Briggs hunting for idle

[JandL]

Greetings,

This one came into my shop yesterday: Snow Blower 536.88150 from Sears Serial: 754712274512359C, Engine Mod: 09A413 Type: 0202E1 Date code: 040621.

Problem, this thing will not hold a steady RPM, the governor does not hold the engine at any given speed no matter where I put the governor spring on the governor arm which has 6 holes for the spring, the other end is on a bendable tab, no other adjustments on the carb or governor system at all.

What I have done: Cleaned carb, yes it was as expected with no stabilizer used by the owner. I verified all passages at least flow with carb cleaner, installed new seat (old one was swelled up quite a bit and held the float way up), new needle and new bowl gasket.

Engine starts with one pull all the time, which is great, but it will not hold a steady speed. I'm thinking a new carb is in order, thoughts?

[bgsengine]

Leakdown test and check for valve issues - hanging exhaust valve or air leak can do the same thing. Also, eliminate governor if you have not already , by manually holding the throttle lever from moving - try it under load and see if it smooths out (which would indicate idle circuit or air bleed problem)

If hunting stops when you hold the throttle steady from moving, it's governor problem (even a slight bind in linkages or gummed up governor shaft can do it) but if it starts to stall out or run rough, it's carburetor or air leak problem. Leaking exhaust valve can suck in unmetered air

[JandL]

Leak down test passes with less than 20% on the gage. If I hold the throttle to idle, it dies, I can keep it running but only at higher rpm range by manually operating the throttle which makes it run smooth but as soon as I get close to idle it dies pretty quickly.

[mwerles]

My vote is for a plugged idle circuit
Les

[bgsengine]

Yup - Clogged idle, or idle stop is set too low. Got a tach? will it idle steady at 1900 RPM? does it run smooth by itself at *top no load* (unloaded)?

If it idles smoothly at top no load, and only dies at idle, could be it is trying to idle down too low.

Also make sure it has time to warm up - they do run lean and surge when cold on those emissions compliant carbs - yours does not have a pilot jet, make sure you run some tag wire through the main jet holes in the bowl nut, and also double check float level - if the new seat is not seated fully, it can pop loose and float is too low ("high" when inverted) and won't have enough fuel in the bowl to run right.

[JandL]

Clogged idle, or idle stop is set too low. Got a tach? will it idle steady at 1900 RPM? does it run smooth by itself at *top no load* (unloaded)?

If it idles smoothly at top no load, and only dies at idle, could be it is trying to idle down too low.

Also make sure it has time to warm up - they do run lean and surge when cold on those emissions compliant carbs - yours does not have a pilot jet, make sure you run some tag wire through the main jet holes in the bowl nut, and also double check float level - if the new seat is not seated fully, it can pop loose and float is too low ("high" when inverted) and won't have enough fuel in the bowl to run right.

By the Tach, it will not idle at 1900, dies at around 2100 or so. There is NO idle stop, unless one counts the carburetor body itself, there is NO adjustment screw for idle at all.

Runs good at top no load speed if held manually but not with the governor.

Ran for 8-10 minutes and it never smooth's out under governor control.

Bowl nut is clear, ran a wire in it as you stated and it squirts cleaning fluid out both sides when sprayed in the jet.

float is right on, needle seat is secure.

Talked to Briggs and Stratton rep in my area today. He states this engine setup like it, has no idle and is setup to run at top no load speed only. So, running at top no load speed when held manually but not being able to do it with the governor would tell him its a fault in the carburetor. At the cost of the carb, around $35.00 I think my customer is better served by me getting a new carburetor for his snow blower.

Thoughts ?

[bgsengine]

By the Tach, it will not idle at 1900, dies at around 2100 or so. There is NO idle stop, unless one counts the carburetor body itself, there is NO adjustment screw for idle at all.

OK then post was mis-titled.

Runs good at top no load speed if held manually but not with the governor.

Ran for 8-10 minutes and it never smooth's out under governor control.

Bowl nut is clear, ran a wire in it as you stated and it squirts cleaning fluid out both sides when sprayed in the jet.

float is right on, needle seat is secure.

Talked to Briggs and Stratton rep in my area today. He states this engine setup like it, has no idle and is setup to run at top no load speed only. So, running at top no load speed when held manually but not being able to do it with the governor would tell him its a fault in the carburetor.

Got it bass-ackwards. If it SMOOTHS OUT and runs steady with no change in engine speed when you hold the throttle *STEADY* at top no load, it is caused by a governor issue. a new carb won't fix it. If you hold the throttle steady and it continues to lean out until it wants to die (or stumbles, or otherwise does NOT maintain the RPM it should) , THEN the problem is carburetion or air leak.

At the cost of the carb, around $35.00 I think my customer is better served by me getting a new carburetor for his snow blower.

Thoughts ?

First make sure which way is correct.
The governor test is to hold the throttle steady, and if the hunting or surging STOPS, and the engine DOES NOT change engine speed from where you hold the throttle, (It has no idle circuit per se, as there is no idle stop screw, as you mentioned, so trying to hold it to idle will cause it to die out) then the problem is in the governor controls somewhere. If you hold the throttle manually at 3600 RPM ,or whatever top no load speed is, and the engine STAYS at 3600 RPM and runs SMOOTHLY, it is NOT the carburetor at fault (Unless of course, the cause of the governor hunting is caused by a worn or binding throttle lever!)