Weak spark on 1973 yamaha rt3

Most of the time by this bike are the mail pipes of the carburator oval https://goparts.eu/en/blueprint/yamaha/road/1995/fzr-r-600/carburetor

I have 2002 road star midnight. I lost completely spark on all 4 spark plugs. Before bike was running OK but sometimes on low RPM while idling would skip a firing on a at least one cylinder making spufff like sound. I put new spark plugs, and wiggled a little coil wires. Bike with new spurk plugs would not fire up at all. Checked for spark on all 4 spark plugs - no spark., not even an electrical I lost completely spark on all 4 spark plugs. Before bike was running OK but sometimes on low RPM while idling would skip a firing on a at least one cylinder making spufff like sound. I put new spark plugs, and wiggled a little coil wires. Bike with new spark plugs would not fire up at all. Checked for spark on all 4 spark plugs - no spark., not even an electrical charge going to spark plug. Went back to coils. Each coil (there 2 of them) has 2 spark plug wires and 2 ignition timing signal wires connected to them. I realized that these ignition timing wires contacts are corroded to the point they would not conduct a charge from the distributor to coil. CLEAN ALL THE TIMING WIRES Contacts on the coils. I did that and bike fired up right away and started running much better without sputtering or skipping a cylinder firing. SO DISCONNECT ALL THE COIL WIRES AND BRUSH THE CONTACTS WITH A SMALL METAL WIRE BRUSH.

make sure the points are very clean and gap is set correctly ! is the timing dwell set ? remove one coil and try it on other cyl and see if it now sparks , if yes then replace other coil , are the 2 sets of points or one ? have you checked condencers ok ?

.....A weak battery comes to mind for starters. A carboned up spark plug is another; start with a new spark plug. If I recall correctly from 39 years ago, your bike has ignition points and condenser. Remove the points cover (on left end of the overhead cam), and check the points. Burned? Pitted? Get a new set of points and condenser but for now, just file the points a bit using an emery board or metal fingernail file. Set the points to .015 clearance at the high point on the cam lobe. If you have a timing light you could check the timing and adjust as needed by rotating the points base plate left or right. Bad points give resistance to the flow of electricity. When the points are closed, the condenser gets charged up. Less electricity going through the points means less of a charge going into the condenser. Now the points open up and the stored charge goes from condenser to coil. The coil then produces a spark. With a low charge in the condenser, the spark is weak and will not jump a wide gap. Set the plug gap to very little and the weak spark can jump the gap. The standard gap is .028. ....... I don't recall when Honda move the points to the flywheel but the images below may help if your bike is that style. Clean any rust on noted parts; magnets and pick up coils. Okay, now I have done my part. Now you gotta do yours; please rate my answer. Thanks!

Problem could be a few different things. Not sure on all the ignition parts on that bike, but could be a bad sparkplug cap, wire, coil or magneto. My recommendation would be to first take the spark plug cap off. Trim a bit off the wire and put the cap back on. Over time spark plug caps move quite a bit and wear out the wire inside cause a weak connection.

Thanks

hi, you dont say if this is only 1 spark plug that does not spark, or the 3 plugs dont spark, lets assume its all 3, and you have checked that the engine run switch is in the run position, this is the switch on the r/ h handleber throttle twistgrip housing, also you have 12volts charge in the battery, the next thing to check is as this bike has 3 ignition coils 1 for each cylinder and also 3 sets of contact breaker points you can narrow the problem down to each cylinder indervidualy, ie if no1 cylinder does not spark check the points/ contact breakers are opening, more importantly closing for no1 cylinder this will be marked on the contact back plate, it may be nessasary to clean the points with some lite wet and dry, with the plug removed and resting on the cylinder head making a good earth, opening the points with a screwdriver between them should make the plug spark, when the ignition switch is turned on, repeat this on all 3 sets of points until you are happy they all spark, do not leave the ignition turned on for long periods of time without the engine running unless the run switch is in the off position as this will cause the ignition coil to overheat and eventualy burn out. realy great bike hope you manage to make it run, any further help feel free to contact me and i will try to answer your question, paul

you need good compression ( at least 90 psi , kicking it with the throttle open) , good crankshaft seals for sucking the fuel/air into the botton end, proper point gap and timing set for spark ( spark should be big and fat,if not the source coil is weak,, this is a flywheel magnito ignition and it needs no battery to fire the plug) if you clean the carb, make sure you also clean the choke pickup tube or it wont choke. also make sure you have the slide installed in the right direction ( not backwards and the idle is not set too high at first...compression/****-good spark at the right time-proper fuel/air ratio and it will run

I haven't worked on that bike in 30 years, but as I recall, the black wire goes to the points. The coil grounds via the mounting bolts.

Firstlly have you a spark at the plug.if you have no spark then it may be your points or even the timing may be out .

Okay, I will tackle a tune up on a 36 year old Yamaha. Warning: I am 59 and haven't touched that bike since I was 23 and a mechanic at Lynns Yamaha in D.M. Iowa. Your bike has CV carbs and I know very little on the carbs.

First let me suggest you get a service manual. Go to www.repairmanuals.com and input " 1973 Yamaha 650 ". You can choose a Clymer or a Haynes manual. I don't care for Clymer and have never used a Haynes. The Haynes is $23.77 which is really a pretty good price considering not many of the manuals still exist.
Also, for future reference, go to the following site where you can see a parts diagram for your specific bike. You will select the brand, year, model, etc., once you go to the site. Part numbers and prices are also shown. Parts can be ordered if the price is shown > no price = the part is not available.
http://www.babbittsonline.com/pages/parts/viewbybrand/1/Yamaha.aspx

Also Google " motorcycle salvage yamaha " and Google " vintage yamaha motorcycle parts ".

Start with new NGK B8ES spark plugs. New points can be gotten at the Babbitts site. Set the points at .015 max opening. Hook a timing light up to the left cylinder. Remove the left case cover to expose the flywheel. Start the bike and point the light at the static reference mark on the casing. IF I RECALL CORRECTLY, rotate the base plate that the points are mounted on to adjust the timing. The timing should advance when the engine is reved up. If it doesn't, the spark advancer needs service. Now put the light on the right cylinder. IF I RECALL CORRECTLY, changing the right cylinder point gap is the only way to set the timing for that cylinder.

I hope this helps. Please rate my extra long answer. Thanks.