Engines been down for three months, missing out on all the duck action, need some help here guys.

I have 2008 23hp vanguard mudbuddy mini surface drive with a X-over BPS exhuast. It has 40 hours on it ran like a champ until......all of a sudden it started backfiring and missing after an hour long run one day. Never saw any smoke, and it never ran sluggish prior to this happening. It just instantly started missing a lot and backfired if I gave it throttle on the water. I took it home and changed all the fuel components and spark plugs. I then checked compression and got 80 and 60....way too low on both cylinders. I figured it was bad headgaskets, so I took it to a shop.

They thought bad gas may have caused valve problems. They completely rebuilt everything from the headgaskets on up(valve seats recut, carb rebuilt, new gaskets, etc). Mechanic said he found a loose push rod/rocker arm and one sticking valve, but otherwise didn't look horrible. The mechanic said the compression was now 147 and 150 and I should be good to go. . ( I Called Micah at Mudbuddy at this time and he said that unless the valves were completely messed up, that was a lot of compression to be loosing through valves. He said that judging by the symptoms and compression, it sounded more like headgaskets). Either way, they said it was repaired, so I took it as fixed. I go to test drive the motor after everything is done, and the engine still does the same exact thing. The compression IS back up to normal, but its having the same misfiring problems.

Here's the funny part:

If I keep the boat on the trailer and give it 3/4 throttle, it has a ton of torque and never misfires. It is under a decent load because its pushing the whole trailer, but it doesnt misfire under a load on the trailer( usually only turns 2200 rpm when its backed down into deep water). When I take it OFF the trailer and run it in the water, as soon as the boat starts to plane (the engine turns over 2500 rpm and the prop starts to surface), the engine starts misfiring/backfiring.

The shop has now replaced my coils, diodes, fuel pump, placed an secondary inline external fuel pump, rechecked the valve and carb job, and changed the easy access plugs on my carb. Each time they retest the boat in the water, it does the same thing. They are floored.

A third party company that does warranty work for Briggs and Stratton (SEDCO) told them to force the engine to run off one cylinder to see if one cylinder ran cleaner. I was operating the boat when we did this. We got the engine to turn over 2500 rpm and misfire, and then unplugged one cylinder at a time. When ran individually, one cylinder ran much cleaner than the other. They also told them to get the engine to misfire and then apply the "choke" to see what happens. When he applied the choke as it was misfiring at 2600 rpm, the motor instantly sounded better. Sounds like some sort of fuel issue, but short of finding a crack somewhere, everything else has been replaced.

My problem is that they have had this engine for 3 months now trying to figure out what is wrong. The motor is under warranty until the end of this month. They are trying to say that it has been bad gas to cause all these problems, but I cannot believe that as they don't even know what exactly is wrong.

I still can't figure out at what point Briggs and Stratton steps in to just replace the motor. They have spent......who knows how many hours diagnosing and replacing parts and continue to scratch their heads.

Anyone got any ideas on what else could be going wrong with this engine. Compression is back up and a ton of new parts have been applied. They are going to take all the shrouds back off this week and spray the block with starter fluid to see if there is a small crack in the head or intake. They aren't magnafluxing anything, just running the motor and spraying it to detect a change in rpms.

I understand that it is somewhat difficult to diagnose as everytime they want to test it, they have to take it 15 minutes down the road to run it in the water. On the other hand, I would think that Briggs and Strat would have stepped in and just replaced the engine. Three months with no boat, they have no clue whats wrong, the bill is probably outrageous by now, and I still have the feeling that in the end, I'm gonna have to battle out the warranty issue. It's not like I can just take my engine and bring it to someone else either, because as we don't know whats wrong, they aren't going to let me take it without paying the bill. Briggs and Strat certainly isnt going to pay the bill until the engine is back running properly.

Any ideas/suggestions? I'm pretty much disgusted with the whole situation at this point. If anyone has some insight on what else could be wrong or what measures I can take to get this thing fixed, any input would be greatly appreciated.

Take it back before warranty is up and blow the f*cker up!!!

Then they will have to give you new block. Thats what my mechanic always tells me. If ya got a problem make sure ya make it good before warranty is out.

If Briggs would warranty the engine, I would believe it would go by the date it was placed in the shop.

Any ideas on what could be wrong with the engine.

Sounds like you have either a bent push rod or a bad camshaft !!!!!!

I'd have SEDCO file a warranty claim for a new engine or at least have them do the troubleshooting on it.

change ur wiring harness and ur diodes, sounds like one is crapping out past 3/4 throttle. or possibly a bad wire in the wireing harness.

any mech worth a flip should be able to figure it out, it ain't a big block chevy, it's a lawnmower engine.

hope u get it figured out and good luck!!!

You need to get it right before your warranty is up. What is the shop saying to do next?

We had a Briggs powered generator in the Army- would bog under load like you described. After alot of times to the shop and head scratching, an old Sgt gave us a tip. Drain the oil, run it till it locked up, pour the used oil back in. After that we got the motor replaced. Took 45mins for it to lock up (engine just didn't want to die).

dead animal - thats what I keep saying.....its one of the simplest engines out there. They already checked the diodes and they were fine.

deadbird - I just found out that as long as it was in the shop before warranty expired that I'm still covered no longer how long they keep the engine. The shop says they are going to spray starter fluid on the block to check for a crack or porous spot in the head or intake. After that, they have no clue.

Thanks for trying guys.....seems like all the suggestions here have already been attempted by the shop. The only thing that hasn't been changed is the wiring harness, so that might be something to look into.

hey my 23 hp gdsd began doing the same thing ran perfect out of the water but once in the water began backfiring an would not go past 2500 rpm i took the carb apart three times cleaning out all gets each time but never removed the 2 idle jets on the top of carb so i remove them an had to replace one an did a lot of adjustin on the water and it did straighten out an stop the backfiring an am usin it to this day i hope this helps good luck

I am thinking camshaft...Had a 350x 3 wheeler do the same thing..I changed all the electronics and carb..Still did it..Tore the heads off and they were good.Dug a little deeper and had a flat cam.

Its the camshaft had the same thing happen when I wore the lobes on mine you can check it roughly by removing the valve cover and turning the motor over slowing and measure with a tape the distance between the min lift to max lift at the push rod pivot point this will not exact but it will give a quick idea, bet your exhaust lobes wore out it will run at a slow speed but not a a high speed because the valves don't open enough to let enough fuel/air mixture in when it demands it.

Also if you want to check the coil diodes just unplug them it will run without them just fine they are only used to stop the engine when you turn off the engine it grounds the pickup coil in the main coil and the diode just stop current flowing back and forth between the two coils cause they don't fire at the same time and you only have one ground wire to kill they are like a check valve for electricity.

BASINLOVER and COASTAL....yall are saying that the cam exhaust lobe/lobes may have worn down, but that (too me) would imply that the motor would have ran semi-sluggish as it wore down. The engine ran 100% top notch and then just started missing suddenly. I would think that if the cam started to wear down I would notice some deficiency before the big problems.

Also, like I said in the main post, if I put the choke on when it misses, it runs "cleaner". It doesn't run 100%, but just sounds a lot better. Yall said you're engines did the same thing - did it happens suddenly and get better with choke on? I think its some sort of fuel problem, but like I said, the shop has been through the fuel system 3 times already.

I did forget to mention that the cylinder walls had hot spots on them when they took the heads off, so something caused the engine to run hot when this all happened. The hot spots weren't too bad and there wasn't any scarring. Just wanted to throw that in there if its helps with a diagnosis.

When my lobes wore out it did it within five minutes of running from my camp to the boat landing ran fine than all hell broke loose as for the scaring that makes sense because if the exhaust valves are not opening properly then the burning gas cannot excape and the engine will overheat, also it should of messed up the valves ether warping or something and because when you run with the choke means you are putting more fuel which creates a bigger flame front and it will try to run better but it just can't get out of the engine so unburnt fuel is still residue in the cylinder and it detonates cause of heat and detonation making it backfire. This is exactly what happen to me, the engine even after all of this would run fine at a slow speed but would not run at a high rpm. I would just check the lift its easy, I don't have the lift specs but you will notice it cause the intake and exhaust is very close the only way you will not is if all 4 lobes wore out then you have nothing to compare to you will have to know the lift. Also when you ran compression did you have the throttle wide open because this makes a difference. The thing that concerns me is that your compression came back up. I would check again. Start from the basics unplugg the diodes, remove the air filter cover and watch the fuel being picked up by the venturi in the carb (does it increase as you throttle up), put a timing light on the plug wires(one at a time) and watch the firing in the light is it at the same time as the engine is firing or is it firing when it is not supposed to, measure the lift at the push rod pivot point not the rocker pivot point are they the same. remove the nut on the flywheel and look at the fywheel key is it exacly the same as the the crankgroove. If all else fails and all this test out try some iriduim spark plugs in it because some engines will foul the plugs quickly(briggs expereance don't ask) which is also what mine does alot and it will not run right with regular plugs, I have no explanation for this but I know this works. You may of had a avalance effect I think one thing may caused another. The repair place may of put the same plugs in which were fouled after this all happened. Sorry for the long message but you have to start somewere.

basinlover - they checked the cam and said all was right on. They are ordering a new carburetor this week to try that.

It sounds like it could be floating a valve which usually occurs at high RPM's! It would prolly be worth there time to check the valve springs. My next suggestion would be the carbs air/fuel its sounds like its trying to lean out on the top side this would also cause the motor to run hotter than normal. Where the plugs white on the tips when you pulled them out? These are just suggestion im surely not a pro but have a few back yard builds under my belt!

Is it possible that it is running up against the rev limiter? or govenor?

It was the carb. They replaced it with a new one and I'm up and running. Briggs and strat paid for the carb and labor for the carb replacement under warranty.

They probably would have paid for the head work if the idiots would have put it in the warranty claim, but the shop didn't. I'm just gonna pay the difference ($300) and go get my boat. Not worth fighting with these fools.

Thanks to those who tried to help. Getting it back just in time to freeze my balls off in this weather