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Discussion Starter · #1 ·
Hey everybody -



The VTR250 forum isn't coming up with many answers, so I'm turning to my friends here for help. I think there's a lot more technical knowledge floating around here than over there, so I'm hoping for a fix.



I've had a 1990 VTR250 for about 48 hours now. When I got the bike I got an email from the 2nd owner (I'm 4th) about it.



Bike has 2710 miles and is in perfect condition (other than this problem).



2nd owner had stuck rings, so he had new rings put in, and new front and rear head gaskets.



1st owner rode it for one season then quit.



2nd owner inherited a non-runner, had the carbs rebuilt and tuned, but as it cranks, it'll fire only if the throttle is held wide open. And then it might run for 5 seconds before dying. That's the same thing I'm running into now.



Spark plugs are gapped and have strong spark in both cylinders, so the coils and CDI are fine. Ignition timing could be suspect though.



I did a quick once-over of the carbs after I pulled them last night, but they were *****-n-span clean, no corrosion or chunks of anything. Fuel tank is also perfectly clean on the inside, no rust at all.



Both CV slides are in good shape, move freely, and there are no holes in the diaphragms. The CV slides in this bike have rubber diaphragms and plastic slides, and metal needles, but the plastic slides seem a little stiff when moving up and down.



The PO said he suspected a timing issue (since the 2nd owner pulled the heads). I pulled the valve covers and checked the timing with the rear cylinder at TDC T1 mark, and all the cam sprockets line up with the head surfaces (this is a DOHC engine with chain driven sprockets. 4 cams total, 4 sprockets). I turned it over by hand and the IN/EX valves were opening and closing at the correct times (unless I counted off, but I'm pretty sure I was right).



Today I threw the air filter back on and fired up the bike. It ran at only WOT for 3 or 4 seconds at a time. If you back off the throttle 1/8, it stalls. Rear header pipe was stone cold and the front got warm.



Pulled the air filter and sprayed a bit of starting fluid down each carb throat. Opened each bowl drain to make sure gas was getting to both carbs, but the rear seemed to only have about a teaspoon of gas in it. Seemed suspect to me. Re-pulled the carbs, blew them out with aerosol carb cleaner and compressed air (again), removed all the jets, cleaned them, cleaned the pilot screw holes and adjusted to 2-3/8 turns out (where they were originally). Now I walk inside, eat lunch, have a beer, and walk back out. Now I hit the starter, vrooms to life, revs up to 10k, then starts bogging down almost immediately. For those 5 seconds, it sounded like it should sound. Now, I've been working on Honda motorcycles and riding for 6 years straight.



It seems to be happiest with the choke about half on. Doesn't want to fire with the choke either on or off completely.



Petcock flows well, and now both float bowls fill with the correct amount of gas. Float levels are within exactly 6.8 mm, which is spec. I've had fouled plugs on both cylinders, then replaced, then fouled just the rear, then replaced, then fouled just the front. The front was flooded, then the rear was flooded, and at first, both were flooded.



I don't have any vacuum leaks anywhere either. The needles are in clean and in good shape. Both carbs are 100% perfectly clean. Not a speck of dust anywhere on them, so I have to assume it's something else at this point.



Both headers are still getting hot, but it's still only firing for 4-5 seconds at a time only with the throttle wide open. The rear header got burning hot, which makes me think starting fluid ignited inside the header, which makes me think timing. The front header never got more than hot-to-the-touch. Brand new fresh gas and oil too. If the throttle is held wide open, it's only running at 1500-2k RPM's...not like it's revving.



This thread sounds exactly like what is going on with mine. But checking and rechecking the cam sprockets makes it seem like the marks line up with the top of the head walls evenly.



A rubber sealed compression tester showed 100/120 rear/front, but I could hear blow-by past the rubber seal. My brother will bring over his screw-in compression tester tonight and I should know more then. 188 +/- 28 is the spec, so 160 - 200 is where it should be.



Any suggestions on where to go next? I realize y'all won't be familiar with this engine, but hopefully someone has come across something similar at some point. I did a quick search of the forum but didn't find much.



In a nutshell:



My suspicions are compression, cam timing, or ignition timing. I believe the flooding and fouling plugs are both from WOT starts and idles - too much fuel. Air filter off makes no difference. Bike only starts at WOT, but has fresh gas, clean carbs, low miles, etc.



Bring on some suggestions!! I'll try just about anything at this point.



Thanks in advance!



--jinbtown
 

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Well you sure put a lot of effort trying to find the problem, which does seem to elliminate a lot of things. It could be a timing issue, but not being familiar with the engine I can only go by OHC engines I have worked on in cars :-(



Are you sure there is no vacumm leak, as it sure sounds like that. That or an ignition problem (thats hard to find). I had a problem with my CX500 where one cylinder seemed to not fire (which I used as a crappy excuse to buy a hand held digital scope lol dont tell the wife). Turned out the be a bad connection with the plug wire (thats ok, got my scope out of it lol).



If the plugs are fouling wet it seems like something is messing up the spark (may be timing or an intemittent spark). I would try to find a way of monitoring the spark when it is running (this is an ideal job for a scope, to look for missed spark pulses). Timing could be the issue, but not sure if there is any way of adjusting it without knowing the engine (most just require the chain to se set properly on the sprocket)



Hopefull, someone here will know this engin and be able to offer better help than me :-(
 

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Discussion Starter · #3 ·
So...



I just had my brother come out with me, and we both agree that the cams are off by about a 1/2 a tooth. Unfortunately, the front is off a half a tooth and the rear is off half a tooth. It looks like the rear is a little more off, so I believe I'll adjust that one. When it was running on one cylinder, I'm pretty sure it was running on the front, because that header got warm. So I'm off to adjust the rear!! Pics and video of it running forthcoming hopefully!!!!!!



--jinbtown
 

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Discussion Starter · #5 ·
so it doesn't appear to be the cam timing - I removed the whole top end of the rear cylinder, reseated the chain, retimed the cam sprockets / cams per the service manual specs. Re-gapped the tappets to spec.



Fired it up on starting fluid and it ran for a bit, then put the carbs back on and it ran for about 60 seconds on gas (which is 15 times longer than any previous runs), at 2/3 - full throttle, rear cylinder firing only. Front plug is fouled.



So that's progress at least. I'm hoping the top end rebuild might have re-timed the cams correctly, or they may have been 180* off and I just missed it during my checks.



Whenever a plug is fouled, they're soaking wet...so tons of fuel is getting into the cylinder.



All the jets and the mix screw were perfectly clean when I took them out. 18 months ago the PO had the carbs rebuilt and tuned at a shop, but the bike still wouldn't run. This was after he had rebuilt the top ends, new rings, new head gaskets. Which makes me believe it was timing related (or the shop did a sh*t job on the carbs)



Either way, I'll get new plugs @ NAPA tomorrow (4.89 apiece for NGK's) and see what happens. Before it was only running on the front cylinder...so running on the rear cylinder and for 60 seconds is a big step forward.



Next on the list of things to do is check coils and CDI, although with 2700 miles these should not be an issue. Worth checking still.



I'll keep you updated
 

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Well, you are making progress, just hope its something small.



With the plugs being wet fouled, looks like your getting gas but maybe not spark, so the carbs may be ok. Is it always the same one that gets fouled ? if so try swaping the coils and see if the problem moves to the other cylinder, this would if nothing else allow you to elliminate the coils
 

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Discussion Starter · #7 ·
Well, you are making progress, just hope its something small.



With the plugs being wet fouled, looks like your getting gas but maybe not spark, so the carbs may be ok. Is it always the same one that gets fouled ? if so try swaping the coils and see if the problem moves to the other cylinder, this would if nothing else allow you to elliminate the coils


So each coil is actually controlled individually by the CDI box on this bike - no wasted spark. Swapped coils have been a problem for other non-starters in the past - each coil has to go to the right cylinder.



Plenty of gas in each cylinder, and when I pull each plug they spark hot and white against ground, so I know there is spark in there. I'm still waiting on a compression test...the missing piece of the puzzle.



It's just curious to me - prior to the rear cylinder top end rebuild, I was running on the front cylinder only. After fouling a couple plugs and rebuilding the cams, now it's running on the rear cylinder only. That really makes me hope getting a new set of plugs will at least mitigate these problems so I can start tuning it. But we'll see, once I get new plugs and compression tests done I'll know for sure what it is (or maybe not)
 

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Either way, I'll get new plugs @ NAPA tomorrow (4.89 apiece for NGK's) and see what happens. Before it was only running on the front cylinder...so running on the rear cylinder and for 60 seconds is a big step forward.


After 40 years of not riding I bought a GL500 Silverwing. I had problems and the good folk on this site walked me through all possible problems. One confirmed problem was with the ancient 30 amp main fuse. I finally found that I had 2 bad NGK plugs by using a plug from my son's dirt bike that sparked like a flame thrower when held to ground ( as it did not fit my engine.) Two new plugs and I have been on the road ever since. Billrod
 

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I do not know that bike and I am pretty new to bike mechanics so I could be a few dozen miles off but have you confirmed that the correct coil is plugged into the correct CDI output? You know how on the CX500 it is pink wire to right coil and yellow to left? Are you sure they are not backwards?



It might be silly but that came to mind.
 

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just to rule it out i once had a bike with a bad wiring harness and the cables would pull at full throttle and help it make contact



try using a jumper wire direct from the battery to power at the primary connection to the cdi or ignition source i cant tell which wire but



a look at the wiring diagram should te;; you it could just be a little electrical gremlin i had a cylinder dropping out on my 1970 cl450



after doing everything but removing the head i finally found a cracked bullet connector from the one set of points to the coils,
 

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See if there's any difference when you cover the airbox with your hand or something, so air cannot enter. If it runs better when you're blocking the air flow, then you definitely are either running lean somehow or have an air leak.
 

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Discussion Starter · #12 ·
just to rule it out i once had a bike with a bad wiring harness and the cables would pull at full throttle and help it make contact



try using a jumper wire direct from the battery to power at the primary connection to the cdi or ignition source i cant tell which wire but



a look at the wiring diagram should te;; you it could just be a little electrical gremlin i had a cylinder dropping out on my 1970 cl450



after doing everything but removing the head i finally found a cracked bullet connector from the one set of points to the coils,


I'm very suspicious of electrical gremlins at this point, cold compression (obviously I can't test it hot) is 150 rear / 152 front. Cold is typically 15-25 psi under hot, and that was a dry test as well. So I'm well within specs of 188 +/- 28 psi.



compression isn't the issue.



I'm looking at ignition and fuel delivery again. I really wish I could get my hands on a set of carbs just to test..but I may just buy a set off ebay and re-sell them if it doesn't fix my problem.



I also double checked that the coils are plugged into the right wires from the pulse generators (they are) and the coils are plugged into the right cylinders (they are) and the coils primary and secondary resistances are within spec (they are as well).



On this bike, the CDI controls spark advance I believe. But I pulled the CDI today and it's perfect. I'm off to throw in some new plugs, new battery (been jumping it), new flasher relay and a couple missing fuses (nothing to do with running).
 

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Discussion Starter · #14 ·
--just kidding, electrical problems only LOOKED like problems. Solved--



New plugs and actually grounded coils tomorrow (I'm an idiot...) and we'll see what happens.



I still have a weird suspicion that my electrical problems might be part of it...



At our turn signal relays, we have a ground there. On this bike, we use the ground for a 3-prong flasher.



But when I turn my ignition on, I lose continuity to battery negative on that ground wire. Resistance goes to 880 ohms, which could be faulty ground? That COULD be my whole problem. I'm ripping into the wiring tomorrow in an effort to find all the ground points and clean them. No, wait, when the ignition is OFF I have perfect continuity to battery negative. Anyone know why this is? Does the same thing happen on GL/CX's? Green wire at the flasher relay ---> battery negative: Ignition off --> perfect continuity, ignition on (key on) --> lose continuity?
 

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--just kidding, electrical problems only LOOKED like problems. Solved--



New plugs and actually grounded coils tomorrow (I'm an idiot...) and we'll see what happens.



I still have a weird suspicion that my electrical problems might be part of it...



At our turn signal relays, we have a ground there. On this bike, we use the ground for a 3-prong flasher.



But when I turn my ignition on, I lose continuity to battery negative on that ground wire. Resistance goes to 880 ohms, which could be faulty ground? That COULD be my whole problem. I'm ripping into the wiring tomorrow in an effort to find all the ground points and clean them. No, wait, when the ignition is OFF I have perfect continuity to battery negative. Anyone know why this is? Does the same thing happen on GL/CX's? Green wire at the flasher relay ---> battery negative: Ignition off --> perfect continuity, ignition on (key on) --> lose continuity?


You may want to unplug everything but the essentials, if that's an easy thing to do with this bike. Unplug the headlight, turn signals, everything but power to the starter and the CDI box. If that starts the bike up just fine, then you know it's a short outside of the ignition system.
 

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Discussion Starter · #16 ·
You know, it's AMAZING how much havoc leaving the frame ground off can cause.



ALL my problems went away in 30 seconds. I spent 3 hours going over electricals, the entire wiring harness, before I found the stupid 12 gauge green wire that was just hanging there.



Thanks PO.



It's a good reminder, nonetheless, to check the simplest and easiest things first.

Now, to deal with this rubber diaphragm that's sticking....



Thank you to all that pointed me in the right direction - incredibly helpful. I love this board!! I'll have a new GL soon enough (250cc isn't too good for hauling the trailer around
)
 
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