't seem to have full throttle, and bend the governor spring tab? I've read that bending that up a bit can give you more throttle.


----------



## z28man (Apr 4, 2017)

Well I adjusted everything back to how it's supposed to be, at least according to that video, and it seems throttle and everything is where it's supposed to be. full throttle feels normal now as does idle. However after it warms up it seems to idle a bit fast, I'll probably just have to adjust the idle itself some. Anyways, I don't think the surging is related to the governor honestly, it's probably this new carb I put on as we said before lol.


----------

