Question about timing

[pearljam724]

What is the easiest way to be certain that you are at the highest point of the cam without using a dial gauge ? I realize that you can see a knot at the end of the cam that sticks out from the points plate. It seems to me that it's kind of a guessing game that you are dead smack in the middle of the highest point on the cam. I also realize that your points will be the widest once the bridge of the points reach the highest point of the cam. But, that too is kind of a guessing game or it takes 3 hours of checking, rechecking, adjusting plates, readjusting plates. Any suggestions ? Also, does changing the timing, points gaps effect the idle air adjustment screws on the carbs ? Prior to messing with my points. The bike was running great. Yeah, stupid I know. At that time I had to adjust my air screws a little past 3/4 of a turn. It was somewhere around a full or 1 1/4 turn out. Would I have to go back and readjust the air screws now that the points have been adjusted ? I'm dropping the left cylinder. The bike fires up on all 3, runs ok down the road for 3 miles then loses all power up hills and drops a cylinder. Once I get back on flat ground I regain all 3 cylinders, but it still doesn't run quite right. The battery has been checked several times. I never lose power to the battery. I've changed plugs, changed 2 of 3 points, changed rectifiers. This pertains a 76 750.

[Craig380]

That's always a problem with the GTs, the cam profile is so gentle. I just try and measure the point gap about 30-odd degrees of cam rotation after the points open.

Might be worth cleaning the point faces with some residue-free cleaner as they can get greasy easily.

[pearljam724]

Yeah, it seems that way. I cleaned them a few times. Maybe I should invest in a dial gauge.

[ConnerVT]

I feel you are over thinking this one.

The point gap isn't as critical as, let's say, the ignition timing. The main goal of setting the point gap is twofold: To make sure there is sufficient time to allow the ignition coil to energize while the points are closed; and to allow enough time for the coil to discharge when the points are open.

There is usually enough time for both of these things to happen when riding on the street. It would be much more critical if the engine is running near the red line all of the time, and you are trying to squeeze the most energy out of the coils for a run around Daytona Speedway.

Setting a point gap with a feeler gauge is a less than precise method anyway. More accurate would be to set it by a dwell meter, which nearly nobody mentions when talking about these motorcycles.

[GT750Battleship]

Hi,just be aware if you invest in a dial gauge you'll have to buy an adapter also to get TDC right due to the angle of left @ right cylinder plug holes ! easier to do it with head off ? Adjust the point gap on all three to correct settings,making sure they are not pitted or burnt,could be a bad condensor ?
I agree with the comment about 30 degree of dwell for the points,measured with a dwell meter with engine running,or if all else fails....bin it..& go Electronic Ignition
Cheers,
Roger

Four Wheels Move The Body
Two Wheels Move The Soul

[Vintageman]

get TDC right due to the angle of left @ right cylinder plug

This is very good point. Other engine manufactures stated if the published distance before TDC was to be found Direct (inline with piston motion) or Indirect( inline with spark plug hole) which may be at angle with piston motion.
I always assumed Suz is “Direct “even though plugs maybe on an angle.

[pearljam724]

I have not been over thinking the correct point gaps. However, maybe the ignition timing I have. I checked and rechecked the gaps and the ignition timing via the window below the points cover several times. It's not the condensors or the points as I have swapped those out from my 550 and are in like new condition. One of the points and condenser I have not changed on the center cylinder. I'm waiting on a new complete set to change them all. But, seriously doubt it's the points or condensors causing the problem. I believe it's one of 2 things. Either my timing is slightly off or I need to readjust the air screws on the carbs. But, if the timing is slightly off. Than why do all 3 cylinders fire up until the bike warms up a few miles down the road ? I sense that the bike is running slightly warmer than it should. The bike cools off and I regain all cylinders. Most of these bikes run at the 1/4 mark on the temp gauge, it seemed my bike ran at that reading prior to my problem. Now it runs at the half way mark on the gauge. I'm aware of the different cylinder head angles, does anyone make or sell an adaptor to accommodate that as Battleship mentioned ? One reason, I believe the air screws may be a factor. The manual states not to adjust them, until the gaps, timing, etc. have been adjusted prior. Plus, I know I adjusted them past a 3/4 turn prior to messing with the points and timing. I just haven't had the moment to readjust the air screws as of yet. Appreciate your thoughts on this guys.

[ConnerVT]

I have not been over thinking the correct point gaps.

Point gap isn't changing. So it will either run, or it won't, regardless of temp or terrain. Tolerance for point gap is pretty wide (don't know the GT750, but the T500 is 0.012-0.016 in). In a pinch, many points have been set with a matchbook cover.

It's not the condensors or the points as I have swapped those out from my 550 and are in like new condition. One of the points and condenser I have not changed on the center cylinder.

Than why do all 3 cylinders fire up until the bike warms up a few miles down the road ? I sense that the bike is running slightly warmer than it should. The bike cools off and I regain all cylinders.

So it seems temp related. Hot, no work. Cool, works. My first suspect would be the center cylinder condensor -- It hasn't been swapped out yet, and it is closer to the heat generating engine. Next would be one of the coils (could be any of the cylinders). My first T500 used to foul a single spark plug. Engine would run, but lost a lot of power. Would move you on level ground, but needed to be walked up hills. A coil dropping out could possibly give you a similar result.

Most of these bikes run at the 1/4 mark on the temp gauge, it seemed my bike ran at that reading prior to my problem. Now it runs at the half way mark on the gauge.

Running hot(ter) than usual, I would think either the timing is too advanced (hear any pinging?) or fuel mixture running lean. Not familiar with the 750 carb tuning, but tuning carbs after sorting out ignition adjustments is pretty standard fare.

[pearljam724]

So it seems temp related. Hot, no work. Cool, works. My first suspect would be the center cylinder condensor -- It hasn't been swapped out yet, and it is closer to the heat generating engine. Next would be one of the coils (could be any of the cylinders). My first T500 used to foul a single spark plug. Engine would run, but lost a lot of power. Would move you on level ground, but needed to be walked up hills. A coil dropping out could possibly give you a similar result.

That's exactly what it is consistently doing, even after I readjust or recheck the ignition timing it is still having the behavior you described above. It starts, idles fine, but as soon as the bike gets warm 3 miles down the road it does exactly as you describe. I know it's not battery or charge related. Because, the battery remains strong. Checking my plugs afterwards, they are pretty wet. But, that probably has to do with having to fully open the throttle because it has no power at that point. I understand the timing for all cylinders is based off the left cylinder. That being the case, can I just rotate the points plate to advance or retard all three points equally at one time ? If so, which direction would it be for retard ? I'm thinking, because the crank rotates to the left looking at the points plate. Retarding the ignition, the points plate would also need to be turned to the left ? The air screws needing to be readjusted probably is the cause of it running a little warmer than it should ?

[Craig380]

Other engine manufactures stated if the published distance before TDC was to be found Direct (inline with piston motion) or Indirect( inline with spark plug hole) which may be at angle with piston motion.
I always assumed Suz is “Direct “even though plugs maybe on an angle.

I had the pleasure of borrowing a factory Suzuki dial gauge, and the extension rod which touches the piston crown has a rolling ball-bearing in it (like a large ballpoint pen) so it 'rolls' across the crown as the piston rises. A beautiful instrument to use

The Suzi factory BTDC timing specs are for with the cylinder head in place, which is why the measurements for the left and right jugs (on the aircooled 380 and 550, anyway) are slightly different from that for the centre cylinder. The left & right jugs have heavily offset spark plugholes, which means the measured distance BTDC via the plughole is a little longer than with the centre cylinder, where the plughole is much closer to central . If setting timing with the head removed, all 3 jugs should be timed to the spec for the centre cylinder.

[T350guy]

Back in 78 I use to use a cig paper to tell when my points opened and this can be very accurate once you get the feel down.
Today I use a dial gauge and a Suzuki Buzz box.
Both my 74 & 77 propeller marks are off not advanced but retarded..IF I set by the Propeller then check the dial gauge it reads approx 3.1 not 3.4, this may not be a big issue with the GT but my 72 Kawasaki H1 it certainly does.
I don't think it's a timing issue but electrical..either point/condenser or as suggested a bad coil.
About 4 years ago I had a 72 GT 750 here just to get running for the owner. It ran great for about 1 mile then the center crapped out, once cool it fired up and ran great. On the second ride I took a spare plug for testing.Once it crapped out again I switched plugs ..NO spark.Turned out to be a bad coil.
Both GT's run near the center mark on the temp gauge
Ian

[pull the wire]

I find it a lot more accurate to use a degree wheel to set up timing. You have to determine perfectly TDC left cylinder and have all your point gaps set up first. Set up left cylinder at 24 degrees BTDC, center cylinder at 144 degrees on the wheel and 264 degrees on the wheel for the right cylinder. Just use and ohm meter or a buzz box and your good to go. You can try Ford 6cyl condensers for some added protection. They are bigger so you gotta make sure the fit behind your cover. Ohm out your coil. The primary side should be around 5 ohms and the secondary side around 12K ohms with the spark plug caps removed. If your using resistor style caps you need to use non resistor plugs and vice versa. You can use a hair dryer on the coils to simulate heat and retest them. You can cool them down with some of that computer spray air. If you hold the can upside down it will frost bite you pretty quick. LOL Could be a mechanical issue as well. Do a compression test to make sure she's still got a heart beat. The SRIS hose on the bottom of the right cylinder crankcase ends up at the bottom side of the left intake port. It could be a bad dreaded crank seal leaking there and transferring transmission oil over to the left side. It could be a failed left crank seal too. A good carb sync after the points and timing are set can be helpful. I attached a printable degree wheel link that you can glue or tape to heavy cardboard or plexi glass.

The best way is go with electronic ignition and a known good set of coils, secondary wires and proper spark plug caps and plugs. Maintenance free brother. Set it and forget it

Hope this helps


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[pearljam724]

I wouldn't even know where to begin using that degree wheel, lol ! It took me a couple of days to pretty much teach myself, timing it through the factory points plate window. The next day I get a chance, I'm going to test the coils with a multimeter and set the air screws on the carbs back to the factory recommended turn out and see how it acts. I have 3 brand spanking new coils that I purchased for it several months ago. But, was never able to use them as I haven't had the time to figure out how to wire them. Not knowing which black, black ( with yellow stripe) and white wire from the wiring harness goes to which negative terminals on each coil ? I understand that the 3 orange wires are the positive leads to each coil. But, those other 3 wires I haven't had the time to figure out yet. I appreciate the responses.