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78 GS550E driveability and startup issue

  • Thread starter Thread starter AOD
  • Start date Start date
A

AOD

Guest
78 Suzuki GS550E
Kerker 4-1 exhaust
stock otherwise
11,700 miles

Hi guys, i just got back from a 60 mile ride on the bike...the first good cruise i've had with the new bike. Here's whats going on:

So the bike starts up okay when cold but wont run well until its warmed up. generally i have to drive with the choke on halfway for 5 minutes keeping the idle around 2500 RPM. once i'm going i usually shut it off while driving, and the engine will then idle down to about 1500 RPM. about 10 minutes of running after that, the idle will go up to 2500 RPM, and remain there consistantly.

My first question is what causes the idle differences when its cold? My idle jets are dirty?

Second situation occured about 15-20 miles into my cruise. I got a chance to get it up over 50, and i went on it a lil harder. The bike sputter, coughed, popped and hestitated at exactly 6000 RPM - ~9000 RPM. I haven't really noticed it do that before, but it would do it in each gear. It would make some power, enough to keep going up in RPM, but it was definitly hesitating a lot.

I don't know if this is a timing issue, but i removed the point cover today, and investigated there. I sprayed some more rust penetrant/lube into the backside of the points plate...where the mechanical advance is. I revved the bike a little bit, but didn't see anything moving in there? its a tight view...but should i see things moving? I held back on buying a timing light yesterday...i want to get one off ebay for cheaper.

Other than that, the bike makes decent power from idle to 6000 RPM and cruises really nice. I'm happy except for the driveability issue. I'm going to note that the bike sat for over a year prior to one month ago when i got it running. I decided not to take apart the carbs at the time, and it ran okay. I have more carb cleaner in the gas tank now. I also checked the plugs this afternoon before going riding...they were a little greyed...no white residue on them, semi black electrodes. i checked the gap on them to .030 inch.

Thanks in advance for your thoughts,

~Adam
 
Hey Adam

Let's deal with the points first... If you take off the backing plate for the whole points/condenser mechanism you will expose the weights on the shart that provide the advance timing. Check to see that those move freely. If so, then without a timing light the only thing you'll be able to do is to set the points gap and static time it. You'll need the manual and a circuit tester. You really won't be able to see anything shift position as the engine revs..

As for the 6000-9000 spluttering... I could make a guess, but best thing is to check the timing first.. If it turns out ok, then you're probably onto the whole carb cleaning and balancing (sync'ing) thing. And you've read about that in my other posts !

With regards to the idle not settling down.. There have been a few posts about that in this forum. I've had the same problem, and I think it was related to the carbs not being in sync.. However, you really should start with a clean carb setup before doing any sync'ing.

So I'd recommend the static timing, then get the timing light from eBay or borrow one and set the timing correctly including the points gap.

Then remove the carbs and clean the jets, float bowls etc. I ended up getting a can of carb dip from the auto parts place and cleaning mine with compressed air etc.. Its surprising the amount of crap and varnish that builds up in the carbs. Be careful with the gaskets etc when disassembling the carbs.

With clean carbs and correct timing, then go about checking the fuel/air mixture.. Again there have been many posts about this process but essentially you start with clean plugs, run it idle speed.. check the colour and adjust. Clean the plugs.. run it at WOT. While at WOT shut the engine off, coast to the side of the road and check the colour of the plugs.. Adjust the needle accordingly.

With clean carbs, correct timing, correct idle and WOT fuel/air mixtures you're then ready to sync the carbs. Only a guess, but I bet that the idle not settling down is related to the carb sync.

Oh, one other thing I from my many carb removals.. check that the vent hose from the #3 carb is hooked to the fuel petcock.. I didn't a couple of times and it starves the engine of fuel. The vacumm off of this line opens the petcock.

Once that's all done.. get a map, a good nights sleep, and take the GS550 for a 1000 mile ride !! Check to make sure the front srocket nut is on first !

Regards,
Tim
2002 Concours
2000 KLX300R
1978 GS550 with 4-1 pipe, pod filters, Dyna 3 ignition, golf tee in #3 vacumm line, and perfectly balanced carbs !!... Still waiting for front sprocket nut.
 
Tim, thanks for the info. I have a Suzuki and a Clymers repair manuals for this bike. I do not know how to statically time the bike. can you walk me through the process for this?

I removed the air filter today, and examined it. It was oiled and grey in color...didn't look so bad. to rule it out as the problem for the 6000 RPM situation, i drove the bike for a minute without the filter on. it drove the same way, so its not a filter problem.

when i did get on it hard (6000+ rpm) it seemed like the engine lost something when it cut out. the tone of the engine changed and it went really flat. sometimes it will bounce and hesitate through the 6000+ points, but this time it went flat.

i dont want to think the 4-1 exhaust could cause this. but i can't believe the engine is running out of air at only 6000 RPM.

i rode it about 40 miles today...drives good from 1500-6000 RPM, so its okay for cruising...but still was hesitant above 6k.

~Adam
 
i'll try something that i dont think is the problem...but i'll switch the bike to prime while driving it, and go WOT. i have the vaccume line hooked into the petcock, and i know it works fine cuz this is the tank off my old GS550E.

~Adam
 
Adam

the static points setting is in the maint/lube section of the clymers.. I think its the 1st or 2nd chapter..

Just to clarify... if you're driving at 3000rpm, and you whack the throttle open does the bike pull cleanly and smoothly until it hits the 6000 rpm range? And when you say it goes "flat", does it feel like its running out of gas when you hit the 6000 rpm mark, or does it misfire?

Regards
Tim
 
boy, today was sure interesting.

before this morning, when i'd whack the throttle, the bike would respond fine up to 6000 RPM. on my startup this morning to go to work, the idle didn't come up high when i choked it. i noticed it running on less cylinders...mainly the middle ones not working right. i can tell when they dont fire because my exhaust header is loose there on both. anyway, so i got it running good...and all four seemed to be going, i headed on the road.

halfway there, it did the 'flat' thing lower then 6000 RPM. i noticed those cylinders cutting out again...and the bikes power dropped horribily. if i got going, and got the RPM's up over 5000 i could hear the two cylinders popping and firing every once in a while. at a stop light, i'd have to keep revving the bike to keep it running, and you could hear the cylinders firing every 2-3 seconds... :oops:

before today it felt like the carbs would run out of gas when it did the 'flat' feeling...and it felt like it was missing when it'd get rough about 6000 RPM. i guess the 'flat' feeling is associated to the bike only running on half the cylinders.

so i'm at work now, and i'm gonna hopefully get the bike started and make the 5 mile ride home with a GS275. :? :cry:

i've decided to switch the bike over to electronic ignition. i am going with a Dyna S, new Dyna 3-ohm (green) coils, and new plug wires. I am probably going to order today. If the bike makes it home...its going to sit a few days. :(

i have to replace the alternator in my car tonight...that's a priority.

~Adam
 
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