302 888 Mercruiser smokes during startup with choke on

[dklortie]

Hi All,
I am having a problem with my 888 Mercruiser(302 Ford Block, 188hp). When I start the engine up from cold, there is a lot of smoke coming from the exhaust, and the engine runs rough. This only occurs on start-up from cold with the choke closed. As the choke opens up (electric choke), the engine idles much better and the smoke disappears. Engine RPM at warm-up I usually set around 1000rpm, as the choke comes off, rpm will rise to a little over 1500rpm. The engine doesn't seem to be burning any oil. Check it each weekend before leaving the dock, and is always at the full mark, so I don't think that it is burning oil. However, I seem to constantly be cleaning a black film off the back of the boat. I have switch this season to using premium instead of regular, and found that the engine does idle better now than before.

The question that I have is, is this a normal situation and just a symptom of the choke being on, or could I possibly have a problem with the carburetor? It is a Rochester 2 barrel with the 2GM marking on it. Forgive me if I am wrong, but I thought that the Ford engines used a Holly carb. My 302 block that I had in the other boat (OMC engine), was a Holly carb.

I was also told that the Holly carb is also better on fuel and provides more power from the engine than the Rochester carb. I know that I am pushing a 25' Bayliner (4500lbs), with a 15 pitch prop on it doing about 22 miles per hour cruise at around 3300-3400 rpm depending on load. I am burning around 60-70 litres of fuel for around an hour round trip from dock to the anchorage and back. My OMC granted on a smaller boat (20') with the Holly Carb, used to get almost double the fuel mileage that I am getting with this boat.

Any guidance on this would be more than appreciated.

 

[hivoltg]

Re: 302 888 Mercruiser smokes during startup with choke on

I have the same setup as you and I cant explain the gm logo on the side of my ford engines carb either. I thought someone just used a gm carb on a ford motor. Im kind of glad to hear someone else's is like that also. :joyous:

What color is the smoke?

If you have used a fuel additive like seafoam it will smoke some. Especially if you added too much. If you have carbon build up in that motor (black film) seafoam works pretty good at cleaning it out.

I would also pull the sparkplugs and check for any water intrusion. If they look like they have been wet (rust), then I would point towards your riser gaskets leaking alittle (white smoke/steam). Get it fixed if this is the case.

 

[dklortie]

Re: 302 888 Mercruiser smokes during startup with choke on

Hi. The smoke is black, and like I said, once the choke comes off it is non-existent, it is only there when the choke is on at start-up. I am not running any fuel additives in the gas, and like I had mentioned, I switched from regular fuel to premium this year (only had the boat since last spring), thinking that that could be the reason, but it made no difference to the smoke, only smoothed out the idle. Plugs are fine. Checked them this weekend, and they are just as they should be. I ran a can of the seafoam spray through the carb last year and cleaned out the engine. I haven't done it this year. I tried a carb cleaner, but maybe I might need another seafoam treatment. Thing was, it still did the same thing last year after the seafoam treatment.

Previous owner had the engine under tremendous load. The boat had a 19 pitch prop on it when I got it, (WOT at round 2300rpm). I put the 15 pitch prop on when I got it, and made the world of difference (WOT now at around 4100rpm). I am just hoping that he didn't fry a valve or something when running it so hard.

 

[RCAnderson]

Re: 302 888 Mercruiser smokes during startup with choke on

The merc 888 used the rochester 2 barrel, so that is normal. The GM is just a casting mark I think. It sounds like it is running quite rich, so if you haven't done so already, take the carb off and completley rebuild it. The only external adjustments on the carb are the idle speed screw, and the idle mixture screw. If you are constantly cleaning soot off the back of the boat, it sounds like it's running rich through the whole rpm range, so probably not the idle mixture screw.

 

[RogersJetboat454]

Re: 302 888 Mercruiser smokes during startup with choke on

FWIW, Rochester was a division of GM, but the engine doesn't really know or care who made the carburetor (both Ford and Chrysler used Rochester carbs for some of their production vehicles).

If you're concerned about the health of the engines mechanicals, perform a compression test on it to see where you stand.
As far as the black smoke is concerned, your choke might be closing too far and not allowing enough air to bypass it, or your idle mixture may be off.

 

[hivoltg]

Re: 302 888 Mercruiser smokes during startup with choke on

I would pour some seafoam right down the float fill on that carb and let it sit overnight, or add it in heavy at the water separator before I spent the time to rebuild/adjust the carb.

Is your choke electric or vacuum?

Im glad to hear you don't have white smoke.

 

[Bt Doctur]

Re: 302 888 Mercruiser smokes during startup with choke on

have you tried adjusting the choke when cold? when cold advance throttle slightly, loosen the 3 screws and rotate the element untill the plate is open about an 1/8 of an inch, tighten screws and retest.

 

[dklortie]

Re: 302 888 Mercruiser smokes during startup with choke on

Hi All,
Thanks for the advice... I have gone to the boat and adjusted the choke. It was almost completely closed when on. I adjusted the choke to be open around 1/8" and voila, no smoke. Idles much better now when warming up as well. I also noticed that the choke plate also opens up a LOT more now when in normal running mode with the choke open. It is now straight up and down sitting against the stop on the air cleaner stud. Was about a 5 or 10 degree angle before. Might just see some fuel savings and possibly more power now that the engine can finally breathe again.

Thanks to all who responded. It is great to have a forum that you can get the knowledgeable help you require without having to go to a mechanic.

Regards,
Darren

 

[RogersJetboat454]

Re: 302 888 Mercruiser smokes during startup with choke on

Glad to hear.
You may just save a few more stipends on fuel if the choke was restricting the carb enough when it was supposed to be open.