'93 stuttering, hesitating, annoying.

ACL 9000 · April 14th, 2016, 08:28 AM

A friend of mine recently purchased his first motorcycle; a 1993 Ninja 250. The PO claimed it had "a carburetor problem". The bike would start with some coaxing, but only ran on one cylinder.

We went to clean the carbs, expecting them to simply be gunked up, but we discovered they were missing pieces. We used some rebuild kits to replace the missing parts.

So far we have adjusted the valves. We have changed the oil with Rotella T6 and a Wix filter. We replaced the PO's Champion plugs with the correct NGKs. We synchronized the carburetors.

The bike is a little reluctant to start at first. Even with the choke lever all the way back it wants to die without a touch of throttle. It's my understanding that opening the throttle leans the intake mixture, so I would assume that backing off the choke a little would have the same effect, but it doesn't seem to.

Eventually it will idle on its own. If you attempt to ride the bike the power delivery will be very erratic. There is no torque at lower RPM, so leaving a stop can be challenging. When accelerating the bike seems to jerk, or stutter, or whatever word you would use to describe sudden temporary losses of power. This is accompanied by a change in the sound of the engine. It becomes quieter and sounds much more loaded up, like if you'd cranked the throttle all the way open at a low RPM.

After riding for a little while it will try to stall at every stop, and has to be kept alive. Choke doesn't seem to have an impact at this point. If you turn off the bike for even a short time, maybe 3 to 5 minutes, it will fire right up and immediately assume the ~1800rpm idle I set back when I thought we were getting close to being done.

So I have no idea what's going on and I'm sick of doing things I've done already hoping maybe I screwed them up before and this time it'll all be fixed.

The intake boots from the airbox to the carburetor are very old and have no clamps. What are the symptoms of an air leak at that location?

The airbox itself is barely secured in the bike. The top anchor is missing, and only one screw beneath the battery connects the whole plastic shebang in any way to the bike, through the rear inner fender thing.

The gas that was in it was very old and full of water, but we've added fresh gas twice now, and ridden it about 100 miles in total, so I feel like bad fuel can be ruled out as a cause.

At certain points along the way in this process the bike has run seemingly better. Prior to synchronizing the carbs and changing the oil the bike seemed to run smoothly, but wouldn't idle correctly and the clutch seemed to slip (which I attributed to nasty old oil, since the PO did every possible thing wrong). I also replaced the top two vacuum lines on the carbs with some hose I got at Advance Auto, could that have this affect?

So I'm running through the possibilities in my head: Carbs somehow still out of sync? Air leak in a critical place? Float problems? If this was my bike I'd have raided a parts catalog and possibly even bought new carbs just to skip over having to deal with this negligent-PO bullcrap, but I'm trying to keep an inexpensive bike inexpensive.

What causes a Ninja 250 to start somewhat poorly when cold, die occasionally when warm, and stutter at all throttle positions at all speeds, seemingly flopping from making 5hp to full power abruptly and repeatedly?

Thanks for your help, guys. I tried searching around, but I couldn't find anyone describing the same problem, nor anyone supplying solutions I haven't already tried. (I remember when I first got my Ninja I spent almost a month searching for my problem [tight valves] by symptoms and got nowhere, so I've learned that while search is handy, sometimes you just have to ask directly).

HoneyBadgerRy · April 14th, 2016, 08:37 AM

First off are you sure it runs on one cylinder, because I'm almost positive it doesn't.

I would start off with verifying that all the vacum lines are routed properly, and that there are no vacuum leaks at or after the carbs.

If this doesn't solve the problem recheck that all the valves are adjusted properly, and replace the sparkplugs, check the sparkplug leads.

ACL 9000 · April 14th, 2016, 08:53 AM

Back when we first acquired the bike it was definitely only on one cylinder because one carburetor was missing a jet. That was the initial problem we spotted, but it hasn't cropped up again since we installed the kit parts.

I can check that I ran the lines properly. I will try to make sure there are no vacuum leaks. Would replacing ancient OEM vacuum lines with lengths of vacuum hose that may be narrower than stock cause a problem?

I'm 99% sure the valves are good because I triple-checked them before I buttoned it up, but I'll check again. Would improper plug gap do this? I didn't gap the plugs because I couldn't find my gauge. I have new plugs I can put in; I'll gap those correctly.

HoneyBadgerRy · April 14th, 2016, 09:03 AM

Quote:

Originally Posted by ACL 9000

Back when we first acquired the bike it was definitely only on one cylinder because one carburetor was missing a jet. That was the initial problem we spotted, but it hasn't cropped up again since we installed the kit parts.

I can check that I ran the lines properly. I will try to make sure there are no vacuum leaks. Would replacing ancient OEM vacuum lines with lengths of vacuum hose that may be narrower than stock cause a problem?

I'm 99% sure the valves are good because I triple-checked them before I buttoned it up, but I'll check again. Would improper plug gap do this? I didn't gap the plugs because I couldn't find my gauge. I have new plugs I can put in; I'll gap those correctly.

After market hoses would only be a problem if they didn't seal on the barbs, or had holes in them. (Unlikely)

You might have thought the specs were standard (the book list specs in mm and newton meters).

Unless the plugs were gapped grossly off it shouldn't cause the problem. I would renew the leads and check the color of the spark. You might have a weak spark.

HoneyBadgerRy · April 14th, 2016, 09:04 AM

Also, verify every passage in the carbs. Fully dismantle the fuel enrichment circuit and clean in. Make sure the mixture screw and pilot holes are clean.

SLOWn60 · April 14th, 2016, 09:06 AM

My dollar says you still have dirty carbs. Maybe give @ducatiman a shout and see what it will cost to get it done right? And flush & clean the gas tank & lines and a new fuel filter.
That's where I'd spend my time & money if it were me. (I would do the carbs myself but because I'm familiar with them on my bike.)

April 14th, 2016, 08:28 AM	#1
ACL 9000 ninjette.org member Name: A Location: CT Join Date: Jun 2013 Motorcycle(s): 2005 EX250, 1975 Suzuki T500, 2018 Kawasaki Z900RS Posts: 28	'93 stuttering, hesitating, annoying. A friend of mine recently purchased his first motorcycle; a 1993 Ninja 250. The PO claimed it had "a carburetor problem". The bike would start with some coaxing, but only ran on one cylinder. We went to clean the carbs, expecting them to simply be gunked up, but we discovered they were missing pieces. We used some rebuild kits to replace the missing parts. So far we have adjusted the valves. We have changed the oil with Rotella T6 and a Wix filter. We replaced the PO's Champion plugs with the correct NGKs. We synchronized the carburetors. The bike is a little reluctant to start at first. Even with the choke lever all the way back it wants to die without a touch of throttle. It's my understanding that opening the throttle leans the intake mixture, so I would assume that backing off the choke a little would have the same effect, but it doesn't seem to. Eventually it will idle on its own. If you attempt to ride the bike the power delivery will be very erratic. There is no torque at lower RPM, so leaving a stop can be challenging. When accelerating the bike seems to jerk, or stutter, or whatever word you would use to describe sudden temporary losses of power. This is accompanied by a change in the sound of the engine. It becomes quieter and sounds much more loaded up, like if you'd cranked the throttle all the way open at a low RPM. After riding for a little while it will try to stall at every stop, and has to be kept alive. Choke doesn't seem to have an impact at this point. If you turn off the bike for even a short time, maybe 3 to 5 minutes, it will fire right up and immediately assume the ~1800rpm idle I set back when I thought we were getting close to being done. So I have no idea what's going on and I'm sick of doing things I've done already hoping maybe I screwed them up before and this time it'll all be fixed. The intake boots from the airbox to the carburetor are very old and have no clamps. What are the symptoms of an air leak at that location? The airbox itself is barely secured in the bike. The top anchor is missing, and only one screw beneath the battery connects the whole plastic shebang in any way to the bike, through the rear inner fender thing. The gas that was in it was very old and full of water, but we've added fresh gas twice now, and ridden it about 100 miles in total, so I feel like bad fuel can be ruled out as a cause. At certain points along the way in this process the bike has run seemingly better. Prior to synchronizing the carbs and changing the oil the bike seemed to run smoothly, but wouldn't idle correctly and the clutch seemed to slip (which I attributed to nasty old oil, since the PO did every possible thing wrong). I also replaced the top two vacuum lines on the carbs with some hose I got at Advance Auto, could that have this affect? So I'm running through the possibilities in my head: Carbs somehow still out of sync? Air leak in a critical place? Float problems? If this was my bike I'd have raided a parts catalog and possibly even bought new carbs just to skip over having to deal with this negligent-PO bullcrap, but I'm trying to keep an inexpensive bike inexpensive. What causes a Ninja 250 to start somewhat poorly when cold, die occasionally when warm, and stutter at all throttle positions at all speeds, seemingly flopping from making 5hp to full power abruptly and repeatedly? Thanks for your help, guys. I tried searching around, but I couldn't find anyone describing the same problem, nor anyone supplying solutions I haven't already tried. (I remember when I first got my Ninja I spent almost a month searching for my problem [tight valves] by symptoms and got nowhere, so I've learned that while search is handy, sometimes you just have to ask directly).

April 14th, 2016, 08:37 AM	#2
HoneyBadgerRy ninjette.org certified postwhore Name: Ryan Location: Beaufort SC Join Date: Aug 2015 Motorcycle(s): 05 Ninja 250, 04 KTM 625 SMC, 01 Xc250 Posts: A lot. Blog Entries: 3	First off are you sure it runs on one cylinder, because I'm almost positive it doesn't. I would start off with verifying that all the vacum lines are routed properly, and that there are no vacuum leaks at or after the carbs. If this doesn't solve the problem recheck that all the valves are adjusted properly, and replace the sparkplugs, check the sparkplug leads. __________________________________________________ Because Unregistered sucks at riding.

April 14th, 2016, 09:04 AM	#5
HoneyBadgerRy ninjette.org certified postwhore Name: Ryan Location: Beaufort SC Join Date: Aug 2015 Motorcycle(s): 05 Ninja 250, 04 KTM 625 SMC, 01 Xc250 Posts: A lot. Blog Entries: 3	Also, verify every passage in the carbs. Fully dismantle the fuel enrichment circuit and clean in. Make sure the mixture screw and pilot holes are clean. __________________________________________________ Because Unregistered sucks at riding.

April 14th, 2016, 09:06 AM	#6
SLOWn60 n00bie to wannabie Name: Bill Location: St Ives, BC (Shuswap Lake) Join Date: Sep 2015 Motorcycle(s): 2012 250R (Red), 2005 VFR800A (Red), CRF450X (Red), 2012 F800GS (Wants to be Red!) Posts: A lot. MOTM - Nov '15	My dollar says you still have dirty carbs. Maybe give @ducatiman a shout and see what it will cost to get it done right? And flush & clean the gas tank & lines and a new fuel filter. That's where I'd spend my time & money if it were me. (I would do the carbs myself but because I'm familiar with them on my bike.) __________________________________________________ The Smart Money: #1 - ATGATT, #2 - Training (machine skills and survival skills), #3 - The bike; whatever floats yer boat with the money you have left over
	1 out of 1 members found this post helpful.

April 14th, 2016, 08:53 AM	#3
ACL 9000 ninjette.org member Name: A Location: CT Join Date: Jun 2013 Motorcycle(s): 2005 EX250, 1975 Suzuki T500, 2018 Kawasaki Z900RS Posts: 28	Back when we first acquired the bike it was definitely only on one cylinder because one carburetor was missing a jet. That was the initial problem we spotted, but it hasn't cropped up again since we installed the kit parts. I can check that I ran the lines properly. I will try to make sure there are no vacuum leaks. Would replacing ancient OEM vacuum lines with lengths of vacuum hose that may be narrower than stock cause a problem? I'm 99% sure the valves are good because I triple-checked them before I buttoned it up, but I'll check again. Would improper plug gap do this? I didn't gap the plugs because I couldn't find my gauge. I have new plugs I can put in; I'll gap those correctly.