Suzuki 2 Strokes

Hi, new to this forum but not to a 1975 GT750 that I've had for 42 years. I should know how to fix it by now, but I'm looking for advice to save some time. It's been running ok until just recently, it started losing power at low rpm, especially when starting off from a standstill, it can barely get going. But as soon as I get over about 3500rpm it's fine, and then drops a cylinder when I slow down. I replaced points and condensors, and checked the plugs with little or no effect. I'm assuming the next steps would be taking off the carbs, cleaning the pilot jets and anything else I can find, then ignition coils if that doesn't work. But has anyone gone thru this already and can offer some words of wisdom? Usually losing a cylinder on this bike involved points or condensors. Thanks!
John A.

As you said, most likely the pilot jets starting to clog. Before you go through the painful process of removing the airbox to get the carbs out, you could try to run a bottle of Seafoam or good injector cleaner though a tank of gas and see if that helps any.

You should also give it a decent service, clean out the baffles and check compression just to eliminate a few other possible issues.

It could also be crank seals, but if you have to do a leakdown test, wait til you take the carbs off, then you can pop off the exhausts and test it.

Nice bike BTW.

Where are you located?

Yeah, my GT750 was terrible to ride with just one blocked pilot jet. What you describe was pretty much exactly how mine felt.

Keith

Thanks tz and gamma, I'll try the pilot jets next. Because it's rpm related I'm hoping to find a plugged jet, I think it did happen once before but many years ago, and I remember getting the airbox out was less of a challenge than getting it back in. But oh well, there's only one way to do it, get the toolbox and dig in. I'll start it first just to be sure, I did put some injector cleaner in the tank but I didn't really run it long enough for it to work, maybe it will magically loosen up just sitting there. Probably not. I'm located in central CT, I'll post a reply after the weekend if it works.
John A.

I didn't have any luck cleaning the carbs. I took them off and there was very little contamination inside, I checked and poked wires thru the jets, but when re-assembled the center cylinder still isn't running. I pulled the plug wires from two cylinders at a time, and it will start on the left or right cylinders, but not the center. The spark and timing looks good for all three. Not sure where to turn next, I suppose I could have missed something in the carburetors but it didn't look like it. Any other suggestions?

Of course the boots won't go back on the airbox, they're dried out.

And, I hate to say it, but is there a market for this bike, running good or not? I may need to sell it "as is" due to an upcoming change in living arrangements. Located in central CT.

Thanks,
John A.

jallen1000 wrote: ↑Mon Jun 28, 2021 10:26 am I checked and poked wires thru the jets,

You need to do more than just jets, you need to make sure all passages are also clear. I spray carb cleaner and compressed air through all passages to be sure I have flow.

There are a couple of us in the US that can rebuild those carbs and check all the circuits, replace jets with new ones, fit new shaft seals, bench synch them etc. It's a lot cheaper than selling the bike. I have done multiple sets of GT750 carbs. They take time but come back almost like new.

Baz in the UK also has a good reputation for carb rebuilds but I have no idea what he charges or the cost of shipping.

But if you plan on selling, do you have more pictures and a price?

I'll give it another try, I need to identify the problem in order to see if I can repair it or not. If I do decide to sell it, I really don't have an idea of what a fair value would be, but that also depends on what's actually wrong with it. I'm hoping to get some time over the holiday to work on it.

I have the carbs off again and I'll do a better cleaning, but here's a few things I noticed:
The spark looks good on all 3 cylinders, and they all seem to have compression. Taking off 2 plug wires it will run on the R cylinder, not as well on L, and not at all on C. The plug is wet on C when I take it out after trying to run it on all 3. Now the scary part, with the plugs out and carbs off, if I hold my hand over the carburetor throat on the motor and kick it over, I can feel the air pulsating on the R cylinder, but not on C, maybe a little on L. Does that mean the crank seal is gone between L and C? Is there another easy way to check?

Thanks,
John A.

jallen1000 wrote: ↑Sun Jul 18, 2021 3:07 pm if I hold my hand over the carburetor throat on the motor and kick it over, I can feel the air pulsating on the R cylinder, but not on C, maybe a little on L. Does that mean the crank seal is gone between L and C? Is there another easy way to check?

That is a definite possibility, I never did it, but you can do a leak down test, i believe you block the intake and exhaust on cylinder and add 5-7 psi and see how long it holds the pressure.