83 maxim wont idle or run right

I just bought this bike, fixed a few things and cleaned the carbs and it wont idle or run like it should. I havent done a compression test yet but it ashould be fine considering it only has 8400 miles. Anyone have any suggestions?

 

Valv clearences checked? At 8400 miles it is overdue
Durring your carb cleaning did you check float levels, clean jets and blow carb passages, bench sync? If you did all that then its time for a running sync.

 

Well, you can at least do a finger check for compression. What exactly is it running like? How does it idle? More details.

 

I am in the process of checking the valves the clearances are tight on the right side and decent on the left side Im going to reshim them but waiting to get some pads and a new valve gasket. I have a compression tester but didnt do it before i ripped the valve cover off because I figured the valves have never been checked and the cover was leaking. I cleaned all passages but didnt set the bench sync, I will have to do a little research. The bike just wont idle and sometimes it will idle for a few seconds then rev high then die, it also has no throttle response.

 

-You'll need new "donuts" for the valve cover hold down bolts or your new gasket will leak. Those donuts are what actually push the cover against the top of the motor, the bolts have stop collars on them that limit how far they can be tightened.

-Float LEVELS need to be individually "wet-set" using fuel and clear tubing. This is a precise adjustment and very important to getting the bike running properly. If you didn't do this you need to revisit.

-A "bench sync" simply refers to physically synchronizing the carburetors as closely as you can "on the bench" before returning them to the bike.

-Once they're back on the bike and your valves are in spec, then you'll need to do a running vacuum sync with the YICS blocked.

 

Ok I will do that, where is the best place to find the donuts, the gasket and shims for that matter. Or should I just rtv the valve gasket?

 

For parts, see XJ4Ever. Click the logo/link in the site banner, PM member chacal or send an email to "info AT XJ4Ever DOT com" with what you need. You'll have the correct parts in a matter of days.

I wouldn't "RTV" the gasket; the cover has to come off again in 5000 miles anyway. Just replace everything now, and then it can be reused the next time. The original one's baked or it wouldn't be leaking.

Valve clearances: http://xjbikes.com/Forums/viewtopic/t=14827.html

Part Deux: http://xjbikes.com/Forums/viewtopic/t=29209.html

 

Ok thanks, from what I see with the bike the guy I bought it from purchased it as a project and was in over his head so he did what he could and still couldnt get it running. When I bought it the carbs were a mess and it had no spark. Hopefully after I sync the carbs and get the valves buttoned up I will see a huge difference. The valve clearances are tighter than what they should be and if anything I would think there would be more clearance between them.

 

Just keep at the carbs. They can be a pain to set. But once set these bikes are a blast to ride. Make sure you also have a strong battery. When mine runs low on water it starts slower & does not run as good.

 

The float levels are more important than you might imagine.

 

Anyone have a video or pictorial for this clear tube method you speak of. I have always had single carb or fuel injection on my bikes so ive never had to mess with this before. I tried youtube but its tought to find a decent one that applies to my bike.

 

Ok the float levels checked out to 3mm below top of the float bowl. Anyone have any more suggestions? I am waiting for a gasket and dognuts for my valve cover before I can run it again but any suggestions are welcome. I dunno how but could the jetting be messed up? I have a 120 and a 40 in there now.

 

Did you clunk test your carbs? And make sure your pilot circuits are absolutely clean? Getting these CV 4 carb engines running right is a little like juggling 4 balls, it can be difficult-best to start at the beginning and check EVERYTHING off the list. Valves, Carbs (clean, synched, dry set, wet set, running synch, no leaks), Idle set right, Battery, Plugs/Wires, good gas-and safety of course (brakes, etc.). Do it all and ask for help on here if you get stuck.

What kind of bike is it (year, cc's, etc.)? Did I miss that? Do you have Hitachi or Mikuni Carbs? Add your bike to your signature line and use your location feature. It will help you with the advice and possible help you can get.

Those symptoms def. sound like badly out of synch and possibly fuel issues as well.

 

So far I have done a dry sync, cleaned carbs, set float height, shimmed valves, new gasket and donuts, replaced old fuse panel, new battery. It is a 1983 Maxim Midnight 750 with the Hitachi HSC-32-10c.

 

Cool.

Now put the carbs back on the bike, and do your running vacuum sync with the YICS blocked.

You're almost there.

 

And post pics of the bike or no one will ever help you again!!!!
Just kidding, make sure the carbs pass the clunk test. I did mine THREE times before they where right and the bike kept running! Also put new plugs and spring clamps on the vacuum tubes! They can leak and you won't even detect it with a propane test!

 

I put it back together and it is running better and will idle but when I hit the gas it revs to the moon then I have to turn the idle screw back down to get it to stop revving then it will sputter out and die if I dont keep giving it gas. Is there a cheap way to do the vacuum test or do I need an actual vacuum test machine? Im so close, it almost seems like the needle and spring arent doing their job.

 

You can build a DIY manometer. (The "vacuum test machine.")

The reason it "races" is because it's far enough out of sync that one or more carbs has come up off the idle circuit, pulling the rest of them along and the revs climb.

IN ORDER:

-VALVE CLEARANCES IN SPEC. They get tighter with wear, not loosen; this has to be done FIRST or you won't get a good sync.
-Carbs religiously clean.
-FLOAT LEVELS "WET SET" using fuel and the "clear tube method."
-Good, precise BENCH SYNC.
---then put the carbs back on---
-Running vacuum sync with the YICS blocked.

IN ORDER and you cannot skip over anything or try to jump ahead in the process or it will only lead to more frustration.

It sounds like you've accomplished some of these things but not all of them; and they all need to be done and in order.

 

What is the best way to block off the YICS without the tool?

 

You can use an oil-soaked cotton rag twisted into a tight rope and pulled into the passage using a hooked piece of wire.

For the manometer (vacuum comparing device) there are a number of different DIY solutions; ranging from a 6' hunk of tubing zip-tied to a yardstick partially filled with ATF to a much more "sophisticated" two-bottle rig made with a couple of plastic bottles and more vinyl tubing.

Get the valves in spec and the carbs bench-sync'ed first or it will be nothing but an exercise in frustration.

 

I have already done the sync and valve shimming this is hopefully the last step. With the YICS plugged the bike runs almost normal!!! Hopefully after the vacuum test ill be on the road!

 

I was unable to get them synced every time they would be good the the "idle circuit" would pick up and cause the motor to rev therefore throwing the gauges off. The best it ran was after I plugged the YICS to do the vacuum.