The ongoing technical challenges of the FZX250... When we first got the 1999 FZX250 home, it was difficult to start. A squirt of carb cleaner or ether down each carb throat would convince it to run, but it would die with any application of throttle until it was really warmed up - then it'll rev easily. It hasn't been ridden yet, so we have no idea how it performs under load, but my first thought is that it's running way too lean. Are there common issues we should be looking for? Is this a common issue with the Mikuni carbs?
The most common issue is Carburettors... specifically FZR carbies. They will drive you to distraction but... there are plenty of people in here with lots of experience on them to help you through the nightmare that is FZR250 fuel systems. I am not one of those people.... good luck
Running rich from worn emulsion tubes is more common. Best first step before removing anything at all carburetor related would be to check the fuel level visually Lots of instructions on the various steps, checking, setting, adjusting etc https://www.2fiftycc.com/index.php?threads/fzr250-3ln3-carb-problem.8770/page-8#post-140180 How to visually check the fuel level, [clear plastic tube] which is my suggested first step as the carbs remain installed on the bike https://2fiftycc.com/index.php?threads/my-fizzer.872/page-32#post-15537 Specs: Zeal fuel is 10.5mm above the casting line on the float bowls https://www.2fiftycc.com/index.php?...8-26mm-carb-settings-specs-3ln-3yx-zeal.9787/ The other element to check would be the idle mixture screw
I am unfortunately, but I can say that with the correct parts if necessary and the correct adjustments, carbs can be conquered, quite easily in fact
@Duncan16 Disregard my levity... in all seriousness the assistance you will get in here from the FZR Gurus will save you lots of heartache etc. The accumulated knowledge in here is second to none and you will find every encouragement to get your bike running as good as it ever has...
No need to disregard your levity, if I have one regret on my deathbed it will be the time taken to conquer FZR carbs, and a HUGE part of that final success was down to @GreyImport I think it was finding the emulsion tubes, otherwise I'd probably still be adjusting fuel levels, in my sleep nightmares
The first thing I would check is the fuel level in the float bowls, i.e., float height. This makes a big difference for the mixture if incorrect. Maybe also check the needles are set at the right height, they may have been tampered with before you got the machine.
Theres more posts about Mikuni BDST carbs than probably everything else combined If you manage to get away without pulling off the carbs 101 times and overhauling them at least once then Ill eat my hat The other thing that can be affecting your startup is the valves clearances need to be done https://www.2fiftycc.com/index.php?threads/fzr250-zeal-fzx250-valve-clearances-howto.1697/ The magic spray is never far from my FZR
Starting high strung 250cc fours is not simple. 1/Test the compression and do a leakdown test first 2/ The batteries are weak and cranking causes a significant drop in voltage at the spark plug. They often catch just as you release the button because it finally has a decent spark. In fact this is how I used to start a Honda 250 4. 3/ The carburettors need to be clean and functional. 30 year old o-rings, wrong settings and worn needles are not going to cut it. Full rebuild is often the case. 4/ They often need new spark plugs for no apparent reason 5/ They are never lean. In fact the opposite is always the case. Fuel starvation however, is common. Blocked fuel taps etc the most common cause. 6/ Once that is all good the carbs need to be synchronized and the mixture settings set perfectly, preferably by ear or ride and adjust. 7/ To start cold: full choke no throttle and short dabs on starter. Release choke as it warms up. It will flood very quickly under full choke, so if it doesn't start walk away and try again later. 8/ To start hot: no throttle no choke. If all this sounds scary buy a virago.
I think I may have identified part of the problem with starting and rough running. :-D I drained the old tank today. The bike gets my respect for managing to even ignite this…. Got a new tank that’s been cleaned and prepped ready to go on. The old tank can get in the bin.
You're going to need to at least pull off and clean the carby bowls and fuel tap. And flush the tank.
We have a new, spotlessly clean, tank ready to go. Cleaned the fuel tap, replaced the fuel filter and hose. Next job is to flush the fuel pump and fuel bowls.
We're in the process of cleaning out the fuel bowls and cleaning and blowing through the jets and passages and we've noticed that the carbs get less grotty from left to right (seated on the bike). The float bowl for cylinder 1 was absolutely putrid, number two was grot, three was not so bad, number 4 just a bit meh. I was expecting that the carbs would be equally grotty but that's not the case. Any ideas as to why? All the idle jets were at least partially blocked (1 and 2 were completely blocked) and they're clean now. Looking forward to getting everything back together and see if the sod will run. :-D
When the bike is on the sidestand, the lowest carb will be #1, then #2, then #3, then #4. When bikes sit, grot accumulates at the lowest point. With everything clean, make sure you set the floats, mixture screws and needles to factory settings. It may also need a throttle balance.
A progress report on this: we got the now spotlessly clean and carefully adjusted carbs back on the bike last night. It now starts first time, every time, and settles down to a smooth idle on the choke (haven't fully warmed it up yet). Thanks everyone for the guidance and help!
Well done. If you run that horrible ethanol blend garbage then you can't leave it in your float bowls for any length of time or everything will go green and rotten again, but I'm guessing you know that already.
The bike got its first sniff of the outdoors yesterday afternoon with rides up and down the lane out the back. Goes like stink... aaaaand found a bunch of other things to fix. :-D
