750 SECA Engine Rebuild Question

Question BLUF: how do I know if something is wrong without a known-good reference engine or cringing while on a post-breakin test ride?

The Background
A few years ago I began the process of rebuilding my 750 SECA (1981), starting with the engine. I am a total novice and this was my first engine rebuild ever, but since I bought a second much newer bike I figured why not.

Fast forward to today and things are finally running well enough to ride. Except now I have no idea if everything is good enough. I will list some minor issues below but the real concern I have is that I'm not actually sure if I succeeded. I'm treating it gently until I hit an arbitrary 100 mile breakin duration. But it's been so long since I've ridden it that I can't even remember how it ran before (and it wasn't in great shape before anyways).

So here's where I decided to call for help.

The Question
What do I need to do in order to verify the thing won't go kaboom between my legs? What sort of tests should I be doing? What should it sound and feel like?

The Symptoms

• Strong(?) Vibration (no idea how much is normal and at what RPMs)
• Harsh Sound in the mid-RPMs? (I forgot how much anxiety those cams used to give me)
• Slow to drop revs (I suspect carb adjustment issues)
• Highly sensitive to choke adjustment until fully warmed up (probably the carbs again)
  
• Had to increase idle to closer to 1,500 for a stable idle

Some other (possibly) important things about the bike:

• Deck was professionally surfaced, so compression might be ever so slightly higher
• Cylinder sleeves and pistons are in spec (verified by the same shop that surfaced the deck)
  
• Leak down test looked good
• Compression seemed low, so I'm wondering if I did that test wrong
• Coils have been replaced
• Timing advance check with a cheap timing strobe didn't seem to match the specs in the manual
• Exhaust is in terrible shape and likely leaky at the crossover. I can't get the exhaust test port screws loose.

 

I had to shorten this because of the spam filter but I can add details as requested. Thanks for reading.

 

- Has the engine ("carbs") been vac-synched (running engine)? If not, many of the seemingly "carb" issues may go away.

- Have the carbs been rebuilt?

- Have valve shim clearances been checked? This is especially important on an engine that had surfacing or valve-lapping performed.

- Are you sure that you installed the cams / sprockets and chain correctly?

- Teach, leave that (exhaust test port) screw alone! Only sorrow and heartbreak can result from messing around with them.

-

Could be, or the gauge may be inaccurate, or the head was not torqued down in proper sequence and or to the proper specs. Do you have a shop manual or the Hyanes manual for the 650/750 engines?

 

1. The carb was synced on a running engine with the YICS port blanked, but I guess if the carb needs a rebuild then that will only go so far.
2. At one point but I think I'm going to get a carb kit and do it again because it's probably been too long.
3. I checked clearances during final reassembly but I can always pull the valve cover and check again.
4. I am fairly certain I did, but I'll check my manual and see if I can verify it.
5. Appreciate the Pink Floyd reference!
6. I do have the manual. I'll redo the torque sequence after I check the clearances. Failing that I'll see if I can get a different gauge or find a way to "calibrate" it for that particular test.

I swear there was some other thing I forgot to mention but I forgot it again. >.<

 

Update:
I've started cleaning the carbs. #1 is apart and I gotta say it's filthy. I definitely made a poor assumption about how clean they were. So I'll be replacing a few seals and gaskets and the float valve filter. Are there other parts I should pay special attention to?

Also, I need to look up all the nominal jet sizes to make sure it's not been messed with from what it was originally spec'd at.

Oh, and I remembered that last little thing I changed from stock: I replaced the vacuum petcock with a traditional manual because I kept having leak issues when not running.

 

Valve clearances checked and two of the exhaust side clearances are too small. E1 is at 0.004 inches and E3 is at 0.005 inches. I need to go from 270 to 260 on E1 and 275 to 270 on E3 (lucky me!) so I'll need to add a shim to my parts list.

During the carb rebuild I discovered that one of the permanently installed retaining clips on one of the diaphragms is busted. So I either need to do a replacement of all 4 diaphragms with the aftermarket slip-on style or I need to source a replacement. Anyone have any thoughts on which is the better route to take?

 

I have been using the jbm industries ones and they work great.
One caveat don't ever run a fuel system cleaner through the system.
Basically they swell and don't really seal onto the piston after that.
Yes, I didn't read the website properly.

 

Should I worry about the mixture screws?

They're blocked off on my carbs but I'm wondering if I need to get those plugs out so I can adjust them. Still trying to find a colortune though.

 

You're not going to be able properly clean the carb with the idle screws in place. Remove the caps and take them out making sure to count how many turns out they are from being seated all the way in. Then when you reassemble them be sure to put them back with the same number of turns out, that should get you pretty close to where they need to be.

 

Break the rack and order new butterfly seals from xj4ever, it is worth it after 35 years it would be time to replace.