Just traded my ninja 250r for an xj750, I rebuilt the carb on my last bike so this isn't anything new. However after the re build and putting everything back on I got it to start and it ran for a little bit then rpms slowed and killed it. Not sure if I just need to adjust idle mix screw or what, any input? Ps. I know the battery is dead and I've been using a jump pack to get it running again but that couldnt be the issue right?

Thanks again, $wim

miles, maxim or seca? Sitting a long time dormant?

Gotta be about 35 year old, no?

34mm Mikuni CV, correct? With the infamous YICS system.

edited to note.... Hitachi CV, not Mikuni my error

To my knowledge its a maxim and was running last spring. But yeah its got the yics system

fresh fuel in tank? sufficient quantity reaching bowls? Pilot circuits confirmed clear? Verified no floats sticking?
Where (number of turns out) ARE the pilot screws set right now?
Air path clear?
Spark plugs not fouled?

Diagnosis by keyboard a bit difficult, nothing surprising....all the usual suspects via a question and answer period...unless you can add more? When cleaning, what methods did you use? Any specialized equipment? Ultrasonic? Spray can carb cleaner? Strong compressed air?

Swapped out everything with a rebuild kit, pilots are 2 1/2 turns out. Scrubbed the whole carburetor with brush while spraying it with carb cleaner. Spark plugs are all new, haven't checked them since the initial start up though

likely pilot circuits are not truly cleared, more aggressive cleaning methods are called for

Got it started with some fuel additive, tomorrow im gonna let that run for a bit hopefully burn off any excess crud in the carbs

Yes, you need deeper disassembly and flossing of fuel-circuits and jet-holes with wire (modern carb-cleaner is useless, non-chlorinated).

Also soda-blasting of all those fuel-passages at high-pressure.

Also need complete ultrasonic tank soaking.

If the bike started easily and idled fine but then slowly died is sounds like the carb bowls are running dry.

I would verify tank venting is good, petcock not plugged and functioning properly.

Did you clean the tank and petcock also?

on a 35 + YO bike...anything and everything fuel related maintenance should be "on the table". A safety factor involved as well.

In particular those ancient Mikuni's are going to require attention above and beyond just getting it to run.

I'm surmising.... but its highly unlikely.... the carbs have ever been "split"......the interconnecting fuel rail orings and seals are ancient, way beyond their intended service limits, were never intended to last a lifetime. Consider also the ancient throttle shaft seals on each carb. Pretty important stuff.

And those old Mic's are truly bitchy to split, been there numerous times.

Owners discretion going forward, of course, but "vintage" ownership comes at certain preventative investments.
Carbs and fuel related items (safety) certainly apply.

Here's an example of rail seals from 24 year old Ducati/Mikuni carbs....

I am just basing my suggestions on the info given by the OP. I can not say exactly what the issue is and I am definately not going to say that you are wrong on the carbs needing a much better cleaning.
But giving him the benefit of the doubt I would start with simpler solutions.

Got it started with some fuel additive, tomorrow im gonna let that run for a bit hopefully burn off any excess crud in the carbs

He's found his chosen solution. No doubt pilot circuits that needed further "attention".

He's got it running...but I'm suggesting above and beyond...on 35 year old carbs, SAFETY becomes a factor. Integrity of orings/seals becomes critical at that age machine....no short cuts exist.

I'm doing a set of mid-2000 250 carbs right now, today. Owner reports leaking. I chose to wet test right out o' the box....running like a kitchen faucet from the fuel rail (between the 2 carbs). Sure enough, the orings are hardened and flat....add another 18 years to the age of these orings....would you ride on that?

I'm making a well advised suggestion to the owner (who is solely focused on getting it running) to consider ongoing SAFETY factors as well.

Look. I understand the liability/lawsuit driven society we live in and the fear used to control people from using their brains. Obviously you offering services for money makes it very difficult to offer advice without this coming into play. I will keep my opinions to myself.

Look. I understand the liability/lawsuit driven society we live in and the fear used to control people from using their brains. Obviously you offering services for money makes it very difficult to offer advice without this coming into play. I will keep my opinions to myself.

I'm not convinced the OP has even given a 2nd thought to riding around on 35 YO (probably original) carbs.....I mentioned it out of SAFETY concern, based on some very intimate carburetor experience and knowledge, nothing more.

I'm a longtime enthusiast and participating member here (10 years now, whoa) ....freely, frequently offer advise. Even been voted MOTM twice here. Never accused of "overburdening", never had issues with anyone on this forum.

Your comments off base, uncalled for.

He's found his chosen solution. No doubt pilot circuits that needed further "attention".

He's got it running...but I'm suggesting above and beyond...on 35 year old carbs, SAFETY becomes a factor. Integrity of orings/seals becomes critical at that age machine....no short cuts exist.

I'm doing a set of mid-2000 250 carbs right now, today. Owner reports leaking. I chose to wet test right out o' the box....running like a kitchen faucet from the fuel rail (between the 2 carbs). Sure enough, the orings are hardened and flat....add another 18 years to the age of these orings....would you ride on that?

I'm making a well advised suggestion to the owner (who is solely focused on getting it running) to consider ongoing SAFETY factors as well.

35 years is just getting broken in around my place :rotflmao:

This sure sounds like fear mongering to me but whatever man. You charge for your services so I'll take that for what it is.

This sure sounds like fear mongering to me but whatever man.

I can understand why you might think that, but I've had carbs leak gasoline onto my garage floor, and that's no joke. I've also seen the results of a carb fire on a running motorcycle and that's no joke either.

Gordon's a good guy and I really don't think he was motivated by greed. Heck, I once posted about my carb bowl gaskets leaking and he sent me a set of bowl o-rings free.

Fair enough. I will not post on such matters in the future.

had it running for a bit but then it died out again, abd now I have gas leaking out of the back of my carbs into the air box and all over the floor. Any suggestions with that leak? Ill be taking it back apart for further cleaning

had it running for a bit but then it died out again, abd now I have gas leaking out of the back of my carbs into the air box and all over the floor. Any suggestions with that leak? Ill be taking it back apart for further cleaning

Thankfully, it wasn't while riding, simultaneously lubing the rear tire with fuel while presenting a fire hazard as well.

Please heed *well intentioned safety warnings*....not to be confused with "fear mongering".

had it running for a bit but then it died out again, abd now I have gas leaking out of the back of my carbs into the air box and all over the floor. Any suggestions with that leak? Ill be taking it back apart for further cleaningRemember, there's multiple "levels" of cleaning and if you search here for 'clean carbs', you'll find that even most skilled and adept mechanics have had to remove their carbs 4-5 times and do ever deeper cleaning until finally they got it "factory-fresh" clean as when bike left showroom floor.

What was suggested earlier was to skip these 4-5 attempts and go straight to full-refurb job as very first step. It will save you time, save you money and frustration and you'll only have to do it once. Now you're on your 2nd or 3rd attempt. How many more do you want to try? Don't forget, every short-cut has potential risks.

https://www.ninjette.org/forums/picture.php?albumid=1659&pictureid=13614

Remember, there's never enough time to do it right the 1st time, but there's always time to do it again!

Got a much better looking set of carbs that I'm swapping the rebuild kit on, sorry its been a while

Also got a new gas tank and petcock, since the old one that the previous owner had just a pipe valve with a loose on off valve

So after I got it all back together, switched the airbox out for pods; the bike rev'd up loud as hell and shot oil outta the hose that goes from the engine to the air box(which I forgot to clamp) why did it rev up. Possibly an boot not fully tightened?

Revving higher than intended can mean it's sucking in extra air somewhere:


1. yes, rubber-boot leaking between carb & head can suck in extra air.

2. throttle-cables too tight? Can you rotate throttle couple of degrees before it starts pulling on cable?

3. idle-adjuster set? Adjust to lower idle?

4. throttle-plate stop on carb? Need adjusting?

5. carbs synced? all sync ports capped off?

6. choke on or off? Verify choke-plungers are sealing all way down.

7. carb-slides stuck

8. non-stock jetting?

9. pilot-circuit mixture-screws not adjusted properly

10. throttle-shaft seals new? Using too much starter-fluid, or carb-cleaner or too much hot-tanking will destroy the seals and create vacuum-leak there.

11. clogged starter-jets will cause high idle as well.

12. clogged low-speed jets will cause high idle also, or clogged low-speed circuit feeding jets

13. jets for main and pilot circuits swapped? Can actually do that on this model.

14. leaking accelerator pump




Basically if you don't buy brand-new factory-fresh carb in OEM box, it will be used unit and will need disassembly and thorough cleaning. Given age, that's a step that should be automatic. Running bike on used carbs without full refurb can risk destroying engine due to lean mixtures and detonation.

https://youtu.be/An7X2uSO2gA

https://www.ninjette.org/forums/showthread.php?t=333573
https://www.ninjette.org/forums/showthread.php?t=333176
https://www.ninjette.org/forums/showthread.php?t=334365
https://www.ninjette.org/forums/showthread.php?t=330213
https://www.ninjette.org/forums/showthread.php?t=330960
https://www.ninjette.org/forums/showthread.php?t=323737
https://www.ninjette.org/forums/showthread.php?t=323452
https://www.ninjette.org/forums/showthread.php?t=322846
https://www.ninjette.org/forums/showthread.php?t=321223
https://www.ninjette.org/forums/showthread.php?t=317977
https://www.ninjette.org/forums/showthread.php?t=317810
https://www.ninjette.org/forums/showthread.php?t=316395
https://www.ninjette.org/forums/showthread.php?t=315193
https://www.ninjette.org/forums/showthread.php?t=299855
https://www.ninjette.org/forums/showthread.php?t=280658

Update: ive fixed the idle, there was a crack in the boots, but now I dont have a throttle response, but its a step in the right direction. Thinking probably something with the throttle cable, thoughts?

Why would cable cause lack of throttle response?

Measure inner-cable:

1. measure free-end of inner-cable on both sides
2. pull inner-cable X-millimeters
3. measure movement of inner-cable on other side
4. does it equal X-millimeters as well?

Again, your answer is in here:

https://www.ninjette.org/forums/showthread.php?t=333573
https://www.ninjette.org/forums/showthread.php?t=333176
https://www.ninjette.org/forums/showthread.php?t=334365
https://www.ninjette.org/forums/showthread.php?t=330213
https://www.ninjette.org/forums/showthread.php?t=330960
https://www.ninjette.org/forums/showthread.php?t=323737
https://www.ninjette.org/forums/showthread.php?t=323452
https://www.ninjette.org/forums/showthread.php?t=322846
https://www.ninjette.org/forums/showthread.php?t=321223
https://www.ninjette.org/forums/showthread.php?t=317977
https://www.ninjette.org/forums/showthread.php?t=317810
https://www.ninjette.org/forums/showthread.php?t=316395
https://www.ninjette.org/forums/showthread.php?t=315193
https://www.ninjette.org/forums/showthread.php?t=299855
https://www.ninjette.org/forums/showthread.php?t=280658

Why would cable cause lack of throttle response? :

The cable was super close to those knobs where the gas tank sits and I was thinking it couldve possibly been pinched

Here's tip: spray carb-cleaners DO NOT WORK

With removal of chlorinated compounds (carbon-tetrachloride and tri-chloroethylene), "carb-cleaners" are just useless weak solvents with no cutting action.

You need to completely disassemble carbs down to constituent components:
http://i1100.photobucket.com/albums/g420/nfortch332/FC074AB8-86E9-4EF6-AE91-D1DF4323B01F_zpsl2sdzmmq.jpg

Then clean every component by physical scrubbing with acetone, flossing and reaming with guitar-wire of matching diameters. You need to physically poke out every bleed hole as no spray cleaners will remove dried gas varnish. You'll find when poking wire in, it pushes out little plastic plug like grain of sand out other side. Then drip dye down centre to verify every hole "bleeds" correctly.

https://drive.google.com/uc?export=download&id=1zSzSn8eAISUj1yCtRPB0-DNCIQdWQx57

You'll also most likely need to replace the float-valves since they're not sealing and dribbling petrol out vents.

Best bet for you is to get factory service-manual. Follow step-by-step 16-page guide to rebuilding carbs. There are no short-cuts.

The cable was super close to those knobs where the gas tank sits and I was thinking it couldve possibly been pinched

That would just require more force to move cable; you'll just have to twist throttle harder. But travel would still be exactly same as if they were not pinched. Measure movement of both cable-ends and verify travel is identical at both ends.

Also, don't try to force past this with more throttle and higher-RPMs without doing proper deep-cleaning and rebuilding of carbs. The resultant lean air-fuel mixtures will cause super-hot mixtures, detonation/pinging and eventually this:

http://i1232.photobucket.com/albums/ff368/RacerX9623/engine010.jpg

If you are having trouble cleaning your carbs properly, it's A LOT more difficult to replace pistons...

hasn't this thread gone full circle.....4 months later?

Pump the brakes on the cleaning and the full circle part. Ive been cleaning these ****ers enough times to know its not a stuck float bowl, looking at it further, I realise I forgot the bracket that holds the the cable at an angle on the carb

When removing an airbox and changing to pod filters, you can have multiple issues. Some bikes will idle poorly without the airbox and others will bog badly on acceleration. The carbs are jetted to work with the specific air flow volume the airbox provides. Adding in higher flowing pod filters may cause multiple issues until you rejet. I am not personally familiar with the Maximum line of bikes but learned this lesson with a Kawi Vulcan. With just the covers off of the filters, the bike would barely idle and would not accelerate cleanly. Once the covers were replaced it ran perfectly. Hope you get your bike sorted soon, good luck