Stuck- Should I shim needles, or leave stock?

[puma22]

I've been reading this forum for a long, very long while now, and have read many threads on countless topics, but this is my first question I pose to the community here with regards to my bike. Here we go...

So, I just bought a 2008 ninja 250R with around 680 miles about 3 weeks ago. I've replaced the battery. Once the weather allowed for some riding I started it up and rode it for a few miles. I've prob put around 7 miles total, so barely rode it. But I've noticed a few things:

When I have the bike idling and I rev the engine, there is not a smooth increase in rpms. If I would quickly open the throttle to the end and release I would expect responsiveness, but it would go to like 4k-6k rpms then die. In order to rev the engine to a high rpm, I would have to fully open the throttle for like a second or two and the rpms would gradually climb, and then shoot up quickly. Is this normal?

I thought this would be due to the carbs not being clean, so I just took out the carbs, opened them up, and surprisingly found them to be clean...?? Now when I'm thinking that its acting this way due to not being broke in yet? I have no idea atm...

I also noticed when I accelerate that it runs really anemic until around 6k or so then pulls hard after. Is this the nature of a stock 250?

So... right now I have my carbs out, which I just finished taking out around an hour ago. I was thinking of shimming the needles with 1 washer each, keeping the stock exhaust, and possibly taking out the snorkel.
I also have an aftermarket Delkevic slip-on exhaust that I got with the bike, but it is insanely loud, so I'm sort of avoiding to use it.

What do you guys think? Need some advice here. Should I keep everything stock? Or should I shim the needles with 1/2 washers each, take the snorkel out, and either keep the stock exhaust (more preferable) or use the aftermarket exhaust?

[DaBlue1]

2 washers, snorkel out, stock exhaust. If you like that, you can then replace the stock air filter with an aftermarket replacement and add a set of Iridium plugs. Once you get it broken in good, switch to synthetic oil. You should love the results.

[puma22]

Thanks Blue, I was sort of leaning towards that. I'll give it a try tomorrow once I get the washers. Do you think this will get rid of the lagginess and slow responsiveness of the bike?

If anyone else would like to add something, do not abstain!

[tubarney]

how cold is it when you go for a ride? How long did you ride for?

A stock ninja 250r has no balls below 6k, it will pull nicely from around 8k to 12k.

If you have not removed the snorkel out of airbox you don't need to shim the needle.

[tubarney]

Also, shimming the needle will not help you out below 5-6k. You need to turn the pilot screws out 1 turn.

[DaBlue1]

Originally Posted by puma22

Thanks Blue, I was sort of leaning towards that. I'll give it a try tomorrow once I get the washers. Do you think this will get rid of the lagginess and slow responsiveness of the bike?

The stock Ninja has a natural lag when you turn the throttle too fast. Shimming should help your throttle response starting at the 1/4 throttle range. Once the bike is nice and warm, you may need to adjust the idle speed down a tad.

This is a good piece of info to read. How CV Carbs Work

[puma22]

Originally Posted by tubarney

how cold is it when you go for a ride? How long did you ride for?

A stock ninja 250r has no balls below 6k, it will pull nicely from around 8k to 12k.

If you have not removed the snorkel out of airbox you don't need to shim the needle.

Brad - if I can remember correctly, it was in the 20's or 30's (F). Pretty cold. I rode for about 45 min, not exceeding 35 mph with many frequent stops.

As for the pilot screws, are those the ones right next to the main jets? Do you recommend I mess with these? So far I haven't read anything about tweaking the pilot jets so I have no information with regards to this mod.

Blue- the link you posted is not functional.


So this is what it's looking :
2washers under each needle, snorkel out, stock exhaust, pilot screws?

Again, thanks for the much needed help guys.. Have my carbs just layin out here till I figure out what I will do.

[tubarney]

Holy crap that is cold!! Theres your problem my friend.

If the temperature is under 50F your going to have trouble starting the bike, and trouble riding it as it warms up. Its going to die if you give it too much gas when cold. It is a struggle keeping it going during the first 5 mins. This also explains the surging.

In that kind of temp its going to need at least 10-20 mins of decent riding to warm up.

[tubarney]

Second photo is of a stock Ninja 250r with Snorkel still in. As you can see you the AFR is lean below 6k revs. It has stock 98 jet and No shims under needle.

First photo is off the pilot screws. They will have covers on them that need to be removed. They are on the side the connects to cylinder head. They are the gold flat head screwdiver screw

[BlackNinja8]

Brad, I live somewhat in your area, and like you I bought my bike in mid winter. Let me tell you that it is a completely different bike in Feb than it is in May. My bike idle rough, ran lean, and was very herky jerky at low rpms. Once the weather warmed up things improved greatly.

My advice would be to wait out the winter and make your adjustments under more normalized conditions. Congrats on your new bike.

[scottg]

Originally Posted by BlackNinja8

Brad, I live somewhat in your area, and like you I bought my bike in mid winter. Let me tell you that it is a completely different bike in Feb than it is in May. My bike idle rough, ran lean, and was very herky jerky at low rpms. Once the weather warmed up things improved greatly.

My advice would be to wait out the winter and make your adjustments under more normalized conditions. Congrats on your new bike.

Couldn't agree with you more. I live in Boston and even the difference between from when I first start riding in the spring vs. summer is huge. As tempting as it is, I wouldn't mess around with anything until it gets warmer out.

[puma22]

Blackninja, I think you were addressing me. Thanks and you don't live too far away indeed. You can imagine my concern... I was very frustrated and had thought my carbs needed major cleaning.. Went through the trouble of taking them out and they turned out to be crisp clean.

I will take your words for it and will reassemble everything stock for now,and wait for better temps. Then I'll look into shimming the needles with the setup I had mentioned earlier.

Thanks for the speedy advice guys! This forum is fantastic.. You get the help right when you need it.

[puma22]

And below are my carbs for the record... Pretty clean ey?

[DaBlue1]

Despite the cold temps in your area, shimming the needles is not going to affect your bike so much that you will need to re-tune it in the summer. In fact a little richness is what you want in winter for a couple of reasons. Cold dense air leans out the fuel mixture and winter gas tends not to vaporize as well when cold until the engine reaches a good operating temp.

Don't mess with the pilot screws at this point. Just adding 2 shims will add fuel so that the AFR will be a tad bit richer. The Ninja really does not like temps below 50, but it will run fairly well once warmed up good. Once running, keeping the rpms up, the engine will naturally heat better.

AFR's above 14.7:1 are considered lean. The target AFR for our bikes under ideal conditions happens to be the 12:8:1 - 13:4:1 range under load. It is not uncommon in the low range (2k-5k RPM) to hit the 15.0:1 mark under moderate to hard acceleration, but is only sustained at this level for a several seconds. However, this area is cleaned up (richened) by shimming the carbs.

I wouldn't worry about AFRs too much at this point, because the change you are doing is minor compared to removing the airbox, re-jetting, installing pods and adding a full exhaust.

How CV Carbs Work needs a flash player to open. You may need to update your player or just give it time to load properly.

Here are a couple of more good things to read.

Motorcycle Carburetor Theory 101
https://docs.google.com/file/d/0B8nS...eDg/edit?pli=1

Pipe Jetting (A Must Read)
http://www.motorcycleproject.com/mot...s-jetting.html

[choneofakind]

Originally Posted by tubarney

Also, shimming the needle will not help you out below 5-6k. You need to turn the pilot screws out 1 turn.

no...

rpm ranges vs carburetor settings have much less to do with each other than carb settings vs throttle openings.

The main jets control fuel at WOT. The needles control fuel at partial openings. The pilot jets control fuel at very small throttle openings.

The needles do make a significant difference under 5k because when you snap the throttle wide open, the slides open up gradually as the airflow increases. This is due to a pressure difference in the carb. The slides moving up slowly keeps a constant velocity of air through the carb. That's why this is called a CV carb; it keeps a Constant Velocity of air.

Read through that tuning guide I sent you in that other thread, tubarney. The method it suggests (which works well) for testing needle height is to get the bike putzing down the road at 3k in 2nd, then snap the throttle to WOT and hold it there. As you bike takes in more air, the slides will raise gradually. If your needle height is correct, this test will result in a smooth acceleration from 3k all the way to where the slides are completely raised and the main jets are in charge, which is around 10k.

Also, you do realize that turning the pilot screw out 1 full turn will result in a really rich idle that will bog right? You adjust those in 1/8 or 1/4 turn increments, not full turn increments. Leave those at the standard 2.5 turns out for now; the idle is perfectly fine to be running as close to a 14.7 AFR as you want because there's no load on the engine at that point. Besides, the pilot screws are at 2.5 turns out. If you get to 3.5 turns out, you need to go to a larger pilot jet. The OP's stock bike does not need a larger pilot jet.

If anything, the OP only needs to leave their stock setup for now, shim their needles with 1 washer, and then do everything else in the spring when they have more representative temps and can better tune their jetting. This will help their mid-range a touch for now without being too rich for when it warms up.

[puma22]

Ok, I hadn't seen your reply Blue, and I re-installed the carbs this morning without shimming. Its ok though, I will shim the needles the next time I open the bike up. Maybe in a week or two.

I have one minor problem though. After re-assembling all the parts, I started the bike and opened the choke fully and the bike revs very strongly to 6k-7k rpm. It had been indoors, in a heated environment since I had removed the carbs yesterday. Is it normal to rev that high, or do I have to adjust the choke? I pushed back the choke all the way off, and it idled at around 1k. Is this just due to the bike being warm?

[DaBlue1]

Originally Posted by puma22

....I have one minor problem though. After re-assembling all the parts, I started the bike and opened the choke fully and the bike revs very strongly to 6k-7k rpm. It had been indoors, in a heated environment since I had removed the carbs yesterday. Is it normal to rev that high, or do I have to adjust the choke? I pushed back the choke all the way off, and it idled at around 1k. Is this just due to the bike being warm?

It can rev that high it's warm with the choke fully on. just make sure your cable are adjusted properly and not binding anywhere. When you adjust the idle make sure the bike is completely warm. Adjust the idle to around 1300-1400 rpms.

[tubarney]

Originally Posted by choneofakind

no...

rpm ranges vs carburetor settings have much less to do with each other than carb settings vs throttle openings.

The main jets control fuel at WOT. The needles control fuel at partial openings. The pilot jets control fuel at very small throttle openings.

The needles do make a significant difference under 5k because when you snap the throttle wide open, the slides open up gradually as the airflow increases. This is due to a pressure difference in the carb. The slides moving up slowly keeps a constant velocity of air through the carb. That's why this is called a CV carb; it keeps a Constant Velocity of air.

Read through that tuning guide I sent you in that other thread, tubarney. The method it suggests (which works well) for testing needle height is to get the bike putzing down the road at 3k in 2nd, then snap the throttle to WOT and hold it there. As you bike takes in more air, the slides will raise gradually. If your needle height is correct, this test will result in a smooth acceleration from 3k all the way to where the slides are completely raised and the main jets are in charge, which is around 10k.

Also, you do realize that turning the pilot screw out 1 full turn will result in a really rich idle that will bog right? You adjust those in 1/8 or 1/4 turn increments, not full turn increments. Leave those at the standard 2.5 turns out for now; the idle is perfectly fine to be running as close to a 14.7 AFR as you want because there's no load on the engine at that point. Besides, the pilot screws are at 2.5 turns out. If you get to 3.5 turns out, you need to go to a larger pilot jet. The OP's stock bike does not need a larger pilot jet.

If anything, the OP only needs to leave their stock setup for now, shim their needles with 1 washer, and then do everything else in the spring when they have more representative temps and can better tune their jetting. This will help their mid-range a touch for now without being too rich for when it warms up.

Thanks Chris. I posted that hoping someone would correct me. I think I'm getting this now.

With the dyno I posted earlier. Is the AFR ok? Or should something have been done like shimming the needle to smooth it out?

[DaBlue1]

Originally Posted by tubarney

....With the dyno I posted earlier. Is the AFR ok? Or should something have been done like shimming the needle to smooth it out?

It is fine for emission standards, also keep in mind 14.7:1 is the ratio to achieve a stoichiometric burn. However, this is not the target ratio for maximum power (just an optimal burn). 14:7:1 is great for cruising down the highway or coasting along down a small decline, when there is very little load on the motor. But under WOT, you have a huge load on the motor. Temperature (and subsequently cylinder pressure) increases and can cause detonation. Adding more fuel (running rich) effectively lowers cylinder temperature creating a “cooler” and “longer” burn… this in turn creates more power per combustion stroke.

You can shim and it will enrichen this area a small bit, but it will never be completely smoothed out in the stock engine set up. You will find a slightly better throttle response and cold starts.

[choneofakind]

Originally Posted by tubarney

Thanks Chris. I posted that hoping someone would correct me. I think I'm getting this now.

No problem. Read through some of Blue's links. He's always got some good info and advice.

At the shop I go to, they aim for a WOT AFR of 12.8-13.2 on the dyno.
Low-load cruising can be around 14 or so.

Don't worry so much about AFR, worry about how it feels when you ride it. If it surges or stumbles, it needs more gas. If it bogs or feels soggy, it needs less gas. Remember, throttle and carb parts are dependent; carb parts and rpm's are independent variables.