Poor running at low revs

[Gaz 88]

Hi my 1988 vmax runs like a pig at low revs and back fires but if i put the choke up about a quarter it runs ok
Any moor than a quarter throttle and she runs great. Any idea's i think it may be the pilot jets ??
Thanks for reading

 

[Fire-medic]

Yes, possibly the pilot jets, 1 or more. Do you have access to an ultrasonic cleaner? The 'cheapest by price' is probably a Vevor.

Here's a decent sized & powered one, 15 liters. It pays for itself the first time you use it.

https://www.vevor.com/ultrasonic-cl...nic-cleaner-heater-w-timer-usa-p_010646323549




13" X 11" X 6" should allow you to split the carbs into 2 sets of two carbs, and to soak them at the same time. Be sure that you immediately purge all cleaning liquid (water) from the idle piston and the coasting valve. Failure to do that will result in seizing of the idle piston in its bore and crud in the coasting valve. Of course, if you completely break-down the carbs into 4 separate pieces, and then remove the idle piston and the coasting diaphragm, that will take care of having to purge them of the cleaning fluid (water w or w/o detergent) This one is $134 and there are larger ones.

Reading this entire thread may help you.

https://www.vmaxforum.net/threads/whats-going-on-here-k-n-pods.53979/#post-540719

https://ia800204.us.archive.org/14/...ice-manual/yamahavmaxvmx12-service-manual.pdf

 

[MaxMidnight]

Agree that it sounds like pilot jets.
My Step 1 would be to run some fuel system cleaner through. It won't do any harm and may well solve your problem.
Step 2 would be to do the 'Shotgun'.
Step 3 would be to go down the ultra sonic cleaning route.

 

[Gaz 88]

Agree that it sounds like pilot jets.
My Step 1 would be to run some fuel system cleaner through. It won't do any harm and may well solve your problem.
Step 2 would be to do the 'Shotgun'.
Step 3 would be to go down the ultra sonic cleaning route.

Will try the carburetor cleaning spray. I don't know what the shotgun is or how to do it ??? Thanks for your ideas. I will see if the shotgun method is on YouTube

 

[Fire-medic]

Use the search function on here. Upper right hand of the page.

https://www.vmaxforum.net/threads/shotgun-carburetor-clean-results.53469/

https://www.vmaxforum.net/threads/frustrated-with-idle.54173/#post-542274

https://www.vmaxforum.net/threads/2004-fuel-carb-running-problems.53509/

https://www.vmaxforum.net/threads/poor-running-at-low-revs.54258/#post-543111
MaxMidnight has a link to the Shotgun in this thread
https://vmax.lvlhead.com/tips/shotgun.htm

There are many more.

https://ia800204.us.archive.org/14/...ice-manual/yamahavmaxvmx12-service-manual.pdf

 

[MaxMidnight]

Will try the carburetor cleaning spray. I don't know what the shotgun is or how to do it ??? Thanks for your ideas. I will see if the shotgun method is on YouTube

If you click on the link (yellow text) in my post it will take you there