Backfire at slow speed or under stress

[bosshoss07]

New to the forum. Bought a 90' 23ft Celebrity Cuddy. Has 7.4 in it. First mistake bought it off EBay. Guy I bought it from said it ran great had new "built" motor close to 480 HP. Showed me some rcpts that showed some a "Now out of business shop" had done the work, he did not mention that part. Of course bought it over winter time. He cranked it on the trailer, started fine all trim, etc worked.

Now we've started to find the truth. Started with the thermostat (overheated the first day out), next impeller and pump were toast and last , but not least....the outdrive went on it after our first 15 minutes in the lake this year.

Got most all of that fixed to the tune of about $4500, but now I'm getting a backfire after it warms up and runs for about twenty minutes, throttle it up some and a few more backfires and it clears up for about another twenty or so minutes, also when warm under slow speed pressure (ie. trying to pull a tube etc), but then clears up again with a few pumps of the throttle. Not a major problem...just annoying. I have changed all the fluids twice, next is the plugs and a good carb cleaner...Looks to be factory carb was left on it. It does hold a good idiol after warm.

The boat looks great, we have redone all of it so I really do like the boat even though I got the short end from the seller. I think it will be a great boat after I get the kinks worked out. Also, while I've got an hear.. the trim gauge is not working correct. I am assuming I need to adjust the trim range on the of the outdrive. The gauge shows all down and then will spring up all of a sudden. I will put the muffs on it this weekend and reset the perameters of the trim., also making sure it is moving up and done, the auto trailer button does fine ..is that the correct way to get them lined up??

Okay experts.....should I start looking to replace the carb, or what direction would you suggest??

Your helps appreciated..

 

[Bondo]

Re: Backfire at slow speed or under stress

Ayuh,....

It could be the Carb needs a Cleaning,+ Rebuild,...
Or theFuel Filter is dirty,...
Or a Bad fuelpump,...
Or Bad fuel lines,...
Or even a Bad fuel pickup in the tank,.....

I'd start with the Fuel Filters,+ Check things out from there.....

 

[bosshoss07]

Re: Backfire at slow speed or under stress

Thanks for the response,
Fuel filter was serviced-replaced about two weeks ago (I had a guy do it who swore he knew boats "Cycle-ATV-Jetski Shop") of course he was supposed to have it ready to go. That was before I found out I need the rest of the " issuses". He apprently did not notice them temp gauge getting maxed out or that there was no water return flow from the stuck thermostat. If I just go w/ a replacement carb..what would be your suggestion. I think the guy that sold it to me, or the engine builder was "full of it" to say it was a 480 hp motor. I have a 530HP smallblock Boss Hoss bike and this boat is not even in the same league motor wise. Like I said before my PrinceCraft with a 115 will stay pretty darn close topend wise. What carb would you suggest? I have no doubt that there has been motor work, sounds more like a mild cam. I am into my bikes and cars, my expertise ends there...any info on this would be appreciated. I see carbs listed all over the place from $200 bucks to $900+, also what would be the best source to purchase. I see Summit offers a nice marine carb??any other ideas or what size would you suggest?? Thanks again guys...as usual, these forum are the best answer to questions.

Thanks,

Tom

 

[Limited-Time]

Re: Backfire at slow speed or under stress

I'd find out what came stock on the engine and start from there. I know Edelbrock (sp) makes a great marine performance carb. several of the old salts here swear by them. I'll see if I can find a link or model number, and post it................It's a Model 1410, 750 CFM (square bore). Price is right at $330.00

 

[chiefalen]

Re: Backfire at slow speed or under stress

y not just rebuild the carb.15 bucks for a carb kit any napa has them.than u wont have to worry about different adapter plates spacers and all the other stuff associated with a non stock carbdon't u have enough money tied up and not one day of enjoyment yet?

 

[Limited-Time]

Re: Backfire at slow speed or under stress

Shade tree carb rebuilds are a crap shoot at best.....IMO. Getting back on the water ASAP, with no further carb issues seems to be the OP's main objective. That calls for a new or remanded carb...............bolt it on.........a few simple adjustments, and go.

 

[paulrfrancisco]

Re: Backfire at slow speed or under stress

Couldn't the backfireing be a cracked distributer cap dirty plug wires, dirty or oily plugs, or worn cross firing plug wires?

 

[paulrfrancisco]

Re: Backfire at slow speed or under stress

I see carbs listed all over the place from $200 bucks to $900+, also what would be the best source to purchase. I see Summit offers a nice marine carb??Tom

http://www.marinecarburetor.com/index.html

 

[Bondo]

Re: Backfire at slow speed or under stress

If I just go w/ a replacement carb..what would be your suggestion.What carb would you suggest? any info on this would be appreciated. I see carbs listed all over the place from $200 bucks to $900+, also what would be the best source to purchase. I see Summit offers a nice marine carb??any other ideas or what size would you suggest??

Ayuh,......

Maybe it's Just Me,.... I donno.....But, I'd prefer to Find the Cause of the Issues,....
Rather than just Throwing Parts At It, til you Just Happen to hit the Jackpot.....

In all probability, You've got the Merc/ Weber Carb,...
Which is the exact same thing as the Edlebrock, which is just another Carter AFB Clone....
I think Merc had dropped the Rottenchesters before your boat was Built....Maybe not...

I have a 530HP smallblock Boss Hoss bike and this boat is not even in the same league motor wise.

Ayuh,.... At what RPMs,..??
We're talkin' Boats here,... Not Hot Rod Cars or Bikes....
That motor would be either a Pig, or a Disaster in a Boat.......

Same Game,..... Very Different Rules......

 

[Coors]

Re: Backfire at slow speed or under stress

This always gets one issue out of the way.
http://forums.iboats.com/showthread.php?t=167561

 

[bosshoss07]

Re: Backfire at slow speed or under stress

Thanks guys..gives me some good places to start checking. I also noticed my gear resovoir is now empty. I filled it Sat. Its old and the bottom is shot (leaking some) did not realize that until today looking at the carb. A new one on the way. The forum is the best, can't wait to dive in and get checking this weekend. Start from basic like plugs, wires, carb, cap and work my way up..I guess the weekend is shot.

Adios,

Tom

 

[rodbolt]

Re: Backfire at slow speed or under stress

your just not describing a carb issue.
I would carefully test/inspect all ign components.
when you pull the plugs carefully inspect them with a good light.
your description is exactly what a leaking riser or riser gasket.
water drawn into the exaust,especially if the wrong cam was used for marine applications, will cause your exact symptoms.
in freshwater applications it will leave a reddish deposit on the plug grond electrode,in saltwater you will see tiny green flecks.
if you see silly cone seal on the riser joint gasket simply go ahead and drain the manifold,remove and correctly reinstall a new riser gasket.
but long before I bought a carb I would do some testing.

 

[MikDee]

Re: Backfire at slow speed or under stress

Nice boat! I had an older 86' 22.5' Celebrity SS with twin V6 205hp OMC Cobra's in it. Those boats are built strong, & sleek, with a good performance hull design, that was neglected also, the pics are in my signature, sorry your having so much trouble with it. It sounds to me like a fuel delivery issue, not serious enough to warrant a carb. As you said it runs, & idles fine. As bondo mentioned I'd go over it good to find the problem first, before replacing parts. Is this a Mercruiser, or an OMC, you didn't say? The general servicing, and the trim guage adjustment is different on each.

 

[bosshoss07]

Re: Backfire at slow speed or under stress

It's a Mercruiser. 454. NEW Bravo 1 outdrive. I just did an eyeball check on the carb last night..wow, nasty. I am also going to install a through hull exhaust. The one that uses the stock riser and a new tri-through hull hardware. Might as well let it breath better. The exhaust is last. The trim adjustments are on the outside with a puck on each side. A set of wires off each side feeding through the transom.
One of the set of wires on the left side has little to no insulation left on it (looked burnt off). I am assuming that is why my trim gauge is working funkie. I saw a post somewhere here how to get the gauge back in line with the actual trim gauge. The wire is not broken, I just need to put some shrink tube or some insulation around the left side wires. The right side is okay. Can somebody give me or tell the post to allign the trim w/ the limiters and guage. If I recall it was a short sequence by adjusting the screw limiters.
It sounds like a turd, but actully should be a great boat (when and if I get done).

Thanks again guys..

Tom
Dyersburg, TN

 

[paulrfrancisco]

Re: Backfire at slow speed or under stress

I think this is the link for the trim limit switch adjustments... I think this is for a Bravo1

http://www.mercstuff.com/trim_limit.htm

Also, I wonder if the trim wiring could cause the backfiring... behind the carb near the distributer is a black 2 wire plug that you can disconnect. This disconnects the trim sending units. Bare wires on the sending units in salt water can cause pretty bad electrolisis...

 

[bosshoss07]

Re: Backfire at slow speed or under stress

Thanks,
That was the thread I was looking for. Wow..it's gonna be a long weekend. Thanks again!!