Mercruiser 250 - won't run

[brodie123]

Hi everyone.

I have a Mercruiser 250 4.1L L6 that won't run. I tried to find the serial # but can't find it - the valve cover is not the original I think. (does not have the Mercruiser stickers etc.)

It was rebuilt (complete) 3 years ago at a shop. It was a used engine I acquired.

I had challenges with it last year - not running well, it seemed to bog out or flood easily. It ran ok 90% of the time but for sure hard starting. I had the carburetor rebuilt last year thinking that may be the issue.

I installed a new electronic distributor thinking that would help - the exact same distributor I have on my other 250. (In a cabin cruiser with twin engines)

I haven't been able to get her to run at all. I manually added gas (added some gas in carb) and I am also using fresh gas.

I have fuel pressure no problem. I've checked for any air leaks - can't find any. I checked each plug individually for spark - no problem.

On cylinders 2 to 6 I have 120+ lbs compression and 95lbs on cylinder 1 - so maybe I need a new head gasket or something but I would think it should still run with 1 cylinder a tich low.

The one part that confuses me is the timing marks. On my other 250, looking at the front, the timing marks are on the left - has a timing plate and a tube. On this engine, the timing marks on the right with a plate marked 0 and A. Is it possible that the front cover has been replaced with the wrong timing marks??? This is the only thing I can come up with - but I am guessing. Is there anyway of knowing??

Any assistance is appreciated to get this thing running.

Chris

 

[Scott Danforth]

Stop changing parts

First, fix your carb, your first issue was a dirty carb

Then go back to the ignition, bring motor up to TDC on cylinder 1, and install the dizzy properly

 

[brodie123]

Update: Ok, I got it running - even idling at 500 rpm without any issue.

I took a chance and rotated the distributor so that the timing mark is over to the left like on the other engine and Vroom!

Obviously, my timing marks are way off for whatever reason.

In order to get it to run smoothly, I had to rotate the distributor to the point where I cannot see the timing mark at all.

So here's my updated question - How the heck do I set the timing so that I'm as close to my proper timing as possible without timing marks??

Please and thank you.

 

[scoflaw]

Locate TDC on #1 and make a new mark on the balancer, then either use a timing light with an adjustment dial or put a degree tape on the balancer

 

[kenny nunez]

Mark the outer ring of the balancer to the inner hub, then. Look at it after running to see if the outer ring has slipped. A good chance for an engine that old this is a common problem. They are easy to change and they are rebuildable if you cannot get a new one. There is a service in Hemming’s Motor News that can do that.

 

[brodie123]

Thanks guys. I made a new timing mark as suggested and set the timing to that. I'm going to check and see if the balancer has slipped as well.

Sincere thanks.

 

[gm280]

Since you got it running good, like you alluded to, even if the balancer is slipping, if you don't change the distributor position, it will run good. Once you move the distributor, all bets are off. But it would be interesting to know if the balancer is slipping so you can get a rebuilt or new one. JMHO