pumper carbs

oxo · 17-08-2011, 08:46 PM

Anyone help on this one?
Still tinkering with the old WHM A1 pumper carbs on the xr2 at the mo purely cos I went and ordered the run in jets for them. Got a set of newer carbs for when she's completely run in. Trouble is, on reading an old manual that describes these pumper carbs (WHM 4-6's to be exact) it states that the mixture adjustment screws at the top of the carbs should be 1 1/2 to 1 3/4 turns from seated position. Mine seem to be about 3 1/2 turns out??? She does seem to be spitting a bit of fuel but runs and idles well. Is there a difference between the WHM A1 pumpers and the WHM 4-6's? Or should I screw all my adjusters in and do as stated in the book?
Stiil very cautious till she's completely run in!!!

oxo · 21-09-2011, 10:12 AM

Can anyone help? Just don't know what to do on this one. I can't seem to find any information on these carbs anywhere!
Does anyone have pumper carbs fitted? If so, can they tell me how many turns their mixture screw is turned?
Any help sincerely appreciated!

lloyde · 21-09-2011, 10:27 AM

Try pm ing driver510 on here Ihe may be able to help

oxo · 21-09-2011, 10:36 AM

Thanks, will try, its just that these carbs came off an engine that blew up so I DEFINITELY wanna be sure the carbs are properly adjusted!!!

Jon Holmes · 21-09-2011, 11:32 AM

I can only comment on carb settings relating to two stroke motorcycles and i am assuming your outboard carbs operate in a similar manner:

The mixture screw settings in the manual are generally used as a basic setting guide for when rebuilding them. This position will generally give you an idle in order to be able to start and run the engine but can still be adjusted either way in order to obtain the correct idle mixture for the particular engine. (Brand new engines could be adjusted differently to each other to obtain optimum idle mixture).

Also the idle mixture screw only affects the mixture strength at idle, it will have no influence at other throttle positions. If the engine starts and idles evenly, the fact that the mixture screw is further in or out compared to the manual should not cause any concern as it would be very unlikely to cause any damage to the motor.

This is my opinion for what its worth and i am sure someone with Outboard experience will chip in to help.

oxo · 22-09-2011, 07:56 PM

Thanks Jon,
I'm used to small engine carbs chainsaws etc. But what you've said makes a lot of sense.

still no worries · 22-09-2011, 08:14 PM

Just bin the pumper carbs and fit new ones, why risk f___ing up the motor

mojo?offshore · 23-09-2011, 08:54 PM

HI, OXO.
The adjustment screws on WHM carbs are for idle only,
ALL Mercury XR2 Carbs have fixed H/S jets.
Idle screws should be 3/4 of a turn open from seated.
Regards ,
mojo?offshore

oxo · 01-10-2011, 10:10 AM

thanks for all the input.