79 GS1000 - sudden loss of power & backfire

[whiteboyslo]

I need a little help.

Background:

I just bought a used 79 GS1000 a week ago, and this is my first bike ever! If the odometer is correct, she has just a little under 60K miles on her. I'm the 3rd owner. The 2nd owner bought the bike a few months ago, basically brought it back from the dead with new plugs, battery, tires, etc. The bike's only noticeable issues (aside from being just a bit too ugly for her own good) are a VERY noisy clutch (think rock crusher) and a leaky tach cable.

Issue:

So, when I first got the bike, she had GOBS of power. Full throttle damn near scared the bejesus out of me, and she didn't hesitate one bit. I went to ride her this morning, and something's definetely not right. The bike idles fine, starts fine, and revs up in neutral ni problem, but she has maybe 2/3 of her power, if that. WOT from a slight roll causes her to bog and die. I'm fully in the throttle going up some hills, and in general she just doesn't seem to happy to go forward. She also seems to have developed a little bitof a pop on decel from high revs, which is slowly working itself into a little but of a backfire

What I've done so far:

- Cleaned the plugs. Outside were fowled (black). Inside were somewhat white, but nothing out of the ordinary for lovely CA fuel. Plugs are only a few months old

- Filled the tank. 91 octane (is that right?). Good stuff from Shell, where I fill all my vehicles and have for years with no issues

Any ideas? I know the previous owner didn't touch the carbs, but why would the bike go from 'awesome' to 'crap' in one day?

Mike

 

[Guest]

First off, congrats on the new bike!! :-D Second, if you have not taken care of the clutch, please do so...you do not want that clutch basket desintigrating on you...major bad juju.

Carbs are not my strong suit when it comes to diagnosis, so Keith(GSResources Carb King and Undisputed Heavyweight Champion :-D ), RenoBruce, or somebody else much smarter than me....please chime in. I do not wish to lead a new guy astray!!

check the plug caps on cyls. 1 & 4 for cracks?
check coil for cyls. 1 & 4?
stuck float needle valves?

Hope I helped!!

Mike

 

[Corax]

I had this exact same thing happen to me 2 years ago. Engine did not have any compression so I pulled it &tore the whole thing apart. Found out the valve lash was too tight. Check for compression & if it's low, pull the valve cover & check valve clearance

 

[Big T]

Also, check the inside of your gas tank. Is it clean or rusty?

It sounds like some debris got into the carbs and clogged the jets. Try draining a carb or two and capture what comes out for inspection.

 

[SPARKSS]

Howdy Mike. With an abrupt loss of power, the first thing I do is notice whether it sounds right - 4 cylinders contributing or perhaps it's now a smooth running 3 (there'll be a distinct change in the sound as well as the power). Touch the exhaust pipes briefly (or shoot 'em with an IR temp gun if you have one)......Are any markedly colder (not firing)? With the engine running (and maybe with what you know above), remove the plug wires one at a time and look for a consistent RPM drop (contributing ok) or NO drop (that's your dead cylinder). Unless you have reason to suspect otherwise, with a dead cylinder, I'd try a new plug irregardless of what it looks like. IF you find 2 dead cylinders (either 1+4 or 2+3) suspect a common ignition failure here.....point open or closed for that pair or bad coil.

Is there any new or noticeable mechanical noise associated with this recent loss of power? Does the bike appear to have good electrical power (starts good....good lights etc)? Just a couple of cents worth

 

[whiteboyslo]

actually, i DO have a IR temp gun. bought it for the track for my other toy, but i guess i've found a new trick.

the neck of the tank (from what i can see), has some spotty rust. i suppose it's possible that some particulates got in and are now blocking a carb or two. i'll do a fuel filter replacement and likely some new plugs as well since all that can't cost all that much.

the bike sounds fine. it's maybe a little raspier, but there's no hiccup or stumble. she'll go right up to redline if i ask her to; i'm just not getting the power on i KNOW she has. i'd almost suspect a slipping clutch, but the revs don't slip like i'm used to on a car AND the recent of addition of the popping/backfire leads me to believe something else is going on.

i'll also try a compression test while i'm at it. i'm pretty sure i have a compression tester.........somewhere.

little late tonight to start playing, though. i'll start first thing tomorrow night after work and report back on what i find.

thanks guys!

Mike

PS - while i have some attention here, i have some general questions about other maintenance on the bike. i've never adjusted valve clearances on anything before, nor have i eve rrebuilt a carburetor. all of my vehicles have been fuel-injected cars where the work's been fairly simple. turn a bolt here, cut here, grind there, etc. am i getting in over my head in trying to perform these basic maintenance jobs on my own? if so, what should i expect to pay a shop for this? i can basically change the oil and plugs no problem, but anything beyond that i'd rather leave for someone who actually knows what the hell they're doing. any recommendations for shops in the San Diego North County area would be a HUGE plus!+

 

[SPARKSS]

Sllllllooooooowwwwwww down Mike One thing at a time! First, a slipping clutch is like any slipping clutch.......revs will indeed be higher than calculated when it slips (same as your car experience). Don't start ripping carbs apart and deciding on compression results yet. Concentrate on the problem and it's history......reread what I told you and try out your IR gun (I shoot the pipes just as they turn downward). DO NOT drive the bike in this condition until you determine the problem. You noted the change in exhaust note.....this may be a key to it now running on 3 as I mentioned. Reread my post and let us know what you find out.

If you're not patient enough to learn about your bikes systems accurately and take small steps at first to repair.........AND competent enough (at this time) with using tools to do the work you may need, then you should hire a pro or ask for assistance from experience to make your repairs. If you have no patience and a big bank roll then by all means let the pro's handle it and enjoy the driving For what it's worth

 

[Tom MLC]

Simple stuff first, Mike. Replace that fuel filter. It may be clogged. Check your fuel lines for kinks. Make sure it's not routed with a high spot, resulting in a bubble in the line. Check the vacuum line for kinks or cracks. Check the petcock for clogs or a defective diaphram.

 

[whiteboyslo]

http://www.thegsresources.com/_forum/showthread.php?t=109941

well, i must admit this bike felt like a bad idea from the get-go. realistically, i just don't have the time, patience, and money to take on a project like this. i guess i got a little caught up with the whole family starting to ride and wanted to partake, but this is just a very bad time for me to have another money pit.

my loss, your gain.

Mike

 

[Guest]

If it's a sudden problem I'd check the petcock and clean the petcock screen especially if you see rust in the tank. When I had petcock problems it lost alot of power all of a sudden. Popped on decal and generally ran like crap. New petcock and all was well.

 

[KEITH KRAUSE]

1 and 4 plugs are black, bike is backfiring more and more, sudden loss of power.
Sure sounds like a coil. If the coil is good, then points are probably badly pitted too/bad condensor.

 

[whiteboyslo]

ok, i've slept on this. i'm still apprehensive about spending a ton of money on this thing, but i'm willing to give some stuff a shot. i don't think i'm gonna have people lining up for this thing soon anyway.

so, i'm going to go home tonight and try shooting the pipes with the IR thermometer. i'm also leaning toward fuel-related issues as all of my woes seem to have developed right around the time i put in my first tank of gas.

let me go through my scenario from yesterday to see if this sheds light on anything. it'll also give you perspective on why i just gave up and decided to throw this thing up for sale:

rode her to work yesterday. less than 5 miles one way, no freeway. rode fine, with the exception of the low power. got to talking with a guy at work who rides dirtbikes, and he started asking about the petcock, which lead to this thread:

http://www.thegsresources.com/_forum/showthread.php?t=109894

turns out, i've been riding in 'prime' for at least a day, maybe more. went out to the bike, flipped her to 'ON', and walked away for a few hours. went to leave last night, and the bike just would NOT stay running! at first, she wouldn't fire up, which is odd because the one thing this bike always does for me is fire in less than a second of thumbing the starter. FINALLY got her running and starting to warm up when she died. i could get her running again, but not happily. revved the snot out of her, and she'd do that just fine, but once i got off the throttle, she'd die. after FINALLY getting her to stay running at idle, i rode her around the parking lot at work to make sure she'd stay running. seemed fine. even shut her off a few times and started her again. no issues. i got out on the main roads and got maybe a mile from work when she just died. pulled off a side street and tried to start her again. no luck. finally flipped the petcock to RES and she came back to life. so, apparently, the whole issue was being out of fuel? odd with only 120 miles since the last fill-up, but i may not have topped her off completely. but what i don't get is how i could get her to run for so long previously. my experience with cars is that when they run out of gas, that's it. you can crank your life away, and the dang thing won't turn back over because, well, there's no go-juice.

so i got her home after stopping to fill up the tank (which is oh so fun. i'm sure you're all familiar with the new gas pump nozzle designs and how much a PITA they make it to fill a gas tank, esp. on bikes). again, she ran OK, but was still down on power. i ran out to get the parts i had ordered to fix the leak around the tach cable seal and to get some new plugs (NGK B8ES, i think). got home and put the plugs in (gapped at .028"). the ones i had JUST cleaned up the day before where showing the same symptoms again in just a day's-worth of riding. outside are very dark. inside are a little chalky, but what i would consider 'normal' on CA gas. new plugs didn't fix the issue (i know they're only a symptom anyway).

so, giving up on that, i went to start on fixing the oil leak, at which point i came upon the straw that broke this camel's back. can anyone tell me why someone would design a vehicle where nearly every piece of hardware is a phillips-head screw? could you choose a worse design? i mean, a hex bolt works OK over and over again, as does an allen bolt or even a torx bolt, but a PHILLIPS-HEAD? cripes! turns out someone had apparently tried to fix the thing before me and had royally stripped the bolt already. i tired to get some channel locks on it. no go. it's in just the 'right' position where the frame gets in the way from the side and the front wheel gets in the way from the front. i tried a Craftsman screw extractor set that has bailed me out more times than i can remember. no go. just stripped the thing out worse. i would have just used a dremel tool to cut a notch in the head, but i was out of cut wheels and it was getting late and dark at that point and i had just about had it. i got frustrated and decided to list the bike for sale. maybe the smartest thing i could do, maybe not.

anywho, that's my long ramble rant. now, some questions:

1) if it is the petcock, do you guys recommend rebuilding it with the kits i can find on ebay all day long for $25, or should i just pony up for a whole new petcock?

2) where can i find a fuel filter? everywhere i look shows it as being discontinued? does anyone have the PN of, say, a FRAM filter or something i could use in its place?

lastly, i've made a soft appointment with a guy who works at a local major cycle shop and does some work of his own on the side to look the bike over and give me an honest assessment of what kind of shape it's in to detemrine if it's even worth it. that comes next week. if he has good news, i may keep it. otherwise, ........

Mike

PS - i already ordered up the hex-bolt replacement kit a couple of days ago, do if i ever DO get these screws out, i'll be sure to replace them with something a little more adequate.

 

[Tom MLC]

Mike, long rant. Frustrating story. I can only answer with "I feel your pain". Most of us here have been down this road. It comes with the ownership of a 28 year old bike. The rewards are worth the pain though. Believe me. Just wait until you get her dialed in. You'll be the happiest kid on the block! And you will turn heads witht that old GS whereever you go.

To answer your technical Q's, get a replacement petcock. www.flatoutmotorcycles.com or www.bikebandit.com are good sources. Bikebandit is more expensive, but they're right there in San Diego. 120 miles on a tank is a bit low. But if you have crud in the tank, it will settle and clog the lowest part of the petcock screen.

Every M/C shop I've been in sells small in-line fuel filters. They come in a couple of sizes. Get a larger one.

Keith's call on the ignition sounds right to me. I guess I missed that last night. Dirty, pitted points. Bad condenser. Bad coil or wiring. Definately stuff to check.

Good luck.

 

[whiteboyslo]

ok, i'll plan on a whole new petcock and fuel filter. if someone comes along with enough money in hand to make this go away, i may take them up, but having something to tinker with in the garage won't kill me, i guess.

what ID is our fuel hose? 5/16"?

and how do i go about checking a coil? i know i learned once back in HS shop class, but that's a wee bit back.

*starting to get the motivation*

Mike

 

[Guest]

Yes 5/16" is correct.

 

[Tom MLC]

Easiest way I know of to check the coil is to look for a strong spark. Take 1 & 4 spark out and lay it across the top of the motor. Crank & watch the spark. Looks for a strong spark & a consistant one. If the spark is weak or intermittent, check the points & condenser.

You could also use a timing light. Look for a consistant flash of the lamp. This would be a good chance to check your timing marks while you are at it.

 

[whiteboyslo]

ah, timing lights, points, condenser.....

this is all starting to remind me of my old 71 Ford pick-up that my dad and i spent a majority of our free time working on. never did run right, but it was fun to do nonetheless. i suppose if i approach this project in the same light i'd enjoy it more. of course, back then, the truck was my only mode of transportation. now i can do it purely for recreation.

step 1 is to go home and do a compression check, though. if this motor's headin south, i'm probably biting off more than i can chew.

thanks for all the help guys! PLEASE keep it coming!

Mike

 

[whiteboyslo]

OK. had some time to play with the bike tonight. here's the rundown.

ran a compression test, and the numbers look good. they were all 150psi +/- 5psi. here's my method. please critique:

1) started the bike and let her run for about 5 minutes at least. i let her idle to the point where the bike would idle steady without choke

2) shut the bike down, remove plug wires, and remove one plug. install tester

3) cranked the bike at WOT (wide open throttle) until the gauge peaked out. tapped out somewhere around 150 for each one, give or take a tick mark.

so, i THINK those numbers are good, right?

i also took some IR temps of the pipes right at the initial down bend. all were very close in temp to one another. they seemed to hover somewhere around 500 deg F, but don't hold me to that. i question the accuracy of my IR, but the consistency of the numbers tells me i'm firing on all cylinders.

replaced the fuel filter. the old one seemed to actually be fairly new and in good shape. the new one flowed more when i gave it the old 'puff on one end' test, but not by much. also checked the petcock. with the fuel line disconnected, she didn't leak any at 'ON', but POURED at 'PRIME'. that's good, right? should i still be thinking the petcock is a concern?

the bike still isn't up to snuff, though. it starts quickly, idles well, and revs up quick. there's no wierd thump to the idle to indicate a non-firing cylinder, but there is a bit of a pop. i took her for a quick ride on the cul-de-sac, and she's still hesitant and lakcing power. when i hit the throttle from a low speed, it bogs for a sec and either dies (if it's low enough speed) or hesitates but then surges through.

so, where should i be looking now? petcock still? points maybe?

Mike

PS - the numbers on the cylinders look good and give me hope that this bike isn't a lost cause. she'll probably stay.

 

[KEITH KRAUSE]

You could have more than 1 problem. Hard to say unless you troubleshoot and eliminate things.
If there's any tank rust, a clogged petcock will cause problems obviously. The cure is to seal the tank, not a fuel filter.
Part of your story describes the bike responding well to revving it hard, but then it wouldn't idle right after that. So it responded well during a moment of higher fuel need, but responded poorly during a low fuel need. Doesn't sound like a clogged petcock to me. Also, any petcock issues wouldn't cause 1 and 4 plugs to run rich/black. Only poor compression, weak spark, or jetting issues would cause that. Yes, all 3 causes should be checked, but since one coil happens to fire 1 and 4, the most likely cause is a weak coil or bad points/condensor. If you have the tool to check compression, then do that first because it's simple and quick to do.
Lots of info here on checking things. A good manual will also tell you how to test coils, etc. Check the primary side terminals for correct resistance range, then check the secondary side (plug cap to plug cap). Clean/tighten all connections first (plug caps too) and be sure the battery voltage is OK.
You can also swap the coil wiring and plug caps around (1 and 4 swap with 2 and 3) to see if the problem follows the swap.
120 miles 'til reserve isn't unusual if a weak spark is causing poor combustion at 2 cylinders.
The least likely cause for the black plugs is the carbs. Possible, but I'd focus on the electrical and compression check first because it's not that hard to check and should be done as normal maintanance anyway. If all checks, then focus on the carbs.

 

[KEITH KRAUSE]

By the way, I just noticed you posted as I was replying to older info.