79 GS1000 - sudden loss of power & backfire

[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.

[whiteboyslo]

ok, i'll start looking into the ignition system. i suppose the quick and easy thing to do would be to check out the points/condenser and eliminate that first. cheaper anyways.

also, i got a little confused on all the lines underneath the tank last night. i have one vacuum hose that was hooked up to the petcock. it runs down to the carbs right next to the fuel line. i also have (2) hoses just hanging off the carbs, one on each side. do these get hooked up to anything?

Mike

[shawzygs850]

Two hoses you refer to are breathers and don't get hooked up to anything

Great thread here, I am in similar waters. Hang in there - the guys on this board are your saving grace. Once you figure this out the satisfaction is immeasureable and will put a perma-grin on for days.

[whiteboyslo]

ok. thanks!

i may hold off on doing much more to the bike right now. i have an appt to have the bike looked over by the head mechanic of a local dealership who does work on the side in his house. i may have him tear down the carbs and rebuild them because i'm not comfortable with doing that. hopefully he can help me narrow down this problem as well.

i'm just stoked the compression test came back so well!

Mike

[shawzygs850]

I just rebuilt carbs on my gs850.

DONT BE AFRAID to try this yourself!! it really isn't bad and it's fun to boot!!

The carb rebuild section on this board is the ticket - with that and the forum you don't need anything else save patience and courage.

You can do it man. Best way to learn.

Worst thing you can do is wreck the damn philips screws (or jets themselves but not as likely). A pro can do the same depending how bad they are jammed. Impact driver saves the day (ask me how I know)

I cleaned my carbs for about $65 including cleaner, new o-rings, and new socket-head screws to replace the philips. Other guys have done it for much less.

"Only thing to fear is fear itself" no kidding.

HAVING said this, please get advice from other more experienced members to confirm that you should in fact strip and dip the carbs. I don't want to point you in wrong direction if other probs exist (i.e. ignition). It sounds like you may have other gremlins to sort out before carbs. I just want to point out that you can do it yourself with confidence.

[whiteboyslo]

well, from my readings, this is something that probably should be done on any bike after a while, especially if it's been sitting.

the previous owner got this bike up and running after several years of isolation, but he admitted he hadn't touched the carbs yet. even if it doesn't 'solve my problem,' it's probably a good idea.

i wouldn't mind doing it myself, but i'd rather watch someone do it once who knew what he was doing.

and yes, i bought an impact screwdriver last night. already stripped out one screw. won't make that mistake again!

Mike

[whiteboyslo]

i think it's the points on the 1-4 side. they don't look too good. ordering up new ones, and a condenser for good measure.

to clarify, i opened up the ignition side and checked out the points on 1/4. they looked clean and somewhat new, but since that bike never sees any outside environment or engine oil, looks can be deceiving. the contacts on the point aren't lined up with one another. you can see the mark the one is leaving on the other when it smacks it off-center. the magnet that rides on the hoodily-doo in the center is not all that worn, but what's really wierd is after i took the thing off, i could NOT get the damn magnet to ride perfectly flush on it once i tightened down the holding screw. it just won't happen, unless my point gap is supposed to be 1/4"!! looking at the backplate of the points, i think it's bent. did i do it? i dunno, but it needs replaced.

it's a start, and would explain why 1 & 4 look fouled while 2 & 3 look OK.

so, points, condensers, and go from there. maybe a coil, but i'll check 'em first by pulling the old switcharoo.

Mike

[whiteboyslo]

back from the dead, in more ways than one!

so the bike and i spent some quality time together tonight. i started out by giving her a nice oil change. i used Valvoline 4-stroke Motorcycle 10W40 and an OEM Suzuki filter. good? oh, and i also replaced the drain plug with a magnetic one.

then i got to the good stuff. first up was the ignition work. i replaced the condenser and points for 1&4. i followed the procedure exactly as described for the Clymer's manual. went to fire her, and she didn't even try to fire. hmmmm.....

upon further investigation, the points for the 2-3 side didn't seem to be moving at all. perhaps i moved them the other day when i tore it all down? dunno. but no biggie. i had already bought new points for that as well, but felt i didn't want to tempt fate by doing more than necessary.

so, in went the 2-3 points per the Clymer's. still nothing. i hooked up the timing light, and i was definetely getting spark to the wires on all cylinders.

discouraged, i took apart my hack job of a fuel line/filter switch from the other day with some brand new 5/16" hose (no filter). she fired on the first try! i dialed in the timing (again, per Clymer's) and revved her up a bit. the hesitation is gone, and no pop.

a quick ride around the block says she's pretty much back to what i remembered. i have a new fuel petcock coming, as well as a fuel filter and other knickknacks. i hope to have her on the road by the weekend in time to do some riding with the folks.

thanks to all for the help! this definetely was a rollercoaster ride, but i'm glad i stuck it out.

Mike

[KEITH KRAUSE]

Glad you have it running better. Fuel filters are nothing but trouble.
I still wonder why the dark plugs at 1 and 4 though.

[whiteboyslo]

i'm thinking it was from the crappy points for those cylinders. not sure, though.

the laundry list of stuff that needs done on this bike is quite long. next up is new front brakes (pads ordered this morning), a noisy clutch, and fixing the oil leak around the tach cable (which should be an easy job, but the screw holding it to the block is stripped. go me). then there's the cosmetic issues.......

Mike