Timing Gt750 problems

[tz375]

Yamaha TZ750 also runs "backwards"

[H2RICK]

This whole thing looks a lot more complicated than it really is.
To figure out the proper rotation of the points cam on any engine with 3 or more cylinders all you really need to know is the firing order and which points are hooked up to which coil/cylinder (or alternatively which plug wire goes to which cylinder from the distributor).

The firing order for all of our Triples is 1-2-3.

On the 750, with the ignition mounted on the left side of the engine, the points are positioned on the plate thusly (with the letters L, C and R nicely stamped):
#1 (Left) = 4 o'clock
#2 (Centre) = 12 o'clock
#3 (Right) = 8 o'clock

Ergo, the points cam HAS to turn counterclockwise to give the correct firing order.

On the 550, however, the cunning devils at Suzuki moved the ignition over to the right hand side of the engine....but kept the firing order the same, so.....to make everything work correctly, they reversed the position of the #2 and #3 points thus:

#1 (Left) = 4 o'clock
#2 (Centre) = 8 o'clock
#3 (right) = 12 o'clock

Sooo.....the 550 crank has to be rotated clockwise during the timing
procedure.

All bets are off on the 380 because, although the ignition system is on the right side of the engine (like the 550) AND the engine has the same firing order as the 550/750, it uses the same procedure as the 750 (but not the 550) because the 380 points cam is NOT driven directly from the crankshaft (like the 550) but rather by a spur gear from the crankshaft. After all that blather, the 380 points cam must be rotated in a counterclockwise direction.

WARNING: Since the 380 uses a spur gear to drive the points cam, you CANNOT turn the points cam using a wrench directly on the nut on the end of the cam. The spur gear is made of nylon and is NOT intended to accept the load of trying to turn the engine over. It WILL break if you attempt to turn the points cam this way. Rather, put the bike in 4th or 5th gear and rotate the rear wheel to turn the engine and the points cam for this procedure. Alternatively, you can use the kick starter with the transmission in neutral instead. You've been warned.

[smokin gt750]

Hello and thank you for the reply. My previous post was to correct the manual, as you have to turn the engine clockwise IE:backwards, to get the points to open BTDC. I was confused by the manual which stated turn the engine counterclockwise after you have gaped the points. It will seem as though the points will not close enough. Could you guide me as to where I could find a stencel for the seat?
75,GT750, Grey, 23k miles, and an every day dependable rider, or at least until the woodruff key broke on the timing cam. Is this common? is there an upgrade?
Bob.

[H2RICK]

I was confused by the manual which stated turn the engine counterclockwise after you have gaped the points. It will seem as though the points will not close enough.

Bob, which manual are you using ?? The Clymer can be confusing if a guy doesn't understand the logic behind their instructions. The factory manual is a little better...but not much.
Firstly, the points gap MUST be set with the points rubbing block on the highest point/bump of the cam. Remember that the gap can be from .012" to .016" and that it doesn't have to be EXACTLY .014".....which is just the "ideal" postion.
Once you are satisfied with the Left cylinder points gap setting, then you adjust the whole plate to set the timing for THAT cylinder ONLY.

[[If I was you I would NOT attempt using a dial gauge for checking piston position. The dial gauge adds another layer of complexity for a novice. Rather use the markings on the little 3 bladed "propellor" to check your timing. The "propellor" markings are plenty good enough for unmodified engines for street use. Once you become more adept and understand how all the bits work together, you can then try setting everything with the dial gauge involved.]]

After you have set the gap for the Left cylinder points, rotate the engine COUNTERCLOCKWISE until you can just see the leading edge of the "propellor blade" for the Left cylinder come into the window. At this point, start watching your meter dial/readout which SHOULD change from Zero ohms/closed to infinity/open just as the slot stamped on the "propellor blade" reaches the small "post" cast into the engine housing.
If the meter changes its reading BEFORE the slot reaches the post, then rotate the plate slightly COUNTERCLOCKWISE to retard the timing.
If the meter changes its reading AFTER the slot has passed the post, then rotate the plate slightly CLOCKWISE to advance the timing.
In either case, continue rotating the engine counterclockwise all the way around in order to recheck your setting. Keep doing this until you get it correct.
If the points plate ends up most/all the way to either end of the slot where the plate retaining screw at the 2 o'clock position is, then that USUALLY means that:
AA) your points need to be replaced because the rubbing block is worn down too much, or
BB) your points gap setting is incorrect.....either too close or too far apart.

If it's BB), then go back and start all over again.

Remember, it's always BETTER/SAFER to have your timing set SLIGHTLY RETARDED rather than slightly advanced. You will never "ventilate" a piston if you have the timing retarded. All that can happen is that you lose a little performance and get a little worse gas mileage.

Has this helped ?? Confused you worse ??
This is a VERY complex subject to explain via the written word and both Clymer and the FSM descriptions are rather.....umm.....opaque at best and terribly confusing at worst, depending on your skill level.

[smokin gt750]

Thanks H2Rick,
I set mine with the dial indicator, I made a tool out of a spark plug to hold it. It worked well on R and L but C was a hard one to hold.
I am pretty sure I came close though. The propellre blade is off the mark the same amount on all three cylinders, just slightly retarded. Do you think I should do it again on the mark?

[H2RICK]

just slightly retarded

Bob, I'm not clear as to which is retarded.....

Is the propellor retarded as compared to what the dial gauge shows???
Or is the engine retarded as compared to the propellor shows ??
You have to be careful that the propellor hasn't been damaged where it fits onto the shaft. That slot on the propellor that engages the pin on the shaft CAN be augered out somewhat which allows the propellor to rotate slightly on the shaft.
If you are confident of your measurements with the dial gauge AND there's no heavy carbon on the piston tops, I'd go with that. HOWEVER......keep your first test hop (or hops) short (max 15 minutes or so), keep your ears open for any pinging, no lugging the motor or short-shifting, no overrevving, no heavy loads, no high ambient temps (over 75*F) when testing.....and I'd run premium non-ethanol fuel for your tests, if it's available. Those measures will greatly lessen the chances of holing a piston.
Check the plugs after the first hop and that will give you a good idea of how close you are with your timing, all else being set up and working correctly.

[smokin gt750]

Thanks again H2Rick:
Now Im scared about holeing the piston. I buttoned it all up and it starts fine and seem to run well on the lift. I am going to open it all up and re check it with the propeller just to be safe. I am not sure about carbon buildup and the center cylinder was just a guess. As far as my original set up the propeller was just to the left, ie: at just about 7:00 of the mark.
By the way what makes the woodruff key break in the first place?
Bob.