Help me tune my 84 R - revised

[atctim]

Hi All,

After taking the advice from some experts on the site I have gone ahead and added a few things to my stock powerplanted 1984 ATC 250R. Last night I installed an aftermarket pipe and silencer. Not sure on the kind as there are no markings on it whatsoever. I then swapped out the stock 84 carb for a considerably bigger 85 R carb.

It fired right up first kick with the new parts installed. Sounds wicked good too!!! After a test run I have found something to be pretty wrong with the tuning - more specifically I would say the jetting. I started by having the needle clip centered. At WOT it misses and spits and sputters - until I get into 4th and 5th gears, then it seems to rev out fine. Makes me think it is running good while under heavy load. I then moved the needle clip to the top of the needle (lowering the needle - thus making it more rich?? I think) and had the same effect. A plug chop showed the plug to be wet and black - telling me too rich (I think). Looking back - I think maybe I should have moved the needle up, not down to lean it out some. This is my 1st two stroke so I am still a novice at this.

Anyone know what stock main Jet an 85 R carb has in it? Also - I need to go buy some other main jets. I assume I want to go smaller than stock - am I correct? Also I will be installing after market reeds for it soon - will my jetting be affected after I do this? If you can - give me suggestions as to what main jets to buy and change out. Again this is a 1985 250R carb on a 1984 250R with an after market pipe.

Thanks in advance for any help.

Tim

[Pete]

if you raise the clip (and lower the needle into the tube) you are actually leaning out the mixture. It restricts the flow of fuel, thus leaning the mixture out.

[TtownJoeShow]

142 is stock, if i was you i'd get 135, 138, 140, 145, 148 & 150...er wait what do you have in it now?

[atctim]

Gosh - I am not sure what size main is in it - I can assume stock, but that is only an assumption. Will my local Honda dealers have these in stock?

[Derrick Adams]

Tim, WOT isn't really effected by the position of the needle. That's mainly for low to mid throttle.

I would suggest putting in a fresh plug and warming the bike up real well before you take it for a spin. Also, pop off the airbox lid, if you haven't already. She needs more airflow to really see the benifits of the carb swap.

The aircooled R's have a much lower powerband than the waterpumpers as well so you'll probably want to shift it a little lower than you would think. (Jason can hook you up with a ported cylinder to fix that!)

Once that thing is warmed up I would take a WOT 4th gear plug chop. That should tell you where your at. I think I ended up with the 142 in mine with the open airbox.

[atctim]

Thanks Derrick - that was what I was looking for. I'll give it a try and see what happens. I have read through Dammits! jetting sticky and am not real sure on alot of it - my lack of understanding is the problem - it is written very well - I just need some real world experience in carb tuning to better understand it. It is not running smootly yet. I'll try the open air box lid as I have not done that yet. I had the engine plenty warm before testing it last night.

[atctim]

Derrick -

You were 100% correct. I took the air box lid off and it runs great. When I originally mentioned it running fine in 4th and 5th - that was because I do not have the hose that runs from the frame to the airbox. So the faster I went, the more air poured into the air box.

Thanks again Derrick. You are a smart man!

[dirtface]

So, have you been able to tell the difference from the stock pipe and carb verses your "new" pipe and carb. I always liked how much meaner a aftermarket pipe makes a 2-stroke sound, compared to the stock setup.

[Liquid-Darkness]

All you need now is Boyesen power reeds, a fresh top end and you are ready to rock, if you do not already have those.

[atctim]

Dirtface - It sounds really mean. Although I need to repack the silencer. There is a huge difference in power. I'll get some pics up soon of the "new goods"
Liquid - I am getting Boyesen reeds for Christmas and I just rebuilt the top end so it is tight and it really screams for an air fooler.

More to come in a while.

[atctim]

OK guys - need some more help. It seems I am running good one I get moving - (3rd gear and up) IE my airbox is getting air forced in (the tube that goes from the frame to the airbox is not hooked up). Is there any tuning I should do to get the engine more air, or should I do away with the airbox completely and run the filter right off of the carb?

[BigGreenMachine]

Keep the airbox. Its invaluable out in muddy/wet conditions and does a great job of keeping crap off your filter.

Tim, time to buy jets and start tuning. Some pilot/needle work sound like what you really need. Plug chops and testing is the only way you will get jetting correct.

http://justkdx.dirtrider.net/carbtuning.html

[chris200x]

(the tube that goes from the frame to the airbox is not hooked up).

Tim, I believe that if your going to keep your airbox. you should have everything hooked up and connected properly. In other words, have all the breather tubes, lid, etc. hooked up as if the way your going to be running it all the time. Or vice versa. (just running the filter to the carb)Then start moving the clip or changing jets sizes. It will make it a heck of alot easier that way IMO.

[atctim]

OK - I know I need to run this machine without the airbox lid - because it does not get enough air into the 85 carb with it on. I have been doing some plug chops and they actually look really good (This should mean jetting is fine?)(I have been doing tons of carb tuning reading and studying). It's just that at low speed - it is not getting enough air. I just put on a new UNI air filter and moved to an 8 plug from a 9. The 9 looked wet when pulling it after chops - meaning to rich. The 8 plug being hotter looks great after a chop. Just looking to get more air to the filter at low speeds (1st and 2nd gear). Any ideas guys? BTW - moving the needle clip has not proved to do very much plug chop wise)

[Tri-ZNate]

Get a k&N if you want more air.

[atctim]

Is there a huge difference?

[Tri-ZNate]

I think it was Dammit who said that he had to bump up a jet size because it flowed so good compared to a foam uni

[BigGreenMachine]

The answer is a leaner pilot and move the needle clip up. You need less fuel, not more air. The K&N will allow more dirt in with the extra air. Try it all the same.

[Tri-ZNate]

The K&N will allow more dirt in with the extra air..


Thus why they make outwears

[Derrick Adams]

The answer is a leaner pilot and move the needle clip up. You need less fuel, not more air. The K&N will allow more dirt in with the extra air. Try it all the same.


I think I disagree with this. If your K&N filter is cleaned and lubed properly it will work perfectly. I don't prefer the foam filters because I think they release the oil from them to quickly and allow dirt thru.

I agree that you need less fuel down low. I'd say your idle circuit is still a little too rich causing your wet plug just off idle. Lean out your needle all the way then tune your air/fuel idle screw from there. The idea is to get the bike to idle for long periods of time without loading up or surging. If it loads up, obviously it's too rich. If it surges and searches for idle it's too lean.

Tim sounds like your real close already! Don't get too settled though, cause it will all change when it warms up next summer!