Topic: 400/4 running rich??

[fat lad]

hi all, im from the uk and i have a restricted bike licence for 2 years which means i can ride upto a 33bhp-25kw bike, so i had the 400/4 on the dyno today and its only putting out 24bhp the dyno man said its running rich right through the range, it also has a flat spot about 2-3000 revs when warmed up,he advised air filter check failing that carb kits and ballence/sync. I got back from a 60 mile run around and decided to check the filter, its fine but i did notice that the air intake is under the seat a small afair with a grill over it, now im no light weight ( hence my username ) and i had the wife on too, could the seat( after market one ) be squashing down too close and resricting the air flow? if so  can i drill the air box ?( a scooter tip when using big carbs ) or anything else to try before going the carb strip down route? many thanks jonny

[dave400]

Those plastic base seats suck, put some rubber blocks around the intake hole so the seat can’t block the intake and see if that helps. Nice looking 400 you have.

[fat lad]

Thanks dave400 ill give that a try, regards jonny

[fmctm1sw]

Yes, do some experimentation before you make any permanent mods (drilled hols)...  What do your plugs look like?  Mine fouled so bad my bike would refuse to start....

[fat lad]

hi i havn't checked the plugs yet as it starts and runs spot on besides the flat spot, ill try some blocks around the air intake to make sure its not getting restricted as advised then maybee let the dyno guys do the carbs as im not that clued up on 4 strokes cheers jonny