R25 Idles Ok coughs at higher revs

[rolf]

richtig

[rolf]

[Heiko]

I do not know these springs on singlecylinders either... 

[strichzwojan]

What about posting a picture of the advancer here?
Or at least posting the ZG-number, that is stamped on it...

[Kees]

Oh sorry, my fault. I am mixing the twins and singles again.

[Ligarosa]

This is the advance unit (sorry I am posting from the mobile phone), if they are not clear I will try tomorrow again.

[strichzwojan]

Sorry, but that is useless. Try to make the picture with the fixing bolt just in the centre an keep your hands still...

[4Taktix]

I wonder if there is just to much fuel from the carburetor that floods the cylinder, if we take into account the fact that it works better with the idle mixture screw removed.

I'd say your mixture is too rich from approx 2/3 to full open throttle.
If it runs slightly better with idle-screw removed, the carb takes additional air through this opening,
weakening the problem.
Heiko already gave the right advice in Post #21.
First you should retard your ignition timing slightly. At revving to 3000 U/min and above, the "F"-mark should
establish near the lower edge of the check opening.
Before we come up with further advice, please let us know, which particular carb model is mounted.
Then compare the mounted jets with the recommendations of stock factory setup.
I suppose your Airfilter is already cleaned and all testrides were done with full open slider ?

[Ligarosa]

I tried to modify the ignition timing by trial and error (mostly error) and now the F mark stays on the bottom of the inspection hole. The S mark is not in the middle though. Result is it starts easily and revs ok at higher revs without black smoke in the exhaust, better than nothing So the problem might come from wrong ignition timming. Will do a test ride to verify results.

Carb is 1/22/44 I will disassemble it and check for the jets etc.

[Kurt in S.A.]

My Bing manual suggests that the /44 carb is for the R25/2.  For the R25, it indicates that the 1/22/28 was used.  The idle jet is smaller on the /44 but the main jet is bigger on the /44.  There are differences in the jet needle and clip position.

Kurt

[Ligarosa]

Hello all, small update:
I have replaced needle jet, needle, main jet and sealings for the carburetor and readjusted ignition timming so that S mark is on the middle of the isnpection hole (timming light died..chap Chinese things so i did it with a multimeter). Have not checked if the F mark is ok (toothpick trick) but I hope springs are ok since they are new.

Also replaced the ignition points.

Results: bike starts easilly, idles and revs ok (in a handfull grip it chokes a bit). Performance is poor though, i get approx 70 Km/h.
I have observed something like a leak from head gasket but have not verified it.
I suspect the valves timming is off so the next step is to check valves timming and proceed accordingly.

[4Taktix]

Hi Ligarosa,
another thing came into my mind, when I resume your posts. Just a thought.
You should check the center bore hole in the float-bowl-lid and clean it, if clogged.
This hole guides the float-needle - if it is clogged, the float needle can't plunge into it and thus it prevents
the float to go completely up and close the needle valve. Resulting in a permanently "too rich" mixture.
This would explain the noticeable gasoline smell and black smoke.

Another completely different aspect: Has the exhaust muffler been replaced in the past ?
There were many aftermarket-mufflers with a very simplified Inside-design - many members here (including myself)
reported significant loss of power and top speed ( 10 km/h or more ) using these mufflers.
They can be identified by looks into the outlet using a flashlight e.g.
If you see some kind of pierced taper/cone, it is highly likely the original muffler.
If you just see a perpendicular "wall" with one hole in the center and 10 or 12 holes around the outer dia,
then it is the simplified muffler and contributes to the lack of topspeed.

Regards,
Sascha

[rolf]

check the "F"

[strichzwojan]

If you just see a perpendicular "wall" with one hole in the center and 10 or 12 holes around the outer dia,
then it is the simplified muffler and contributes to the lack of topspeed.

The poor muffler has got 6mm-holes. You can modify it to 7mm holes and the muffler will be fine!

[4Taktix]

wasn't it 8mm ? ( in emm's post - containing the flow-tests and X-ray pictures )
However - I enlarged mine to 8 mm and can state: better, but still not yet 'fine'.
I'd rather say: "less bad".
At least it get's you into the ball-park.

[strichzwojan]

Nope! 7mm is the deal...

[Ligarosa]

Thank you all for the recommendations.
Checked again the ignition timing: S in the middle. F mark (toothpick trick) at the bottom of inspection hole. Can this afeect that much the performance?

Exhaust is aftermarket from ulis.

Sprayed the cylider gasket while motor was running and I can clearly see a big bubble forming. That leads to compression decrease to such level that performance drops?

I recently watched a video with an R25 with the same symptoms (except leaking gasket) and the root cause was false valve timming, that is why I have to test this also.

[BSA Bob]

I've seen many references to retarding the ignition timing here.
If the F mark were at the bottom of the viewing hole the timing would be around 5 or so degrees retarded.
So this is OK?

[rolf]

". That leads to compression decrease to such level that performance drops?"

yes

[Borgward]

I've seen many references to retarding the ignition timing here.
If the F mark were at the bottom of the viewing hole the timing would be around 5 or so degrees retarded.
So this is OK?

not retarded but earlier ignition; this seems to be OK for todays fuels

Hubi

[4Taktix]

That's not true Hubi!
The lower the 'F', the 'later' the ignition !
= less advance
Divide the flywheel-circumference
by 360, that's the length for 1 degree difference in ignition advance. So you can determine, where the 'F' should settle in the opening, depending on the deviation from 42° for Center Position.
You'll find the Flywheel Data in the comparisonlist. 'Schwungscheibe' in 'Vergleichsliste' ( Startpage )

[Borgward]

That's not true Hubi!
The lower the 'F', the 'later' the ignition !
= less advance
Divide the flywheel-circumference
by 360, that's the length for 1 degree difference in ignition advance. So you can determine, where the 'F' should settle in the opening, depending on the deviation from 42° for Center Position.
You'll find the Flywheel Data in the comparisonlist. 'Schwungscheibe' in 'Vergleichsliste' ( Startpage )

oops, you're right. Was a little confused...


Hubi

[BSA Bob]

This timing thing seems to be hard to get your head around for some reason. I might print out a little card & carry it with me.
At least as far as English translation goes some of the terminology used can seem a bit contradictory.
So anyways, what do people think of running with about 5 degrees more retard?

[strichzwojan]

If the plug fires at 37 degrees BEFORE Top Dead Center (= OT in german) at revs above 3000 rpm IT IS FINE. No need for 42 degrees today.

Have a close look at the automatic advancer (little springs, lubrication, non-worn-out-condition...) and check ignition timing with a stroboscope!

[Kees]

You should realy try it out yourself. Is it still having full power (topspeed) at the 37 versus 42 degrees? Or maybe better somewhere in between?

[Ligarosa]

Hello all,
Performed a compression test and result is no more than 80 psi. I added a bit of engine oil in cylinder and conducted another test with no significant increment.

Probably the leakage from the head gasket causing this.

I will have to order a new one, replace it (without destroying the engine) and perform another test.

Just fyi there is a youtube playlist demonstrating the process on an R25/3 by Onkel.

I think this is the first step and if compression is acceptable then I will deal with ignition timming. Correct me if wrong but based on info collected here and there a measurement of 100 psi is considered acceptable?

[rolf]

"Probably the leakage from the head gasket causing this."

see #47

[4Taktix]

supplement: the diameter of the flywheel is ~ 185 mm
The circumference is Pi x D -> 3.14 x 185 mm = 581 mm
divided by 360° = ~ 1.6 mm/per degree advance

[Ligarosa]

Hello all,
We have updates, I changed the head gasket and took a small test ride around neighbourhood. Overall performance is better, exhaust poppings stopped but had no time to measure compression but I can feel a resistance now when crancking it . During dismantling I found a "lake" of oil in intake valve space and pieces of probably burned oil in the outtake valve space. There is a lot of axial "play" on both rocker arms which is not  permitted as far as I know so more things to fix.

[Ligarosa]

https://postimg.cc/gallery/nQL9GPY

[Eppo]

Looks like a lot of burned oil in the backflow of the outlet valve.
Did you remove the valve springs and check if the valves might be too loose in their valve guide?
Did you check the conditions of the inlet and outlet channel? Was there oil too?