1981 Yamaha 550 Seca Resurrection

[Max]

I finally had a bit of time to look at the Seca again. When I last left it, it was running, but weakly. The throttle response was slow and it didn't idle that great without just a touch of choke. Previously it ran well for about a day and a half, during which time I was able to re-synch the carbs. Before ignoring it for awhile I did shut off the gas and let it run until it died.

I pulled a plug and used that to test for spark on cylinders 1, 2, and 4 and it looked the same across all of them. Not the biggest and bluest spark I've seen, but it was there and similar from cylinder to cylinder. An inductive timing light also lit when used on each spark plug wire. I was really hoping it was a bad coil, but it doesn't look that way now.

I mentioned before that the engine seems to heat up unevenly. Here is what I saw with one of those laser IR thermometers testing above the head at each cylinder. In hindsight using the cylinders or exhausts would have been better, but these numbers are from the head:

Cylinder​	Minutes (deg F.)​
​	0.5​	1​	1.5​	2​	2.5​	4​
1​	77​	79​	84​	89​	95​	123​
2​	77​	80​	89​	100​	112​	136​
3​	85​	95​	99​	109​	125​	153​
4​	85​	95​	101​	105​	122​	142​

So it looks to me that #1 isn't working that hard, and maybe #2 as well. I think that I've got a compression tester somewhere that I haven't used in 40 years, so that's the next step. And if it looks good like I expect, then it's time to open up the darn carbs again. I don't mind working on the carbs per se, but I hate taking them off the bike as the airbox design *****. I'm also going to redo the temperature measurements, but this time I'll monitor the exhaust pipes instead.

 

[Firebrick43]

I finally had a bit of time to look at the Seca again. When I last left it, it was running, but weakly. The throttle response was slow and it didn't idle that great without just a touch of choke. Previously it ran well for about a day and a half, during which time I was able to re-synch the carbs. Before ignoring it for awhile I did shut off the gas and let it run until it died.

I pulled a plug and used that to test for spark on cylinders 1, 2, and 4 and it looked the same across all of them. Not the biggest and bluest spark I've seen, but it was there and similar from cylinder to cylinder. An inductive timing light also lit when used on each spark plug wire. I was really hoping it was a bad coil, but it doesn't look that way now.

I mentioned before that the engine seems to heat up unevenly. Here is what I saw with one of those laser IR thermometers testing above the head at each cylinder. In hindsight using the cylinders or exhausts would have been better, but these numbers are from the head:

Cylinder​	Minutes (deg F.)​
​	0.5​	1​	1.5​	2​	2.5​	4​
1​	77​	79​	84​	89​	95​	123​
2​	77​	80​	89​	100​	112​	136​
3​	85​	95​	99​	109​	125​	153​
4​	85​	95​	101​	105​	122​	142​

So it looks to me that #1 isn't working that hard, and maybe #2 as well. I think that I've got a compression tester somewhere that I haven't used in 40 years, so that's the next step. And if it looks good like I expect, then it's time to open up the darn carbs again. I don't mind working on the carbs per se, but I hate taking them off the bike as the airbox design *****. I'm also going to redo the temperature measurements, but this time I'll monitor the exhaust pipes instead.

Did you tune idle with the IR thermometer? I was taught and always have tuned with either a colourtune or IR gun at idle, re sync carbs, check temps again and tune idle closer, re sync, and then run a couple of hard runs killing ignition while still pulling and coast to a stop, pull plugs and see if they are all chocolate brown.

 

[Max]

Did you tune idle with the IR thermometer? I was taught and always have tuned with either a colourtune or IR gun at idle, re sync carbs, check temps again and tune idle closer, re sync, and then run a couple of hard runs killing ignition while still pulling and coast to a stop, pull plugs and see if they are all chocolate brown.

I synched the carbs with a Carbtune Pro. I thought that using a manometer like the Carbtune Pro was the gold standard? What you suggest is a new process to me. I am willing to give it a shot if it's worked for you in the past.

And great suggestion on checking the plugs - I'll add that to my list.

This is what I used to synch the carbs:

 

[Firebrick43]

I synched the carbs with a Carbtune Pro. I thought that using a manometer like the Carbtune Pro was the gold standard? What you suggest is a new process to me. I am willing to give it a shot if it's worked for you in the past.

And great suggestion on checking the plugs - I'll add that to my list.

This is what I used to synch the carbs:

The issue is that tune affects sync and sync can affect tune. So many times it takes going back and forth to get everything set right. If you tune, and then sync you have thrown the tune out which by the temp numbers is very much the case. Its rare to need more than 2 cycles to get it on but some times things are finicky and I have done the processes 3 or 4 times to bring everything in as close as possible. I prefer using a colourtune on the first round especially to set cylinder number 1 and then match every cylinder after so they are the same temp. This assumes the boots aren't cracked. Many just tune by ear, setting midway between running rough rich and lean with the low speed jet needle and that works ok with a single cylinder but you cant really do that well with a multicylinder engine.

That is fine to use to do the sync, looks like it uses stainless rods? , I use a mercury filled manometer, aka sync stick.

 

[Max]

The issue is that tune affects sync and sync can affect tune. So many times it takes going back and forth to get everything set right. If you tune, and then sync you have thrown the tune out which by the temp numbers is very much the case. Its rare to need more than 2 cycles to get it on but some times things are finicky and I have done the processes 3 or 4 times to bring everything in as close as possible. I prefer using a colourtune on the first round especially to set cylinder number 1 and then match every cylinder after so they are the same temp. This assumes the boots aren't cracked. Many just tune by ear, setting midway between running rough rich and lean with the low speed jet needle and that works ok with a single cylinder but you cant really do that well with a multicylinder engine.

That is fine to use to do the sync, looks like it uses stainless rods? , I use a mercury filled manometer, aka sync stick.

Thank you. It was so much simpler when this all was new.

I refused to pay almost $300 for the colorsync on Amazon, so I ordered one from the EU. Which will take awhile, but it'll get here.

And yes, the carbtune pro uses stainless rods instead of mercury. I had read of people actually sucking mercury into the engine and I figured I'd avoid the issue.

 

[jamesfjamesf]

In 1981 I was able to buy my first new motorcycle.

So time moves on, and my BiL is cleaning out his house and downsizing, so I now have my old bike back again.

I had one of these, same year and color. I loved that motor. I saw your carb issues, I do not miss r&r ing inline 4 carb racks one bit! But if you get the carbs clean and adjusted, it will run really well. I didn't go through the whole thread- did you try an ultrasonic cleaner? The harbor freight one is fine. Use Pine sol as a cleanser. I should have never sold that bike, so much fun.

jim

 

[Max]

I had one of these, same year and color. I loved that motor. I saw your carb issues, I do not miss r&r ing inline 4 carb racks one bit! But if you get the carbs clean and adjusted, it will run really well. I didn't go through the whole thread- did you try an ultrasonic cleaner? The harbor freight one is fine. Use Pine sol as a cleanser. I should have never sold that bike, so much fun.

jim

I have a small ultrasonic cleaner that I used for some of the smaller pieces. But it’s too small to hold a full carb body. So the bodies got carb dip, carb spray, and wires. The guide on Mikuni carbs earlier in the thread is excellent when doing this.

 

[Firebrick43]

Thank you. It was so much simpler when this all was new.

I refused to pay almost $300 for the colorsync on Amazon, so I ordered one from the EU. Which will take awhile, but it'll get here.

I am not sure I would buy a colortune for just one bike. You can use a new or cleaned spark plug and let it idle for 5 min or so and kill the bike with the key then pull the plug and look at the plug on the number 1 cylinder and see if it’s white(too lean) tannish to chocolate brown (correct) or sooty black (too rich).

I had a colortune as my first off farm job was as a motorcycle mechanic, and carb cleaning/tuning was 80 percent of the jobs I got.

If you do continue to get it make sure you don’t try to use it in direct sunlight or bright shop lights or you won’t be able to see the color correctly

And yes, the carbtune pro uses stainless rods instead of mercury. I had read of people actually sucking mercury into the engine and I figured I'd avoid the issue.

Yea it was possible if you knocked over the sticks somehow, maybe revved too high as well???

I like the fact that the carbtune pro can be transported with ease or stored in a tool box. Sync sticks have to be forever hung unless you put the mercury back in a bottle which is a royal pia and not safe either

 

[Max]

I am not sure I would buy a colortune for just one bike. You can use a new or cleaned spark plug and let it idle for 5 min or so and kill the bike with the key then pull the plug and look at the plug on the number 1 cylinder and see if it’s white(too lean) tannish to chocolate brown (correct) or sooty black (too rich).

I had a colortune as my first off farm job was as a motorcycle mechanic, and carb cleaning/tuning was 80 percent of the jobs I got.

If you do continue to get it make sure you don’t try to use it in direct sunlight or bright shop lights or you won’t be able to see the color correctly

Yea it was possible if you knocked over the sticks somehow, maybe revved too high as well???

I like the fact that the carbtune pro can be transported with ease or stored in a tool box. Sync sticks have to be forever hung unless you put the mercury back in a bottle which is a royal pia and not safe either

It’s a chance to buy a new and cool tool, so no issue there.

 

[rd65]

I am not sure I would buy a colortune for just one bike. You can use a new or cleaned spark plug and let it idle for 5 min or so and kill the bike with the key then pull the plug and look at the plug on the number 1 cylinder and see if it’s white(too lean) tannish to chocolate brown (correct) or sooty black (too rich).

I had a colortune as my first off farm job was as a motorcycle mechanic, and carb cleaning/tuning was 80 percent of the jobs I got.

If you do continue to get it make sure you don’t try to use it in direct sunlight or bright shop lights or you won’t be able to see the color correctly

Yea it was possible if you knocked over the sticks somehow, maybe revved too high as well???

I like the fact that the carbtune pro can be transported with ease or stored in a tool box. Sync sticks have to be forever hung unless you put the mercury back in a bottle which is a royal pia and not safe either

and when you lose your mercury, you're done. cant buy it any longer.