Getting my son's bike running better

[salamander]

A link regarding the carb venting issues with the wind.

This is my bet on your 55+ mph stumbling problem.

I agree with jester.  Having the carb vent tube all the way back there will cause crosswind stumbling.  It should terminate somewhere that will be out of the wind.  In the stock set up, it terminates behind the airbox between the airbox and the battery, and is held there by a clip.  I think jester routed his over the battery and terminated it behind the battery box...I think.

Thanks to both of you.  I'd read that thread about the wind and the vent hose, but it was a few weeks ago and I'd forgotten about it.  I can see how the hose, right behind my right leg with the pants flapping in the wind might have some turbulence around it.  When I hit the stumbling while riding, and it settled down after easing off the throttle, I assumed it was a starvation issue, but I also would have been going slower, so it could have been the turbulence.  I will re-route the hose, and I also plan on re-checking the float heights with some better clear tubing than I have now.

With the lunchbox air filter, I have a pretty big gap between the filter and the battery -- ending the vent hose between the two might not be a great idea.  That leaves me with really only two options: extending the hose to go behind the battery, or dropping straight down from the carbs to dangle the hose above the rear part of the engine.  Any suggestions about which might be more suitable?

Thanks.

[bombsquad83]

I would go behind the battery for 2 reasons.  I think there will be less wind there for one, and two I wouldn't want the tube going too low or you might actually start siphoning the gas out of the carb bowl.  Probably not, but it's a thought.

[salamander]

Thanks, I might have enough length to make it behind the battery, and if I don't, I can get a longer piece of hose.  Either way, I'll be sure to keep the end of the hose above the fuel level in the carb bowls.

[salamander]

Sad as it is, my son goes back to school in about ~2 weeks, and I'm almost out of vacation days.  Trying to be realistic, I think we can get a couple more things done before we have to get back to the real world: 1) check the valve clearances, and 2) try to fine tune the carbs.

Figuring that #1 needs to happen before #2, I cracked open the camshaft cover and measured the clearances.  Both of the exhaust valves are the same: a 0.102 mm gauge slides in easily, but the next size up (0.127 mm) does not.  Both of the intake valves had clearances of less than 0.038 mm.  So, here's my plan -- if something sets off a red flag, let me know.

1. leave the exhaust valves as is -- I've seen the posts about using a larger-than-spec gap on the exhausts, and I'm going to give it a go.
2. order shims 0.05 mm thinner than the current ones to get back into the spec range.  Problem is, the numbers printed on the current intake shims are both 2.?5 -- on both, the second number has been worn away.  I have a micrometer around somewhere and hopefully I can dig it up; if not, I'll try to get one of the local machine shops to measure them for me.

Once I know the size of current shims, I'll order some new, thinner ones.  While I'm waiting, though: out of curiosity, when I eventually take the re-shimmed bike on a test drive, should I expect to see a difference, or am I just catching up on maintenance that probably should have been done sooner?

Thanks.

[bombsquad83]

I wouldn't expect to see much difference with those measurements.  Might have to adjust the idle screw a small amount.  That is about it.

[salamander]

Finally got around to getting the new shims for the intakes, and hope to have time today to get it all back together.  Just a couple of questions for those of you who have done this before -- it would be really nice to do this right the first time with no leaks.

First, the service manual says to put sealer in the groove in the cover before putting the gasket back in, so that's what I plan to do.  I have some of the Permatex Ultra Black.  Would this be a good choice for the valve cover, or would one of the other sealer types be better (higher temps, better resistance to gas etc...)?

Second, do I need to put anything on the lower surface of the gasket that contacts the cylinder head?

Thanks.

[bombsquad83]

What you have there will probably work fine afaik.  You want to put a VERY SMALL amount in the groove of the cover just to hold the gasket to the cover for install.  If you put too much, you will be cleaning up the excess that squeezes out for a long time.  Dont ask me how I know.

The only place that you put any gasket sealer on the face of the gasket is a dab in each corner of the half moon shapes.  Just enough so it squeezes down to cover the whole surface on install.

If you don't have the special valve shim tool to hold the buckets down, I would suggest holding off this job until you get one.  It will save you a lot of headaches.  Some here will say you can do it with a couple screwdrivers, or by removing the cams, but it was way more trouble than it was worth trying to do it those ways for me.

[salamander]

I agree with jester.  Having the carb vent tube all the way back there will cause crosswind stumbling.  It should terminate somewhere that will be out of the wind.  In the stock set up, it terminates behind the airbox between the airbox and the battery, and is held there by a clip.  I think jester routed his over the battery and terminated it behind the battery box...I think.

I re-routed the vent to behind the battery.  That looks like the most out-of-the-wind spot I have available, but the stumbling is still occuring.

After a few more test rides using the same route, I noticed the stumbling happens at about the same place on the ride -- after starting off from a stop sign, I'm accelerating (fairly aggressively, for me at least) up to 55 mph while climbing some shallow hills, and it's shortly after that that the stumbling starts.  Going back to a fuel flow problem, I ran the route again with the petcock on PRIME and there was no stumbling; immediately ran it again with petcock in the ON position, and it stumbled at the same place in the ride.

I can't rule out a problem with the vacuum line to the petcock, but it seems more likely that there's something wierd with the petcock itself.  I'd like to get into the petcock to see if the ON passages are maybe partially blocked before I decide to replace it.  I saw the screws on the backside that I think would get me in, but is it possible to remove the rotating part of the selector from the front without destroying anything?  The backside would get me to the diaphragm (I think), but I'm more interested at this point in the passages in the rotating part.

Thanks.

[bombsquad83]

Replacing the petcock seems to be a very common repair when people buy older GS's.  I think that rubber diaphragm just gets stiffer over time and impedes fuel flow.  Ethanol in gas is probably contributing to the stiffening rubber these days.

[BockinBboy]

Edit: Somehow posted message on wrong thread?..

- Bboy