Yamaha Seca 750, 1982 model

B

Bonz

Joined
Jun 5, 2013
Messages
2,056
Location
Colorado, USA
Been rehabbing the fuel system/carbs and brakes on a 1982 Yamaha Seca 750. My wife's uncle rebuilt this 20 years ago. Took it down to the frame, powder coated, new wiring harness, all NOS parts to replace the stock parts that showed wear. Including an NOS gauge cluster with 0 miles. It's been sitting in his climate controlled garage/workshop since it was last plated in 2007. Aren't five of these bikes in the country that are in this visual condition.

Anyway, I'm running 15w40 conventional HDEO in it as I get the engine up and running and tune the carbs. Thought I'd share my plan to run conventional 20w50 in the engine, as oil change intervals are 3,000 miles from back in the day. By the time 20w50 starts breaking down, the oil is going to be contaminated from blow by and show the effects of heat from the air cooled engine long before synthetic would make a difference.

I did a similar routine with a Yamaha XS1100 that I had for a good number of years. Point being, if the oil change intervals are fairly short, and I consider 3,000 miles fairly short because miles not time are an oils downfall, conventional will serve just fine for these older UJM's.
 
Bonz said:
Been rehabbing the fuel system/carbs and brakes on a 1982 Yamaha Seca 750. My wife's uncle rebuilt this 20 years ago. Took it down to the frame, powder coated, new wiring harness, all NOS parts to replace the stock parts that showed wear. Including an NOS gauge cluster with 0 miles. It's been sitting in his climate controlled garage/workshop since it was last plated in 2007. Aren't five of these bikes in the country that are in this visual condition.

Anyway, I'm running 15w40 conventional HDEO in it as I get the engine up and running and tune the carbs. Thought I'd share my plan to run conventional 20w50 in the engine, as oil change intervals are 3,000 miles from back in the day. By the time 20w50 starts breaking down, the oil is going to be contaminated from blow by and show the effects of heat from the air cooled engine long before synthetic would make a difference.

I did a similar routine with a Yamaha XS1100 that I had for a good number of years. Point being, if the oil change intervals are fairly short, and I consider 3,000 miles fairly short because miles not time are an oils downfall, conventional will serve just fine for these older UJM's.
Click to expand...
Pics or it ain't real...
 
Ok, I think there is a law against what you just did, after reading your first paragraph I couldn’t wait to scroll down and see some pictures….. come on man! Where’s the pics? I can’t wait to see it! My best friend had one of these when we were 16, I had a 1984 Nighthawk 450, we use to spend a lot of time trading bikes. Pretty sure his was a 82 also.
 
You guys are too much. Need to put that in the by-laws of BITOG, "Pics or it ain't real".

20250613_180947.webp
 
Jaso MA was introduced somewhere in the 80s because the then new "Energy conserving" car oils starts to become to slippery for wet clutches and casue problems. JASO MA was the answer for this Problem.
So, motorcycle and wet clutch: JASO MA is the correct choice..
 
With respect Castrol 20w50 ,correct, I picked up six quarts at Advance Auto literally this weekend but it was not the classic and it was $4.99 a quart. That's what I was planning on running.

Now, going to swing by AutoZone and see what they have in 20w50 GTX classic. There's a Lake Speed Jr. comparison of 20w50 GTX versus GTX classic. GTX classic is what I would prefer to run.

With that said I have so much 20w50 between Red Line, Amsoil, Valvoline conventional and Mobil 1 V-Twin, I need more 20w50 like I need a hole in my head after 6 qts conventional 20w50 GTX at Advance which I was planning for the Seca.
 
Do yourself a favor and bet Delvac 1300 15w40 in there. Can’t ask for a more robust oil at such a great price.

BTW, that’s one beautiful machine. Very well done for sure, congrats!

You should not let any fuel sit in the carbs if you don’t plan on riding it. Just drain the carbs and you should be good to hibernate it for a very long time. Quality parts are becoming an issue with tons of cheap Chinese reproductions that won’t run correctly.
 
I love these old seca’s with the shaft drive. I’d like to hear how it performs for you and what type of MPG you’re getting. A friend of mine had one for years as his only form of transportation. He totally abused that bike and it just kept going.
 
KrisZ said:
Do yourself a favor and bet Delvac 1300 15w40 in there. Can’t ask for a more robust oil at such a great price.

BTW, that’s one beautiful machine. Very well done for sure, congrats!

You should not let any fuel sit in the carbs if you don’t plan on riding it. Just drain the carbs and you should be good to hibernate it for a very long time. Quality parts are becoming an issue with tons of cheap Chinese reproductions that won’t run correctly.
Click to expand...
Thanks for the post. I have had decades of experience with 1980s UJM's, 20w50 is going to be fine. The thin air of Colorado is much less effective cooling at any speed and absolutely brutal on air-cooled bikes in slow traffic. Especially with summer temperatures getting as hot as the devil's crotch here in the front range over the years.

To satisfy the 15W40 HDEO bug in you, there's some T4 in there right now as I'm working through getting it ready for a summer of riding. As soon as it's all good to go, I'll be going to the 20w50.

Haven't drained a carburetor in years, typically there is opportunity to ride every few weeks here in Colorado even when it's cold out. Starting in October through April however, fuel always has stabilizer in case there's an extended stretch of snow or cold that keeps me off the road for more than 4 weeks. Snow melts fast and the sun is warm in Co.

Colorado with the low humidity is much less of an issue with fuel sitting in carburetors from experience. Humidity is a huge factor in carburetors getting gummed up and looking like a biology project. Having rehabbed carburetors on numerous bikes that came from lower elevation, they have green stuff growing in them that looks like it should be in a Petri dish.
 
Last edited:
Oliveoil2 said:
I love these old seca’s with the shaft drive. I’d like to hear how it performs for you and what type of MPG you’re getting. A friend of mine had one for years as his only form of transportation. He totally abused that bike and it just kept going.
Click to expand...
Will continue posting as I get it on the road.

The short ride I did a week or so ago shifted cleanly, pulled cleanly, synchronized the carbs and that cleaned it up with respect to returning to idle and steady idle. Before I do anything more than around the block so to speak the new tires need to be mounted. This thing hasn't been plated since 2007 and the tires were put on a few years before that.
 
ChristianReske said:
Jaso MA was introduced somewhere in the 80s because the then new "Energy conserving" car oils starts to become to slippery for wet clutches and casue problems. JASO MA was the answer for this Problem.
So, motorcycle and wet clutch: JASO MA is the correct choice..
Click to expand...
I can't recall a post on this forum in many years or ever that said an automotive oil in a motorcycle sump caused issues with the clutch. I have seen numerous posts about different motorcycle oils causing issues in clutches when going from conventional to synthetic, etc. But that is something with the clutch not the oil, IMO

I have said this more than a few times on BITOG , no magic pixie dust has been identified as a friction modifier even by oil specialists familiar with the industry on this forum.
 
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