How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Wayne S. Your Own Question
Wayne S.
Wayne S., Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 1255
Experience:  Experienced and Licensed Motorcycle Mechanic - all sizes and brands welcome.
Type Your Motorcycle Question Here...
Wayne S. is online now
A new question is answered every 9 seconds

I have a 1982 yamaha maxim xj 550 and it has a constant

Customer Question

Hi doug. I have a 1982 yamaha maxim xj 550 and it has a constant misfire when i open up the throttle. It will only alow me to maybd go 55 miles per hour. Any ideas? Im running pid filters and straight open exhaust. Also a couple plugs seem to get a sooty coating over them..
Submitted: 2 years ago.
Category: Motorcycle
Expert:  Wayne S. replied 2 years ago.

It is running to rich on fuel. Check the choke and the fuel petcock

for problems. Vacuum petcocks can leak fuel into the vacuum hose.

Let me know. (I am not Doug but thought you were waiting awhile.


Customer: replied 2 years ago.
Thanks for the response wayne. It doesnt seem to be the fuel petcock, and it only seems to be misfiring bad when the rpm is increased. Iv checked the compression, and it seems to be good ( 135-149 psi ) all the slides seem to be opening up consistently, just when i open up the throttle past half it seems to sputter and misfire. Could it be a bad set float? Or a bad choke plunger?
Expert:  Wayne S. replied 2 years ago.

Make sure the chokes are bottoming out if they are plunger type.

Might want to clean them up and lube lightly.

Over half throttle is controlled by the main jet as long as your air flow into the carbs is not restricted. Check the air filters and check for loose jets if it was running well before. If the floats are too high the carbs would leak fuel from the overflows.

You have too much fuel or a lack of air flow by the sounds of it.

Main jets and slide needles handle all the half throttle and up mixtures.

Let me know if the choke plungers were hanging up or adjusted too tight.


Customer: replied 2 years ago.
No the choke plungers look like they are oporating normally, the slides also are opening as they should be. I adjusted one of the floats to a more rich setting and also re adjusted the idle and pilot air screws and it seems to be running pretty decent now. The only thing i can notice now is a bit of a sputter after a while when i hold the throttle wide open in my final gear. It does seem to be running somewhat better though...
Expert:  Wayne S. replied 2 years ago.
The chokes plungers need enough cable slack to bottom out, the plungers can wear out also. a plug color check can tell you what is happening inside the engine at full throttle. Read the plug and make your fuel and air adjustments according to that.
The main jet affects full throttle operation and also the condition of the plugs, plug caps and wires are important.
Check your battery and charging system as well.
Customer: replied 2 years ago.
It actually ended up being the emulsion tubes under the main jets that were plugged, resulting in a rich running condition. The choke plungers are oporating good.
Expert:  Wayne S. replied 2 years ago.

Very good, hope it works well now.