Another Surging Quandary

[Murray40Rider]

Murray 40", B&S 13.5 HP, MDL: 21B807-0239E1, Nikki 699475 carb.
Hello,
Carb rebuilt. Fuel solenoid good. Gas good. Governor good. RPMs good. Valves good.
No surge at low idle. Surge at high idle. No surge under load.
Unable to locate vacuum leak using carb cleaner spray.
What to do?
Thanks for your time.
Mike

 

[Richard320]

I would have to say "governor is not good".

It runs good under a heavy load so you can rule out fuel starvation, whether clogged jet or misadjusted float or a vacuum leak. And an ignition breakdown would manifest itself worse under load, so it's not in there. Compression doesn't just come and go. So what's changed between idling good, high idle bad and high load good? The load. And load is tied to the governor. Maybe a link or a spring didn't get put back together properly when the carb was off? Or a hole is worn oval so things bind?

 

[bertsmobile1]

Your low speed jet is clogged
Some times an ultrasound will clean it up
It is up inside the carb and difficult to get at
he main jet is of course inside the plastic intermediate housing
Did you get the right one?
There are a few of them and they all look very much the same.

 

[StarTech]

It also to note there were three different main jets used on that engine depending upon the date code. Also you can not go by the Nikki PN on the carburetor as is Nikki core carburetor PN to Briggs before Briggs make mods to it.

591936 JET, Main -(Standard) (Nikki Carburetor 794458, 794459, 799246, 799247)
-Used After Code Date 08110500

699897 JET, Main -(Standard)
-Used Before Code Date 07011500

794352 JET, Main -(Standard)
-Used After Code Date 07011400 -Used Before Code Date 08110600

Since I have used either of these jets here I don't have their size recorded but it is usually engraved into the jet itself. they are done in hndredths of a millimeter so a 112 labeled jet had a 1.12 millimeter through hole.

And said Briggs PN for the carburetor is actually one of the two following carburetors. Actually none the carburetor PNs listed above is even in the Briggs price file here.

590400 CARBURETOR -Used After Code Date 08110500

593433 CARBURETOR -Used Before Code Date 08110600

 

[Murray40Rider]

I would have to say "governor is not good".

It runs good under a heavy load so you can rule out fuel starvation, whether clogged jet or misadjusted float or a vacuum leak. And an ignition breakdown would manifest itself worse under load, so it's not in there. Compression doesn't just come and go. So what's changed between idling good, high idle bad and high load good? The load. And load is tied to the governor. Maybe a link or a spring didn't get put back together properly when the carb was off? Or a hole is worn oval so things bind?

Thanks Richard320, suspect governor. Will readjust and let you know.

 

[Murray40Rider]

Your low speed jet is clogged
Some times an ultrasound will clean it up
It is up inside the carb and difficult to get at
he main jet is of course inside the plastic intermediate housing
Did you get the right one?
There are a few of them and they all look very much the same.

Thanks Bertsmobile1!, This carb does not have low speed jet. Research shows correct jet.
"699897 - stnd nikki 699475 carb, used before code date 070115OO"

 

[Murray40Rider]

It also to note there were three different main jets used on that engine depending upon the date code. Also you can not go by the Nikki PN on the carburetor as is Nikki core carburetor PN to Briggs before Briggs make mods to it.

591936 JET, Main -(Standard) (Nikki Carburetor 794458, 794459, 799246, 799247)
-Used After Code Date 08110500

699897 JET, Main -(Standard)
-Used Before Code Date 07011500

794352 JET, Main -(Standard)
-Used After Code Date 07011400 -Used Before Code Date 08110600

Since I have used either of these jets here I don't have their size recorded but it is usually engraved into the jet itself. they are done in hndredths of a millimeter so a 112 labeled jet had a 1.12 millimeter through hole.

And said Briggs PN for the carburetor is actually one of the two following carburetors. Actually none the carburetor PNs listed above is even in the Briggs price file here.

590400 CARBURETOR -Used After Code Date 08110500

593433 CARBURETOR -Used Before Code Date 08110600

Thanks Star Tech! My engine code 041025ZA. Installed 699897. My research showed same carbs you noted except I did not note the code dates. Thanks for that. I'll let you know how this turns out.

 

[bertsmobile1]

You might like to read this https://outdoorpowerinfo.com/repairs/briggs_intek_single_ohv_nikki_carb.asp
Note the carb shown actually does have an idle jet
Also all of them use the idle jet air tube and the idle passage which sprays an air/fuel mix into the carb.
In the bad old days there was a a needle where the plug is.

 

[Murray40Rider]

I would have to say "governor is not good".

It runs good under a heavy load so you can rule out fuel starvation, whether clogged jet or misadjusted float or a vacuum leak. And an ignition breakdown would manifest itself worse under load, so it's not in there. Compression doesn't just come and go. So what's changed between idling good, high idle bad and high load good? The load. And load is tied to the governor. Maybe a link or a spring didn't get put back together properly when the carb was off? Or a hole is worn oval so things bind?

Hi Richard320,
Fixed surging with gov adjust. Instead of rotating arm clockwise to control bracket (youtube), I let arm spring dictate position. Holding in place tightened jam nut. All is good now. Thanks for your comments. You guys are always great help. Mike

 

[Murray40Rider]

Your low speed jet is clogged
Some times an ultrasound will clean it up
It is up inside the carb and difficult to get at
he main jet is of course inside the plastic intermediate housing
Did you get the right one?
There are a few of them and they all look very much the same.

Hi bertsmobile1,
Fixed surging with gov adjust. Instead of rotating arm clockwise to control bracket (youtube), I let arm spring dictate position. Holding in place tightened jam nut. All is good now. Thanks for your comments. You guys are always great help. Mike