Something puzzle me so I need your help and advice

[georgesgiralt]

Hello !
Context : 1982 made R65. Has around 200 000 km. I bought her new in '84 so can't blame the PO.
In 2012 I started rebuild her. Bits by bits. I've addressed everything except the engine main bearings and the cylinders and pistons. (new rings though). Valve train was rebuild in 1994 at 120 000 km.
She runs fine and is willing to go up to red line in 5th gear with a pilot weighting 102 kg.
But suddenly, since a fortnight I'm unable to go above 5000 RPM in fifth gear in full throttle. If i get her in 4th everything's fine and she goes up to the red line.
If I back up the throttle a bit it seems to ease her a bit and she goes a little faster without crossing the 5k rpm barrier.
I've checked the valve lash and it is good.
I've checked oil consumption and it is normal.
I've checked carb balance and it is good.
I've checked fuel flow and it is double the minimum figure CHITECH gives on their literature. Tested on both carbs, one at a time.
I've checked air filter (put a new one) and it is OK.
I've checked the plugs and they are fine (less than 5 000 km on them).
I've checked static advance and it is good.
I've tried to vaporize Start Pilot around the rubber between carbs and head to see if there was an air leak. No, none.
I've checked the main jet and the mixing and emulsion chamber of both carbs. It's OK.
I've the factory prescribed jets and needle position in carbs which where totally rebuild in 2013 (needles, jets, gaskets, floats, diaphragms, you name it).
I've the right plug getting a strange red color on the porcelain. Brick red.
I've noticed that if I open the choke when in fifth gear and throttle wide open she goes further  the 5K rpm barrier. .....
So as I'm out of options and would like to go on a ride next week to enjoy this very hot winter we have, I ask for help.
What do you think ? What should I check ?
Thanks in advance for your advice or garlic and Holly water !  

[Bob_Roller]

Have you checked the rubber diaphragms in the carb tops ??

The red color is usually caused by an octane boosting additive, have you been adding any to the fuel ??

[georgesgiralt]

Hello Bob,
I use lead substitute. It is old (the can was bought when the bike was in constant use prior 1998. When I bought the Triumph, she was used once in a while when the Triumph was in repair)
I do not know how to test the diaphragms except by replacing them by new ones. Which begins to be costly. I already have a couple of them with "doubtful" written on the boxes.
The actual rubber in use is from BMW and I've not heard that they suffer from quality problems.
I've not tell you that I live in France and the fuel contains up to 5% ethanol. I use the high octane version (said to be 98) which is supposed to contain the less ethanol.
How could I test the diaphragms ?

[Barry]

How could I test the diaphragms ?

If they have no holes and the slides move freely over their full travel then the diaphragms should be fine.

You could remove the carb elbows and observe the slide movement while you rev it. I'm not sure how far they will lift but it might least show and difference between one side and the other.

[georgesgiralt]

Good idea !
I've looked at the doubtful ones, and they look perfect to a naked eye. I've lighted them with a powerful white led and looked through them to check for pinholes. Not found any.
So I put talcum powder on them in order to conserve them a bit more.
I'll check the slide from behind with the pipes off.

[Matt Chapter]

I use lead substitute. It is old

I assume the bike ran well using this before, but I would consider not using it or getting some fresh.  Is the lead substitute necessary?  I just use whatever 87 octane (US) I'm near when I hit reserve, I'm sure it's full of ethanol.  I had my '84 motor spun all the way up to the red line in 5th gear over this past weekend...

[georgesgiralt]

Matt,
My exhaust valve close themselves. Every time I adjust the lash, i find one or the two under the clearance.
This is why I put lead substitute because I'm still searching for a capable shop to replace the seats and the money to pay for.
Today, I ran the bike to get some errands attended to. She was very rough and was complaining between 4K and 5.5K RPM even on low gears.
As I had to get my job done, I continued at the legal speed   and, then when going back home she was as sweet as a cherry pie...  Tomorrow I'll take her on the back roads to see what's in her guts...

[montmil]

I would be suspect of the diaphragms.

My 1981 R65 would, on occasion but not every time, lose power and revs when I was slightly exceeding the speed limit in fifth gear. Backing off the throttle with reduced revs brought things back to normal. Did this not every time but stopped entirely when I replaced the rubbers with BMW OEM diaphragms.

[georgesgiralt]

So,  this morning I checked my logbook and it appears that the problem was the same last year between December and January.
I then exchanged the diaphragms for brand new BMW ones. The problem went away at some point without me clearly identifying the cause.
I've done a nice 100 km ride this morning using small, medium roads and a bit of highway.
The problem is on and off.
So I called the local BMW Guru and he told me to look at the tank to see if it is open for air; (I cant translate correctly "mise à l'air"). He said that there is a valve in the tank cap and sometimes it stays closed.
And if nothing cures it, I'll look at the ignition. The hall sensor is new (HKZ101) as is the wiring but something could be wrong sometimes.
All in all, I had a wonderful ride this morning. Not too many people on the roads, not so cold, and giving a sense of the coming spring.  

[Bob_Roller]

The fuel tank is vented through the fuel cap, I don't think there is any type of valve in there, but then I have not taken one apart either .

Simple test, leave the fuel cap a bit loose so, you know fuel tank venting is not the issue .

[Barry]

I've had gas cap venting problems occasionally which slackening the cap off cured. The cap has to be designed to let air in as there is no other route and if BMW tried to design some way of preventing vapour coming out I guess it's no surprise that it sometimes doesn't work after all these years.  If the the cap came apart easily without damage I'd say take it apart and have a look but I don't think it does.

[Lucky_Lou]

You all know I am not a fan of additives...... reading this i am thinking that there cannot be a diaphragm problem as the vacuum would be lost in 4th as well as 5th gear at the higher revs, Opening the "Choke"/ enricher points to the mixture being weak try lifting the needles a notch and if you have time strip the carbs check the main jet.
Lou

[georgesgiralt]

Lou,
I've done this a fortnight ago during the 10 000 km maintenance.
I remove the main jet, the main jet holder and mixing chamber. There is often water mixed with "some dirt" which increase gas use as the air is restrained. So at every oil change I clean there. It is a 5 minute job during oil dripping.
The needle is at the top already so if I've to enrich the mixture I've to change the needle jet.
Two things plead against a carburetor problem :
1) the problem is not here given the same throttle opening but at maximum power.
2) it is intermittent.
So I guess the cap not properly venting the tank could be a cause. Or something on the fuel tap reducing fuel flow sometimes.
I never found paint flakes in any filter (gauze in the tank, gauze in the fuel tap) or in the carb bowl. But there is a start for everything, right ?
I'll check the lower, in the tap gauze tomorrow (I filled her up today...)

[Lucky_Lou]

Is this bike Points or electronic ignition ? I cannot remember when points were phased out.. after 1980 though. You mentioned the right plug colour..... I would focus on that side.
Lou

[georgesgiralt]

Electronic ignition which has been completely overhauled a couple of years ago.