2017 Apollo 250 Build - Have questions

[Megadan]

Originally Posted by Douglass

Megadan - Thank you so much! you gave an excellent explanation. I am really trying to learn the functions. Of erverything on the bike this is probably the only thing that I am a little intimidated by. I can tune my car using a computer, but have the nessessary gauges to see what my fuel trims and WOT fuel readings are. If/when I decide to change the carb on my bike, I want to be able to do things with purpose, and understanding rather than guess and hope.

Thanks again, your explination I know took time to type up, and it is greatly appricated!

Douglass

It was my pleasure guys. Just remember that my explanation is pretty simplified, but if you do a little google searching you can come up with all sorts of information that will go more in depth than I did.

If you really want to get into tuning, you can always install a wideband O2 on the exhaust to really aid in dialing in carb tuning. Kind of an expensive route to go, but it can always be used on other bikes in the future. Simply put a plug in the sensor bung when not in use.

The old fashioned way is to read the spark plug. You can find a charts like this one to help point you in the right direction. http://bustekhub.com/wp-content/uplo...on-Chart-1.png

Really, once you start messing with carb tuning you realize how simple it really is.

The only other thing to really keep in mind is that since these carbs are purely mechanical in nature, if the air density altitude changes via temp swings or large enough elevation changes, the bike will run leaner or richer.

The general rule of thumb with Mikuni jetting is a full jet size per 5000ft altitude or 50 degree change in temp. Aka, you have a 115 main jet that is perfect in 90 degree temps, once the air temp drops below 40 degrees it is a good idea to step up a jet size to a 120, or at least half a step like a 117.5

[Douglass]

As far as jetting recommendations, what I would recommend is just a generic, and likely too rich setup to start with, but too rich is better than too lean. You will want to have a few sizes of each jet to really dial it in.
My recommendations still stand with a 27.5 pilot and a 115 or 117.5 main jet with the OHC motors. If you have an OHV motor like me I can give you far more precise jetting suggestions, because I have hands on experience with it, and I don't have an idea of how different, if any, the OHC engines are in terms of fueling.

I would say to buy a 25, 27.5, and 30 pilot. And have a 110, 115, and 120 mains, at minimum. If you feel like it, grab a 112.5 and 117.5 as well. With my bike, the 115 was a touch too lean, and the 120 was too rich, the 117.5 worked out the best for me - being just ever so slightly on the rich side, which is what I prefer with aircooled engines.

Dan I bought the Mikuni Carb after talking with Sean. His bike ran great, and his idle/acceloration improved a lot. He used a 27.5 pilot, and a 115 main, and did not make any needle adjustments. Bike ran/started perfect. He is at about 800ft, and it was about 45-60 degrees.

I am at about 60-200 ft where I'll be riding the bike, and the temp will be about 50-100 degrees (right now were around 50-60 deg) (Summer will be around 90-105). should I start with the same 30/115, or should I start with a 30/117.5? Currently I have it jetted at 30/117.5, but I have 27.5, 25, 112.5, 115, & 120 jets if needed. I am planning on installing it this weekend.

[Megadan]

Originally Posted by Douglass

Dan I bought the Mikuni Carb after talking with Sean. His bike ran great, and his idle/acceloration improved a lot. He used a 30 pilot, and a 115 main, and did not make any needle adjustments. Bike ran/started perfect. He is at about 800ft, and it was about 45-60 degrees.

I am at about 60-200 ft where I'll be riding the bike, and the temp will be about 50-100 degrees (right now were around 50-60 deg) (Summer will be around 90-105). should I start with the same 30/115, or should I start with a 30/117.5? Currently I have it jetted at 30/117.5, but I have 27.5, 25, 112.5, 115, & 120 jets if needed. I am planning on installing it this weekend.

I would say to start with the 30/117.5, and then dial in the jet sizes. Dial in the pilot with idle mixture tuning and the main jet with a plug chop.

[Douglass]

I would say to start with the 30/117.5, and then dial in the jet sizes. Dial in the pilot with idle mixture tuning and the main jet with a plug chop.

Perfect, thank you for confirming Dan. Sent you another PM.

[Its_not_a_honda]

I know I've read a thread about a guy putting a Honda shock on one of these. I was just wondering around looking at parts and ran across this shock. https://www.gvabrands.com/parts-acce...x37/rear-shock . It is for an apollo 250 water cooled bike. I am wanting to try it out but don't know if it will clear on a DB38 apollo 250. It has a reservoir off to one side. My shock is a little stiff for my needs and I thought this might be a bolt in. It would really beat welding and fabricating a new air box.

[Douglass]

So I was starting to have some idle issues with the bike, and it would not stay running at idle, so I decided it was time to change the carb out to the Mikuni. I am at sea level, and decieded to start with the 30 pilot, and 120 main jet. The air screw came preset at 2 1/2 turns out, and I left it at that to start with. The bike started right up with the choke on, and ran perfect once the choke was turned off. The bike idles soooo much better. No driveability issues at all, idle, very light throttle, heavy throttle, and WOT throttle were spot on. All I had to do is just make a very small adjustment to the idle.

One thing to note was the cap on the top of the stock carb were the throttle cable goes through was loose, and not seated. This could have been causing some of the issues, but I had already taken everything apart so Installed the new Mikuni carb anyway.

You will need to remove the plastics, seat, gas tank, loosen the two nuts holding the carb to the intake manifold, air box clamp, pull the carb towards the air box, and push it down, remove the upper intake manifold bolt, loosen the lower intake manifold bolt, swing the intake manifold out of the way, and remove the original carb, and install the new one. Then assemble everything back together.

I was also able to reuse the stock throttle cable with no modifications. There where also no cleance issues with the new carb. Great upgrade. Next project will be to take the bowl off the stock carb to see how it was set form the factory.

[Megadan]

Now you see why so many of us just switch to the Mikuni. It isn't really necessary, but it makes dialing in the bike so much easier. Specifically thanks to all of the other people that have been running them. Lots of examples to kind of get a baseline setup for.

I am rather impressed that the 30 pilot takes 2 1/2 turns to idle on your bike. My bike would barely idle at 1 1/2 turns on a 30 pilot, and I ended up below 1 turn out to get a smooth stable idle. That is why I dropped to the 27.5

[Douglass]

Now you see why so many of us just switch to the Mikuni. It isn't really necessary, but it makes dialing in the bike so much easier. Specifically thanks to all of the other people that have been running them. Lots of examples to kind of get a baseline setup for.

I am rather impressed that the 30 pilot takes 2 1/2 turns to idle on your bike. My bike would barely idle at 1 1/2 turns on a 30 pilot, and I ended up below 1 turn out to get a smooth stable idle. That is why I dropped to the 27.5

I was surprised too. Sean had installed the carb in his apollo 250 with I want to say a 30/115, and it ran great. I think he as at about 860 feet of elevation. I was actually starting to think the 30 might be a little small after I read about a guy on here having to install a 40 pilot into is 250 tao tao atv.

Also, I read your right up a few times to get a better understanding on how each jet, and needle role. Thank you for your help!

[Megadan]

Glad to help. So many people view carb tuning as some sort of black magic thing, but in reality it is all rather simple. Understanding each jets role at given throttle positions and getting a feel for how an engine sounds and behaves when too rich or lean is 90 percent of it.

The HARD thing to do is tune a carb from scratch. I am not looking forward to setting up my VM30 when I get around to it.

[Douglass]

The HARD thing to do is tune a carb from scratch. I am not looking forward to setting up my VM30 when I get around to it.

I agree 100%, I'm sure I would have spent a good part of the day trying to figure it out if it had not been for your help. Sean also helped me cheat a little bit too.

Here is the finished pictures of the bike. I installed the Tusk Racing CV high bars, 52T rear sprocket, new 530 unibear o ring chain, Pro taper gripps, and the Mikuni 30mm Carb.

[Megadan]

Love the bars. The Renthal fat bars I put on my Hawk made a huge difference in feel and looks. I love them.

It's a sweet looking bike, and that rear sprocket is huge lol.

Honestly, if they would have sold the Dual sport version of that bike here in the States, I would have bought it. I love these bikes.

[Douglass]

Love the bars. The Renthal fat bars I put on my Hawk made a huge difference in feel and looks. I love them.

Thank you, I was going to get the Protaper bars, but after looking at the specs the Tusk bars were almost identical, but half the price. I have seen both bars, and if the pad was changed, it would be very difficult to tell the difference.

It's a sweet looking bike, and that rear sprocket is huge lol.

I found a picture on the site were a guy installed the 48t sprocket, so I had an idea how big I thought the sprocket was going to be. When it came in, and I opened the box, I thought for sure I made a mistake some how LOL. It is HUGE! But, it makes going up hills a breeze. It will pull hard, and makes 1st very usable on a steep grade. So happy I installed it.