my 421 is running hot! why?

[RadarRacing]

When they were talkking about orings in the head they were talking about pressure from compression blowing past the orings pressurizing the coolant system. They can puke without even getting hot. If you are woods riding slow a lot you might get an oversize radiator, go richer on needle, take a degree or two of timing out etc.

[WINDYCITYJOHN400]

hey guys HELP... vitos 421 full drag port ... 4mill vitos stock rod crank, 34mm kehin pj carbs , 172 mains .needles 3rd from bottom.pilots 32, elevation 1100ft... fmf fattys ..kn pods ,timing +4 ...hemi head 2 with 22cc domes . pro flow billet intakes with v force 3 reeds.. i installed a billet high flow impellar too!

plenty of oil ....32 to 1 mix... and high octane fuel....mixed it 50/50 115 and 93 oct..

 

 

dam thing keeps heating up and bubbling into the reserve tank when not MOVING through the wind!! runs great other wise but a little rich in the mid..WHAT WOULD CAUSE THIS..THE BIGGER PISTONS...? .the engine only has 2 hrs total on it.. cant barelly be ridden in the woods!

 

any help or comments would help .... thanks

 

 

Full drag porting and your wondering why it can "barelly be ridden in the woods" ???

 

Well, there IS a reason WHY many people say a cub isn't a great choice for a woods/trail machine. A cub makes all it's extra power in that upper RPM range. Your "Full Drag Porting" will only add to high reving nature of that motor. Now spend your time in a high rev mode in 2-3 maybe 4th gear at lower speeds and your not going to get enough air into the radiator to cool that motor. Also full drag porting will require a nice high flow set of pipes. Don't know what your running, but it might be backing heat into the cylinder over time while you ride.

 

REASONS YOUR CUB CAN OVERHEAT WHILE TRAIL/WOODS RIDING

 

#1....Your jetting is Lean. (Always the first thing to think...because 80% of the time THAT's the problem)

 

#2....You need an aluminum radiator. (Not the most likely issue, but the real problem is most likely jetting and since most people won't bother to go a few jets richer to see if it gets better....why not throw money at the problem?)

 

#3....You have an issue with the water pump impeller or it's drive gear. (Get a billet one. I've got one on my 472 cheetah and it's fine, so don't listen to the billet impeller haters. Might as well order one along with your new aluminum radiator.) LOL

 

#4....You put a drag motor in a trail bike and are wondering why it's over heating. Could be because it's drag ported and making so much power that the tires just spin and the motor just gets hot. (Wonder why John Force and Jeff Gordon don't just put race motors in their street cars? )

 

#5....If you bought the motor from Trinity....It's because the domes are the wrong shape and your detonating.

 

Do like the last guy said...Back that timing out of it. Then go a size smaller on you pilot, but go a size or two bigger on your main. (should clean up your mid and stop the higher RPM Lean/Detonation that's most likely causing the overheating issue.)

Get a temp gauge too while your at it.