Mileage/Plug/RPM issue

[dw200]

I want to run this by everyone and see if I am on the right track. The 82 650GZ is on the road again after a complete carb overhaul, valve adjustment, brakes, and several electrical improvements. First tank showed horrible mileage (15 mpg) and would idle around 2K when warm. While tinkering today, I found 1 plug loose in the head. Tightened and no change. Replaced the plug with an old one (existing one was fouled) and when the bike started it immediately went to 4K rpm and stayed there. Pulled the plug wire and it went back to the same warm RPM as before (2K).

The exhaust pipe spit out soot for a few minutes and settled down. I adjusted the idle RPM down to about 12-1300 RPM and it seems to be running fine. Somehow we missed a loose plug and the idle seting with all of the work the bike has had in the past few months. Can't make a test run due to storms. Does this sound like I am on the right track? It can't help but make it better.

[koolaid_kid]

First, you need to make sure all 4 cylinders are firing. It sounds like you did.
Second, you need to go back and redo the carb sync. It is difficult to judge when the cylinder ceased firing. It may be O.K., but it may not. Best to verify to be certain.

[dw200]

All 4 cylinders are definately firing. Exhaust pipes are hot. I'll check the carb sync again. I hope the mileage goes up considerably after finding this. All things considered, it ran pretty good on 3 cylinders. It will be next week before I can ride again to see what happens.

[koolaid_kid]

You should be in the 40-50 mpg range.

[Nessism]

Is the bike stock or modified? Carb jets stock or modified? 15 mpg indicates something drastic is wrong; floats stuck maybe and over rich condition. You might want to check the oil level to make sure there is no gas inside the crankcase. Also, check the fuel height (make a gauge).

[dw200]

Everything is stock. The oil was fine (no fuel). Now that all 4 cylinders are firing and the idle is right, I'll see what happens and report back when I make a test run on Tuesday.

[dw200]

36 MPG today with about 30% in town riding. Not a bad improvement from the other day.

[OldVet66]

I get that mileage on my GS1000 with 4 into 1 pipes pod filters and a stage 3 jet kit when I'm running the heck out of it. You have a bit of a problem. I would re-read the links on Nessism's post.

[dw200]

I may have found the problem. The #2 plug had fouled and continued to do so within 50 miles of being replaced. I have good spark. Swapped the 2/3 leads and the issue did not follow. The plug was wet so I assume too much gas in the carb. Valves are good and compression check is good. I am off tommorrow so I'll do the petcock check and see what happens with it.

[tom203]

Suspect fuel being sucked down vacuum line to #2 intake when running

[dw200]

Petcock checked out ok. I decided to double check the valve clearances and imagine what I found. The exhaust valve on #2 is way out of tolerence on the loose side (around .013). Lesson learned..this is the last time I let someone else work on the bike for me. Shim tool ordered from Bike Bandit and I'll fix it myself.

[tom203]

While it's an excellent idea to recheck valve clearances, excessive exhaust valve clearance wouldn't foul plug. Put some clear tubing on petcock vacuum nipple and suck - to rule out a torn gasket. Mine did this last summer.

[dw200]

I blocked off the vacuum port and let the bike run on prime for several minutes with a fresh plug. The cylinder still did not heat up. This was before I found the exhaust valve.