On the road again at 40.............the bike that is

[robinc]

Thanks Pete.

Just cleaning out the scrap bins....lol.
What are those 3r's......Reduce, Reuse, Recycle.

 

[5twins]

I've been into the 650 for about a dozen years now and in that time, I've seen the knowledge base grow by leaps and bounds, mostly due to forums like this I think. Maybe some of the stuff was previously known but I think we discovered lots of it on our own. I doubt anyone considered using an automotive regulator or rectifiers from the electronics world before Pamcopete figured it out. K&N style pods were the norm before we figured out through trial and error that they just don't work right. In fact, I started out with them myself. I never heard of anybody adjusting their cam chain while the bike idled until I brought it up. That's actually a Yamaha technique I borrowed from their 4 stroke singles. I saw no reason it wouldn't work on the 650 and well, it works just fine, better in my opinion than the manual specified "motor off" method. And the list goes on and on. And it keeps growing. We're still coming up with more stuff to make these better bikes and ease the servicing routines.

 

[robinc]

I've seen the knowledge base grow by leaps and bonds, mostly due to forums like this I think.

I think that's very true 5twins.

This forum is what it is because of the amazing contributions made by you and the other guru's.

You guys are not only very skilled technically you are also excellent communicators and teachers and help those of us at the earlier stages of learning understand and have the confidence to tackle pretty much anything.

I believe manuals are obviously necessary and always start there, but many a time you or one of the other guru's have explained and documented something better than any of the manuals has.

Thank you!

 

[retiredgentleman]

Yes, Pamcopete is a very innovative guy. Over the years, I have learned a great deal from him. If there was an XS650 Hall of Fame, I think Pamcopete would be one of the first admitted.

 

[TwoManyXS1Bs]

Good sleuthing there, Rob.
I run my fuel level a bit lower.

Here's a closeup of yours:

Your fuel level is about even with the carb flange.

And mine:

Currently about 2mm below the carb flange.
I've had it as low as 6mm below the flange.
Still tweaking, I may lower it to 4mm below the flange.

 

[robinc]

Thanks 2M. Interesting. That pic was where they were set before work was completed.
I had set them to allow a little more fuel in the bowls as I originally thought I was chasing a fuel starvation problem, not flooding.

I now have them set to the bottom of the float bowl flange.

Next time they're off I will try lowering them even further.

Thanks for the info. Still fiddling here as well.

 

[TwoManyXS1Bs]

Gonna explain myself here. I have a problem with the manual's depiction of the "clear tube method". It calls for a specific tube diameter, plus shows the fuel level in the clear tube as being higher than the level in the bowl.

This would be an appropriate accounting for the capillary action of water in a tube. I haven't seen this with fuel.

I'm also considering that gasohol may displace floats a bit differently from the fuels of the '70s, slightly different specific gravity.

Floats can also become heavier, from surface deposits, allowing higher fuel level. Your weighings of different float offerings calculates out to a little over 1mm in resultant fuel level height.

Kind of a personal project, I've been playing around with fuel levels, to acheive the best balance of idle stability and gas mileage. Right now, on my '71 carbs, the preference leans heavily towards higher float settings, 27mm or more, compared to the book's 25mm...

 

[robinc]

Another interesting project 2M.

So you're saying that fuel does not have the same capillary effect in a tube as water? Once again due to differing SG's.

I always look at the bottom of the meniscus as the true level.
I have been running Shell V Power gas which is supposed to be ethanol free and the highest octane I can find around here. I wonder how that might affect float levels. Will try some standard gas one time and see.

Am going to try a 26mm setting next time. 2mm over spec.

 

[TwoManyXS1Bs]

Yes, water has a much higher capillery action, a polar liquid, with a much higher surface tension.

The capillery action would be ignorable using the more-convenient larger tubing. That callout for a specific 2.5mm (3/32") tube, to purposely induce the capillary effect is ridiculous. The chemical nature of the tubing would also have to be specified, as it would influence the adhesion forces. Using a larger 5-6mm (1/4") tubing is simply easier, eliminates the capillary accounting, and gives you a direct reading. My 2-cents...

 

[robinc]

Yup. Makes sense.

 

[5twins]

Just keep in mind, if you get too low on the fuel levels, the bike may become difficult to start. Keep an eye on that as you're experimenting with lower levels. I ran across this on one I worked on last year. It was very hard to start, even warm, but seemed to run OK once you did manage to start it. I figured it just needed a good tune-up but that didn't cure the starting issues. Then I checked the float levels. Both were low but one was really low, about 8mm below the flange .....

The 6mm setting 2M tried may be about the limit. Get much lower and you may suffer starting difficulties.

 

[robinc]

Ok, good heads up 5twins. Thanks.

 

[TwoManyXS1Bs]

Agreed, that 8mm below the flange is a bit too low.

Interesting, your "24mm spec, Set at 28mm" implies 4mm too low, which would have the 24mm setting showing fuel at 4mm below the flange, right in the middle of my 2mm-6mm settings...

 

[5twins]

The spec number refers to the recommended internal setting or measurement. That seems to indicate that a 1mm difference there will show up as about 2mm in the tube. That's a '78 carb in the pic which should be set to 24mm. The pic shows it how I found it, which turned out to be at 28mm once I opened it up and measured. Here it is corrected .....

 

[TwoManyXS1Bs]

So, that pic is of a BS34?

 

[5twins]

No, it's a BS38. The point I was alluding to now is that how much the tube level is off (below the flange) isn't the same as how far off your internal setting is. It appears to be about a 2 to 1 ratio. 1mm difference on your internal setting will show about a 2mm difference in the tube reading.

 

[TwoManyXS1Bs]

Ok, got it. I can see that 2:1 on the BS34s (measuring nearer the posts).
On the BS38s, I'm of the 1:1 mindset, so I'll have to experiment to confirm...

 

[robinc]

Wow, thank you so much guys for all this info and updates. I've gotta say that I find all this fascinating.

My bikes running really good considering, and I was planning on just riding out the rest of the season. But here I am fiddling, tweaking, experimenting. Look what you guys have started!
Hey, I think this is great.

Here is a pic today of where my settings are at. Floats are set at 24mm.

I was pretty anal about that height setting this time. Checked, checked, rechecked and then checked again with a digital caliper. Made sure all twists were out. Interesting how my 24mm setting fuel level is lower than 5twins.

I wonder:

1) My settings really weren’t on 24mm. Possible I guess.

2) I had just installed new OEM Mikuni float valves. Maybe 5twins were older valves and valve return spring tension was different?

3) A difference in our floats lead to different levels when in use.

4) Or. After I finished up there was something nagging at me that I had read earlier today:

Using a larger 5-6mm (1/4") tubing is simply easier, eliminates the capillary accounting, and gives you a direct reading. My 2-cents...

Huh. When I was done and putting everything away I checked the tubing I was using and sure enough it was 3/16" ID and not 1/4".
Maybe..... this difference in smaller tubing ID had an effect on the level reading.
I checked the parts boxes and still have some 1/4" tygon fuel line. Will try this tomorrow and see if there is any difference. I would have thought that a liquid will seek it's level no matter the size of container/tubing but who knows.

Easy to try and see.

Thanks again guys. Veeerrryyy interesting!

 

[5twins]

The different readings may be a case of either (or neither) bike being perfectly level. If the bike and carbs aren't sitting level, that can throw the reading off. In fact, in some of the manuals, the instructions tell you to bend the tube up both sides of the carbs and compare readings. This will tell you if the carbs are sitting level (readings match) or not (don't match).

 

[robinc]

Yes I guess that could be true 5twins. In general we tend to think of these as pretty old/crude devices when in fact they are very precise instruments.

This is all happening on a concrete slab but as we know that is no guarantee of level. I'll put some small levels on as well and see what that shows.

More great info, thanks!