ccohesh@ucdavis.UUCP (Hesh) (08/19/86)
i've got a suzuki GN400X which is having problems. although i enjoy
working on it, i don't have much time (and even less money!); i'm hoping
that somebody on the net will be able to help me diagnose the problem....
it has 18K miles, and has been well maintained. i regularly change
the oil, oil and adjust the chain, adjust the valves, etc. despite my
care, it has started acting a little funny:
o hard to start
o runs very roughly -- like it's not firing half the
time -- and unsteadily -- the rpm never stays steady
o a slight loss of power (it doesn't wheelie anymore :-)
o bad gas mileage -- down to 50 from 65 mpg
o acts like i need to put on the reserve tank (you know,
when your main tank runs out of gas and the bike starts
surging and nothing happens when you mash on the throttle)
i've made sure that the valves are adjusted (btw, what does a bike act
like when the valve seats are worn?), the chain is adjusted, it has a new
spark plug, the gas tank was flushed, the carb was cleaned (not one speck
of dirt!). i ran through some tests on the CDI (all electronic ignition on
this bike), but nothing is conclusive with just an ohmmeter, and the coil
seems fine (no obvious shorts). the battery seems to be running out of
juice, but i don't know if this is because it is losing charge (magneto
going bad?) or because it is getting old (it is only about a year old,
so i doubt that). i did find some corrosion, though, so that (bad ground)
may have been the cause [of it running out of juice].
i believe that the carb is not the problem -- all the important adjustments
are factory set. i'm leaning towards the electrical system, but which part
i don't know (is it the pickups or the CDI?) i have some suspicions with
the valves, because of an incident about a year ago: i rode very hard for
a few hours, and it required valve adjustment because of it. but it hasn't
acted the same since -- it is more noisy, a little rougher. but i don't
know what a real valve seating problem is supposed to feel like, so i dunno.
a gentleman at the local bike shop says he'll diagnose the problem
for $50. i figure i could start replacing parts and solve the problem
before i spend that much!
i suggest responding to the net, since we all may benefit from some
sound advice.
--
-- Hesh
-- ucdavis!ccohesh@ucbvax.berkeley.edu (ARPA)
-- ...!{dual,lll-crg,ucbvax}!ucdavis!ccohesh (UUCP)
--
-- "M-hM-^VM-$@M-&M-^IM-^U@M-#M-^HM-^E@M-^WM-^YM-^IM-)M-^EO%"
--dob@ihlpa.UUCP (Daniel M. O'Brien) (08/19/86)
> i've got a suzuki GN400X which is having problems. although i enjoy > working on it, i don't have much time (and even less money!); i'm hoping > that somebody on the net will be able to help me diagnose the problem.... 1) check the fuel petcock filter/strainer for gunk 2) try simple compression check: a) pull plugs and check it - good? bad? get a shop manual and find out. b) squirt a little oil into plug holes, crank to distribute, then check again, get any better? then rings gone else valves. 3) how's your floats (i beg your pardon :-) in the carbs bowls? cracked? swelled? taken on gas? float levels ok? jets really clean? run better with choke half on? then carb problem. 4) some people can "read the plugs" to determine what's wrong - i can't but clymer's shop manuals usually have pictures of plugs/conditions. And all this advice is free free free! Good luck. -- Daniel M. O'Brien (ihnp4!ihlpa!dob) AT&T Bell Laboratories IH 4A-257, x 4782 Naperville-Wheaton Road Naperville, IL 60566
curry@nsc.UUCP (Ray Curry) (08/19/86)
First bit of advice is to not try to lean toward carb or electrical yet. When debugging a bike, a general approach is that it can usually be anything. From the sounds of the symptoms, it could be electrical or carb. To eliminate engine mechanicals, run a compression check first. Piston/valve problems will show up quickly then. Assuming compression is okay, odds with Japanese bikes favor electrical with older bikes, carbs with newer. I follow a ritual. First, examine the spark. Put the wire on a loose plug, hold it to the side of the engine and crank it over. Used plugs are best for this test. The spark should be sharp and firm. Multis are nice because they will run and you can see if the spark falls off at speed. Spark problems can be caused by bad spark wires or worn/cracked/dirty caps. The caps usually have carbon resistors in them and go bad in a few years. Other electrical problems to check are the voltage regulator and the diode bridge. The voltage regulator especially will fail by causing lower battery voltage for a while, then none. Check the regulator by unplugging it. Measure the voltage at the battery while running at idle and then at slowly increasing engine speed. 14.5V should be min. increasing with speed. Dont run the engine too fast without the regulator though. 15.5 should be max. Repeat with the regulator in. 14.5 min and 15.0 is a good min/max. This will point out problems with the alternator as well. Since there are generally two sets of coils in an alternator, one for lights and one for ignition, problems can crop up in one and affect the other. Dirt bikes ran the two seperately and a bad light would still affect the ignition. If the charging voltage is high enough, and the battery won't stay charged, the battery is probably bad. They fail because of intermittant use. My street bike keeps a battery 3 to 4 years since I ride every day. A bike that sits for a week at a time will kill a battery in as little as a year depending upon the temperature extremes it sees. One of the new nitrogen filled long life batteries might be better for that case. With the carbs, there are a few things to check. The carb could have some internal passages blocked. The main and idle jets can be removed and checked for particles. The needle and seat for the float should be checked as well as float level. The air screw and be removed and the slide taken out, and air should be blown into the idle hole in the venturi. One last thing to check is the sediment trap if there is one at the base of the fuel valve. If its a vacuum operated valve, check the hose for leaks. Modern gas has a tendency to grow crystals and flakes. If the valve doesn't have a sediment trap, you should add a filter. My last bit of advice is that bad parts can look good and vice versa. Shops also don't take electrical stuff back.
bob@madvax.UUCP (Bob Palin) (08/20/86)
> a gentleman at the local bike shop says he'll diagnose the problem > for $50. i figure i could start replacing parts and solve the problem > before i spend that much! > > -- Hesh > -- ucdavis!ccohesh@ucbvax.berkeley.edu (ARPA) > -- ...!{dual,lll-crg,ucbvax}!ucdavis!ccohesh (UUCP) > -- You don't mention the air filter/cleaner but I'm sure you've looked at that, how about a fuel line filter on the tank outlet - how dirty was the tank when you flushed it ? $50 doesn't get you many parts nowadays specially in the electrical department where things come in expensive lumps, doesn't sound like a bad price but you can't be sure they will find the problem. Let us know the outcome. Bob Palin, Varian Inst. Walnut Creek, Ca. zehntel!varian!bob
ccohesh@ucdavis.UUCP (Hesh) (10/13/86)
this is me: >i've got a suzuki GN400X which is having problems. although i enjoy >working on it, i don't have much time (and even less money!); i'm hoping >that somebody on the net will be able to help me diagnose the problem.... >it has 18K miles, and has been well maintained. i regularly change >the oil, oil and adjust the chain, adjust the valves, etc. despite my >care, it has started acting a little funny: [lots of symptoms deleted] well, i have finally solved the problem: first, the chain, although correctly adjusted, was badly worn. i changed it, and it promptly broke while i was on the highway (yikes. no problems, though). i bought yet another chain, but this time i also replaced the sprockets. surprise, surprise: most of the roughness went away (and while i was waiting for the parts, some jerk stole my turn signals -- it wasn't parked near my house). next, after reviewing all of your helpfull hints (thanks!) i decided that i didn't do a good enough job cleaning the carb. today, i took all the jets out, cleaned them with a rag, put it all together, and tested it... it wouldn't run any higher than 5000 rpm (!). that was easily fixed though: i had forgotten to put in a small plug (you mean all those little parts are necessary ? :-). i tested it again, and now it runs like a dream (and now it wheelies again :-)! so, i've saved myself $50! i appreciate all of your hints and experiences (about 10 came in); they've all helped me properly diagnose the problem. to sum up, the correct diagnosis was: crud in carb, and worn chain and sprockets. oh, and about those turn signals: the dealer says they cost $20 each! instead, i went down to the local car parts store and bought some turn signals for $2 each, and i expect that with another $5 of hardware, i'll have them back in working order (ya, it won't look as good, but hey, it works and it's cheap!) -- -- Hesh -- {lll-crg,ucbvax}!ucdavis!ccohesh -- -- "M-hM-^VM-$@M-&M-^IM-^U@M-#M-^HM-^E@M-^WM-^YM-^IM-)M-^EO%" --