20hp briggs & stratton surging

[oldntired55]

ok, i fixed one problem, over rich belching black smoke,,, now, i have an annoying surge...rpm rolls up and down, tried another nikki carb off my craftsman, whcih did not surge... same problem... i have adjusted governor, and checked linkages...could the springs be out of whack? i give up...help?

 

[ILENGINE]

Hold the throttle steady on the carb to prevent movement and see how the engine runs. If smooth then could be a governor issue. If the engine is stumbling and not running smooth than carb issue. Also you could try adding a little choke and see if the surging stops. Smooth running with some choke but surging without would also point to a carb issue.

 

[hlw49]

Model type and code would help to identify the carb. Had a T30 MTD today that was surging. Took the carb Nikki which in my opinion sorriest carb on the market. It was a night mare to get off since I had to take the engine cover, seat and seat bracket off. Bracket that the seat bracket bolted to just to get the carb. off. Once I did found the welch plug for the idle circuit had come out. Fixed it good to go.

 

[oldntired55]

Model type and code would help to identify the carb. Had a T30 MTD today that was surging. Took the carb Nikki which in my opinion sorriest carb on the market. It was a night mare to get off since I had to take the engine cover, seat and seat bracket off. Bracket that the seat bracket bolted to just to get the carb. off. Once I did found the welch plug for the idle circuit had come out. Fixed it good to go.

thats interesting... ill have to look for that, my only question being... why would the carb off a good running v twin act exactly the same

 

[oldntired55]

thats interesting... ill have to look for that, my only question being... why would the carb off a good running v twin act exactly the same

Hold the throttle steady on the carb to prevent movement and see how the engine runs. If smooth then could be a governor issue. If the engine is stumbling and not running smooth than carb issue. Also you could try adding a little choke and see if the surging stops. Smooth running with some choke but surging without would also point to a carb issue.

no change with choke, already thought maybe a bit on the lean side. and, as i said... this surges with a carb off a separate tractor that ran fine. im beginning to think i may have to pull the engine and check governor.

 

[oldntired55]

no change with choke, already thought maybe a bit on the lean side. and, as i said... this surges with a carb off a separate tractor that ran fine. im beginning to think i may have to pull the engine and check governor.

also, most small engines have an anti-surge spring from gov arm to carb link... i wonder why these do not?

 

[StarTech]

thats interesting... ill have to look for that, my only question being... why would the carb off a good running v twin act exactly the same

Because the carbs be jetted differently. You can't just simply put any old carb on and expect it to run perfectly. This why you must match the correct carburetor to the engine it being installed on. This is why many of the eBay and Amazon aftermarket fail when installed. All it takes is a hundredth or so of millimeter jet to cause problems. This why you can't mix the jets on a twin barrel Nikki as there might as much as 5 hundredths of a millimeter or more between L and R sides.

Those springs are there to remove slack only not to prevent surging per say; although, worn linkage mounting can cause problem of surging. Never had a problem without them.

As IL said try holding the throttle vane steady and see what happens.

Plus on twins many have a governed idle and the carburetor first must be set minimum idle speed and the governed idle speed is set. If you only adjust the idle stop screw you can get some strange carburetor problems as governor tries to govern the idle speed but can't. I have seen an engine to very at first start up to racing after it warms just because someone adjusted the idle stop screw incorrectly. These have to be set using tach.

 

[oldntired55]

Model type and code would help to identify the carb. Had a T30 MTD today that was surging. Took the carb Nikki which in my opinion sorriest carb on the market. It was a night mare to get off since I had to take the engine cover, seat and seat bracket off. Bracket that the seat bracket bolted to just to get the carb. off. Once I did found the welch plug for the idle circuit had come out. Fixed it good to go.

mod 407777-0128-E1 000607YG

 

[oldntired55]

Because the carbs be jetted differently. You can't just simply put any old carb on and expect it to run perfectly. This why you must match the correct carburetor to the engine it being installed on. This is why many of the eBay and Amazon aftermarket fail when installed. All it takes is a hundredth or so of millimeter jet to cause problems. This why you can't mix the jets on a twin barrel Nikki as there might as much as 5 hundredths of a millimeter or more between L and R sides.

Those springs are there to remove slack only not to prevent surging per say; although, worn linkage mounting can cause problem of surging. Never had a problem without them.

As IL said try holding the throttle vane steady and see what happens.

Plus on twins many have a governed idle and the carburetor first must be set minimum idle speed and the governed idle speed is set. If you only adjust the idle stop screw you can get some strange carburetor problems as governor tries to govern the idle speed but can't. I have seen an engine to very at first start up to racing after it warms just because someone adjusted the idle stop screw incorrectly. These have to be set using tach.

appreciate your reply, so...how do i proceed to set governed idle speed? mine does have 2 separate springs...on attached to a fixed point on bracket, the smaller (idle) spring on a bendable tab , also, both these carbs have the single jet fuel tube (black) , so i ruled out one of those affecting the surging... maybe im shooting in the dark, im beginning to wonder if the fuel pump is not keeping up with a filled fuel bowl... have a new one ordered as there is a small wet spot on bottom of fuel pump..

 

[Forest#2]

After I posted this I see now that you just posted the engine info.
Below is some hints. You WILL FIND the answers to your questions about proper adjusting in the governor section of the Briggs twin Intek OHV service manual. But you need to do the test ILengine suggests in post #2 first. If you have a air leak at the manifold it will have your issue and no adjustments will correct. source of air leak is the o-ring at the intake manifold.
Appears MAYBE from your hints you have a dual throat Nikki MAYBE on a twin engine?
Model type and code would help us?????????????
Most likely not the governor inside the engine.
Have you ever seen the engine operate normal or is this a new to you engine?
Yes Bubba could have messed with the springs???

If that is a Briggs twin each time you change to another NIKKI carb you will HAVE TO go through the steps in the service manual for STATIC governor adjust then low idle the governor idle (which is bend adjustment for the gov idle spring) and then HIGH rpm limit (which is a bend adjustment) You will have to go through these steps if the donor NIKKI carb governor and throttle control is not correct when tested. (look in the correct service manual for the correct steps for such.

ILengine has some GOOD info in his post @2. Did you try that?
Sometimes on those Briggs with the Nikki you can back off little bit CCW on the CW rotation of the governor shaft when doing the static gov adjust for full throttle on the carb and get less governor control hunting. When I say little bit it's only about 1/16 of an inch difference and mostly a adjust and try because the governor shaft only rotates 1/4 turn or less full travel for the static adjust.