Couple of timing questions.

Post by **Scorch** » Sat Jul 03, 2010 7:38 pm

Following this thread closely, I'm trying to time my GT380 as well...

jbswear · Post by **jbswear** » Sat Jul 03, 2010 8:12 pm

AAAAAARGHHHH~!!!!!!!1!

Got it running...smoking quite a bit as the 30+ year old oil in the system burns away...then it gets to the cleaner, newer stuff I put in today...stops smoking.

That's the good part.

The bad part is that the right cylinder stops firing. I pulled the plug and ran it, holding the plug against the engine and get beautiful, fat, hungry, blue sparks from the right plug.

But the cylinder doesn't smell of unburned gas. The plug is wet with fresh oil. Gonna have to pull the carbs AGAIN to find out why the right cylinder's carb is clogged...

If it ain't one thing, it's three others!

Not only that, but running on two cylinders and it STILL diesels. I can't figure it out. I pulled the head and found no build up of carbon on the piston heads or in the combustion chamber. Had to drop it into gear and stall it to kill the engine.

What else should I look for?

Barry S. · Post by **Barry S.** » Sat Jul 03, 2010 8:20 pm

I have seen 2-stroke dirtbikes rev when running out of gas and going lean from fuel starvation, one had a stopped up carb and would get a trickle of gas and would run a few minutes, lean out and rev up and die, wouldn't start again until it trickled full. Your petcock may be the problem.

Coyote · Post by **Coyote** » Sat Jul 03, 2010 10:25 pm

Also check the gas cap vent. When it starts acting up, crack the lid and see if that helps.
The opinion is no no to wire for cleaning jets. I couldn't disagree more. Find a wire that fits through the hole. Put some kinks in that wire and drag it through the jet hole. This hurts nothing and will clean out any varnish that has accunulated. Pay particular attention to the holes in the 'waist' of the pilot jet. While the jet is out, use compressed air to see if that circuit is open into the carb main bore.

gt-keith · Post by **gt-keith** » Sun Jul 04, 2010 8:01 am

Sounds like you've got more than just timing issues.
When I rebuilt the points timing shaft with a new timing plate and 'key' which is just a 3mm pin, I found there was quite a bit of play between the plate and pin, enough I would say to give you an error of about 1mm either way at the timing marked end.
Which is why I suppose it's better to use a dial indicator.
Interestingly the motor I'm rebuilding didn't have a timing 'key' in it at all !!
The bloke I bought it from claimed it came from a running bike, makes you think doesn't it.

jbswear · Post by **jbswear** » Sun Jul 04, 2010 8:50 am

gt-keith wrote:Sounds like you've got more than just timing issues.
When I rebuilt the points timing shaft with a new timing plate and 'key' which is just a 3mm pin, I found there was quite a bit of play between the plate and pin, enough I would say to give you an error of about 1mm either way at the timing marked end.
Which is why I suppose it's better to use a dial indicator.
Interestingly the motor I'm rebuilding didn't have a timing 'key' in it at all !!
The bloke I bought it from claimed it came from a running bike, makes you think doesn't it.

What is this key you're speaking of? I pulled the side cover and lined up the marks inside, and then lined up the timing indicator before sliding on the side cover.

Well, I set the timing just last night by going on the timing mark--which is no where NEAR 2.4mm BTDC. By going on the timing mark, my timing is several degrees advanced. I'd rather go on the pistons' positions than the timing mark.

Thoughts?

tz375 · Post by **tz375** » Sun Jul 04, 2010 10:31 am

Suzuki specifically say NOT to use the timing marks for timing except in an emergency. They recommend using a dial gauge to set timing.

jbswear · Post by **jbswear** » Sun Jul 04, 2010 11:50 am

tz375 wrote:Suzuki specifically say NOT to use the timing marks for timing except in an emergency. They recommend using a dial gauge to set timing.

Then I'll reset it to the dial indicator method. But this will put the timing mark to the right of where it "should" be when the points open.

Coyote · Post by **Coyote** » Sun Jul 04, 2010 3:30 pm

The timing plate 20 is slotted and is located by pin 27. I think I would dig into it and make SURE the pin is in place. Without the pin, the timing plate can be antwhere (360).

jbswear · Post by **jbswear** » Sun Jul 04, 2010 4:40 pm

I'll pull it and look, though I don't remember pulling that off. We'll see!

tz375 · Post by **tz375** » Sun Jul 04, 2010 10:15 pm

jbswear wrote: Then I'll reset it to the dial indicator method. But this will put the timing mark to the right of where it "should" be when the points open.

And that tells us that the marks are in the wrong place and cannot be trusted or used. I can understand that people think the timing marks are for doing the timing, but there is so much slop in the system that as a rule, they are useless for timing at best.

Craig380 · Post by **Craig380** » Mon Jul 05, 2010 2:12 am

One thing worth doing when using the dial gauge is to see how the correct piston position compares with the 'timing marks'.

On my own 380, the timing marks measured at 1.9mm BTDC. Having set the timing to factory spec using the dial gauge, I found I was getting a little detonation in the mid-range ... so I knocked the timing back a little.

Oddly, the engine runs happiest when strobed to the ORIGINAL timing marks

. But's that's just my engine, your mileage may vary, etc etc

jbswear · Post by **jbswear** » Mon Jul 05, 2010 6:44 am

Craig380 wrote:One thing worth doing when using the dial gauge is to see how the correct piston position compares with the 'timing marks'.

On my own 380, the timing marks measured at 1.9mm BTDC. Having set the timing to factory spec using the dial gauge, I found I was getting a little detonation in the mid-range ... so I knocked the timing back a little.

Oddly, the engine runs happiest when strobed to the ORIGINAL timing marks . But's that's just my engine, your mileage may vary, etc etc

The correct position (2.4mm BTDC) puts the timing marks about 20 degrees to the right of the one stamped in the case.

It'll run when they line up; I haven't tried running it when they're set with a dial indicator.

gt-keith · Post by **gt-keith** » Mon Jul 05, 2010 11:12 am

What I'm saying is like the other guys are saying, don't rely on the timing marks.
As shown in coyote's diagram, pin 27 is the key that drives the timing plate.
Yours could be missing from somebody else's hamfisted rebuild now causing you problems.
In short I'd use a dial gauge and ignore the timing marks, and like craig says 'fine tweak' manually to optimize running.

Craig380 · Post by **Craig380** » Tue Jul 06, 2010 2:11 am

@ JBS -- which specific model 380 do you have?

The factory timing spec changed from 3.0mm BTDC for the J model to 2.05mm BTDC for the A, although the actual allowed tolerance is HUGE ... the shop manual for the J gives the tolerance range as 2.52 - 3.76mm BTDC. That 1.24mm range of piston crown movement equates to a LOT of degrees of crank rotation ...