R65 It's not a GS but maybe someone can help

[BigyellowGS]

A friend has just purchased a 1981 R65... But it has a "slight" issue..

The bike will run and tickover okay.. no nasty noises and the gearbox is actually nice enough.

BUT... If you rev it passed about 3K and let go of the trottle the revs seem to hold on... not dropping off again... A little bit of brake/clutch and you can force them back down... once they drop below about 2.8k revs.. they drop as per normal.

The bike is fitted with Bing CV carbs.

I have checked:

No cables are snagging anywhere and that the throttle butterflies are actually shutting when the throttle is released.
Checked for any air leaks between carb & engine and between the carb and air box.
Checked the Diaphrams... These appear to be brand new, as do the slides.

Now all I can think of is that the slides could be jamming as they drop back down? or when the last owner replaced the diaphrams he attached them wrongly and the slides are the wrong way round (is this possible - should the holes in the bottom of the slide be at the front or back?)?

Any ideas on things to check would be great... As I intend to spend some time in the workshop tonight, stirpping and checking as much as possible.

Cheers!

 

[Deleted Member MS]

Someone will be along to verify this but once the diaphrams are fitted to the carb top, i think its impossible to get the carb top on the wrong way round as there is a small "lug" on the diaphram thats sites in the carb body.
I suspect however you are questioning if the "D's"/carb tops have been put together correctly. ??? On that one, im not sure if thats possible.Sorry.

Daft question, are the return springs ok (and in place). (Both inside the carb top AND on the throttle body . . . . cable returns).
Take the inlet rubbers off, open the throttle . .see what happens, have a look into the carb..
check for returning slides for instance.

Good luck.

Ps . .bet its something simple. ?????

 

[(RIP) Proff]

Check the little caps in center of Carb tops they should be airtight !!
causes the problem you are outlining if they ain't

 

[Kenny]

Proffs right....but also chack that the tickover isn't to high with the stop screws..this also causes the revs to stay up ( don't ask me how though )...

 

[BillN]

When you get a problem like this I always look at the following, before touching the carbs.
Go through these basic procedures and see if there is a change, (improvement), after each step:

1). Take the tank off, empty it and clean it out. Petcocks and filters. Then use fresh petrol.
Any improvement?
2). Always begin by checking the tappets, remember this must be done cold.
Any improvement.
3). Have a look at and check the plugs, HT connections etc.....make sure all contacts are clean
4). Check for air leaks, spray WD40 on all carb junctions, if you notice a change you have an air leak.
Spray plug leads and coils with WD40.......any changes......any improvement
5). Choke cables, make sure that they are seating properly.
6). Throttle cables, same as 4).

Then start on the carbs .......Clean float bowls, air line........Sync carbs………..as per the manual ………..if you cannot sync them then you need to look further.

Correct tappet gaps are really important on airhead engines and check for any change after each step

Good luck

 

[BigyellowGS]

Thanks for the replies:

An update:

After working on the bike till the wee hours this morning we now have some semblence of a tickover and clean revving.

I checked and adjusted the valve clearences as a starting point.. And then my mate piped up:

" Oh I forgot to mention I just had the bike fitted with a restrictor kit to bring it down to 33bhp... "

Once he mentioned that I thought it best to check that the mechanic had refitted the carbs correctly... And low and behold one of the circlips was only figer tight.. quick dose of wd40 confirmed an air leak... Not letting him take the bike to that guy again!

This sorted some of the issue, but a good tickover was still difficult to obtain, and it still hesitated on the drop off...

So I grabbed the factory settings for the idle mixture screws and trottle stop screws and reset the carbs to these... Better... but still no cigar.

So.. at 2am I stopped.. The bike now revs perfectly cleanly.. dropping off smoothly..

But I cant get the tickover right.. it ticks over at about 900rpm reasonably faultlessly, but the charging light is on...So I'd like to get the tickover up a little.. But if I tweak the idle mixture screws it makes it worse, if I increase the throttle stops we start to get back to the hestitation in the revs dropping...

Getting the balance between clean revving and a good tickover seems almost impossible! Anyone got any suggestions of where to go from here?

 

[BillN]

It should "tick over" with the gen light flickering

What did you use to balance the carbs..........your ears.......or a some kind of gauge to ensure that they are both the same..........once the engine gets hot things slightly change.............so you have to keep letting it cool down and starting again........if you see what i mean.

You seem to be at the stage where.............set the carbs up......go out for a run........stop...see what it is like........tweek........come back and check

Don't spend hours on it....you will only p1ss yourself off

Have you had the air cleaner off to check that all is OK

Good luck

 

[BigyellowGS]

Thanks BillN.

I have replaced the air filter, so there should be no problems there...

I used the good old listen approach to get the basic balance on the carbs done.. But used vacuum guages to try and fine tune them.

I think your right though.. We are going to take the bike out for a really good run tonight and then recheck the carb balance etc.

I'll let you know how its goes!

Cheers, J

 

[Deleted Member MS]

The only time tickover on my GS is good is when it is warm. When cold,it wont tick over at all.
Re any jets, esp idle/air screws, make sure there is NO crap, dirt or dust in there.
I have had similar probs to you, and found lots of "sludge" on the airscrew "tip". Once cleaned, it was perfect

Re valves, timing etc etc etc ALWAYS set carbs last ! (IMHO)

 

[Steptoe]

R65 1981 - does it have the bing flat top carbs fitted ?? or the usual dome top.

 

[BigyellowGS]

martin's - I will check for sludge when I get down the workshop later..

Steptoe - It has the normal dome topped style fitted, not the flat ones.

Cheers for all the advice and help everyone.. Hopefully with an hour or so tomorrow and a good ride out the bike will be sorted

Hopefully

 

[FW190]

once you get it all balanced, you can if memory serves me correctly... de-restrict the airbox by removing the right hand inlet trumpet...

My old R65 was a bugger to keep the carbs intune, always used to take it to Angelo Donato... back in the day.. bit of a job to get it too him now though as he's in Greece!

I remember that they used to suffer from a lot of condensation in the carb bowls... sorry mate, can't be of any more use.

 

[BigyellowGS]

A big thankyou to everyone for the thoughts and help..

We finally got the bike running well about 11pm on friday 20th... And set off in good spirits for the lakes and scotland on the saturday morning at 4am.

Not only did the bike behave itself for the 1300+ mile blat round, but Phil the owner of the bike managed the whole lot without suffering too much pain! (Especially good as he only passed his test the week before).

I'll be posting something about the trip once I've got copies of the pictures from Phils camera.

Cheers again! J