82 GS450T Low RPM RH cyl dead

[racer510]

First post. Getting back to bikes after about 30 years away racing cars. Bike experience was with 1970's vintage Yamahas. Pre-electronic ignition. Were just starting with vacuum carbs.

Resurrecting a GS450T that was parked for 3-5 years before I bought it. Rather than part it going to sell to a new rider-great starter bike. Everything was complete and stock.

Don't know if it was running properly when parked. Previous owner was vague on this point.

Has 10K on motor/chassis. Appears generally well cared for. Sat with fuel in tank-cleaned out with no rust remaining. Replaced petcock-fuel flow normal. Changed all fluids. Cleaned air filter. Replaced battery. Checked all electrical connections. Installed H4 headlight. Wrapped rusted exhaust crossover with stainless flashing and hose clamped (new exhaust is new owner's project).

Started right away but idles and runs to 2000-2500 on LH cyl then RH kicks in too. Backfires through airbox occasionally until RH kicks in. Checked balance with vacuum gauges - very close. Checked idle screws and set to 2 turns each. Checked and adjusted timing - spot on and advance works to spec. Have spark on both cylinders although RH spark seems to run from the center electrode up and down the wire electrode a bit. RH spark seems strong enough for ignition (blueish yellow). LH spark is stronger. New plugs are sooty although LH is keeping insulator clean. Bike has idled a bunch and hasn't been run at speed much for the last while.

Both coils show about 4 ohms.

Went through carbs. Cleaned up nicely. Only problem noted was RH carb diaphragm had been mis-seated previously, kind of folded over. I reseated and applied a bit of sealant to area where it had been folded. Float heights were in spec and identical on both. Appeared to have 115 mainjet although hard to make out.

About to do another round of troubleshooting.
1. Plan to disconnect headlight (too much voltage draw)?
2. Going to check ground on coils.
3. Going to check voltage while running (idle-4k)
4. Compression test.
5. Swap diaphragms between carbs.

Any advice on this one? Am I on the right track?

[Nessism]

Spark plug caps sometimes have issues. You can unscrew them from the wires and check electrical contact although the wires themselves are not replaceable since they are built into the coils.

My "guess" is you still have issues with the carbs. These GS bikes are very sensitive to vacuum leaks and the carbs are very lean from new so any false air entering the system causes problems. In particular, the rubber carb runners have a large o-ring trapped between the head and the boot, which almost always leaks if they are not fresh.

Regarding the charging system, check voltage at the battery with the engine running a 5000 rpm - should be in the range of 14.5 volts which is plenty to keep the battery up even with the headlamp on all the time.

Good luck.

[racer510]

Thanks! I'll check them out.

[racer510]

Well, Checked inspected o-rings and they looked ok. Used some high-temp sealer to make for sure. Sprayed starting fluid (less messy than wd and easier on paint than carb cleaner) all around carbs, manifolds, etc without any change in rpm.

So--started noting the backfiring. Happening both through pipe and airbox on RH. Makes idle go haywire after a backfire through carb. So, in an effort to do first things last, thought I ought to check valve clearances. Hadn't done it because don't have the tool or shims to adjust anyway.

Well they ALL seem tight. My smallest gauge is .002 mm and couldn't get it through any of them. Didn't even seem close. My guess is I've got valves leaking. I did compression test and got 100 psi cold RH 110 LH.

So, after I get a .001 mm gauge and double check I'll need to gear up to do valve adjustment.

Make sense?

[racer510]

Update

Well, all four of the valves were way tight. Replaced shims and got that cleared up. Better but still not running great. Kind of concerned about having burned valves or at least coked them up a bunch. Any thoughts?

[nabrams]

You've done your valve adjustment. Now do some mid/high RPM running for a few minutes and re-check compression.
If your compression is above 120 then that can't be the reason for your RH cylinder problem. It's got to be carb or ignition or air leak. I suspect a bad ignition component (pulser/ignitor/coil/wire/cap) based upon your descriptions. When they are are on the verge of failure they can misbehave intermittently. Have you swapped coils? Have you swapped carb diaphragms?