1982 Suzuki GS550E - Ideas Please

[mattb31daytona]

Both me and my local Jap bike garage in the UK are completely bemused by what is happening with my 82 Suzuki GS550E.

Bike was running fine but suffered a suspected pilot jet fuel blockagewhen I was leading a rememberence day club run -limped home carb's removed en masse stripped and noticed very slight evidence of fuel pipe rubber in bottom of float chamber.Bank of four carb's taken to garage for ultrasonic cleaning new fuel pipes, gaskets etc float heights checked and float chamber levels all set up as per specifications.

Bike started on button and quickly settled to 1000rpm tick over with instant response on throttle right through rev band both steady and bliping throttle sounded really great! Took her out on the road and pulls away great until 4000 revs (50 mph in top) and then nothing won't rev under load in any gear above 4000 revs. Stripped again and fuel system totally rechecked all spot on - new plugs fitted just in case and I noticed left hand pot running correct pots 2,3,4 rich, but I had been trying to ease more revs by opening throttle etc..

Also tried playing with choke at 4000 rpm makes no difference whatsoever doesn't lift or splutter - it is the 82 model so has transistorised ignition, but as I said starts on the button and really sharp and instant response both in neutral and in all gearsbut only up to 4000 rpm / 50mph.

Really is a head scratcher anyone any ideas - have looked for a specific Suzuki site like yours in UK but none exist that cater for the older machines.
So hope someone out there can offer me some help and guidance.

Matt

[Griffyn]

Check for vacuum issues. Boots, O-rings, etc. Chances are you have a leak.

Also check valve adjustment just because it can make a difference too.

[JEEPRUSTY]

I had a similar symptom form my bike when the plug caps finally gave out.
Worked fine at low RPM and sputtered and eventually died at higher rpms.

Sucked a lot of gas into the cylinders and complicated things by making them a bit wet.

[Mop Bucket]

No expert, but mine did that when crap was getting into the carbs. Cleaned them 4 times till I found rust under the botched tank sealer. Had to do the 24 hour carb dip and blow out all the holes with carb cleaner. So, getting rid of the rust and cleaning the carbs fixed my issue.

[mattb31daytona]

Thanks - the amount of times these carbs have now been stripped and cleaned including ultrasonic cleaning I really hoped the carbs could stay in situ as they are such a pig to remove / replace. Spark plug caps Ihadn't thought of and worth a try although the difference is there is no worsening, coughing, spluttering ......just immediate brick wall at 4000 rpm.

Any other thoughts?

Matt

[jabcb]

Had a somewhat similar problem on my 82 GS550L.

Acted like it had a rev limiter around 5k rpm.
Carbs had been overhauled & had replaced the plug caps.

Problem was a combination of voltage drops & the igniter.
Solved with the relay mod & Dyna S ignition.

Am a newbie working on GS bikes, but it does seem reasonable.
Dwell time decreases with increasing rpm, so at high rpm a marginal ignition system might not have enough dwell time to produce a good spark.

[tom203]

I'd suspect the ignitor too- bike needs full advance by 4k rpm or it won't be happy. Try to borrow one to test.

[mret430]

Even though you redid carbs try running some Seafoam engine cleaner in the gas. I was actually able to avoid a carb pull as I ran a couple of tanks of gas with 4-5 ounces of Seafoam.

Burned out alot of garbage and now I run 2 ounces per tank on a regular basis. Worth a shot.


Ed

[bonkas]

Have you checked the output from the generator ?

[mattb31daytona]

4 into 1 Motad Exhaust is clear and Generator throws out plenty of Juice.

What is the ignitor ? I have had the right cover off and it has two pick ups either side - are these the ignitors' it also has the mechanical advance retard weights which turn freely and spring back under their weight fine, I don't have a strobe light but as the engine in neutral revs right through the range and responds perfectly surely the advance retard mechanisim is proven to be working.

What is seafoam? I am guessing it is some from of petrol additive which is supposed to clear the carbs etc when the bike is running....but the problem lies in the term running as although fine to 4000rpm I am not sure that I wish to venture too far from home.

Yesterday spent another three hours messing about, tank on tank off in order to access the pilot air screws as the Mikuni carb rebuild link states that the main cause of poor running resulting in either poor starting on lack of power when cruising is the idle screws - tried various combinations from lean to rich and everything exactly the same - nothing over 4000 rev and to really cap it all when I was a couple of miles from home the clutch cable broke.....................snap.........PUSHING THE GS550 home when you have lung cancer is something I can't recommend!

I still hope to eventually get it running otherwise I will have to put it on E Bay as an ideal bike for riding round town (sub 50 mph) - but not sure anyone would bid.

Thanks again and if anyone has further ideas please keep them coming!

Matt

PS sorry about delay in replying the site decided not to accept my password.

[mret430]

Never give up, never surrender! Seafoam is an engine cleaner and fuel stabilizer, fyi. Air/fuel mix screws seem to do well with 2 1/2 turns out each. I also found on my 750 that once the carbs got cleaned out I then adjusted the valves and this was an improvement.

Try pulling the air filter out temporarily and give it a short run; maybe your starving for air.

[bonkas]

Check the vent in the tank cap.

[Crankthat]

I am not sure what RPM the jets change over but a jet clogged would be my first guess.
My second after reading JeepRusty replies makes me think spark/time.
I have been able to diagnose a clogged jet buy taking a laser thermometer to the headers and finding the correct carb by temperature comparison.
Possibility may be able to diagnose better if the problems are coming from one carb with a blocked jet, (would think only one header low temp) Or from a set ( two pipes from the same coil with low temps leading to think problem with Fire system)