backfire mercruiser

[chesire_catt]

I have a 140 i/o 1986 It will start but it back fires through the carb (I think) It is a popping sound doesn't run long I have replaced the coil. I have tried to adjust the timing no no avail. It pops with every revolution pop pop pop pop pop sounds like a lawnmower with no baffle please help. I have been told that it sounds like a timing issue I have never set timing before what I did was loosen the dist bolt and turned it as iut was running what else could the problem be? thanks.

 

[Trent]

Re: backfire mercruiser

Backfire (actually afterfire) is a lean condition most of the time. If it were me I would remove the carb and clean really well and install a kit. Also check the compression.

 

[dick]

Re: backfire mercruiser

Probbly ether a bad valve or a bent or broken pushrod or even a backed off rocker nut. Do as trent suggest and check the compression then pull off the valve cover and check the valve train.

 

[denniz]

Re: backfire mercruiser

I agree with Trent could be a lean pop, on acceleration. Id deffinetly check the firing order should be 1-3-4-2 If I remember correctly. Could just be a crossed plug wire.

 

[geriksen]

Re: backfire mercruiser

Time for a compression check. Sounds like a valve to me.

 

[chesire_catt]

Re: backfire mercruiser

I headed out to do a compression check and it turned twice then stoped won't do anything. Im gonna pull starter as soon as Im done hanging the X-mas lights lol anyway to check starter wilwe its ont the motor?

 

[Waterbugtoo]

Re: backfire mercruiser

If your compression shows ok, points are adjusted properly, and timing wont smooth it out, make sure you didnt accidentally cross a plug wire. Also check for spark jumping across the distributor cap (cracked cap) and/or coil.<br /><br />

 

[coupedeville]

Re: backfire mercruiser

It stopped cranking, and wont turn? Oooh, that dont sound good at all. <br />Maybe you had a valve going away, and its broken off inside the cylinder. Aye yi yi. Can you turn the engine by hand, or with a breaker bar?

 

[chesire]

Re: backfire mercruiser

Ok I know Its been a while but with X-mas- 2 kids Blah blah you know anyway I got the engine started. Was the starter. <br /> still backfires, no afterfires through the carb. compression check Not good #1 and #2 142 3 and 4 170 Help

 

[chesire]

Re: backfire mercruiser

Oh yea also book that came with the boat says 140 for the compression . What could cause this? also what could cause the backfire? it pops from the very second it starts. =(

 

[Monte Cryts]

Re: backfire mercruiser

Like the others said, be sure the plug wires are correct!!! Some friends like to play jokes and swap em. It's not that funny!!! also check for sparks coming from the plug wires by running it at dark and looking for a blue light or listen for poping sounds. May be a bad pug wire. <br />Be sure to also double check that you have both ends of the plug wires pushed on all the way. If not completely seated on the voltage will try to ground out and cause a bad miss and backfire.

 

[chesire]

Re: backfire mercruiser

Ok I have done that wires are new and i the correct order. ran at night no sparks what next?=(

 

[Trent]

Re: backfire mercruiser

Compression readings look fishie...But Id not worry. Tear the carb down and clean very well and look at the bottom gaskets. Put a kit in it. Cheap. You did try to adjust the idle mixture? Their is a service bullitin for that year model for a gasket problem.

 

[chesire]

Re: backfire mercruiser

thanks trent im on it ill let you know i ordered parts yesterday<br />thanks again

 

[chesire_catt]

Re: backfire mercruiser

 

[kenimpzoom]

Re: backfire mercruiser

Have you checked to make sure the rotor is pointing towards the #1 plug wire when the #1 cylinder is a TDC?<br /><br />I once had a car the had a hideous backfire problem. Turned out the distributor cap had microcracks in it and it got wet and was causing the sparks to go everywhere. Cracks werent easy to see had to look very hard and I thought they wouldnt cause a problem, but... new cap, ran great.<br /><br />Ken

 

[akriverrat]

Re: backfire mercruiser

sounds like head gasket between 1 and 2 to me.

 

[chesire]

Re: backfire mercruiser

Head gasket ahhhhhhhh No water in oil but I guess that is not always the case. still working on backfire problem. thanks

 

[denniz]

Re: backfire mercruiser

Trent, do you ever feel like your talking to a wall.....

 

[akriverrat]

Re: backfire mercruiser

head gasket between 2 adjacent cylinders doesn't get into waterjacket. the 2 cylinders involved will read about the same and low. the copression/powerstroke cylinder will make the lawnmower sound through the open valve of its neighbor.it gradually gets worse because the hot exhaust gas eats a groove in the exposed metal of the head and block. unless you want to mill the block to get rid of this groove fix it quick. don't even think about putting a new head gasket down on a grooved block. it won't last.