Return of the Bumble Bee

[(RIP) maverick]

Right where do I start with this one

Jaqhama bought this bike for a recent trip through the UK (May-July)

All went well until the shaft gave up after a few hundred miles, bike has done just over 40k so should of seen this one coming although there was not even the slightest hint of a vibration or anything pointing that it was going to go.

New shaft fitted and off they go again touring through the UK covering a good 1500 miles and a mighty noise coming from the motor. At first it sounded like the bike was running only on one cylinder and I though maybe it is only a dead plug

When they got back to our place took the right side rocker cover off and the play on the exhaust valve is well about a thumb thickness if you can imagine how big the gap would be. My immediate thought is a valve or something has gone. At this point Jaq and Lin lost a bit of confidence in the bike and decided to do some final travelling by train, car and bicycle before setting off to OZ again.

Due to family commitments (8 month baby boy) and work I only got chance to strip the bike down a week ago. Started by checking the rockers for any problems and eventually pulled both jugs.

Put everything on one side making notes of where all goes and which side is what not to mix things up later again.

Initial PM from well known "airhead guru" on the forum told me that he refuses to believe it is a valve it is more than likely a cam follower breaking up. After carefully taking each camfollower out the last one came out in 4 pieces Right side front cam follower collapsed. I drained all the oil and tried to see if any piece could of gone into the motor but all clean and looks like a clean metal break. He was right and goes to show he certainly has seen it all!

Ordered new camfollowers for the right side and refitted it on Monday evening. Set the valves and triple checked everything to make sure it is all ok.

Last night I had time to fit the carburettors, exhaust and fill with new oil and tighten and check all the last things. Then came the big test pressing that little red button, at first it would not start and I thought ohh no. Then realised the fuel taps should maybe be opened

It fired up and damn even though the valves are in spec still rattles alot compared to my HP2 But nothing out of the ordinary from memory how airheads sound though One thing I did not set was the rocker clearance. Only reason is because I need to order a couple of shims to get them tighter even though they are still in spec and think the noise is coming from that rather than the valves

Took it for a test ride and the idling is very rough, the bike is fitted with a Y-piece and for the life of me could not get the idling set properly on tick over.

I will try again tonight following some of Rob's instructions to see if I can get it a bit smoother on tickover.

Set the mixture screw to their standard settings, 1.25 to 1,5 usually, then when the engines warmed up slowly turn one of the mixture screws out a little, you should hear the revs pick up, just turn it slowly out until the revs peak, if you go too far the revs slow down, if this happens turn the mixture screw in until it peaks again. Don't worry about the actual revs. Now do the other side the same. Once you are at optimum tick over revs on both sides fit the balance gauges and balance them up using the tick over screws and set them to a slightly low tick over. The bike will probably be over heating at this point so go for a spin round the block to get it to it's normal temperature and then see how it ticks over. Once you are happy that it ticks over properly you can then balance at higher revs using the throttle cables. You will probably have a problem on your 80 with the carbtune rods disappearing from view - you can turn them upside down to assist.

I am however thinking if someone has a old catylitic box taking up space regardless of age and looks please let me know I will have it

I rode into work with it this morning as a test and it runs and purrrs so lovely between 50-75mph. Had to stop on the pavement outside Limehouse Link as it would not idle and made a small adjustment to the idling screws which seem to have made a difference. The low and midrange seems to be rough and vibey and hope this is due to the carbs not being setup properly at the moment.

Any comments, tips, warnings, pisstake as always very welcome

 

[SJRoome]

Hi

The instructions for tuning and balancing the carbs are fine, but before you do this you need to:

1) Get the valve clearances right

2) Check the compression

3) Check the timing

4) Strip and clean the carbs

5) Check and probably fit a new air filter

6) Check that there are no air leaks around the carbs or in the exhaust system.

Hope this helps

Steve

 

[John Armstrong]

Below 3000 rpm my 100GS isn't as smooth as above, I suspect the y-piece is the prime suspect.

Usefull upgrade to the front brake is the HE larger disc, worked well for me out in the Alps two up.

 

[(RIP) maverick]

Hi

The instructions for tuning and balancing the carbs are fine, but before you do this you need to:

1) Get the valve clearances right - Done

2) Check the compression - Done

3) Check the timing - Don't have a timing light

4) Strip and clean the carbs - I think this was done not very long ago by the previous owner

5) Check and probably fit a new air filter - Airfilter is about 2000 miles old and clean

6) Check that there are no air leaks around the carbs or in the exhaust system. - Nothing visible that I could detect

Hope this helps - - Thanks
Steve

Below 3000 rpm my 100GS isn't as smooth as above, I suspect the y-piece is the prime suspect. - Reading through loads of threads and all the effort Rob Farmer put into this subject think so as well

Usefull upgrade to the front brake is the HE larger disc, worked well for me out in the Alps two up.

Just sourced an 1150 caliper from a mate who was about to bin it, just need to make a bracket to fit it properly

 

[SJRoome]

Hi

The Y pieces seem to be very sensitive to air leaks. One thing to look out for is popping on over-run. To test this find a suitable piece of road, accelerate hard and then shut the throttle. If it pops you have an air leak in the exhaust system.

To find airleaks around the carbs spray WD40 or something similar over the carbs and the rubbers either side while the bike is idling. If the speed changes you have an air leak.

Steve

 

[(RIP) maverick]

Right been up and down the road a few times over the last two days. Tried the convential method balancing the carbs which seems ok. The main problem is the bike won't idle properly and very rough in low revs. Setting the stop screws 1/8 of a turn to get it to idle results in the rpms not dropping when you rev it. It takes a while to go down. There seems to be only these two settings either no idle or to idle with consequences

I am a bit for a loss at this point and not sure what to check or replace at this point anymore. There does not seem to be any leaks and the valve clearances etc has been set to spec. Anybody around Essex way who can give a hand with the timing and fiddle with the carbs by any chance?

It runs but it ain't right

 

[Kenny]

Lube the throttle cables and ensure there is about 2 -3 mm of free play in them

Some Y pieces are good and some bad

 

[Rob Farmer]

It sounds to me like the carbs are still clogged up. I know it's a pain in the arse but if you take them off again one of the easiest ways of cleaning out the carbs is to take a can of WD40 with the nozzle on and blow the air ways through.

 

[Ogmios]

Setting the stop screws 1/8 of a turn to get it to idle results in the rpms not dropping when you rev it. It

reminds me for some reason i cant feckin' remember fully of a problem i had involving the carb 'O' rings.
hope thats some use
~~
with
KRAFT*
Og

*Kant remember A Feckin Thing

 

[SJRoome]

Hi

It definitely sounds like a carb problem, probably a blocked idle jet. Take them off, dissassemble, clean and check them. Make sure you only do one carb at a time and dont disassemble the throttle valve. You are looking for blocked jets, blocked airways and perished or missing o rings.

Be gentle - as carb parts are made of brass which is a soft metal. Use a spray can of carb and injector cleaner, available in any car part factors. Dont poke anything made of metal down or through any holes.

Comprehensive instructions are here http://www.buchanan1.net/carb_rebuild.shtml


Steve

 

[(RIP) Proff]

If it's still got the white breather pipes pointing down the inlet manifold
BIN 'EM
bloody things drip gunge down to the middle hole at bottom of Carb venturi causing exactly symptoms you are getting................................

 

[(RIP) maverick]

Thanks for the comments and help guys. I am ordering the o-ring and gasket kit + needles for both carbs today. It has done close to 44k miles and don't think they have ever been replaced so for the sake of a couple of quid might as well get it sorted.

Kenny the throttle cables are free and not sticky. Just to clarify as just in case I have the wrong understanding of the free play on the throttle cable.

Where the cable goes into the metal sleeve where you adjust the tighness of the cable on the carb. Normally if I can pull the cable nearly out of the metal bit it fits in +- 5mm is that the correct way to set the free play

Rob + Steve I have full can of carb cleaner and WD40 so will give it a good clean over the weekend and hope it improves things.

Og ermmmm thanks I think

 

[(RIP) maverick]

If it's still got the white breather pipes pointing down the inlet manifold
BIN 'EM
bloody things drip gunge down to the middle hole at bottom of Carb venturi causing exactly symptoms you are getting................................

Yes they are still there Prof, is this from the breather pipe on the motor into the airbox? If so what is the best way to drain and get rid of the gunge in the future?

 

[Kenny]

Proff and I agree to disagree on the white tube causing problems...never had any problems with these on the numerous airheads I've owned ( Proff is into effemitive Jap cruisers, so what does he know )

Free play is where you say, should be 2 - 3 mm otherwise you'll be all loose at the throttle . I mentioned the cables as having to little clearance will cause the revs to slowly come down or not at all.

You could always empty the float bowl and then fill with carb cleaner and ( obviously with a decent charged battery ) turn over the engine so the cleaner goes through the carb orifices etc. Just a few spins and then as the carb cleaner does its job, spin her over again to flush out the gunge

 

[(RIP) Proff]

Proff and I agree to disagree on the white tube causing problems...never had any problems with these on the numerous airheads I've owned But I've never kept them long enough to find out, unlike Proff who has had most of his BMW's over 15 years

Fixed FOC Kenny

 

[Rob Farmer]

.

 

[(RIP) Proff]

Fixed FOC Kenny

OI ya fecker !! that's an abuse of MOD power

 

[Rob Farmer]

What!

















What did I say about poking a bear with a stick

 

[(RIP) Proff]

What!




What did I say about poking a bear with a stick

OOOOO It's all back as I wrote it now

 

[SJRoome]

Hi

Well here is my view. Prof is right that the airhead engine breather recirculation system can result in oil condensing out of the air from the crankcase and ending up as oil in the carb causing blocked airways and jets. The problem gets worse as the bike gets older due to more air getting past the piston rings.

Where I differ is in the solution. Rather than simply venting the oil laden air from the crankcase, which is bad for the environment, or dumping the oil on the road, which is bad for other riders, modify the beather system to cool the air and remove the oil most likely to condense in the carbs.

Once the bike is sorted and running sweetly you may want to ask how to do this.

Steve