Mercruiser 165 inline 6 Carb help

[Aqua Susurro]

In a 18ft Starcraft SS. The boat, engine and carb have all recently been rebuilt.Stay tuned for a splash post soon. The engine runs well. Achieving 55km/hr at 4300rpm at wot with a 14x21 four blade prop.However the exhaust smell is terrible. It smells ultra rich. Compared to all the other boats in our little marina this one will knock you out. Often I feel light headed and poisoned after a ride. On one occasion we had a small boy in the back seat passing out from the fumes.

Unfortunately I didnt write down the main jet size. At the time I didnt think I would need to mess with jets and just rebuilt/cleaned out the carb. I have plenty of auto/motorcycle experience and was a Millwright by trade. everything was put together properly and some would even say anally

We are on Sturgeon Bay off of Georgian Bay which is approx. 200m (600ft) above sea level.

My question is, “Does anyone have any main jet size suggestions for the ROCHESTER 2 barrel on a 250ci 6cyl at this altitude?

My thanks in advance,

Thomas

 

[kenny nunez]

At that elevation with the engine turning like you said, it is real close. If you change the jets to the next size larger you may not see any difference.
Is the choke opening? Does your engine have excessive crankcase blow by?

 

[Scott Danforth]

there is no need to re-jet until you get to 3000 feet.

anything from 0 to 1000 feet is considered "sea level" as there is not much change in barometric pressure between those elevations

fix your choke and go boating..... Im guessing you dont mean Sturgeon Bay Wisconsin.... that is a bit of a hike from Georgia Bay.

 

[achris]

A year of the engine (not the boat), or its serial number would help.

I agree with the others, sounds more like the choke is staying on, but once you post the serial number I'll look up the jet sizes...

Chris...

 

[Aqua Susurro]

The engine has approx. 250hrs on it and doesnt use any oil. From past experience it smells rich to me.

The boat was repowered before I owned it and the block is out of a car. The MC-1 drive number is 49062222. Boat is a 1974 but the engine is a 78 ish. It has a bimetallic coil choke.

I will check the choke is coming off completely tomorrow but did set everything up as per specs.

 

[achris]

...I will check the choke is coming off completely tomorrow but did set everything up as per specs.

When you do, get the numbers off the side of the carb.... It should be either 17042183 or 17059050. (they are specced with different main jet sizes)



Chris........

 

[Scott06]

Might need work on the float and needle and seat if choke is opening properly. Only other thoughts are if someone Changed the jets which seems unlikely or if the power valve is open all the time. What do your spark plugs look like ?

 

[Aqua Susurro]

Thanks again for the responses. Carb number is 7043183. I pulled the spark arrestor off and checked the choke again. As soon as I give it a pump on the lever the choke sets in the on position as it should. Also the choke is 100% off at 150-160F on the gauge so all is well there. Good news is that the spark arrestor /air filter looks to be very dirty and may be a source of restriction. We ran without it and she seems to smell a bit better and got up to 4400rpm and 59 km/hr via gps.

It will still be nice to know what the original main jet size is though. Just to see if it was ever changed.

Thomas

 

[Aqua Susurro]

Also the plugs looked pretty good last time I pulled them. Tan brown, not wet and not overheated. Its in the ballpark jetting wise just a little rich. The clogged spark arrestor could be the problem. However I will be pulling the carb in the off season and checking what jets are in it and maybe go down a size. I like the power and speed but dont want the excessive fuel consumption and pollution.

 

[Scott06]

Flame arrestor being dirty can act like a choke. If choke is coming open ok would make sure needle seat and float are in good Condition and set at correct level before changing jets if you haven’t serviced the carb yet

 

[achris]

.... Carb number is 7043183....

If you need more information, or the 'how to' on stripping and setting up the carb, let me know.

I would strongly recommend AGAINST reducing jet size. That can lead to a lean condition which can melt pistons, burn valves etc... If it's still running 'rich' after you have got the carb sorted out, then you need to look at the ignition system. In fact, I'd do that first. Good strong spark, new spark plugs and leads. And check the timing is advancing properly and to correct maximum at the right rpm... Here's the timing curve...



Personally, I'd toss out the points and get something electronic in there. When I had my 165, I built a capacitor discharge ignition system and installed that. The difference was quite noticeable. And no more pesky points to service! Timing never drifted, started easier, and idled smoother... And just 'felt' stronger. Also, spark plugs lasted longer.

Chris.......

 

[Aqua Susurro]

Thanks Chris. Thats exactly what I needed. I did check float level and changed / rebuilt the carb as per the spec sheet given with the kit. I am also hesitant to change jets unless it turns out that someone put something else in.

Totally agree with you on the ignition. I havent messed around with points since my very first car. Incidentally my step father invented capacitor discharge ignition along with the radar detector. Now there was an interesting guy. I changed out to a Pertronix kit and replaced the coil too. Plugs looked perfect and were a good make (NGK) so I left them in. The wires were good too. I had a long time Mercury mechanic have a listen to it and he thought it ran great.

It may be the flame arrestor is the problem. It was the one thing I overlooked. A touch embarassing but I never even looked at it because its not a filter that gets dirty, or so I thought.

 

[kenny nunez]

I bet that either your crank, water pump or the alternator pulleys are rusted and chewing up the belt. That is a good reason for the flame arrestor to be restricted.

 

[Tycer]

If you need more information, or the 'how to' on stripping and setting up the carb, let me know.

I would strongly recommend AGAINST reducing jet size. That can lead to a lean condition which can melt pistons, burn valves etc... If it's still running 'rich' after you have got the carb sorted out, then you need to look at the ignition system. In fact, I'd do that first. Good strong spark, new spark plugs and leads. And check the timing is advancing properly and to correct maximum at the right rpm... Here's the timing curve...



Personally, I'd toss out the points and get something electronic in there. When I had my 165, I built a capacitor discharge ignition system and installed that. The difference was quite noticeable. And no more pesky points to service! Timing never drifted, started easier, and idled smoother... And just 'felt' stronger. Also, spark plugs lasted longer.

Chris.......

Chris,
Can I direct you to this thread?
https://forums.iboats.com/forum/eng...engines-outdrives/10803148-2jet-carb-settings

 

[Aqua Susurro]

Had another look at the engine while it was idling. This time with the cover pulled off to check the alternator(bearings are going) While running I noticed there was an oil fog coming out of the breather/cap. Did some checking and it looks like I have an automotive breather while Mercruiser 165s should have just a filler cap without breather. The slight blowby gasses are coming out the Vented filler cap instead of going into the carb. That is definitely cause for bad engine smells. Ordered a cap for $2.09 US. lol the shipping was $10.