heard a funny sound, due to heat? Need valve adjustment?

[kheerema]

I have a '75 R90 that runs like a sewing machine, just a bit heavier though :p .

Yesterday, while commuting home in approx. 103 degrees of heat, my bike made a funny pronounced ticking sound, louder then the usual music heard from below. It happened after 8 miles of open highway, 2-5 miles of stop and go city traffic, during a last stretch of 8 miles or so of open highway.

During that last stretch of open road, i had to whack the throttle open to pass a truck to make my exit. During that "whack" I heard a ticking sound from below.

Is this my bike's way of saying "valve adjustment please?" I tuned everything up when I bought the bike in February, but I'm not sure how many miles I've put on since then. I plan to keep track better going forward.

This morning, in cooler weather, I couldn't replicate the sound no matter what I did with the throttle.

[20774]

Kevin -

Seems to me "whacking" the throttle on a hot day to pass a vehicle would put the sound in the pinging category. You probably just demanded more of the engine for the temperature and gear conditions. Cooler weather seemed to make the difference. I'd monitor the situation and go from there...

What the heck are you doing out at 103 degrees? I guess I'm a wuss...

[kheerema]

i'm out today as well, just hate driving in the cage even with A/C! riding in these temps is a testament to these bikes reliability...

I'm running super pump gas and never experienced this before, but this is as hot as the engine has been, i'm sure in my ownership of the bike.

i guess i shouldn't say whack, it was more like maybe 3/4, or a good turn of the throttle going 65/70 or so in top gear.

[20774]

Were you at like 4K RPM at that point? I'd say rolling on throttle at that RPM in 5th gear, for the conditions, might easily induce pinging, depending on how rich/lean the carbs are. If you really needed to get "smartly" around someone, it might be best to drop a gear and get the RPMs up. That's not my style, but certainly you get a little closer to the power band. Isn't peak power in the 5-5.5K range??

[kheerema]

I think i'm usually a bit higher in rpm's then that since when i'm going 75 its around 5k. I think maybe i was around at least 4.5k if not a bit more, and that to me usually feels like the beginning of the "sweet spot". but, my tach bounces a little bit, its never really totally steady, so i would guess there is some slop there!

well, i think i'm better off "whacking" the throttle on the crotch rocket!! i'm the same as you, its not my style on this bike to downshift for acceleration or whack the throttle. with these "delicate" to operate gearboxes...must concentrate on every single shift, I try to avoid extra shifts!

I may actually be a bit lean, i pulled the plugs a few weeks ago and noted some crusty white stuff on the plugs that cleaned off pretty easily. I haven't messed with the mixture, but I did have a former BMW mechanic synch the carbs when he overhauled the clutch/tranny. I really don't know if he altered the mixture. I am skilled at Honda carbs, but unfamiliar with the Bada Bings. I haven't touched them because this darn thing starts right up first crank with 1/2 choke and a bit of throttle, then back off the choke and she purrs like a stroked kitten. no stalling here! Throttle response is crisp. I've ignored the "if it ain't broke..." mantra a few times and with the 70's bikes i've learned it to be especially true!

[20774]

I also use gas mileage as a way of judging how the carbs might be set. What kind of mileage are you getting? High 40s (leanish)...low 40s (richish)? Once you get past 1/4 throttle, you're essentially operating on the slide needle and its jet. If you put in the next step jet, you're making a small change towards rich. If you were to pull the needle up one notch, that would be a coarse change towards rich. As you approach 3/4 throttle, you begin to use only the main jet.

Changing the main jet is easy, access is from the float bowl...can be done without affecting the basic synch. However, changing the slide needle or the needle jet might require a resynch and is more difficult...the jet is changed from the float bowl but the top of the carb has to come off to move the needle up. But trying the jet changes might be a quick and interesting experiment.

[lkchris]

Since a warmed-up Airhead engine quite normally sees oil temperatures around 200 degrees F, difference in ambient between say 80 and 100 degrees F is meaningless as regards engine cooling.

What is different, however, is temperature of air mixed with fuel as it goes through carbs, and a higher initial mixture temperature can lead to pinging.

No matter what you're doing in relation to engine tune, valve adjustment must be correct to permit correct evaluation of any other changes. Check it anyway, that is. Valve adjustment by itself is unlikely as a cause of pinging.

Your "sound" is likely pinging (preignition) and is likely caused by combo of high intake air temp and lean mixture, and the latter can be caused by carb settings, carb malfunction (see dirt), or vacuum leaks at rubber hoses between carb and cylinder head, etc. Also a possible culprit is any inline--that is nonBMW--fuel filter, which can restrict fuel flow and/or contribute to fuel boiling (vapor lock). They're always a bad idea.

What your engine can consider "too lean" can change over time as deposits build in combusion chamber. These can raise compression ratio and sometimes become similar to glow plugs, i.e doing the same thing as a spark plug but not in a "timed" fashion. Of course it requires removal of cylinder head to evaluate this, so getting mixture to specification should be done first. Using "top tier" fuels is a long-term help as regards deposits, too. (http://www.toptiergas.com)

There is NOTHING to be gained by changing jetting specifications of original carbs or by installing different carbs. There is plently to lose, of course, as so many "shadetree" engineers so often get the opportunity to learn.

[kheerema]

I also use gas mileage as a way of judging how the carbs might be set. What kind of mileage are you getting? High 40s (leanish)...low 40s (richish)? Once you get past 1/4 throttle, you're essentially operating on the slide needle and its jet. If you put in the next step jet, you're making a small change towards rich. If you were to pull the needle up one notch, that would be a coarse change towards rich. As you approach 3/4 throttle, you begin to use only the main jet.

Changing the main jet is easy, access is from the float bowl...can be done without affecting the basic synch. However, changing the slide needle or the needle jet might require a resynch and is more difficult...the jet is changed from the float bowl but the top of the carb has to come off to move the needle up. But trying the jet changes might be a quick and interesting experiment.

when I've calculated it, I was getting mid 40's, and this included nothing but highway cruising @ 65-75 but also some stop and go stretches because I use the bike to commute through I-35 downtown traffic. I'm not crazy about changing stock jets, I have a souped up Honda 836cc that sits in the garage that I'm having a hard time getting the jetting just right since I altered the displacement
...I don't want to mess with the r90 since it runs so good! I think I'll just listen for the pinging, and avoid big throttle grabs until it cools down a bit. I'll try to do a little better at checking the plugs more frequently.

[kheerema]

Since a warmed-up Airhead engine quite normally sees oil temperatures around 200 degrees F, difference in ambient between say 80 and 100 degrees F is meaningless as regards engine cooling.

What is different, however, is temperature of air mixed with fuel as it goes through carbs, and a higher initial mixture temperature can lead to pinging.

No matter what you're doing in relation to engine tune, valve adjustment must be correct to permit correct evaluation of any other changes. Check it anyway, that is. Valve adjustment by itself is unlikely as a cause of pinging.

Your "sound" is likely pinging (preignition) and is likely caused by combo of high intake air temp and lean mixture, and the latter can be caused by carb settings, carb malfunction (see dirt), or vacuum leaks at rubber hoses between carb and cylinder head, etc. Also a possible culprit is any inline--that is nonBMW--fuel filter, which can restrict fuel flow and/or contribute to fuel boiling (vapor lock). They're always a bad idea.

What your engine can consider "too lean" can change over time as deposits build in combusion chamber. These can raise compression ratio and sometimes become similar to glow plugs, i.e doing the same thing as a spark plug but not in a "timed" fashion. Of course it requires removal of cylinder head to evaluate this, so getting mixture to specification should be done first. Using "top tier" fuels is a long-term help as regards deposits, too. (http://www.toptiergas.com)

There is NOTHING to be gained by changing jetting specifications of original carbs or by installing different carbs. There is plently to lose, of course, as so many "shadetree" engineers so often get the opportunity to learn.

If the difference between 80-100 degrees doesn't make a difference in cooling, then I won't feel to bad commutting during these hot days!!!

You know, I did add some inline filters to the fuel lines...thought it would protect against crap in the tank, etc. I guess by now I could get rid of them. I'll run some seafoam through the next tank too and check the valves soon. Thanks for the advice, i'll double check for boot leaks too...

[Isamemon]

what is seafoam???

[kheerema]

what is seafoam???

its a injector/carb cleaner additive for gasoline. it has a lot of uses, and people swear by it on the Honda forums.

[brickrider]

This might be a good time to pull the petcocks and check the condition of the dirt screens on top. I rode an 83 R100RT for 15+ years (~120,000 miles) and changed them at least a couple of times. They do get weak and fail. If these are in good shape, there is no need for extra filters. My experience with most aftermarket gewgaws is not good.

[kheerema]

i didn't even realize there were screens in there! I assume you have to drain the tank to get the petcocks out. I will definitely do this, I'm sure it has not been done in >10 years (i've only had the bike since Feb.)

I'll get rid of the inline "gewgaws" then!

[lkchris]

If your in-tank screens are that old, they're probably old style, i.e. screen and separate fiber washer.

New screens have aluminum washer built on and you then do not use the fiber washer.