Popping Exhaust on Deceleration R25/2

Begonnen von Kurt in S.A., 22 April 2019, 14:37:07

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Kurt in S.A.

My R25/2 makes a popping noise when I roll off the throttle for a gear change.  I think it's the exhaust...hard to really tell but seems like it.  During my gear changes, I pretty much roll the throttle all the way off, wait for the engine to spin down a bit, then select the next gear and roll the throttle back on.  The popping is more noticeable when the engine is cold and I'm just starting out...not so bad near the end of the ride.  Is this too rich and excess fuel is being burned when the exhaust valve opens?

I'm only getting about 50-55 mpg.  I have a 110 main jet and the jet needle is set in the 3rd position from the top, so that is a richer position.

Thanks..Kurt
Kurt in S.A.

Kurt in S.A.

Kurt in S.A.

Dappsull

the popping noise might be due to a leaking seal between cylinderhead and exhaust.

Pederkr

Zitat von: Kurt in S.A. am 22 April 2019, 14:37:07
My R25/2 makes a popping noise when I roll off the throttle for a gear change.  I think it's the exhaust...hard to really tell but seems like it.  During my gear changes, I pretty much roll the throttle all the way off, wait for the engine to spin down a bit, then select the next gear and roll the throttle back on.  The popping is more noticeable when the engine is cold and I'm just starting out...not so bad near the end of the ride.  Is this too rich and excess fuel is being burned when the exhaust valve opens?

I'm only getting about 50-55 mpg.  I have a 110 main jet and the jet needle is set in the 3rd position from the top, so that is a richer position.

Thanks..Kurt

Check the tension on the cylinder head as well. Min had that problem.

strichzwojan

Zitat von: Kurt in S.A. am 22 April 2019, 14:37:07

I'm only getting about 50-55 mpg.  I have a 110 main jet and the jet needle is set in the 3rd position from the top, so that is a richer position.

Thanks..Kurt

mpg or mph??? If you have the BING 1/22/44 you could probably use a 115 main Jet. If ist the BING 1/24/41 or 42 use the 120 main Jet.
As recommended above check the seal between  head and hose. I found that it is much tighter using a "starnut" than the one with the holes. What might be interesting too, is that sand and dirt cannot come close to the thread.

Jan

4Taktix

Hey Kurt,
if she ran fine before the popping started, I'd check two things before I change the mainjet. (apart from exhaust leaks, this is also a good hint)
1st: Obviously the popping is temperature related, so it's very likely the mixture. (too lean) I'd check if the idle jet is clogged and if not,
       tune the idle-setting to rich. (depending on the carb (Less air or more fuel) turn it in or out in 1/2 turn steps.
2nd: If there's no change after 1st, please check, if the flyweights of the timing regulator fold in if you drop revs.
       This can be seen very easy with an ignition flash gun, if you have one.
      ( peferably in the dark, gun connected as for checking the timing. So you have a strobe, causing a virtually non-rotating reglulator )
      If they do not, or very delayed, check lubrication/free movement of the timing-lobe on the Dynamo-shaft.
      It may also be, one of your regulator-springs is broken or they are too weak after all the years. -> replace.
      If you have the Dynamo-cover off anyway, also check if the central Dynamo-bolt is tightened. Otherwise your timing may be out of tune,
      then you have the root cause. Timing should be checked anyway. I'd do this, before I touch anything else.

Good Luck and Regards,
Sascha
Think outside the box !

Kurt in S.A.

That's miles per gallon...I was thinking it would be higher.  Wondering if dropping the needle down might improve that.  Early on the suggestion was to try different main jet sizes and/or needle positions and find out where the throttle didn't help anymore, meaning I had all the gas I was going to get.  I did try different jets at one point, but can't seem to find my results.

I have the 1/22/44 carb.  Going to a larger main jet would run the mpg down more, wouldn't it?  I figure that I'm running on the main jet more than not.  By the point where I'm doing say 70-80 kph, I would suspect that I'm pretty much into the main jet, the needle having pulled almost entirely out.

Kurt
Kurt in S.A.

4Taktix

Do not try to select your jet or needle-positon by focusing the mpg, this is no prosper way!
I myself (R25/3) had a 185 Mainjet instead of the stock 145, and fuel consumption wasn't noticeably higher than before.
the effect of mainjet starts roughly at approx. 1/4 throttle up to full. The needle position similar. It will never ever be "pulled almost entirely out".
If so, than you might have a wrong needle or assembly.
Even the idle-jet and setting influences Performance from idle up to way more then 1/2 throttle, don't underestimate the idle-setting.
Anyway, you should do the suggested checks without considering fuel consumption and come back.
We were not very familiar to measure it in mpg, but you might transfer/calculate: If she slurps up to 4 litres per 100 km (balls to the wall), everything is normal.

Regards,
Sascha
Think outside the box !

Kurt in S.A.

Sascha -

It will take me a bit to check out some of these things.

As for fuel usage, I'm not accustom to KM/Liter, but if I translate that to Miles/Gallon, 100KM/4L is roughly 58 MPG.  If I read you right, "balls to wall" meaning at near wide open throttle, the bike should consume the 4L in 100KM.  I'm riding around not anywhere at "balls to the wall" and I'm getting much less than 4L in 100KM (which is 58 MPG).  I think I'm getting pretty horribly fuel mileage.

Kurt
Kurt in S.A.

Borgward

You're right, Kurt. With your R25/2 you should typically reach a milage in the range of 70mpg.
Another source for your problems could be a wrong setting of the valves.

Hubi

Kurt in S.A.

Hubi -

The valve clearances are where they should be, last time I looked.  I'm using 0.15mm intake and 0.20mm exhaust.  The bike has always gotten this type of mileage before and after the rebuild.

Kurt
Kurt in S.A.

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