140 mercruiser wont start just backfires through the carb

[turbo3]

Not sure of what im doing here but... motor turn over fine but backfires up through the carb tried checking the timing with #1 piston up and making sure distibutor was hitting on that plug. tried pouring a little gas down the carb but same thing? I distributor and checked gear seamed to look fine.... could my timing gear be bad? it wont start just backfires. Seems to be on every plug??

 

[Bondo]

Re: 140 mercruiser wont start just backfires through the carb

Ayuh,.... Welcome Aboard,... 'bout what Vintage is this 140hp,..??

Is it got Points in the distributor, or electronic,..??

 

[Don S]

Re: 140 mercruiser wont start just backfires through the carb

You need to be on #1 TDC on the compression stroke, not just the piston on top. Sounds like you are 180 out on the distributor.
Get the engine up on #1 TDC on the compression stroke LIKE THIS Then reset your distributor and try it.

Have you done any other engine work? Head off for any reason?

 

[turbo3]

Re: 140 mercruiser wont start just backfires through the carb

Ayuh,.... Welcome Aboard,... 'bout what Vintage is this 140hp,..??

Is it got Points in the distributor, or electronic,..??

This is an 86 and yes its points. lastnight i started over #1 piston up, looked up firing order again now its still not firing up just putting out the back back fire through the carb about every 4 or 5 cranks? im lost here could it have jumped time on the gear?

 

[Bondo]

Re: 140 mercruiser wont start just backfires through the carb

This is an 86 and yes its points. lastnight i started over #1 piston up, looked up firing order again now its still not firing up just putting out the back back fire through the carb about every 4 or 5 cranks? im lost here could it have jumped time on the gear?

Ayuh,.... #1 has to be TDC, on it's Compression stroke,....

I'm guessin' yer timin' it on it's Exhaust stroke...

 

[turbo3]

Re: 140 mercruiser wont start just backfires through the carb

You need to be on #1 TDC on the compression stroke, not just the piston on top. Sounds like you are 180 out on the distributor.
Get the engine up on #1 TDC on the compression stroke LIKE THIS Then reset your distributor and try it.

Have you done any other engine work? Head off for any reason?

iive never been in this motor just got it cheap and trying to make something of it . i done every thing you said last night and its still off.

 

[turbo3]

Re: 140 mercruiser wont start just backfires through the carb

Ayuh,.... #1 has to be TDC, on it's Compression stroke,....

I'm guessin' yer timin' it on it's Exhaust stroke...

I my mark is on on my counter balance and #1 piston is TDC that should be it... right?

 

[Bondo]

Re: 140 mercruiser wont start just backfires through the carb

I my mark is on on my counter balance and #1 piston is TDC that should be it... right?

Nope,... The piston, 'n timin' mark goes 'round Twice, 'tween TDC, 'n TDC...

 

[Silvertip]

Re: 140 mercruiser wont start just backfires through the carb

The camshaft rotates at 1/2 crankshaft speed -- hence the timing mark makes two passes for one turn of the camshaft. As you've been told, (I'll say it again) you need to make sure #1 piston is on the POWER stroke, not the EXHAUST stroke. If you have a tough time visualizing this, remove the valve cover and set the timing mark on TDC. If both valves are NOT closed you are on the exhaust stroke. Rotate the engine one more revolution to close the valves. Now remove the distributor and reinstall it so the rotor points to #1 cylinder. Set the point gap with the points rubbing block on the high spot on the cam. Install the cap, fire the engine and then set timing. Unless you have a timing light you are wasting your time and risking engine damage.

 

[turbo3]

Re: 140 mercruiser wont start just backfires through the carb

so im a hole turn off? but instead of it backfiring though the carb now its popping out the exhaust ... just every once in a while it pops back up the carb but still wont start

 

[Silvertip]

Re: 140 mercruiser wont start just backfires through the carb

We don't know what you are doing or if you doing this correctly. We have told you what you need to do. If you don't do it right we can't help you. What did you do to this engine to have to mess with the distributor and timing? If you had the head off, and did not properly adjust the valves that would account for some of this popping back. If you don't know how to adjust hydraulic lifters, better get a manual.

 

[Don S]

Re: 140 mercruiser wont start just backfires through the carb

Do a compression test and post the results. Lots of things could cause your problem.

View attachment 97-25 Compression Test.pdf

 

[artificialreef]

Re: 140 mercruiser wont start just backfires through the carb

With points, accessing a dwell meter would be a good idea too. You can find one on fleabay pretty cheap. I got a half way decent snap-on for 25$.

 

[artificialreef]

Re: 140 mercruiser wont start just backfires through the carb

Like Don said, compression test and post the results too please! I did that BEFORE i bought my planter.

 

[tstock77]

Re: 140 mercruiser wont start just backfires through the carb

Hey Guys, I just wanted to thank you for guiding me in the right direction with my 140. I have been working on this thing for weeks. After following your post i was able to get mine started tonight. Thanks so much