Briggs and Stratton 21 HP Vanguard Problem - Idle up and down

TomAugust 30, 2010

Model: 385777

Type: 0349-E1


2002 or 2003 Model I believe.

Hello everyone. As most, I found this site via googling that I was having an engine problem. My issues is similiar to the post here:

My mower starting doing this thing where it would idle down a little bit when mowing - I could hear it losing power momentarily, then recovering. The problem steadily got worse. I tried all the usual stuff - plugs, fuel, air filter, etc. It actually got a little better with a new air filter, but would eventually come back. I took it to a small engine shop and they charged me a bunch of money just to basically spray carb cleaner in it and do the oil and stuff again - I was not happy, but anyway - the problem still exists. I ended up purchasing a new carb and it still had the same issue, even with a brand spanking new carb. What it is doing now is running fine for about 5 to 10 seconds, then "cutting out" for 2 to 5 seconds and blowing black smoke during those couple of seconds when it "cuts out" - It never actually dies from this. Well I take that back. It will die eventually if the air filter gets even slightly dirty. I mean as in I can't even mow my whole yard one time and it starts to slow down considerably and then just stop. But the problem still exists even if I take the air filter completely off. Now that I have ruled out carb, I want to think it would be a valve problem and that black smoke is oil maybe?? getting into the combustion chamber? Or it is dumping too much gas in there? I'm at a loss for what to do now. That other post mentioned valves and I would like to check the valve clearances if someone could direct me to the right info on how to do that. I really don't think it is a fuel issue, but ehh what do I know. Thanks so much for anybody that responds!!!!! I needs my mower to work!!!

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Also, the mower only has 82 Hours on it all together. I have changed the oil and done all that regularly each season.

    Bookmark   August 30, 2010 at 11:12AM
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By the first 4 digits of the Code #, the engine was built in year '04, month 04 (April of 2004).
Black smoke does not indicate oil burning in the cylinder.
Blue or blue/white smoke indicates oil burn.
Black smoke indicates either "too little air", or "too much fuel".

    Bookmark   August 30, 2010 at 1:14PM
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Ok - so sounds like you are stating it is a rhythmic fuel issue that a new carb didn't fix. What next? Should I try a new pump? What would the fact that even the slightest air restriction in the air filter causes it to get worse be indicative of? Again, thanks for your response!

    Bookmark   August 30, 2010 at 5:13PM
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Had a push mower that had kind of the same problem and would run good as long as I gave it a shot of ether.(must be very careful as ether is highly flammable) The trouble was water in the gas tank. Also the smart guys on the board always remind us to check the vent on the gas cap.

    Bookmark   August 30, 2010 at 6:55PM
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It has fresh gas with stabilizer in it currently. I have tried it with the gas cap completely removed to account for an issue with blocked vents. Still no dice.

    Bookmark   August 31, 2010 at 8:19AM
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Have you had the intake manifold removed from the engine?
If the intake manifold has a leak at either end of the manifold, it will cause the cylinder on the side with the leak to run lean, and can even cause the opposite cylinder to run a bit richer (we are talking "fractional differences" in A/F ratio).
But the real concern of having a vacuum leak on intake manifolds is the dirt and grit that will find its way into the affected cylinder.
Since none of the "cures" have been effective so far, check for a leak at the seam where the intake manifold meets the cylinder head using the following technique.
If you can get the engine to idle, let it idle with the air filter in place.
Using "spray carburetor cleaner" only (never use ether), with the straw nozzle on the can in the spray cap, spray a very low volume stream of carb cleaner along the manifold gasket seam.
If you notice any increase of engine RPM while you are delivering the cleaner to the site, and the RPM drops when you quit spraying.........there is a leak at that gasket seam.

This is about the only thing I can think of that could have such noticable consequences that seem to worsen if the air cleaner "gets even a little dirty".

The very bad and worst case scenario could be that the affected cylinder may already be "well worn out" if it has been eating a diet rich in dirt/grit.

I can send you a copy of a service manual for this engine if you send me an e-mail.

    Bookmark   August 31, 2010 at 1:10PM
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I sent you my email address. A copy of the service manual would be fantastic. Thank you so much. Supposedly, the last shop to look at it did a compression test and it was 145/150 on both sides respectively, but I wouldn't count on that as being done or accurate based on my experience with them. The air filter thing is what is really baffling me. A straight up brand new filter on there and after even 1 mowing of a residential yard it starts to act up and it never did that before. If you take the filter off it improves immediately, but now it does it (the flooding/black smoke/idling down thing) even with the filter completely removed. And all this is with a new carb or the old carb. I sincerely appreciate the comments and suggestions. I'm attaching a link to a video of what the mower is doing on vimeo. It was taken at night after an afternoon mowing, because I had to wait for my wife to get home with her iphone. Looks like it is going to take a while for the site to convert the video, but there is a link in the bottom right corner to download id you want to.

Here is a link that might be useful: Mower Issues - Briggs Vanguard Engine

    Bookmark   August 31, 2010 at 1:55PM
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and no, I have not had the intake manual off the engine.

    Bookmark   August 31, 2010 at 1:56PM
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have not had the intake manifold off the engine rather - sorry - mistype

    Bookmark   August 31, 2010 at 1:59PM
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Head-light is nice and bright!

    Bookmark   September 4, 2010 at 10:28AM
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The audio was a very good description of the problem.
I likened the sound to be nearly identical to my Briggs Twin 422707 when the main jet of the carb clogged with trash.
But, the "up and down" surges with both my Twin and your Vanguard are only the result of the governor as it "hunts" for a smooth and steady place.

After hearing the audio and knowing your carb is new (and presumably good) I wonder if there is something "sticky" about the governor linkage or the governor shaft.

    Bookmark   September 4, 2010 at 1:04PM
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@rustyj14 - yeah, at least it has ONE good headlight!
@mownie7 - that is an interesting thought. Yeah, I couldn't believe a brand spanking new carb had the same problem. I mean it ran a little smoother than the old one when it wasn't flooding out, but still had the same issue. I still haven't had a chance to try the carb cleaner to the manifold thing yet. Hopefully will today or tomorrow.

    Bookmark   September 4, 2010 at 5:25PM
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Ok so I pulled it apart again. I tried spraying with both carb cleaner and ether (even though you said not to) - around the intake manifold connection to the head and it didn't surge or anything. I then took the manifold completely off and inspected the gaskets - no issues. I replaced the caskets in front of/behind that black plastic spacer behind the carb as well just to see if any air was coming in through there. I cannot for the life of me figure out this issue. I checked the governer linkage as well and couldn't see any issues with anything. What in the world is going on with my mower? I mowed with it, but I could still hear/feel it losing power then throttling back up. If anybody knows of any GOOD small engine mechanics in the Memphis, TN - please let me know. Any further suggestions would be most appreciated.

    Bookmark   September 13, 2010 at 3:49PM
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Ok guys, I'm hoping to have some time here to look at my mower again. I was able to mow with it last weekend, but it just really sucks becuase the thing is constantly idling down like it is flooding. I am going to check something else I saw on here about the full pump (something about a vent being clogged on the back of it). Also, I noticed that the hose that runs from the valve cover to the fuel pump appears to be torn. If this is a vacuum driven pump, could that be the culprit. Walt, could you email me instructions on checking the valve's specifically? A gentleman named Larry send me the manual for this engine, but It appears you may have some specifics on how to do the valve adj./check. I already have some feeler guages. Thanks again all! Tom

    Bookmark   September 23, 2010 at 12:26AM
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If the hose from the valve cover to the pump is torn or cracked, yes indeed, the volume of fuel being pumped to the carb will be less than specification.

    Bookmark   September 23, 2010 at 1:26AM
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mownie, do you have any idea of that part number (for the hose)? I can find the pump itself, but the hose doesn't appear to be in the exploded view of the engine.

    Bookmark   September 23, 2010 at 2:17AM
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Is it this the part for the valve cover to fuel pump hose? Could I just use some fuel line I have around the garage?

918 393815 HoseâÂÂVacuum
(Cut To
Required Length)

    Bookmark   September 23, 2010 at 2:34AM
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393815 is the part #.
Yes, you can use standard fuel hose as a replacement material.
Only in certain applications where a "bend" is formed is it actually necessary to use the OEM Briggs hose item.

    Bookmark   September 23, 2010 at 12:08PM
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Well guys I finally was able to adjust the valves and it appears that that was the problem! I checked the fuel pump hose first and it was really the outside that was torn a little. it wasn't split all the way through. So I followed Larry and Walt's info on adjusting the valves and they were WAY off. At 1/4" past TDC the intake valve had no valve lash (IE no feeler guage would fit) and the exhaust valve was way loose. I adjusted both to where the .005 part of the feeler guage would pass through with minimal resistance, but the .007 part of the guage would not go at all. It took me a few tries to get it how I wanted it because of movement when tightening the lock, nut, but I finally got it. Unfortunately, I don't have a torque wrench at the moment. i will get one and recheck/retorque one day this week hopefully. I was crossing my fingers and saying "please Lord, let this thing be fixed" and it was. It still blows a little puff of black smoke when I throttle it up quickly, but I think it always did that. I now have to readjust the idle mixture screws that the losers at the mower shop got all out of wack. It took me a while to get the backfiring to stop. I have to tell you that I am no only excited to finally have a working mower, but also extremely appreciative to all you folks on this forum for the suggestions, advice and expertise. As I stated (I believe I did anyway) - I have contested the charges the mower shop put on my CC for essentially doing nothing to even address my problem. Based on what I have read on these boards, these engines are known to need valve adjustments, right? It is not unreasonable for me to assume that a competent shop should have known to check that after I explained my issue and what I had done, right? I may have to use some of this discussion to show the CC company that I had to fix the issue myself, should the shop contest my contest! thanks again guys! Never thought I'd be so excited about mowing!!!

    Bookmark   September 27, 2010 at 3:52PM
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Ok - well it is a new season, and my valves were not the problem. I mowed for perhaps an hour shortly after my post last Sept. and the problem reappeared. I got the mower back out yesterday and did another valve adjustment on it just to be sure (using the specs supplied by a forum member here - thank you!) and tried again - no dice. Contacted a different mechanic and he said to try some seafoam just as an offchance it might work and it did not. I let the mower run for a good while, pulled the plug wire off of one cylinder to see if I could get it running even fairly well on either cylinder by itself and could not. What finally happened, is after running for I'd say 30 minutes or so, at fast throttle, it just started slowing down, slower, slower, slower - blowing black smoke all the while, and eventually just slowed down to the point of not running anymore - and it quit. I tried to restart and it would not lite. It wasn't seized up as the starter would spin the engine, but would not lite. I am completely baffled as to what could be wrong. I'm about to just give up and buy a Kawasaki and put on the frame as the mower is in good shape otherwise. Deck and spindles are perfect. Anyway, I am really, really, really flustered by the whole thing and was hoping to get some advice before I just give up. I need to do some core aerating badly. Thanks to all the experts on here! Tom

    Bookmark   April 7, 2011 at 10:48AM
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also, if I just give up on this motor, can I replace it with this Honda engine?? It has the same size shaft off the crank.

    Bookmark   April 7, 2011 at 11:37AM
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I bought a new coil and compression tester on amazon - will be here tomorrow. I'll try that. If the coil doesn't work, I'll see if I can run the thing to wear it quits and then test compression then (hot) to see if perhaps there is a problem with one of the valve seats or something.

    Bookmark   April 7, 2011 at 6:19PM
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I take it the warranty out by years? IMO that's why they put time limits cause they know most people won't put to many hours or do any maintenance on or in two years.

When it won't start that's when you need to troubleshoot it. IMO first I would do would pull the plugs see if you getting fire at the plugs (pretty blue spark, no orangish and of course no spark) It you got spark spray carb. cleaner down the spark plug holes and see if it will start up on the carb. cleaner. If it fires of the carb. cleaner and dies you still have carb. issue or compression lost.

I afraid you going to have to take the heads off and look in the comb chamber at the cylinder walls, valves and head gaskets. seems like your problem occurs after the engine heats up and of course that would be the ideal time to take compression when it quits also. my guess would be cracked head, or something causing it to loose compression, that;s why you need to take the compression when it dead, if you got 130 PSI or more then IMO the bottom end, valves are good but that IMO don't over rule the head gasket or cracked head. I would also take the cooling fin covers off and see if I see any sign of leakages before I go tearing it apart.

there alot of engines that will fit Based on the shaft size and length Course it easier to get the same type engine (HP number not that important but hookups are. if they are the same then HP don't matter as long as it close to what you've got. Most problems with going with different brand are the muffler and starter setup and throttle cables arrangement and brackets and of course if it will fit under your hood cowl. For the price of honda you can get you another used mower. and fixing the old one if you can do it yourself would be the best choice money wise IMO.

    Bookmark   April 9, 2011 at 11:07AM
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Did I read this mower only has ONE good headlight? That could be significant! Had one with one good light and one melted headlight. A leak at the exhaust was causing carbon to get up into the area of the carb plugging the air filter and overheating the carb. It would run for a half hour or so and then shutdown until it would cool off. I would not have found the exhaust leak if not for the melted headlight.

    Bookmark   May 4, 2011 at 10:08PM
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i have exactly the same engine and issues as tom. i've done everything he has done with same results. been going on for several years. i think mine has around 50hrs on it. i thought about new engine as well but funds won't allow it.

    Bookmark   May 6, 2011 at 4:57PM
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I finally got mine fixed. Replaced both coils, both spark plugs, adjusted the valves again. and put the carburetor I bought last year back on, and a new air filter, and now it is running like a champ. I just threw everything at it. I think it was really probably the coils as it would slowly "wind down" and quit once it got hot, but it could have been numerous factors that manifested themselves in multiple issues. It runs great now, so I am happy, but I had to spend like $300 on the doggone thing if not more. Also, my mower now has about 150 hours on it because I left the stupid key on for a few days and that hobbs meter was just a gettin it until the battery ran down. Oh well. I suggest doing all the above if you can't figure out what is wrong with it.

    Bookmark   May 9, 2011 at 12:02PM
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Hi Everyone,
Wow, this is quite a trial. I am confident this is a vacuum line issue, and i fixed a similar problem on a Saab a while back. I recently got a YTH2148, and it is missing a vacuum line and you can clearly see this from the missing line on the top of the carburator. I came upon this thread while searching for a vacuum diagram of the Vanguard 3385777-0349-e1 engine to fix my own issue with the hunting idle (like you describe and was posted in the vimeo video).
Best, Alex

    Bookmark   June 17, 2011 at 11:32PM
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Richard444(5 Northern Lower MI)

I have a 3 yr old craftsman riding mower 21 hp Briggs and Stratton, When idle or run it gallops fast and slow fast and slow until I put it under load ( when I engage the blades) then it runs fine, but just riding the mower it pops, and the engine gallops the throttle spring( not sure what it is actually called,vaccume spring?) is not steady and moves back and forth many times. New plug, new gas, new filter checked the cap and hole, good air filter, tried to adj carb no luck. Can anyone give me an idea how to fix this,?

    Bookmark   September 17, 2013 at 6:12PM
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richard444 - start a new thread. See the opening page of this forum for instructions.

    Bookmark   September 17, 2013 at 7:34PM
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