Startup backfire

[mikes 86]

Hi guys i,m back with another problem so here,s the skinny, I have 125x4 1986 every time I start the motor I get a back fire I think at the carb,s or so it sounds like, After it back fires it starts right up and runs good, So I am wanting to know if I advance the timing a little would this stop the back fire or possiblely adjust carbs a little lean I don,t know just guessing any ideas on what would stop this from happening would be great !!!!!

 

[MickLovin]

Re: Startup backfire

There is a sticky on here for syncing your carbs, don't lean it out cause you think it may be the problem as you may have further problems down the track, you need to give us more info, what type of motor is yours when you say 125 x 4 do you mean a 4 cylinder 2 stroke? I take it, it is a force. Maybe try a carbie cleaner while running, give them a quick does and go from there, a can of cleaner doesn't cost much, but be aware that cleaner leans your motor out. Do you use anything like Seafoam, if I lived in America or Canada I would be using it all the time, I use Stabil.

 

[Jiggz]

Re: Startup backfire

You first need to make sure you verify timing. Thereafter make sure the carbs air screws are set at least 1 turn out from slightly seated. Note, do not confuse backfire with "cough" when you are trying to start the engine with the choke on. This is absolutely normal and is caused by too rich of fuel mix caused by the choke. DO NOT SET THE AIR SCREW LEAN AS THIS CAN CAUSE A CATASTROPHIC DAMAGE TO THE ENGINE.

 

[mikes 86]

Re: Startup backfire

Motor is a Force 125 1986 4 cyl. 2 stroke I have preformed the link & sink, carbs are set at 1 turn from lightley seat, ran sea foam through motor last month I dont know if it is a cough or back fire, does this every time I turn the key choke or not set timming static @ 28 not with motor running dont know if that makes huge difference maybe slight advance would help,I get it about carb adjustment so I wont mess with that, motor starts right up almost every time after loud burp hope someone can help me out THANKS!!!!!

 

[Jiggz]

Re: Startup backfire

You need to verify first if it is a "burp" or backfire by removing the cowling before starting. Have someone watch the carbs while starting to look for back fire, which is indicated by blowback from the carbs. If there is such indication, it means the reeds are also not sealing properly. However, if there is no indication of blowback from the carbs, then it means the engine is only "coughing" or trying to start which is perfectly normal. Note this should only be present when the engine is cold. But if it also happens while the engine is warm, then there is more than just "coughing".

 

[mikes 86]

Re: Startup backfire

Ok guys i finely went to the lake and watched to see where the back fire sound was coming from and it looks to be out the exhaust, so could this be from bad reeds? or out of time? Like i said i did link and sink from this site i have had boats for long time and i know this is not normal the guy i got this from used start fluid from time to time to start motor i dont know if he knew where choke was at on key switch motor fires right up after back fire got to be a way to stop this from happing

 

[MickLovin]

Re: Startup backfire

Sounds like a timing issue, have you had a timing light on it? Do you know what the timing is set at? Also what are your carbies set at now?
I am unsure with the Force but with my motor a 100hp Chrysler I can do the timing with a voltmeter, I set the throttle at WOT, put my flywheel on my 32deg mark, voltmeter red probe onto the white cable on my dizzy and I will get 12 volt to ground, when I adjust it to a no volt reading, I set the timing screw lightly at that and hit the belt, it should go from 12 volt to 0 volts by pushing the belt on the dizzy.

 

[Jiggz]

Re: Startup backfire

Ok guys i finely went to the lake and watched to see where the back fire sound was coming from and it looks to be out the exhaust, so could this be from bad reeds? or out of time? Like i said i did link and sink from this site i have had boats for long time and i know this is not normal the guy i got this from used start fluid from time to time to start motor i dont know if he knew where choke was at on key switch motor fires right up after back fire got to be a way to stop this from happing

Has this so called "backfire" been going on since you got the boat or just recently? I also have a 125 albeit it is the '89 and yes, when cold starting and in choke it will do what you described, which is not really a backfire but more of the engine firing on one cylinder and then stop. Thereafter, it will start and will not cough anymore for the rest of the day unless it gets cold again. Anyways, if you can verify timing just to make sure the flywheel key has not been sheared (which I doubt unless the engine performance has abruptly declined), or the timing tower has not gotten loose. But if the WOT performance has not changed, it is most likely the backfire you are referring to is just a "cough".

 

[mikes 86]

Re: Startup backfire

This backfire happens every time I start the engine cold or hot dosent matter choke or not dosent matter timed static @28 once it pops or back fires out exhaust fires right right up I am wondering if static @ 30 might help ??? Has done this since I got this motor it runs great except for smokeing at idle and this poping/backfire THANKS FOR RESPONCES!!!!!!

 

[Jiggz]

Re: Startup backfire

Smoke (more) at idle is absolutely normal. Static timing at 28 is perfect and it would not make a whole lot of difference if set to 30. Since the engine is running great, I would not try to do anything drastic but instead approach the problem cautiously starting with clean plugs and making sure you are using the correct plugs, (BUHW or L76V), de-carbon the engine but make sure you do not overdo it and checking the fuel diaphragm to make sure it is not leaking fuel into the #3 cylinder. Another to look into is if you happen to be idling too much when running the engine. If you idle too much before shutting down the engine you could be puddling fuel on the lower cylinder which can cause the back fire. My practice during flushing, on the last minute I will put the engine on fast idle in neutral around 1500~2000 RPM before shutting down to clear unburned fuel from the lower cylinder.

 

[mikes 86]

Re: Startup backfire

Question how do you check fuel pump diaphragm leaking into # 3 cylinder not sure about that one, have already done decarbing with sea foam, dont idle no more than needed because of smoke, idle at around 1000-1100 dont have warm up leaver that I know about when I come out of gear I always idle for just a minutes or so. will get new plugs and give it a try cant hurt !!!!

 

[MickLovin]

Re: Startup backfire

If it is a fuel pump diaphragm it will leak into the crankcase not necessarily just #3

 

[Jiggz]

Re: Startup backfire

If it is a fuel pump diaphragm it will leak into the crankcase not necessarily just #3

Huh?

 

[Jiggz]

Re: Startup backfire

Question how do you check fuel pump diaphragm leaking into # 3 cylinder not sure about that one, have already done decarbing with sea foam, dont idle no more than needed because of smoke, idle at around 1000-1100 dont have warm up leaver that I know about when I come out of gear I always idle for just a minutes or so. will get new plugs and give it a try cant hurt !!!!

I'm not sure what a warm up lever is but for these outboards, there is a fast idle at neutral control where you can bring up the engine rpm while in neutral gear, which is used for starting and warming up the engine. There are two common ways to do this depending on the style of throttle control you have. There is the button (located on the center of the throttle's axis) that you push and then pushing the throttle control forward and then there is the pull out ,pull the throttle outward (grabbing it by its axis or pivot point) towards the driver and then push the throttle forward).

As for the fuel diaphragm, you will need to disconnect the hose and disassemble the pump to access the diaphragm. This is really easy to do, but if you have not done it before just make sure you take photos each step of the way so re-assembly will not be a problem. If the diaphragm is OK. The next best thing to do is to make a you tube video of what you refer to as "backfire". Just to make sure we are "barking on the right tree" on this one.

 

[MickLovin]

Re: Startup backfire

Huh?

Standard outboard fuel pump troubleshooting (All brands/models)

There isn't really too much involving fuel pump troubleshooting, and I'm rather amazed at how many fuel pump kits we sell in a years time, as standard outboard fuel pumps don't really act up that much in my experience of 20-some years of wrenching. If you feel though the fuel pump is your problem, read on.

A standard outboard fuel pump is a simple device that operates off the pulse of an engines cylinder. A basic rubber fuel line connects the fuel pump to a pulse valve (some models of fuel pump attach directly to the block with a gasket, sealing pulse passage to cylinder), which is normally threaded into the block with provisions of a clear passage to a specified cylinder. The up and down stroke of the piston in the specific cylinder is what causes the fuel pump diaphragm to flutter, resulting in pumping fuel from tank to carbs.

So how do I know the fuel pump is doing what it is suppose to?
As described above, the fuel pump requires an adequate pulse from the cylinder that it is attached to, so first thing is to make sure compression on that cylinder is up to snuff or the fuel pump can't do it's job. If compression checks out, then next thing is to check fuel pump pressure. All non fuel injected outboard motors operate with a fuel pump pressure of about 5 to 7 psi. If consideribly less than 5 to 7 psi exists between fuel pump and carb/s, the motor is likely to be starving for fuel causing idle and/or upper rpm operation to suffer, not to mention a dangerously lean condition.

So what if everything to do with pulse supply to the pump is good, but I still suspect the pump has a problem?
Although I mentioned not experiencing many fuel pumps actually being bad, it is indeed possible for either the diaphragm, check valves, or other problem to develop in a fuel pump. If it's plainly worn out, then so be it, install a kit or replace pump entirely, but I would suggest checking all other things in this troubleshooter page before just taking it for granted your time and money spent on a fuel pump kit or replacement pump will solve your motor's woes.

Could anything else cause the fuel pump to not provide adequate fuel supply to the motor?
The answer is yes. There could be a restriction or loose connection from tank to fuel pump, amongst other things. Assuming you have no leaks (including pinholes in hoses) anywhere in-between, the following would be things to check for:
Fuel tank internal pickup tube clogged, broken off, or otherwise defective.
Anti syphon valve located on tank (is so equipped) could be defective (check ball/spring).
Any kinked hoses between tank and pump.
Defective in-line squeeze bulb (usually the internal check valve).
Defective or incorrectly attached fuel line connectors.
Clogged fuel filter.
Inadequate fuel tank vent or kinked vent hose.

Soory I was under the impression excess fuel went into the crank.

 

[Jiggz]

Re: Startup backfire

"Soory I was under the impression excess fuel went into the crank."

No apologies required. In a sense you are correct that it will puddle in the crank case but only on the cylinder the pump is attached to. Unlike 4 cycle engine where the crankcase is common to all cylinders, in a 2 cycle engine each cylinder crankcase is sealed from other cylinder's crankcase. And this is to allow a slight compression of the intake air-fuel/oil mix with the help of the reed block during piston downstroke. When the piston clears the intake ports the air-fuel mix rushes into the cylinder directed upward by the piston crown with a built in deflector. The compressed fresh air-fuel mix helps in scavenging by pushing exhaust from the top of the cylinder instead of going directly across the exhaust port leaving some exhaust on top of the cylinder. Without the compression of the intake air fuel mix, i.e. broken reed or crank seal, will render the cylinder ineffective and most likely inoperative or misfires.

The puddled fuel mix can be recovered by the fuel recovery system but the engine would have to be operating far above idling speed. And this recovered fuel mix is fed again into the intake manifold.

 

[MickLovin]

Re: Startup backfire

Thanks Jiggz for the clarification

 

[Skychasen]

Did you find the problem? I’m having similar issues with my 20HP Chrysler

 

[jerryjerry05]

Post is 9 years old.

 

[The Force power]

Post is 9 years old.

I guess, someone did not read the rules & etiquette