Yamaha Seca 750, 1982 model

There was a Yamaha tool you inserted into the YICS port that had a lever to expand rubber on rod to block the ports when syncing, don't know how much difference it made.
I believe it makes a difference. Sync'd w/o tool, thought it was good based on gauges. Looking back, they would be easy to line up sharing the same vacuum in the YICS port as has been said many times.

Used the tool, that showed they weren't good if having all 4 lined up is the goal. $68 front ebay, original Yamaha tool, shipped from Japan. Took a while but worth it.
 
A little known fact on the Seca, of course you know it. The front brake MC is not on the handlebar. there is a cable from the lever to the MC.

How's the braking feel with that in between?
Missed this one a while back. Yes the cable between the brake lever and master cylinder takes away some feel for sure. Braking power is fine, however it's rubbery for lack of a better description.

Pulling the brake lever to the bar and securing it there with the bike on the side stand overnight and turning the bars left so the master cylinder under the headlight is the highest point has helped. That firmed things up a good bit beyond the initial bleeding of the calipers. But still not like the direct master cylinder connection on every other bike ever made. Top 10, if not top 3 worst designs ever on any bike system I've known.

Update on the bike:

Had an issue pretty much from the get-go, #2 was not firing at idle, it would come on intermittently as rpm/load increased. Carburetors are fine, ignition checked out electrical wise on the pickup/rotor, TCI and coils. I had fuel, spark and air. Compression was within 10 psi across all four, with #2 being the low one.

Only thing left that I had in the back of my mind was the valves had not been checked by my uncle when he used this engine to build the bike. #2 exhaust valve was .004", spec is .006"-.008". Very tight.

Compression check can't necessarily pick this up, however when there's enough fuel mixture getting pushed out on compression coupled with not creating enough compression at idle because the exhaust valve won't close during compression there's going to be no fire in that cylinder. At least that's how I visualize it in my mind.

Got the valves adjusted back into spec, #2 lit right up. Sync'd carbs with YICS tool, found a good deal on one from ebay.

For grins I checked sync without the tool, they were almost perfect which is to be expected since they share common vacuum via the YICS passageway. Inserted the tool, they weren't as pretty on the readings. Got those dialed in with the tool. Made all the difference with respect to butter smooth at idle and responds like a rheostat in any gear.

Ran the first real tank of gas through it in the last week on a mixture of rides. Approx 70% two lane 50-60 mph, 20% 75-80 mph on the interstate, 10% short runs into town. The bike averaged 47 MPG.

Going on a ride friday, should get a couple hundred miles. Interested want to see if mileage picks up once the engine gets a few more miles on it. It had sat for 20+ years and has 322 miles since it was restored 25 years ago.

Will take it on a ride tomorrow to get it good and warm. Change out the 15w40 HDEO I put in there when I started the process and the final drive fluid. 20w50 going in the engine, 75w90 in the FD.
 
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Going to have a little fun with this post... in another thread there was good discussion about 10w40 or 20w50 in a Nighthawk 750 and the difference in felt power.

One of my riding friends has a well cared for and good running 1998 Honda Nighthawk 750. That bike is running 10w40.

Went on 170 Mi ride in the Colorado mountains yesterday. The Nighthawk 750 and the Seca 750 were representing the carbureted UJM crowd.

The Yamaha Seca 750 had its first oil change after the work to get it dialed in, swapped out the 15w40 HDEO I put in for the tuning process for 20w50 as I had mentioned in the previous post.

I can happily report the 20w50 versus 10w40 power battle is a draw between the two bikes. One would expect the 16-year newer 16 valve head 1998 Nighthawk with 10w40 to trounce a 1982 8 valve head Seca 750 running 20w50. They were neck and neck, no discernible difference in performance. We swapped bikes back and forth, had a good time with it. Probably a good thing 20w50 was in the Seca 750 as a handicap so the bikes could stay even. ;)
 
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Going to have a little fun with this post... in another thread there was good discussion about 10w40 or 20w50 in a Nighthawk 750 and the difference in felt power.

One of my riding friends has a well cared for and good running 1998 Honda Nighthawk 750. That bike is running 10w40.

Went on 170 Mi ride in the Colorado mountains yesterday. The Nighthawk 750 and the Seca 750 were representing the carbureted UJM crowd.

The Yamaha Seca 750 had its first oil change after the work to get it dialed in, swapped out the 15w40 HDEO I put in for the tuning process for 20w50 as I had mentioned in the previous post.

I can happily report the 20w50 versus 10w40 power battle is a draw between the two bikes. One would expect the 16-year newer 16 valve head 1998 Nighthawk with 10w40 to trounce a 1982 8 valve head Seca 750 running 20w50. They were neck and neck, no discernible difference in performance. We swapped bikes back and forth, had a good time with it. Probably a good thing 20w50 was in the Seca 750 as a handicap so the bikes could stay even. ;)
Thanks. What was the ambient at the time?
When I did it, was 50F out. Yes, probably should have ran it longer, gave it a better chance.

Per the chart, 10w-40 is good till 95F so no issue.

Thought for sure the Seca was 4 valve. Yamaha even went for 5 valves for a moment around the same time.
 
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