Ask Mickey Dunlap 3/3/2002
Welcome to the second edition of "ask Mickey Dunlap".. I'd like to thank him again for taking time out of his busy schedule at Four Stroke Tech to answer some questions for us! Now, on to the good stuff!
2 part question for you.
#1) What is the best way to clear up the cold blooded 400EX. Mine starts
hard when its cold out, and it will foul a plug if not nursed to life
just right. I have heard people suggest everything from needle
adjustments to removing the choke. What do you suggest? (400ex with
stock exhaust, drilled airbox lid, and a 155 main jet)
#2) Do you suggest a foam air filter, or the paper K&N type and why?
thanks for taking the time to answer our questions. I have learned a lot
For the most part, we usually only have to turn the fuel screw out 1 to
1-1/2 more turns than stock but usually we have installed a pipe and opened
up the air box. You sound like you have it jetted a bit rich for just
opening up the air box with a 155 main jet. It's difficult to give you
perfect jetting specs without knowing your elevation, temperature, etc.
Another thing that hinders starting is after-market black boxes and valve
settings (usually your exhaust valves go closed). Although I like the K&N
because it flows good, I suggest running an Outerwear on the K&N's at all
times and in real dusty conditions a foam wrap around the K&N also. An
after-market foam filter will work fine for all that you have done now.
It's only when you build the motor up with cams, pipes and port & flow work
will the air cleaner hinder you.
Hey, first of all, it is great that you are taking time to answer our
questions. Now to the good stuff. I was wondering what long term affects
does running my 400ex on the lake (in the winter, of course) have on the
engine? I know that guys are upping the rev limiters, but is it going to
do any long term damage running at high RPM for extended periods of time?
Would studding my tires offset this? I really like bombing around on the ice
racing track, and impressing the snowmobilers that things can actually
turn on the ice, but if it is going to be the end of my fun prematurely, I'll
have to just stick to the trails. Thank you so much for taking the time to
answer my question.
I am glad I can take the time to help give back to an industry that has
been so good to me. Thanks for your encouragement. In most owner's manual,
even on a stock engine, they warn against continuous high rpm use because it
may lead to wearing out the engine prematurely. My only real experience of
ice racing was in 1984 when I rode for Team Honda at Lake George and I found
out real quick that you do not run straight 40 weight oil. We cold seized
the motor in about 10-15 minutes because the wind chill factor would cool
the front of the cylinder and the engine cases enough to make sludge out of
the heavy oil. A multi-grade oil, even a synthetic such as 15/50 Mobile 1,
would be advised for high rpm, high speed running. That's about the best
advice I can give you except for stay on the trails - your motor will last
After reading your answer to TREX400's question, I was wondering how you
get the cylinder volume clearance to 0.040 inch on a 440 engine. I am sure
that the head gasket must be different to accept the new sleeve. Also how can I
check to see what my compression ratio really is?
Decking the cylinder is the proper way to set up your deck clearances.
Most head gaskets will be about .040 thick so you try to deck the cylinder
so that your piston comes up exactly to the top of the cylinder at top dead
center. I suggested going to a thinner head gasket at about .030 (like an
XR400 or Cometic's 3 piece steel head gaskets for the 440) and then not
using the .020 thick base gasket and this would get you close without having
to deck your cylinder. As far as figuring out what your compression ratio
is when your engine is completely together, you need to measure the cc's of
fluid it takes to fill your combustion chamber up to the bottom of the spark
plug hole, make sure your engine is at top dead center and you tip your
motor back and forth to make sure there are no air bubbles in the combustion
chamber. For example, if you have a 440 motor and it takes 50cc's of fluid
to fill it up, you would take 440 + 50 divided by 50 to give you 9.8 to 1
compression. To get a true 11:1 440, you will have to have a 44cc
combustion chamber volume. Most so-called 11:1 pistons will have closer to
50cc's. You can get a syringe that measures in cc's at your local pharmacy
and you can use just regular motor oil to fill your combustion chamber.
Just had a question reguarding the true benefit from having a 406,416 or
426 11:1 vs a Stock bore 11:1. What is the difference that you have seen
between these and how much does race fuel effect the performance at this
Thanks for your time-
Boring a motor 80 over usually makes good benefits but nothing real big.
If you plan on keeping your machine for a long time you will want to keep as
many over-bores as you can. If you are truly running an 11:1 piston race
gas is not necessary but the lead in the race gas will help cool your
exhaust valves and gives better lubricating properties for better ring seal.
The super-unleaded we get these days is usually mixed the methanol and has a
high oxygen rating which makes it a high-performance gas in a way. At our
local drag races in Bedford (where Cannondales are made), super-unleaded is
illegal because it is a highly oxygenated fuel and it blows the meter right
hello...thanx for taking the time to help us at exrider's, get answer's to
some troubling questions'.....here's my question..it's ganna be pretty
long..i'm going try and be as descriptive as possible.....
1996 300EX....i'm having problems with my bike i think it's the rings but
i'm not sure..i've gottn' all sorts of answers from several different
forums all over the net...
I'm runnin 14t / 38t with 18/11/10 tire's on aluminum rims....(i'm
thinking the small tires is what started all this)....one day i ran the
bike hard for a streight streach ran through all 5 gears wide open just to see
what kind of time i got in a certian distance...after i got turned around
i looked down at my left leg and it was coverd with oil....i tracked the oil
down to this rubber tube under the gas tank that goes up over the motor
and back down into the head on the right side....took the seat and stuff off
and found that the tube comes out of the head...and splits (tee's) and one end
goes to what i described above (the left front side of the motor) and the
other end goes to the back of the motor and points down at the ground by
the swing-arm..(chain side) neither end of this hose has anything on
them....they just end.....my question is..what made that oil shoot out
like it did...it lost all but maybe a hair on the dip-stick.....is it my
rings....what are these hoses for......i've riden it since all this
happend and sometimes it will shoot out and sometimes it doesn't....like the other
day.....ran it all day long sometimes hard sometimes not.....then right at
the end of the day...i got on it real good....sounded like my rev-limiter
kicked on.so i let off the gas and happend to look down at my leg......oil
everywhere again.....(although not as much came out that time.just a
little)....it's still reliable cranks easy and runns strong....seems just
as powerful as before.....how should i go about getting this problem
resolved....do you think it's the small tires..i was runnin the stock size
before i got these...and had run these small ones before without any
trouble.....i am about to get another set of rears.maybe 20's or 22's but
these will still be my extra set on rims incase i get a flat......my motor
is stock with a uni filter (clean) 4 1 inch holes in my lid..and rejetted
for the D.G. pipe i got.....i can't think of anything else that would
help you to answer this question any easier.or you may already know the
answer....if you need anymore info...let me know so i can get this figured
out before spring rolles around....also.....i ride my bike all the time
should i stop untill i get this fixed.......
Yes, your smaller tires let you run at a higher rpm and made your
problem more prevalent. At high rpm's your rings are not sealing and they
are letting hot gases blow past your rings into your crank case causing high
crank case pressure and forcing oil out your breather tube. Without knowing
more about your engine, you either have cylinder walls that are scored or
the rings are just worn out and it's time to re-build it. If your motor
hasn't started to burn oil yet, it soon will because you are washing the oil
off your cylinder walls with the hot gases passing by the rings. When you
tear it down you will also want to check out your intake valves on the
300EX. The stock valve springs doen't let the valves float but at high rpm
when they hit on the seat they bounce and it causes them to prematurely wear
out. You will notice the 45 degree angle will be cupped on the valves and
they will need to be replaced. It sounds like you just need a good re-build
and while you have it apart, you can usually build a little bit of
performance into it with a higher compression piston for about the same
I have a 2001 400ex with a T4 slip-on K&N jet kit 14 tooth front sprocket.
I use the bike to race harescrambles. You mentioned in a previous post thast you
used a silicone seal on the cylinder base, along with an XR400 gasket. Would it
be benefitial to do this with a stock bore and piston?
Also, what is your opinion about advance keys for harescrambles? Would it
benefit me to run a XR400 cam with a stock piston along with the
modifications I have done? Any advise would be appreciated.
Thanks ...... fourplay
Yes, you could put an XR400 head gasket and eliminate the base gasket to
get higher compression with your stock piston. This will also give it a
better quench area around the outside of the piston and give you a better
burn rate across the top of the piston. As far as running a bigger cam with
this for cross-country racing I wouldn't. I would like to see at least 11:1
compression before I went to a bigger cam. In cross-country racing we have
put tachometers on our machines and most of the riding is done between 3,000
and 5,000 rpm's so to get through the woods as quick as possible, you need
the most torque to move the machine quickly through the woods. If you run
cross-country races that are more open then a cam may be beneficial. Most
of the time we do not advance the timing except for on a motor that has a
big cam in it and high compression. Motors like this tend to need more time
to burn extra fuel.