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 so far.

answer

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.

Jeff asks;

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.

answer

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 longer!

oynot400 asks;

Mr. Dunlap,
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?
Thanks,
oynot400

answer

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.

Eddie asks;

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 compression?
Thanks for your time-

answer

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 out.

T.B.OILY asks;

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.......
thanx again
T.B.OILY

answer 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 cost.

fourplay asks;

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

answer

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.