'82 Maxim Hard Start

Hey all this is my first time posting here and I'm in a bit of a pickle. About 3 months ago I picked up a 1982 Yamaha Maxim that was having some issues with a high idle and poor running. The bike had been brought to CA from OR and was sitting for 5-7 years in Oregon. I brought it home and found it was flooding and running lean as well. On the ride home and during the test drive it would run beautifully when at 1/2 throttle or more and would run rough when on the idle jet. I also noticed it would misfire and backfire when letting off the gas during my ride home and found it was also putting gas into the crankcase and found gas in my oil. It also would pretty much have to be on 1/2 to full choke to when not riding down the rode to keep it running good. Once home I noticed it would pool gas on the ground until I disconnected the fuel line. In the last 3 months here's what I have done to get the bike back in good running order:

Removed and thoroughly cleaned all 4 carbs and rebuild the bottom ends.
-Removed and inspected all 4 diaphragms (sprayed carb clean until steady spray through)
-Removed all enrichment jets and cleaned (sprayed carb clean until steady spray through)
-Removed idle jets and cleaned (sprayed carb clean until steady spray through)
-Removed main jets and cleaned (sprayed carb clean until steady spray through)
-Inspected needles to make sure there was no damage
-New float gaskets
-New float needles
-New float seat (cleaned when I removed old seats before putting in new ones)
-Polished float pins (1 & 4 looked like they were sticking some)
-Reset float heights to 17.5mm
-Set idle screws to 2 1/2 turns out (seemed to run best here)
-Synchronized all 4 carbs with 4 gauge sync kit (#2 cylinder is the master)
*Carb #4 was the roughest looking of them all
*Was rust from the tank and black deposits that I think came from the fuel lines in the float bowls

Rebuilt front forks and replaced the seals
-Aired up front forks to 10psi each

Flushed brake lines (old fluid was black) and replaced front pads.

Replaced vacuum petcock with non-vacuum petcock.
*Old vacuum petcock would sometimes drip when off and would leak if you moved the tank any.

Added an inline fuel filter and replaced fuel lines.

Added carb clean to the gas.

Replaced oil with 20w50 and replaced fuel filter with Fram oil filter and o-rings.

Replaced old air filter (was covered in oil and gas) with new air filter.

Replaced drive shaft oil. (old stuff was brown)

What has happened was that the was running pretty good with a solid idle about 3 weeks ago. During the last 3 weeks it sat while I rebuilt the front forks on and off over the weekends. After I finished rebuilding them I drained the gas tank and replaced the fuel petcock with the non-vacuum one I mentioned above. After I had done this the bike now has troubles starting after sitting over night (about 90-95 degrees in my garage) and needs to have carb clean sprayed into the intakes to get it to start. Once it starts I can choke it and it will run. If I take it off choke it'll sit around 600rpm and then die if any throttle is applied. Once it has sat on choke for about 5min I can take it off and it'll idle around 900-1000rpm so I adjusted the idle screw and turned the idle up to about 1300. During this time the bike sounds very rough running and isn't very smooth. I don't hear any extra noise from the valves and the spark plugs look brand new (never bought new ones because they looked near new). If I let it idle for another 10-15min it will slowly climb up in rpm and then I can turn the idle back down to 1000-1100rpm. Here it'll sit and sounds much better but only after spending this much time warming up.

Where should I go next? In the 3 weeks it sat could the idle jets have gummed up again???

*Images attached are the bike, old air filter, and current spark plugs

 

Ran fine with the original petcock.
Does not run fine with the new petcock.
I figure that you might want to inspect that new petcock.
Check for rust in the fuel filter too.

What type of filter did you get? Most paper element filters do not flow enough fuel for a gravity-fed system.

 

replace that air filter or blow it out with air hose.

set petcock to prime for 5 to 10 seconds to fill carb bowls.
fuel evaporates from bowls when bike sits

to start bike
full choke press starter button no throttle.
from your post it sounds like you start it first then apply choke,

to set idle properly ride bike for 10 to 15 minutes then set idle to 1100rpm.


you need to wet set fuel levels not just float height

Setting the fuel levels

set mixture screws to 2-3/4 turns from soft bottom.

you should replace the tiny o rings and washer if rusted on mixture screws.

did you spray out the passages on carbs when cleaning ?

check valve shim clearences

Bigfitz's AIRHEAD VALVE ADJUSTMENT with Pics - parts I & II

then resync carbs

 

if you have not inspected the rear brake shoes stop riding and do it. no arguments

SAFETY ALERT Drum rear brake bike owners please take a look

 

I have a metal fuel filter right now.
My next step was to put the old petcock back on, but don't think that'll help since the new one has the same diameter as the old one and fuel flows much better now.

 

Rebuilding the Yamaha Vacuum Fuel Valve w/pics

petcock may be full of crud in link above you will see how some nipples have a filter type thing in them
There's a vacuum port check valve (nothing more than a tiny bakelite disc) in the cover plate. If you can't unscrew the vacuum nipple, don't sweat it; just flush it out with carb cleaner from both directions, and make sure it's free in there. You can hear it rattle about, and test by blowing in the port.

 

I checked the rear brake shoes and its still good to go just had to adjust the rear lever a bit. Also I tried starting it with full choke but it won't. The petcock is brand new and has good flow.