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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

Suzuki Misfire

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Suzuki misfire

Q: I have a problem with a 1979 Suzuki 1000E. It starts fine, but it sounds like it misses a little just off idle. The main problem is at 5,000rpm the engine misfires or cuts out. I cleaned the carburetors, installed new plugs, wires and coils. I am having trouble setting the engine timing using a timing light. I can’t retard the timing to the correct specs because the plate bottoms out on its screws, and you can tell it is worse when I back that down. The idle is about 1,200. Any help would be appreciated. — Ken Erdman/via email

A: This sounds depressingly similar to a problem I had with a customer’s Honda 750. It idled fine, but it wouldn’t rev under load, and the timing was hard to set. Sometimes these problems can be caused by something as simple as a bad connection in the ignition or kill switch that only shows up at certain RPMs due to vibration. It’s easy enough to bypass the ignition switch and run a wire directly from the battery to the coils. You’ll still be using the ignition switch to fire the starter, just augmenting the circuit with a direct link and bypassing the kill switch. If this improves matters, you’ll have to determine whether it’s the ignition switch or the kill switch. Another possibility is the points condensers. Look at the points as the engine runs. Is one set arcing more than the other? There should be barely discernible sparks between the points with the engine running. If one or both sets of points are arcing excessively, replace the condensers and see if that improves things. Bad condensers will definitely make it hard to time the engine with a timing light, as the timing will be erratic. Since you mention the points plate being at the end of its adjustment, it’s probably important that we establish that the auto advance unit (AAU) is in properly and working as it should. Before that, though, make sure you have the points gap set correctly. You can change the timing by having the gap set too wide or too narrow. Make sure you measure the gap when the points are opened their widest. The manual suggests 0.012in-0.016in, I usually set it to 0.015in as that’s the smallest wire on my wire feeler gauge. Check your timing again to see if you can now center the points plate. If not, the next step will be to remove the points plate and then the AAU. The points plate will come off if you remove the three screws holding it to the engine case. You’ll need two wrenches to remove the AAU: one to hold the crankshaft steady and the other to loosen the bolt holding the AAU in place. Once you have the AAU loosened, check that the locating notch and pin are in place in the AAU and the crankshaft, respectively. Those are there to make sure the AAU stays in time with the engine, and if the pin is missing or the notch is worn it could be why your timing plate is at the limit of its movement. Check the AAU to make sure it operates smoothly, lubricating it with a little light oil if necessary. If everything on the AAU checks out, reinstall it, making sure to engage the pin on the crank with the notch on the AAU. With any luck, you’ll find the solution before you have to do anything to the AAU. MC