Rough idle, fuel-line issues.

[leonardhcross]

The 76 project bike was idling better and is now rough. As with most of these abandoned bikes, the tank needed serious cleaning. Today, I check the fuel lines to see if that explains the deteriorating idle. Experienced mechanics will catch my "rookie" mistake right away. But, it took me a while. https://www.youtube.com/watch?v=lH7Te82ec1s

[leonardhcross]

I received a PM asking me what my "rookie" mistake was. I'm not sure why they didn't just reply to the post. The mistake was not filling my gas tank above the level of the petcock when I started. The first couple of times, I got no flow through the lines and assumed that that indicated a blockage. Once I realized my mistake and added more fuel to the tank, gas flowed freely out of the tank but not after the filter. So, my tank lines are fine and I replaced the filter.

[Sidecar Bob]

It isn't related to what you were doing but it reminded me of when I tried using a vacuum operated fuel pump (snowmobile part). It initially seemed to be working really well at first and I even ran it at 5000 RPM in 3rd gear for about 4.5 minutes as a test.
But a few days later the carbs ran dry when the fuel level approached the level that the pump was mounted at. Turned out it was just slightly assisting the gravity feed
After that I rebuilt the mechanical pump and it still works fine

[leonardhcross]

It isn't related to what you were doing but it reminded me of when I tried using a vacuum operated fuel pump (snowmobile part). It initially seemed to be working really well at first and I even ran it at 50000 RPM in 3rd gear for about 4.5 minutes as a test.
But a few days later the carbs ran dry when the fuel level approached the level that the pump was mounted at. Turned out it was just slightly assisting the gravity feed
After that I rebuilt the mechanical pump and it still works fine

Thanks for sharing Sidecar. It does make me feel a bit better about my goof.

[redglbx]

Hey, if you do this stuff long enough it’s bound to happen!!!! Luckily I’ve never had a problem like that .

Anyway,,, Bob at 50000rpm in third what were you doing,,,like mach 2.5 ? Must’ve been a truly well tuned Wing !

[leonardhcross]

There's a ton of good humor on this site. A definite bonus.

[Sidecar Bob]

Anyway,,, Bob at 50000rpm in third what were you doing,,,like mach 2.5 ? Must’ve been a truly well tuned Wing !

Sorry, I meant 5000 (it's fixed).
That was the '83 with the '79 engine (1100 final dive + 1000 transmission = about 1.5 gears higher than stock) so 5000PM in 3rd was about100Km/h. I didn't normally run at 100 in 3rd (& especially don't now that I have the '82 engine) but I was tying to test the pump.

[redglbx]

Yep Bob, I knew that but was just testing my smart azz button, no Ill intent meant !

[Sidecar Bob]

Yep. I had that half typed before I noticed that I'd put an extra zero; I figured what I was saying might be useful to someone so I finished it.

[redglbx]

[leonardhcross]

I wonder if someone can clarify. I have read that using an OEM air filter is very important. What are the differences between an OEM air filter and aftermarket? And..... how do those differences impact idling? One last, simple question.....If the air filter quality is so critical, I would assume that tuning your carbs with the air filter off would cause problems once you reinstall the filter. Is that the case and, again...why?

[redglbx]

Len, this is one of those hot button topics, personally I have been running a K+N oiled filter for the last 40 or so years, I have K+N drop in filters in pretty much everything I own (cars + bikes) so that should tell you where I stand on this subject. I have modified the heck out of my airbox on my 76 GL with many variations and aside from increased intake noise found no real ill effects.

The k+n/ airbox myth is based on the mistaken belief that you need those to increase or produce vacuum above the carbs and that the carbs won’t work w/o it. Pure horsehockey ! The slide vacuum is created by the air passing over/under the slide bottoms with the holes that the air passing over those holes creates the vacuum that pulls the slides up. If you just do an”drop-in” air filter it should run fine, just don’t over oil it, that is not a good thing.

If the airbox/airfilter thing was correct the motor wouldn’t respond to throttle inputs with the airbox removed, but it does.But removing the airbox will lean things out significantly, if you rejetted things to comp for the airbox removal it would run fine ! The only real negative is by removing the airbox would eliminate the slight vacuum created in the crankcase by the vent that imho keeps a negative pressure on the backside of the rings and helps reduce ring flutter there.


So with all that said I’ll go put my flame suit on and wait.

[CYBORG]

No flame here. I agree with what you said 100%

[leonardhcross]

Great feedback. Thank you. You mention "oiled" filters. In most of my small mowers, the filter would be a sponge which I would oil and then squeeze out any excess. My paper motorcycle filters do not come with an oil sleeve so I am unclear about what you mean by "oiled". What am I missing? Also, I have been pretty casual about the hose coming into the air box from the vent. Sometimes it fits in. Sometimes it just comes close. I'll be more attentive to that.

[Sidecar Bob]

I wonder if someone can clarify. I have read that using an OEM air filter is very important.

I imagine that is more important to the dealer's bottom line than it is to the bike.

When I put Mr.H together in '95 I made the mistake of just calling the dealer and asking them to order me a new GL1100 air filter. I was shocked when the total came to over $50 (with inflation that would be $90 now).
The next time I measured it and spent some time in Canadian Tire looking for an automotive filter that would work; I found a round one that was the right height and could be squeezed to an oval shape for about $10 and removed the metal top from the original one to cover it.
I did not notice any difference at all so I went through several of them before I invested in a UNI foam filter.