Backfire/Pop On Brand New 4.3L Mercruiser

[CpaBert]

I have a brand new 4.3l mercruiser with a new 4 bbl carb. When I really give it throttle it likes to pop / backfire, I BELIEVE through the carb. Also, when I am running at about 4000 RPM and punch it to 4500-4800 it starts to pop then too.

I am wondering if there is a setting on the carb I can change or something as it all is brand new, so it shouldnt need any work. Pisses me off, paid DARN good money for the install and the motor, gotta get her running perfect.

Thanks in advance guys!

 

[Blade_Link]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

ok if its brand new its under warrenty id take it back and make them fix it.

sounds like a float or fuel prob, but i refuse to work on newer motors they are way too complex (like car motors these days) ill stick with my older ones that i can fix with my eyes closed being that there is not 50 ft of wiring and distributers and stuff, strail ignotion and carb all the way

 

[Bondo]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

ok if its brand new its under warrenty id take it back and make them fix it.

Ayuh,... Agreed,.... It's going Lean,.. It Could be the Carb, or anything from the Tank on out To the carb...

 

[diehard]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

just becase it's popping threw the carb does not mean it's the carb.it has to pop some where it would be hard to hear in the exhaust ..did this happen the first time you ran it or did it happen after a few hour of use ..it could be a plug wire , spark plug, timing, was it a brand new engine or a rebuilt ? i have instaled rebuilt engine's only to find the machine shop messed up on the valve work [not saying this is your problem] if you paid someone to intsall it have them fix it ..hope you make out ok

 

[CpaBert]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Okay, so here is what I have tried:

I am at the lake so I tried to get the timing more in sync a bit by EAR, POSSIBLY made a bit of a difference, but still is a bit sluggish of the the get go and backfires on full throttle.

I pulled a couple sparkplugs and found them to be REALLY black and "sooty", I'm not sure, but I thought if it was lean they would be almost white, or a really light brown.

If it was sparkplug wires, would it backfire all the time, not just under load or WOT?

Thanks for your help so far, I'll just try to keep trouble shooting with what you guys say! KEEP EM COMIN!?

 

[jtybt]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Could be lean condition as Bill said but from what you say about the plugs(which you should have mentioned in the beginning) sounds like you have those two plug wires crossed.

 

[CpaBert]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

I just found out about the plugs as I just pulled one today after reading into it a little more.

Wouldn't having the plug wires crossed make it run like Shiot all the time, not just under load or WOT?

Also, every plug looks like that, just got done pulling them all.... This sucks, thanks for the tips so far guys, not sure whats gonna be the culprit here...

 

[backyard mechanic]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

There can only be one cause for backfire in 4 stroke engines; timing of the valve and ignition. Think about it... when the spark occurs and the intake valve is open to ignite the fuel in the intake manifold it "backfires" through the carb.

Let me say it more directly; IF valve timing is correct and the ignition timing is set correctly it is impossible to get carburetor backfire because there is no ignition source to ignite the incoming fuel.

Solution... take the boat back to your dealer and have him set the motor up. It's obvious they got it "set up" from the factory and sent it out the door as they recieved it. Bad idea! They need to recheck valve settings by running the engine and resetting the hydraulic lifters. Then they need to reset ignition timing. At the VERY least; they've got to reset timing or they may be buying you a motor for preignition piston/valve burning.

 

[CpaBert]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Thing is do I take it back to the same retards or do I take it somewhere else, I mean ****, if they didnt even check it over before they sent it out the door, do they really have a SNIFF?

Another note: I took my prop off, just to clean it and lube the shaft, and I noticed ALOT of carbon (black soot) on the inside of the prop where the exhaust blows through.

Would the timing issue result in all this damn black ****? What the hell is the black **** exactly?

Thanks for you help so far guys, hopefully I can get to the bottom of this...

 

[jtybt]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

If all the plugs are black and sooty, it's because of fuel not burning. If it was wet with gas smell, it would be too rich.

It may very well be a mechanical problem from the factory...or the dealer fooled around with it.

Do a comp test. Does not sound like a normal 'NEW' boat.



...and I wouldn't trust most dealers.

 

[CpaBert]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

I ordered the motor separately from a company online called ATP Engines, seem like a reputable company.

The only guys I had trouble with are the guys who installed it, being borderline retarded.

 

[diehard]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

it could be in your carb. running to rich would foul out your plugs and cause you to hear that popping sound .. on your carb you have a couple of screws that adjust your air fuel mixture ..find those [2] screws then start your engine set your timing with a light to proper spec. then turn one at a time [ probly out] until you hear you moter run it's best then do the other one same way ..that will help you lean it out ...you may have to clean / change your plugs as there are already fouled ..

 

[Don S]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Okay, so here is what I have tried:

I am at the lake so I tried to get the timing more in sync a bit by EAR, POSSIBLY made a bit of a difference, but still is a bit sluggish of the the get go and backfires on full throttle.

There is your first mistake. You can NOT turn a distributor and time by ear on these new distributors. They have to be put into base timing mode.

Your second mistake is not taking it to a Mercruiser dealer. There very well may be an issue with some engines and a service bulletin is available to the dealers. It's a warranty thing, it doesn't cost you anything.

Of course if you keep messing with it and damage something, YOU will loose your warranty.

 

[Alumarine]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Is this a rebuilt engine that was installed in an older boat?

 

[CpaBert]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

I took it to the biggest boat service center within 200 miles.

Not my fault they turned out being retarded. I don't think they timed anything or did any of the basic checks before they sent the boat out to me.

Like I said the engine was purchased from ATP Engines, because the price that the dealer gave me was absolutely disgusting and they could only get a rebuilt engine.

The engine is BRAND NEW not rebuilt, like I have said 1000X.

My question is, if I'm going to time it by a timing light I need to know what top dead center is and I don't have that info and ATP engines is closed until monday.

Anyone know what top dead center would be, would it be the same on every new block or would there be differences.

 

[backyard mechanic]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

The biggest dealer within 200 miles does not make it a good place to find a reputable mechanic. MOST dealers will do the least to get the product out the door. Sell boats is what they want to do. Service and customer satisfaction is a whole different situation (as you are finding out).

From what I can tell by your posts; If this motor has a warranty it is through the engine manufacturer (ATP) not Mercury marine. If it was just a short block someone had to "build" the engine and set it up. That may be a warranty item as well. Call mercury Marine if you are dissatisfied with service you are getting at this dealer. Ask them what you should do and have them record your complaint. You may end up going to court to get warranty through the dealer. That can be expensive and often counter productive.

I'd take the thing to a reputable mechanic and have them set it up. (Keep your reciepts on all this REPUTABLE mechanic does/finds). In doing so you have record of your call to Merc Marine, and a record of what it took to make this engine run correctly.

The black you see may be residual from the old burned up motor that obviously wasn't set up right. That you still have the same conditions tells me this one isn't set up right either. Either way it is carbon and carbon is unburned fuel.

The end product or end requirement is get this to a REPUTABLE mechanic who can set it up from the start. It's going to mean going through compression testing and assuring the cam timing is correct. Then valve set up, assuring carbs are set correctly and timing set to performance.

Good luck!

 

[n2ostroker]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Make sure you have good gas and a new fuel filter. Then check the firing order. Then the timing. Then the valve adjustment.

 

[Zeeter]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

You are definetely running rich as to why who knows.
I think your beef is with ATP engines. We have no idea what model year this is or what it was meant to replace. Brand new means nothing. Define new.
A 2008 4.3 is not the same as a 1999 4.3 application.

 

[Bondo]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

The engine is BRAND NEW not rebuilt, like I have said 1000X.

Ayuh,.. OK,... Was it Fully Dressed, or did they reuse the components off the take-out motor,..??
What was the diagnosis of the Take-out motor,..?? Why'd it Blow Up,..??

The motor is Seriously Over fueling....
Either a Bad new carb, or poorly set up...

Either way, call the folks you Paid it do the job,+ let them make it Right...
Everybody makes Mistakes,... Don't bad mouth'em here, especially at This point...

My question is, if I'm going to time it by a timing light I need to know what top dead center is and I don't have that info and ATP engines is closed until monday.

Anyone know what top dead center would be, would it be the same on every new block or would there be differences.

Like I said,... Bring it Back,.... Before you F-*k it Up.....

 

[CpaBert]

Re: Backfire/Pop On Brand New 4.3L Mercruiser

Got it going good. Ended up being that the float was set way off in the carb, and the Accel pump was throwing in sparadic amounts of fuel.

Got the timing reset too...

Runs pretty damn good now, sucks that now its time for winterizing...

Thanks everyone for your replies!