NEED HELP with engine issues 1974 GT550

[BDcycles]

Here is my problem. I have a 1974 GT550 that does not run the way I feel it should on the center cylinder. The bike is hard to start and once it does it the center cylinder doesn't run at all like the left and right cylinders. At idle it seems like the left and right cylinders fire something like 10 times for every one time the center cylinder fires. If you bring the rpms up it seems to fire more often but still not as steady as the left and right. I have a set of Jemco pipes on the bike and it is easy to hold your hand over each pipe and feel what it is doing. After several minutes of idling the left and right pipes are good and warm but the center pipe has barely warmed up at all. I feel I have covered the bases of fuel, compression and good spark at the right time several times over yet still my trouble persists. At one time the bike ran well with the set up I have. To eliminate some of the questions I may be asked here is a short list of some more details.

Compression is an equal 125psi across all 3 cylinders.

I have disassembled the carbs several times verifying all jets and carb passages are open and clear.
Jetting= Slow jets are 30 L&R mains are 102.5. Center main is a 100. air screws 1.5 out

I have set the timing to fire each cylinder at 3.37mm before TDC. I replaced the battery with a brand new battery. I replaced all the points and condensers. New plugs. I swapped the center coil and wiring with one from right cylinder swapping the leads at the points and moved the wires within the harness and swapped the plug wire to "trick it". I even replaced it with another coil all together. I even made sure my new battery was fully charged and disconnected EVERYTHING from the electrical system except for the hot lead to the starter relay and then ran a designated lead directly to the coils.

With everything I have done it still runs exactly as I have described.

[pearljam724]

Timing is off. Despite what some people say. The marks are not always accurate. For most bikes, I'm sure they are. Get yourself a dial gauge and a timing light. Very simple to learn to use. Despite the battery being new. It can have a dead cell. Regardless, if it holding a charge, etc. You have to test the battery under load, idle and mid Rpms to check for a dead cell and that the stator and rectifier is charging the battery or not frying it. Double check the 3 point wires that run under the left side frame cover. Sometimes these wires aren't locked into the sockets correctly. Someone connects sockets and it pushes the spades a tad too far out the back side of the socket creating a bad connection. Never, count out a new battery. Trust me on this. You have to properly test it. New and holding a charge, means very little. Using a multimeter to test components on these bikes is must. It will tell you what electrical parts are or not doing correctly. Also make sure the points for center cylinder aren't grounded to the felt mount.

[yeadon_m]

I was going to suspect coil or HT lead or plug cap or plug, but I think you've eliminated all of those? I've several times had dodgy lead / cap paths that sound like your issue.
If its not that, I suspect the carb, despite your cleaning it. Its easy to still have a slight blockage in the pilot circuit. The most reliable test is to squirt carb cleaner into the pilot air intake one at a time and, holding the throttle open, closely inspect the spray patterns from the twin holes in the engine side carb mouth. If they squirt the same on all 3 carbs, you're good.
If you ride it and are at middle throttle or more, does it pull well? and after a ride, is the centre pipe as hot?
Trying to work out if at higher throttle (not higher revs, thats irrelevant to carbs) it runs well, as it gets onto the main circuits.
Good luck!
Mike
ps: to the point about the battery, yes, do not assume. Measure the voltages at the points, in turn, held open by business cards, ignition on. They will usually be 1-2V below battery positive but see if they're the same. Its possible for the points to coils loom bullets to get a bit corroded. There are three bullets behind the airbox.

[BDcycles]

I spent the day working on the GT 550 and still no luck. In an effort to keep my original post to a reasonable length I didn't list EVERYTHING I have tried to fix the trouble. In the past, using a multimeter I have checked every electrical component and wiring for resistance, continuity and voltage where applicable. With both the new and old battery I read just under 14volts after bringing the RPMs up. I don't have a load tester for the battery which is why I bought a new Motobat battery in case of a dead cell but I can make an effort to eliminate that possibility on the new Motobat battery too.

Although I have done both before, today I verified each cylinder is timed at exactly 3.37mm before tdc using a dial gauge in each cylinder. I also removed and disassembled/cleaned the carbs paying special attention to the complete pilot/slow circuit. I also had the same thought about the cylinder not firing until it started pulling thru the main circuit and in addition to today I have checked this in the past too.

When I ride the bike the center pipe does get hotter than it does at idle but still not as hot as the left and right pipe. You can actually feel a large difference in the temp of the exhaust gasses leaving the left and right pipes compared to what is leaving the center cylinder. I did notice today that when reving up the bike that the center pipe is spraying oil onto my hand whereas the left and right do not.

Could a blown crank seal on the center cylinder be a possible cause of my trouble? Would a blown crank seal still allow the cylinder compression to be acceptable? How about a defective SRIS valve?

Thanks for the help and I hope we can get this resolved.

[pearljam724]

Cylinder compression is related to piston rings, cylinder wear, cylinder head and base gaskets. Read and compare the 3 plugs to verify one is not reading too lean compared to the others. If one is and your confident that all 3 carbs are in good order. Air adjustment screws and slides are properly synched to one another. That is a first sign that a seal is shot. If a very lean plug rears its head. It's time to do a compression test and most likely you'll see that a seal or seals would need replaced. If a plug or 2 is consistently reading too lean knowing the carbs are set up right and all 3 air adjustment screws should be fairly close to being adjusted the same. If you find that one air adjustment screw needs to have a big difference in adjstment compared to the others for that plug not to read very lean. Then that cylinder's crank seals are subject. Then it would be best to perform a leak down test. You test the battery under load by verifying the voltage doesn't dip below roughly 7-9 volts when the motor is cranking over via the electric starter. If the voltage doesn't dip below that. The battery is good in regard to a dead cell. If a cylinder or pipe is not firing correctly or getting hot enough. It's an electrical issue. Timing, battery, points, coil, plugs, wiring, etc. Crank seals don't effect a cylinder firing or not. Electric mainly does. When seals are shot. The bike will still, start and run correctly. Until a piston seizes due to lack of lubrication to the cylinders. Due to that cylinder running consistently too lean from a bad seal. 2 strokes spit oil out the exhaust all over the place when that cylinder is running on the rich side. Which is fine, depending how rich. They all spit oil and smoke a lot when the engine is under operating temperature. If it continues long after the motor is warm. The cylinders are running too rich or cylinders may be bypassing crank oil due to bad seals. Reading plugs will accurately tell you what is going on with each cylinder individually. Sorry, for the novel. Just trying to help you.

[yeadon_m]

One rather coarse test on seals is to remove the carbs then turn the motor over by hand while holding a hand firmly over each cylinder intake, feeling it suck on your hand during the piston up stroke. If at TDC you remove your hand you will hear a pop. The key thing is, do all cylinders feel and sound the same? it is only a gross test but if you cannot tell them apart, my guess is its something else.
How does it run on that centre, when bone cold and on choke? does it fire and get hot during that brief running before you have to shut off the chokes?
Mike

[tz375]

It could be an SRIS issue or it could be that cylinder has a leaking oil feed check valve allowing excess oil into the bottom end. If the bike has not done many miles recently it could just be thjat it needs a good long run to burn off surplus oil in the crankcase.

One thing you might be able to do is to pull the SRIS valves and see how much oil drains out of each case chamber.

Are the jets all new, or pre-loved? It is possible that one has been "cleaned out" with something hard causing it to now be too large. Another possibility is an excessively work needle jet on one cylinder.

[BDcycles]

I need a few days away from the bike so I am not wrenching angry. When I dig back in I will start by looking at the battery voltage while cranking the bike over. The plug has never read lean on that cylinder so the crank seal is probably good. This is my 1st triple cylinder 2 stroke so I didn't know since it was the center cylinder that is suspect if that would mask the lean tendencies normally associated with a bad seal. I have always suspected electrical as my main culprit and still do but I am spinning my wheels trying to fix this.

I have ridden the bike far enough to clear the bike out any built up oil in the cylinder and it makes no difference. In fact last June I was participating in an event where I rode this bike from CA to NC (3000 miles) in three and a half days when my trouble started with about 1000 miles to go. The bike finished the event like this but has not been right since. At that time I suspected that I had wiped the rings out and was experiencing low compression trouble. Almost a year later and I am still stumped.

I appreciate the help you guys are offering and will keep you updated.

[pearljam724]

That's the way theses bikes are. They can be frustrating at times. But, I assure you. If you push yourself to learn as much as possible. You'll realize just how easy they are to diagnose. We have all been baffled. Don't give up. I assure you, you'll get it running well in no time. Lot of guys on here that won't give up helping you. You're in good company here. Keep firing questions, keep digging. Leak down tests refer to crank seals and compression tests are related to cylinders. I accidentally said compression test once in a previous post, when I should have said leak down test. Sorry, for the mistake.

[TRC]

Must be very frustrating. What does the center plug look like? I can't imagine if its firing intermittently like you're saying it would look normal so does it end up getting fouled or almost fouled? My bike has Jemco's as well and the left pipe had loosened and started leaking and I was getting fouling on that plug. There were other issues this new-to-me bike had including timing of converted electronic ignition being off, float level on that left carb out of spec, and voltage too high leading to a bad battery. I fixed those things simultaneously and it fixed the fouling plug so unsure which was the primary cause but since you have discussed everything except the pipe, thought I would mention it. No visible or audible sign that center pipe is leaking at the exhaust gasket?

[crazyeights]

I had a very similar issue with my 550 on the right cylinder. It turned out to be a lazy coil and the float height was not correct. If your float height is good, I would look into the coil.

[BDcycles]

The plug actually looks pretty good. As the bike revs up/carbs open up the bike seems to run pretty good. The problem is when at idle the cylinder fires once for about every 10 times the left and right cylinders are firing. The condition is also making the bike hard to start. The exhaust gas temp is almost nonexistent at idle but when you rev it up you can feel the temp increase for that brief moment. Yesterday I spent the day concentrating on electrical. I swapped the condenser with the right cylinder. I ran a new temporary wire from the points for the center cylinder to the bullet connectors behind the airbox. At the bullet connectors I swapped the wiring to the coil with the right cylinder then swapped then swapped spark plug wires to the center and right cylinder. Bike ran the same. This is the 2nd time I did this and I replaced the center coil with another anyway since the first time too. I checked voltage across the battery while cranking over the starter(11.0v) at idle(12.8v) and when revved up(14.0v).

No oil is leaking from around the pipe/head junction.

[BDcycles]

I have verified float height is correct too.

[TRC]

If you pull the plug after only idling for a while, it looks fine? I know you've gone over the carbs multiple times but I can't help to think this is a carb issue at idle. Have you tried adjusting the air screw for the center carb while idle to make it more rich? If so, does the RPM increase when you do so? It kind of seems to me that the center carb is being starved when at idle, then it's fine when the carb is opened up to the non-idle jetting.

[ConnerVT]

First the disclaimer: I have no (read:none) hands on, practical knowledge of the Suzuki triples. But have spent much time troubleshooting my T500.

There are basically three things that could be causing your idle problem:

- Fuel
- Spark
- Chamber integrity.

Seems as you have done enough troubleshooting on the spark/electrical side, so that likely isn't where you will find your answer.

Chamber integrity (vacuum leaks) is a possibility, but seeing as things run OK other than idle, no other symptoms (off color plug, smoky exhaust, etc.) are present, I would also put this possibility to the side for the moment.

This leaves fuel. For the chamber not to idle, it is either getting too much fuel, or not enough fuel. You have been doing some troubleshooting, so I will assume that:

- Carb bodies (and their internal passages) are clean
- Genuine correct pilot jets are installed (and haven't been damaged by improper cleaning)
- Fuel is amply delivered to the carbs, and the float levels are correct.

So what does that leave us? (This is where my lack of hands on experience with triples comes in). What can make the idle circuit too rich or too lean? Remember, as there isn't much flow going on at idle, little things can make a big difference.

I would look for one of the following:

- Leaking enrichment (choke) circuit. If the enricher doesn't close and seal, it can add extra fuel, causing the engine to 4-stroke (as in, fire once ever other to every once and awhile).

- Leaking hose in enrichment circuit (Doesn't the center carb share the enricher/choke with one of the other carbs?).

- Leaking vacuum line/petcock (I'm not sure which carb the petcock gets its vacuum from on the GT550).

I hope this helps. A blind squirrel finds a nut now and again.