Merceuiser 3.0 lx backfire problem.

[204_boater]

So iv had the boat for over a year now, 2 weeks ago it had a little backfire when i was going to my fishing spot. It had a little of an idle issues but that went away for some reason. Any who, I rebuilt the carb. Dipped it for about 6 hours since i read in the manual not to soak it for a bit or else it would kill the coating inside. did that, used canned carb clean, blew out every orfice in there and then did it again. Used a sierra carb kit. got it all done took it to the water and the damn thing back fired around 1800 to 2000 rmp. Couldnt get the idle set for the life of me. so today i did everything that i have been reading on here. Comp test 178 across the board. Pulled the pick up tube no debris. Also note this thing has no ball vale. But a hull vent. That is also new. I checked the tank as best as i could. found no water. Just for reassurance i got a new gas can with new preimium still had a little back fire. checked all my filters new and clean. i did notice the safty hose or what ever ya call it was blocked at the fuel pump not sure if thats a vacuum or what. but i tried to clean it as best as possible. Check the psi on the fuel pump as well 5 psi .reconnected the hose. All of this was done on the muffs. went on i set the timming and noticed it was out when in timming mode. set it to 1 bftdc. Plugged everything back and the timing was dead on as per manual. After that i played with the idle and air mix got it around 850. As much as i didnt wanna do it i put it back up to around 3k just to see. Had a little bit of a backfire. but nothing like it was before. noted i did set everything or try to set the idle and mix with the shift rod off. After all back togeather i checked the spark. Everything good but cyl 4. Its got good spark then drops off its a new cap all plugs and wires are new rotor is new. Well the plugs are black now thinking its a little rich. I also looked at the cap and it was a little rusted since i live dead center of canada the weather is all over the place. but what would cause a spark to drop. Could it possibly be my back fire issue. And as of now i pulled the top of the carb off and going to re check the float level tomorrow. im in need of help because i need to get this thing running before i winterize.

Any help would be awesome ! Thanks in advance Petros. Sorry for the long read.

 

[Scott06]

Yes recheck float level, would also double check you dont have a carb to manifold vacuum leak which will lean it out. Spray starting fluid around carb base while running, if rooms come up your pulling starting fluid in at carb base. When running at 2-3 k rpm do you see fuel coming out the venturis in the carb? May have missed some crud in there and have a blocked passage .

 

[Scott06]

That's if rpms come up. is compression good ? Could have a valve not seating as well

 

[alldodge]

Howdy

What is the motor serial number?

Also note this thing has no ball vale.

If you mean the anti-siphon valve, then it should have one

checked the spark. Everything good but cyl 4.

New wires, cap, rotor and plugs but spark is not good on 4. What are you using to check spark?

 

[204_boater]

Yes recheck float level, would also double check you dont have a carb to manifold vacuum leak which will lean it out. Spray starting fluid around carb base while running, if rooms come up your pulling starting fluid in at carb base. When running at 2-3 k rpm do you see fuel coming out the venturis in the carb? May have missed some crud in there and have a blocked passage .

Tried the spray as well. Nothing used carb clean. Could it be the base gasket ? i used a new one out of the kit but it looked a lot thinner than the old one. The kit also came with a thicker one but didnt have the 2 holes in the center, its wide open. As for the venturis, when running at idel i see nothing but when i throttle down yes i do see it then goes away at around 3-4 rpm. when the boat is off i can push down on the accel rod and get a full stream. I got the top of the carb off now will mesuer it at coffee time.

 

[204_boater]

Howdy

What is the motor serial number?

If you mean the anti-siphon valve, then it should have one


New wires, cap, rotor and plugs but spark is not good on 4. What are you using to check spark?

Morning the ser #0f277795

Yeah the anti siphon. Ill get one from the dealer

And yup all new should of said mid summer. i replaced all of it. And i used the timing light. I still waiting for the mac truck to show up at work. Basicly what i did was attach the the clamp on # 4 and pulled the trigger on the timming light watched the flashes when the eng would drop so would the fash on the light. i sawped out wires did the same thing.

 

[alldodge]

With that serial number and timing at 1 BTDC then you must have the EST distributor and the engine in base timing.

With it staying the same even with swapping wires, have you tried swapping plugs?

 

[204_boater]

So i re measuered the float from base gaskest to the toe of the float 14mm 9/16. now the drop was waaay outa wack and adjusted it to 27 mm 1/32 would that casue the back fire in carb ?

 

[204_boater]

With that serial number and timing at 1 BTDC then you must have the EST distributor and the engine in base timing.

With it staying the same even with swapping wires, have you tried swapping plugs?

Yes i had it in base timming mode. set to 1 btdc. i did sawp the pluggs around didnt keep em in order.

 

[alldodge]

Is a puzzle with the plug. Wonder if its actually not getting spark or its something else going on. The pickup is inductive so wonder if there is something else around that could be canceling out the flash, don't know

Most high rpm backfire happens when the motor starts running lean. If the plug is actually getting reduced spark at higher rpm, this might cause the backfire. Thinking that the fuel mixture didn't burn, and then the intake valve opened again and then it did.

 

[204_boater]

Is a puzzle with the plug. Wonder if its actually not getting spark or its something else going on. The pickup is inductive so wonder if there is something else around that could be canceling out the flash, don't know

Most high rpm backfire happens when the motor starts running lean. If the plug is actually getting reduced spark at higher rpm, this might cause the backfire. Thinking that the fuel mixture didn't burn, and then the intake valve opened again and then it did.

I just picked up a spark tester from mac tools whats the spark suposed to be at? And could it possibly be a moduel under the cap ? i wouldnt know how to test that. also when i pulled the top section of the carb i dod find 3 small chuncks of old paint in the bowl blew em out and soaked the carb again. also i stated in my other reply the float on the drop was waaay out about 44mm. set it to 27 mm. asked my mechanic at work here and he said that could casue a lean and back fire. Im just a body tech.

 

[alldodge]

The color should be blue or white

 

[shaw520]

If float drop was at 44mm and it was supposed to be at 27,.. then from 27mm to 44mm the engine was fuel starved,.. definatly cause backfire, I would also expect spiting and dying if throttled up more.

 

[204_boater]

If float drop was at 44mm and it was supposed to be at 27,.. then from 27mm to 44mm the engine was fuel starved,.. definatly cause backfire, I would also expect spiting and dying if throttled up more.

Thats exactly the symptons ! re did the float today. Ill report back tonight. can also explaine why i had to adjust the air/fuel adjustment so far out...

 

[Scott06]

On. The base gasket the one with one big hole is for a TKS carb, you need the two hole job for a mercarb. The OEM merc gasket is thicker but just make sure it's down even and snug and you removed all old gasket material. Had an old Pontic with a vacuum leak years ago had to fatten up the idle mixture to keep it running...

If you see fuel coming out the venturis until 3-4 k rpm then it disappears looks like it is leaning out at higher rpm. Getting float level and drop correct and if there was debris is a good place to start. Did you remove the Venturi cluster and clean out the passages feeding it from the jets?

What did the spark look like ?

 

[204_boater]

On. The base gasket the one with one big hole is for a TKS carb, you need the two hole job for a mercarb. The OEM merc gasket is thicker but just make sure it's down even and snug and you removed all old gasket material. Had an old Pontic with a vacuum leak years ago had to fatten up the idle mixture to keep it running...

If you see fuel coming out the venturis until 3-4 k rpm then it disappears looks like it is leaning out at higher rpm. Getting float level and drop correct and if there was debris is a good place to start. Did you remove the Venturi cluster and clean out the passages feeding it from the jets?

What did the spark look like ?

Ohhh OK. Yeah I got it all set but I lost the choke cam tonight... I hope I can get one through mercury... u till then to testing.

 

[204_boater]

Well got it all together. Seams like it was the float and that little bit of junk left in the carb. Gunna dunk her on the weekend and fine tune the idle and air mix setting.

Thank you everyone for all the tips and help.

 

[Scott06]

Great to hear, it's usually the simple stuff. Where did you find a choke cam?

 

[204_boater]

Great to hear, it's usually the simple stuff. Where did you find a choke cam?

Yeah no kidding haha. And the cam was in a zip lock bag that fell into the bilge of the boat..... but my merc dealer can get them in 15 bucks Cnd.

 

[204_boater]

Put the boat in the water today did my final adjustments. Everything works better than before ! No hickup no pops no backfire. She idles nice and smooth, and up on plane in no time.

Once again thank you everyone! Now I gotta figure out where to mount my water separter. It's a 1996 crestliner 1750 sport fish. Space looks limited since the dog house is very small not sure if I put it on the transom or make a mount off the center eng mount.