Mercury 100 Back fire

[Scondo]

Hi I have a Merc 100 ,it does not have clean rev up if you move the throttle linkage up on the carbs,it seem to hesitate and pop out the exhasts,it also tries to push presure back to the fuel pump down the pipe which goes into the cranck case when it is doing this back firring,i have just removed the carbs and cleaned and re set the float levels,when it was running i tried to set the fuel air mixture and i can't seem to get it to run smoothly with out popping throught he exhaust.<br />Any suggestions welcomed

 

[Chris1956]

Re: Mercury 100 Back fire

Mers, it sounds like a spark timing problem. When the spart is too retarted(too late), it will backfire out the exhaust. Recommend you set the timing via the manual and timing light.

 

[Scondo]

Re: Mercury 100 Back fire

Hi Chris<br />Thanx for that i will ,try it to day and let you know.

 

[Scondo]

Re: Mercury 100 Back fire

Hi Chris<br />I have been playing with my merc today and have had the timming light on it and if i advance the timming to around 8-12 Degrees it sorts the problem ,is this going to harm the engine in anyway,i will need to put in the water and test it under load.<br />Thanx

 

[kev_79]

Re: Mercury 100 Back fire

What year is this engine? Is it the 2+2?<br /><br />k

 

[Scondo]

Re: Mercury 100 Back fire

This engine was a stollen and recovered engine ,and engine no's removed,i think it is a 1994 ish motor,what is 2+2.<br />Thanx

 

[achris]

Re: Mercury 100 Back fire

Mers,<br /><br />2+2 is the system Mercury use on the 4 cylinder 2 strokes (100, 115 and 125 hp). At engine speeds less than about 1800rpm the carbs for the lower 2 cylinders lean out the mixture to the point that they don't fire. The popping you are getting could be at the 'pickup' point of the bottom 2 cylinders. Does the problem occur to about this engine speed?<br /><br />As for the serial number, you may be lucky. Check the righthand side of the engine (powerhead) and you may see an aluminium plug, about the size of a Euro (I'm guessing you're in Europe somewhere). On this plug will be an 8 digit serial number.<br /><br />The timing for these engines is :<br /><br />Max timing : 1994/1995 model<br />@3000rpm - 20 degrees B.T.D.C.<br />@cranking speed - 22 degrees B.T.D.C.<br />1996/97/98 model<br />@3000rpm - 23 degrees B.T.D.C.<br />@cranking speed - 25 degrees B.T.D.C.<br /><br />Idle timing : 2 to 4 degrees A.T.D.C.<br />Idle speed : 675+/- 25 rpm in forward gear<br />Spark plugs - NGK BP8H-N-10 (1.0mm gap)<br /><br />Chris............<br /><br />Edit : moving the throttle linkages on the carbs without advancing the timing (moving the control lever) will cause popping and backfiring.<br /><br />If you find a serial number and post your e-mail address, I'll send you the timing and synchronizing procedure.

 

[Scondo]

Re: Mercury 100 Back fire

Hi Chris<br />Thanx for that,well the plug looks like is got a grinding disc to it.It really is a pain coz i can't order any electrical parts for it as there seem to be that many different parts and changes between the years.Will have to try and work with what i have.I think i have the timming ok with a timming light know ,but it just does not sound right,i am now thinking stator?? because when i changed the rectifier to get it to charge again the voltage really fluctuates rapidly ,i thought it was my volt meter but it is new,and the resistance between the two yellow wires is higher than the manual says,but the green/white and the white /green wires test ok,this sugests the charge side is faulty.I am alittle worried it might progress to the switch box and then have top replace that too,can the stator go and the switch box as it looks like the spark is a little weaker on No 2 and 3 then on No1&4.I also found the carbs had larger main jets than supposed too,and the manual suggests that the jets be smaller one 1 and get biger going down to 4,on this on they are all the same and larger size than the biggest recomended by the manual.It is funny coz it did run fine a month ago,and just seemed to go bad,electrical??it really has been a test to try and sort this out,my email is cloetewilliam@aol.com