Pilot Jet Questions

[Dieseldog]

So today my carb kit came in and I quickly tore the bike apart and refurbished the carbs. The pilot jet that was in it was a 40 and the kit had a 38 in it. I figured since the 38 is what originally should have come in the carbs , it would be fine to replace the 40. I had already cleaned the carbs once and the bike ran ok. It idled fine but had nothing mid range. I figured the carb kit would take care of that issue. Well now it screams down the road but I can't seem to get it to idle properly. Any adjustments I make no matter how small will either raise the RPM's to 3000 or bring it down to where it dies out. Do you think I should put the 40 back in? I did the battery box today too so it's much easier for me to make internal adjustments. Even though the carbs were still clean looking today I still ran cleaning wires through all the ports and jets and double checked that they were all flowing carb cleaner when I sprayed it.

[Ceeloo Yello]

Could be a vacuum leak.

[Dieseldog]

I'll check the hoses now and I'll let you know what I find out.

[DannoXYZ]

Vaccum leak is not just hoses. Can be leak in rubber tubes between carb and head. Those tubes can also be reversed. Can be leak between carb and airbox. Can also be leak in fuel-rail and carb (did you replace fuel-rail O-rings?). Can also be leak at pilot adjustment screw. Did you replace O-rings, springs and washer in pilot adjuster?

Did you replace float valves? Did you set float level and verify externally with wet test? Did you sync carbs?

Do valve-clearance test?

Any one of above can contribute to your touchy idle setting.

[Dieseldog]

The carb kit I got was from eBay called an All Balls Carburetor Rebuild Kit. I used all the parts it came with except for 4 O-rings that I couldn't locate on the parts diagrams. The kit came with fuel adjustment screws, springs and both of the o-rings. Main jet, pilot jet, float valve, bowl gasket, throttle needles, new screws for the top and bowl, 1 o-ring for the "vacuum valve??" And 4 O-rings that I couldn't figure out where they went. I sprayed starting fluid on the lines and all the boot connections while the bike was running and I didn't notice any change in idle. Before I refurbished the carbs the bike ran ok just had no nuts mid range. Idled at 1400 all day. The only thing that I changed was the pilot jet. That's why I'm thinking about putting the 40 back in.

[ducatiman]

wacky contents are fairly common with All Balls kits. 4 orings present in the kit...but there is no application for 4 matching orings anywhere in a 250 carbset. I'll submit routine QC problems there.

I've had problems with off spec pilot screws, wrong orings/seals, incorrect hardware at various times within various applications. Much prefer my own sources for consumables while restoring and reusing *original* Keihin brass and tuning components....unless mauled.

@Dieseldog you running stock airbox/exhaust?

With 40 pilots present, someone has been in carbs prior. Were other components stock spec? How many turns out did you initially find pilot screws? Did the kit pilot screws "seat" into the housings *exactly* as OEM screws?

I take it you did not employ compressed air within your efforts? Nor address the float system?

[Dieseldog]

The bike is completely stock with 25,000 miles. The only thing that I found to be different from stock was the pilot jet it was a 40. The only changes that were made were the pilot jet back to the 38 and I put the old washers from the mixture screws on the needle to shim it. I'm going to take the carbs off again and put the 40 back in and remove the shims. Then I can test my theory about the changes. The mixture screws didn't look the same because the space between the threads and top of the head was larger but the tip of the needle to the threads was the same and they both seated the same and sat the same in the carb. I didn't check the initial screw adjustment. The floats were in good condition and had no holes. I tested them in a jar of fuel. Now one thing I was told by my Harley mechanic friend is that the float valve seats need to be cleaned really good. He said to get a few cotton swabs and a drill load a swab in the chuck and hit the inside to remove the crud that you can't see and polish the seat. When I cleaned the carbs I didn't even think about that. So my list of things to do on my carbs is completely disassemble but not separate them again, soak everything for a few hours, run cleaning wires through all the passages, use compressed air to blow out passages, use the drill and cotton swabs in the needle seats, recheck float height dry and wet, replace pilot jet back to 40, remove shim from needles, compare mixture screws again to make sure they are identical to the old ones, set to 2.5 turns out, replace all of the vacuum and overflow lines along with clamps, inspect intake boots for cracks, disassemble clean and inspect the petcock, clean the tank again, put fresh 91 octane and stabil marine. Any suggestions on anything else I should do to the fuel system is greatly appreciated. I'll be adjusting the valves while the carbs are soaking so I can remove that variable from the equation.

[jkv45]

You shouldn't need a 40 Pilot Jet with a stock engine.

We ran a 38 with pod filters and a leaky stock exhaust - and it was fine. The difference is just the amount of turns "out" that you need to be on the idle mixture screws to get the optimum setting.

The 40 will need less turns out than the 38 to provide the same optimum mixture.

Bench sync the carbs when they are off, and check it with vacuum gauges after it's running properly. There shouldn't be much adjustment needed. If there is, it tells you there are some other factors involved.

I'd use the stock idle mixture screws unless they are damaged.

[Dieseldog]

I got the carbs redone and I put the 40 pilot jet back, removed the shim from the needle and following the advice given here put the old fuel adjustment screws back in. I bought a digital caliper and reset the float height. The little paper measuring tape I used wasn't accurate at all. The fuel adjustment screws were adjusted to 2.5 turns out but when I looked inside to see if the height was the same one was lower in the port than the other so I adjusted it in just a bit to match the other. So now the needle is even in both. The intake boots were oriented properly and there were no cracks. I used acetone and a pressure sprayer can to blow through the ports and jets. I made mini scrubbers out of stripped copper speaker wire and cleaned all the tubes, ports and surfaces back to shiny aluminum. I also cleaned the tank again and I'm glad I did. The petcock strainers were almost non-existent so I completely removed them because the pieces that came off were inside the valve. Can the strainers be replaced somehow? New fuel filter. It starts as it did before and I was able to set the idle easily. I haven't rode it very far but it runs damn good now. Starts without choke and warms in about 4 minutes. Oh yeah I also replaced the vacuum lines but the hose I got from the local Tractor Supply store was really hard so I used some heat to soften up the ends. Do you think this will be ok or should I just get some fresh hose? I'm using a little bit of oil but I don't have any leaks and I don't see any smoke while riding could this be the valve seals? I'm going to take a long cruise and I'll let you know how it goes.

[jkv45]

Originally Posted by Dieseldog

I got the carbs redone and I put the 40 pilot jet back, removed the shim from the needle and following the advice given here put the old fuel adjustment screws back in. I bought a digital caliper and reset the float height. The little paper measuring tape I used wasn't accurate at all. The fuel adjustment screws were adjusted to 2.5 turns out but when I looked inside to see if the height was the same one was lower in the port than the other so I adjusted it in just a bit to match the other. So now the needle is even in both. The intake boots were oriented properly and there were no cracks. I used acetone and a pressure sprayer can to blow through the ports and jets. I made mini scrubbers out of stripped copper speaker wire and cleaned all the tubes, ports and surfaces back to shiny aluminum. I also cleaned the tank again and I'm glad I did. The petcock strainers were almost non-existent so I completely removed them because the pieces that came off were inside the valve. Can the strainers be replaced somehow? New fuel filter. It starts as it did before and I was able to set the idle easily. I haven't rode it very far but it runs damn good now. Starts without choke and warms in about 4 minutes. Oh yeah I also replaced the vacuum lines but the hose I got from the local Tractor Supply store was really hard so I used some heat to soften up the ends. Do you think this will be ok or should I just get some fresh hose? I'm using a little bit of oil but I don't have any leaks and I don't see any smoke while riding could this be the valve seals? I'm going to take a long cruise and I'll let you know how it goes.

You are probably too rich with a 40 Pilot at 2.5 turns out. You should need some enrichment (choke) to start cold.

I've never seen a Ninja 250 warm up in 4 minutes while idling. Most take some time on the road to get to operating temp, and there is a cooling system design issue that is working against warming quickly.

Set the idle mixture screws to get the highest RPMs and check the carb sync with vacuum gauges when fully warm.

[Ceeloo Yello]

If it aint broke

[Dieseldog]

The only issue I've experienced since the carb rebuild is a small hesitation when taking off but it may just be that it's a 250 LOL. Other than that it runs great. Still starts without choke and when I say warms up I am meaning the time it takes to get to the point where I can take off without hesitation or cutting out.. I also got a replacement rear shock from a crashed bike that had 4000 miles. While changing it I cleaned and regreased all the pivot points. Now it feels really good compared to what it was. I'm waiting for my new tires and when they come I'm going to replace the wheel bearings and seals, chain and sprockets, brakes and strip and paint the wheels.

[DannoXYZ]

Try adjusting pilot-screws in more and see if off-idle stumble goes away. With 40, you'll probably want just 0.5-turns out.

[Dieseldog]

I'll check it out. I haven't checked the sync or made any adjustments since I bench adjusted it. I got a vacuum gauge but I didn't do the valve adjustment while I had the carbs out like I said I was going to do. I will do them now when I take the fairings off to repair and paint them. I don't want to adjust anything until I get the valves done.