Boat name: Lilly the Pink
Boat make: Phantom 21
Engines: XR2 200
Join Date: Aug 2010
merc 2.5 issues
First of all sorry for the long post!!!!
Looking for some help if anyone has any ideas. I recently rebuilt a 2.5 200 merc carb,running wh 46 with mains jetted on 90s ,poppet removed ,thermostats removed,oil cooler removed and oil block off kit used ,left plastic oil pump on crank , restrictors in heads ,1 piece exhaust divider ,new water impeller ,with a set of forged wizard pistons ,balanced lightened rods and wrist pins and sps bolts from JSRE ,full set of seals, big ends, rings,heads clipped to 34cc ,dual stage boysen 4 petal reeds.The machine shop worked the sleeves to 8 thou over ,nice and round , Running an electric fuel pump through the mechanical oem at 5psi with no restrictions in hose .Exhaust and front half are standard .
Set timing at 25 degrees.
Fuel at 32:1 on a blend of oil , compression all within 2-3 ibs of each cylinder starting from 145-148ibs ,Engine run for 9 hours at 1 hour at a time ,then full cool down . Brought her out and ran it in slow,she was a little tight low down under 3k rpms ,with a quick run up to 5k rpm for a couple of seconds ,number 2 detonated and locked up,head temp was very hot 170 plus within seconds
Rebuilt engine again with a cheaper new forged Wiesco piston ,until I found the problem ,rebuilt all carbs,checked all the floats and reset them ,cleaned and checked needles ,seats and gaskets , increased main jets to .98,removed electric fuel pump and ran stock pump,changed fuel for new petrol.
Ran the engine again very,very slowly 1500rpm,2000rpm,2,500 etc up to 4500rpm over 4 hours ,again number 2 detonated .
Spent 2 hours setting the engine timing,but this time at 23 degrees.
On both occasions the exhaust port side of the piston is melting ,still retaining the rings,it is definatley getting enough fuel based on the how wet the cyclinders are .
Now for the third attempt,using a used cast Art piston this time ,changing carbs around putting top set of carbs in middle feeding cyclinder 3 and 4 ,and middle set of carbs feeding cyclinder 1 and 2,also changing head gaskets and putting stock 41cc heads on to lower compression with a colder plug .
And reset the timing to 20 maybe,havent run it yet ,hopefully next week.
If any one has any further suggestions i would be very grateful at this stage,starting to lose patience with this.
Thanks very much.
Paddy the Phantom