Is it necessary to rejet?

[TCWest]

I'm reading that my '75 Century Silver Plus (Long) will smoke like a chimney if I run 10:1 through it. To run the 25:1, I'm reading that I need to rejet with a needle I might not be able to find.
Here's the question. Slap me around and call me Nancy if it's stupid. With the improved 2-cycle oils these days, can I expect the same smoke from a 10:1 mix? What if I went with a synthetic and/or blend?
I'd like to not change from OEM if I can, in the name of keeping it all original...but I can't have her smokin' me off the water, either.

[charlesp]

Not a needle, in the case of the Aml carb that's on your Silver Century, it's a case of a new jet. I'm fairly sure John will have some, and they're very easy to swap. This was an official upgrade available from the factory, and they changed to 25:1 very soon after 1975 anyway. So the issue of originality doesn't really arise.

However I run my Silver Century on 10:1, and I'm using a modern oil made by Comma. There's really very little smoke. Mind you people on this forum know I actually like the smoke. It adds an authenticity to the Seagull experience, but were I a heavy user I'd probably switch to 25:1

[RickUK]

I run most of my Seagulls at a 15:1 mix using synthetic oil, which I am a complete convert for - it hangs around longer on the bearings, doesn't coke up on piston crowns etc., and produces virtually no smoke.
The exceptions to this ratio for me are the Villiers carbed engines which are set up for 25:! either by carb. type (Bing) or have a 25:1 needle in them, or whole engine type eg. Kingfishers
Not critical for older engines, but if moving to synthetic oil, use TCW 3 (named after you?) - the 'W' being for water cooled engines which run so much colder than air cooled engines.

I know 10:1 was the long standing mandate for the older engines, but it seems to be a hell of a lot of oil in a given amount of petrol! Rick.

[CatiGull]

TCW - it might be worth checking your compression to see if your rings need work - my FP runs on 10:1 and barely smokes....I wonder why you are getting so much??

[TCWest]

TCW - it might be worth checking your compression to see if your rings need work - my FP runs on 10:1 and barely smokes....I wonder why you are getting so much??

Rings are clean, compression is strong. I haven't had it in the water yet!! I'm just reading up before I go, trying to live the experience vicariously before actually getting out there and trying it out. I've done the bench test, and was not all that concerned about what smoke I did see. In comparision, though...it would certainly be the smokiest motor running on the lake that day, since most everybody else is running something brand new. I'd like to stand out for better reasons.
I did make the mix for the first time a few weeks back, and man...that is a lot of oil in there! The motor is still fired by the 8 com, which may be part of the smoke issue...if there is one.

BTW, I'm feeling your pain in looking for the 140w for the prop. Something tells me I'm going to have it in time for the weekend, though. I'm pretty tenacious...and I know a whole bunch of old grease monkeys with loads of old Ford tractors, which also used that molasses in their gear boxes.

CharlesP...that's the first time I've seen "heavy user" and "I actually like the smoke" in the same paragraph without having a moderator step in.
I appreciate your post, because it makes me feel better about rejetting. I really want to keep it original, and it looks like I can despite the upgrade.

Rick...does that mean I can use less oil by using the synthetic, and not have to swap jets?

[RickUK]

I know the counsel of perfection is to change jets/needles, but I never do,
and I find it difficult to accept that changing jets - especially in the case of needles - compensates for the different petrol/oil ratios on engines which finally have the same bearings! Even my engines (except the late ones) with 25:1 needles get 15:1, 'cos that's what's in the petrol can!
So yes - I would use a 15.: ratio with mineral oil or synthetic, but synthetic does not burn the same way as straight mineral oil, and does a better job of lingering on the bearings, and if you ever take engines apart after a long while and are able to compare ones run on each type of oil, you will see that the one run on synthetic has vitually no deposits on the piston crown, around the rings or in the crankcase.
Havng said all that, I must say I quite like to see a miasma of smoke, which I suppose is considered anti-social in this day and age, and I still fancy putting a drop of Castrol R in the mix for the perfume! (but I would probably pay for it later with blocked jets/filters) Rick.

[CatiGull]

CharlesP...that's the first time I've seen "heavy user" and "I actually like the smoke" in the same paragraph without having a moderator step in.

I hate being beaten to a wonderful double entendre...

[chris]

I own a silver century the same year as yours and did find it was very smoky.
Mine was a rebuilt one with new rings etc, I changed the jets and it is now smoke free and more economical.

[niander]

I own a silver century the same year as yours and did find it was very smoky.
Mine was a rebuilt one with new rings etc, I changed the jets and it is now smoke free and more economical.

A smoke free seagull!...

[atoyot]

I'm feeling your pain in looking for the 140w for the prop. Something tells me I'm going to have it in time for the weekend, though. I'm pretty tenacious...and I know a whole bunch of old grease monkeys with loads of old Ford tractors, which also used that molasses in their gear boxes.

If you have a Grainger's industrial supply nearby, they have this.

....does that mean I can use less oil by using the synthetic, and not have to swap jets?

It's quite possible. I think the deal with the jet or needle conversion, is that less oil in the petrol/gasoline ends up making the fuel more viscous and it flows more easily than the factory jetting wants it to be, thus, too rich a mixture. Using a thicker #2 needle conversion in the 40 series, for instance, re-tunes for this change

The Maxima's Castor927 http://www.mammothmotorsports.com/By_Ma ... __1010.htm that I use is thicker than what you're used to in 2-stroke oil and so even if you were jetted for 10:1, you'd probably want to mix it 16:1 to get the same flow out of the fuel. That's my experience with another outboard I have - went from 16:1 to 25:1 just on the mix, minimal retuning.

I'm running this stuff, available at a local motorbike shop, in a Featherweight with a 25:1 needle that runs great and doesn't stink nearly as much as typical 2-stroke engines do. Smoke? Sure it does. But it smells "sweet" and not oily, and not as much as it would on the orignal mix ratio to be sure. Even the spouse stopped bitching about me test-tunning the motor with the house windows open downwind of the shed.

Have fun!