merc timming help!!

[trainwrecker22]

I recently bought a 95 citation with a 305 mercruiser in it. thought I got a good price on it. Well......I bought a lemon. the lower end of the motor was gone. I swapped out the 305 for a 350. For the life of me I can not get the dam thing timed. when I throw a light on it, it is advanced about 1/4 to 1/3 the balancer. When I start retarding it the motor starts running like crap. I am still in the break in period of the motor I can not let it idle for long periods of time. I have been running it about 1000 rpm's when timing it. About the motor it is a 350 reman from Michigan motorz, '95 prevortec 12 bolt intake with a 2 barrel carb and a thunderbolt IV(4) ignition. the original engine serial OF358602. any help would be appreciated.

 

[Fun Times]

Hi there, welcome to iboats!

To set the timing, you need to be at idle or you will not get your "initial timing" set properly. Your idle speed should be at 650 RPM warm.

If you find your ignition module part numbers you could try setting the total advance to specs found in the first link below and see if you get a normal idle and timing setting.

http://crowley-cloudfront.s3.amazonaws.com/media/mercuryBulletins/001/04/1991/EN_12.PDF

http://www.crowleymarine.com/search_results.html?string=OF358602

Also keep in mind that since you went from a 305 to a 350, your 305 carburetor internal sizing's may allow the engine run to lean.

What type of carb do you have on your engine?

 

[trainwrecker22]

I did some nosing around the site and found the manual section. I was able to set the timing. now my issue is idle to 2000 RPM's motor runs great. or atleast as far as I can tell. once I start creeping above 2000 r's she starts popping and backfiring through the carb. if I put any load under her she falls on her face and start popping and backfiring. I have checked the intake manifold gasket (torque and sprayed it with carb choke cleaner) firing order, timing (which I thought was what was causing this problem) I have the stock merc 2 barrel carb on her. I am not sure make or cfm. I would not think that if I did not have it jetted right it would cause it to come back up through the carb. I am stumped. I have a bit of automotive knowledge but zero marine knowledge, but a motor is a motor right

 

[Fun Times]

but a motor is a motor right

On a boat, kind of yes kind of no. Keep in mind that running a marine engine in a boat is like driving a car/truck uphill in first gear all the way up to around 5000 RPM for a long time.

Backfiring through the carb (spitting or coughing) usually occurs in the morning when a carb's air/fuel mixture is a bit too lean. This usually goes away once the engine warms-up. It is also commonly caused by the accelerator pump inthe carb not squirting enough fuel before the main jets start working. If you spit the instant you blip the throttle it is probably the accelerator pump in the carb not working, plugged up or out of adjustment.

As with backfiring, coughing or spitting can also be caused by a bad ignition system, such as cross firing, which sends a spark to a cylinder that has the intake valve open. When that plug sparks out of turn, it lights the fuel in the cylinder and the pressure has to go somewhere... so if the intake valve is open, it goes right back up through the intake manifold and out the carb with a "spit" and sometimes even a flame.

When and how it backfires or spits will give you an indication for where to look.

^^^ Source: http://www.badasscars.com/index.cfm...duct_id=95/category_id=13/mode=prod/prd95.htm

In the following link, by looking at some of the part "notes" under the 3 carburetor options found under your serial number, you'll notice the bigger engines went to a 4 barrel.

http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=816596

Check your spark plugs to see what they look like also you may have to check your fuel pressure as it could be out of specs as well.

Hope you find it soon, good luck.

 

[trainwrecker22]

wow well then I beleive I will be looking for a intake and carb. thank you that was alot of help