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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12277
Experience:  25+ yrs. experience
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My monster 620ieS is breaking down under load. Have done the

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My monster 620ieS is breaking down under load.
Have done the plugs n fuel change, had serviced and ran great for about 50km and has started breaking down again.
It rides fine when I am taking it easy, but just boggs when I give it a good twist of the throttle, spark & injectors check fine as does charge coming from stator,
Any insights would be great

Hi Chris, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially and if the sparks are present and consistent, then it would appear to be a fuel delivery/partial starvation issue. Proposed preliminary checks (if have not been done) on suspects:

  • • drain-clean tank and replace with fresh fuel (even if just to eliminate as a suspect);
  • • re-check/re-clean injectors (least likely);
  • • re-check/re-clean fuel path including filters/screen (likely);
  • • test fuel pump output pressure (most likely);
  • • and even if just for test purposes, temporarily disconnect the voltage regulator and run/rev engine (but with a fully charged battery).
Customer: replied 9 months ago.
Have tried all these and it is better but still boggs down with wide open throttle.

I understand; "...better but still boggs down..."

What is the burn color of the spark plug tip?

Have you re-checked the air box and filter to enure fitted/seated fully/correctly with no possibility of an air leak?

Incidentally, what was the measured output pressure of the fuel pump please?

Customer: replied 9 months ago.
Charged battery 24hrs
Removed & replaced plugs
Rear cylinder plug tip blue/black
Front cylinder plug tip is white
cleaned & reoiled air filter.
Sprayed carb cleaner into intakes whilst revving.
Correct install of air filter with no leaks
Test run shows better performance but still slight bog down at wide open throttle
Any insight as to why the plugs tips are burning different colours?


  • Rear cylinder plug tip blue/black - would indicate slightly rich air/fuel mix;
  • Front cylinder plug tip is white - points to a very lean mix thus would and can cause the "...bog down at wide open throttle..." either a partially clogged front injector and/or still a possible air leak.
Customer: replied 9 months ago.
How do I clear partially clogged injector also can you tell me how to remove and check same.
Have checked is not an air leak

Hi again Chris,

To clean the injector, please view videos HERE and HERE. Also consider soaking the injector also with a cleaner solution similar to the product shown HERE.

To locate injector for removal, please click HERE. It would be item # 10.

Customer: replied 9 months ago.
I know where it is.
My question is how to remove and refit injector

Please click HERE to serve as reference.

Customer: replied 9 months ago.
We will know for sure when I get it back from the mechaics. He's thinking along similar lines to you

Appreciate the post back Chris amd would look forward to an update when able.

Customer: replied 8 months ago.
it looks like you were spot on Louie, I didn't even tell this mechanic your suggestions and he has found the same 2 main faults. He replaced the belts as he didn't want to run it on the dyno with the ones that were there.
I will rate your advice tomorrow after I've ridden it.


Good luck and thank you too for the opportunity to share the information.

Louie and 2 other Motorcycle Specialists are ready to help you
Customer: replied 8 months ago.
Well it turns out neither mechanic cleaned the injectors and the front one kept re sticking. I removed them and cleaned them using the links you provived and bingo the bike is like new again. Thanks a million

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