Timing question

[LoHo]

Hey Gurus, if ones timing was off by a single tooth in the same direction on both sprockets, would the bike rev high as if the timing were advanced?

[bikerphil]

Can't answer that for you, do your timing marks line up? I would check them to make sure.

[motoman]

Hey Gurus, if ones timing was off by a single tooth in the same direction on both sprockets, would the bike rev high as if the timing were advanced?

Very well could.......BTW Larry, do U have valve cover off or are U just speculating?

[skids]

I would get those timing marks on the button because when the clearance gets tight, they could contact the pistons if they are off. I know that is can be tough trying to get the marks spot on, but they should not be one tooth off! In my experience, one/half a tooth or less is the best that you can do...and that was with a new cam chain!

[LoHo]

I was speculating, and then spent the day yesterday setting the timing for sure. Today I ran her some, but she started and ran at 5000 rpm until I dropped the idle master all the way down. The idles started dropping and I was getting excited when she started to stumble and pop...almost out of gas. Tilt the tank, and back up she went. She hangs at about 1800 with the throttle master disengaged.

The pilots are all at 1.5 turns, I benched the carbs when they were off using the wire method. Disconnecting the throttle cable does not change the throttle position verses the idle master screw, so it's not a binding issue.

The only really radical thing I've done that was a big departure from when she ran correctly was to reset the floats at the specified 23mm. The bike ran well for years with floats at about 20mm, the tangs nearly flat. I resisted that change as long as possible, because getting the carbs out of whack strikes fear in my heart. Having the floats at 23mm should make her leaner than before, right? That doesn't explain the high idle. I'm going to put them back where they were because I have exhausted whatever else I can think of to do.

BTW, it's an 80G, all stock AFAIK, with plastic floats that all float.

[skids]

The only really radical thing I've done that was a big departure from when she ran correctly was to reset the floats at the specified 23mm. The bike ran well for years with floats at about 20mm, the tangs nearly flat. I resisted that change as long as possible, because getting the carbs out of whack strikes fear in my heart. Having the floats at 23mm should make her leaner than before, right? That doesn't explain the high idle. I'm going to put them back where they were because I have exhausted whatever else I can think of to do.

The bigger number for "float height" is leaner (it is upside down).

[LoHo]

Yeah, Skids, I said that in the third paragraph. That stumps me, as leaner should drop the idle. I'm making progress, I guess, but I'm stumped on why she's reving so high.

[skids]

It looked like a question. I guess it was a rhetorical one.

[conquest87tsi]

I actually think your backwards on that Loho. Lean will cause a higher idle. Think about when your setting the mixture screws. You screw them out(more air=lean) until the idle increases then back in a bit(1/4 turn if I remember correctly). Same with the boot or hose leaks you always here about that cause a high idle. Depending on your setup(pods, exhuast, jetting) your 20mm height could have been masking having too small of idle/main jets. Or you just don't have the pilots adjusted right. Or maybe a leak. If you had been running well at 20mm without black plugs I would have left it.

[LoHo]

Conquest, I resisted changing, but after working on her off and on for two years trying to find spark, I figured I'd reset everything to spec and see if she worked. I figured out the spark issue, did the timing wrong, which led to reworking the carbs. Since then, high revs. The float height is the only change, but moving away from spec sounds foolish.

[TomB]

Reading down the thread I was thinking the same as Conquest, that leaner makes idle higher, then he said it. I agree.

Think of it like shutting the petcocks on your tank with the engine running to use up the fuel in the float chambers pre lay-up, you know when the carb bowls are getting empty coz the idle revs start to pick up and up, until it runs out of fuel, weaker and weaker until out.

I've found engines with one tooth out on both cams' timing, they didn't run so well, struggling to rev out, almost like a miss fire. Certainly never had those engines revving high on idle.




.

[TADracer]

Back to the cams one tooth off, if I remember correctly that will equal around 22 degrees at the crank! could be enough to cause a collision or at the least will put your performance off alot. If you want to adjust your cam timing you really need slotted sprockets, a degree wheel and a dial indicator to do it right.

[LoHo]

No, Mike, my very recent experience indicates that one needs to be off about three, maybe four teeth to get a collision. The bike runs, but poorly, one tooth off. I stupidly set the timing based on the C mark at first, and bent one valve, the one that had the closest clearance, and therefor got pushed the farthest into the cylinder. when I fixed that, I was off one tooth each after attaching the ACCT and she started hard and ran at high idle. Ironically, fixing the timing caused an even higher rev.

It must be the carbs, so I'm going back to what I had and see if I can bring her down to managable rpms. I could now take off the carbs, valve cover, and cams in my sleep, and often my results make it seem as if I did so.

It seems counterintuituive, but I agree, when I've run an engine out of gas, at first it revs up, then coughs and bogs, then stops. I must have my carbs in the lean high-rev sweetspot.

[LoHo]

You know, it's strange, but I've searched the net motorcycle sites for lean symptoms, and the closest I've gotten was mention of surging when lean. I fully expected to have one of our usual saviors announce that lean engines rev high, or rev low, or something.

[DiverRay]

Don't forget, until the carbs are synched once again, you WILL have problems with idle speeds. Just pulling the carbs off, and installing again, the synch can change! BTDT. I would set your floats back to about 21, and try again. If you were a little rich at 20, 1mm will make a difference. 3 mm makes a LARGE difference, and IMHO is too much of a change in one step.