running problems with the RM6 Runabout

I have a Mobylette AV42 which is a similar design. Are you sure re fuel. Could the fuel tap have a partial blockage as I think there is a fine mesh in the tank. To check you'd have to remove the tank to get the tap out the bottom. The fact that it runs to a high speed and then cuts is just what happens when you turn fuel off.

Despite my reputation as the 2nd worst mechanic in the NACC - I also think it is fuel related 

1. The gasket between the carb and the cylinder head leaking
2. Something restricting the petrol flow - best I saw was half a match stick (someone had stuck in to arrest the flow at some stage and forgotten to take out when reconnecting the petrol pipe).
3. Loose needle

I'm sorry to fly in the face of the above advice,but if the plug is wet when you checked it,would'nt that point to an ignition fault? Try a different sparking plug and maybe a condenser too,they're cheap and easy to do and if it makes no difference,you have eliminated  2 more possibilities and done a mini service too! By the way,I used a Honda coil on mine and it works a treat(sorry to rub it in)

Just bobbed in to work to say thans for the replies and give a little more history.
Puchboy - thanks for suggestion but I can confirm that there is and always has been a good fuel supply. I have checked several times the actual float bowl level whilst I have been trying to eliminate the running problem (when the engine starts its antics I have immediately turned off the fuel tap, undone the nut which holds on the filter /float bowl lid and petrol was always in the bowl and the float is floating. The carb also does not flood).
Dolly - thanks for the tip, the gasket from maifold to cylinder is hermetited red and the gasket to manifold is smeared with high vacuum grease - I'll probably make sure that both faces are sealed with a bead of hermitite red. 
Andy - when I first tried to start the engine after its initial rebuid the engine would only occasionally fire so I swapped the condensor from another old engine that I had picked up as spares. Without doubt this did make the engine run and was actually good enough to get me to the MOT station. The performance / relaibility since that day did deteriorate so I bought another new condensor from Aplins
(great service  - very helpful). I would say that although the new condensor is fitted the reliability problem is still not improved and in truth there has been no change. I have tried at least four different plugs, 1 new from Aplins and three off of other makes but none of them have the R code.
When I visisted the Granada section on Monady evening, one of the members mentioned that he had had similar problems even with a newly purchased condensor and that the fitting of one from a suzuki was a cure. I intend today to externally mount a new condensor from a CD 175 Honda that I used to own. On Monday I'll let post a reply to let anybody interested know the results.
Two last questions - for the earlier (1963/4 ish) Gurtner carb does any body know what is the correct size main jet and does anybody know what sort of vacuum reading could be expected from the engine? I do have access to a full vacuum tester but I wouldn't want to suck the seals inside out - if you know what i mean.
Regards to All.
P.S. Dolly - it looks like I have to get in touch with Mackintosh for help with my home pc - talktalk say they can't help. Interestingly I could pick up the replies at home though - just can't send from home. 

Its not something silly like a blocked breather hole in the Fuel cap by any chance ?

If Dolly is the 2nd worst mechanic in the NACC ; then who is the first ?

Hi Carl,
The official answer is of course:

If you don't know then it must be you.

That was what I was worried about.

You have invited me to get back onto my favourite horse!!!!...whne you rebuilt engine, had you had the ignition parts all apart?...may sound daft, but I am always amazed how much ooil gets between the backplate and the main castings, also behind the points and bracket...if you have access to a test meter check the quality of the earths between the points and castings, the main bike frame and engine assembly, whilst you are at it, check the resistance of the low voltage winding of the spark generating coil,(probably 1 to 2 ohms and ensure it does connect to earth)  and that when the points close it is effectively shorted out( to earth)...should you find high resistances,(more than an ohm or two for the earths)  dismantle and clean all contacting surfaces with neat petrol, (don't use already-mixed fuel)   also whilst in this area, check that the points move freely, with no trace of sticking..I had a set of points that did this, and it was a pig to find, in fact it was a lucky fluke that revealed it was happening!!...but isn't that what this game is all about!!

Dear everybody from before, Carl and Kermit, thanks for the interest shown in the problem to date.
Carl - I have frequently tried to run the engine without the fuel cap in place. The results are always the same and removal of the fuel line from the carb shows that there is always a head / flow of petrol.
Kermit - I have not had a chance to check out any of your suggestions but I'll get hold of my works multimeter as soon as possible this week. However I can say that the cleanliness/dryness of the engine faces would have been rally clean without ant traces of oil - I could not say if there was any oil traces on the points assembly but I ll certainly check.
For info - I have fitted a new external condenser off a CD 175. Initially I thought that substituting the new 'Raleigh' condenser for the Honda one, had done the trick. The engine fired up, responded well on the throttle and could be restarted after a period of standing idle - this simple procedure was carried out several times during Saturday afternoon / evening. Today got clobbered up and set off to may mates house approx 2 miles away to show how good it was now running. Arrived at Ron's place only to find that the engine stalled as I came to a halt and normal service was resumed - the bike would only fire up for a short run time and then die away, it would not respond to an increase in throttle even though the engine was spinning at relatively high revs. Fuel supply checked ok but removal of the plug showed the plug to be dry. Further attempts to get the engine to run normally proved unsuccessful only sporadic bursts of life were experienced. It was also noted that there was never any firing of the engine unless the decompressor was activated at the start of the pedal sweep to start the engine spinning. After allowing the engine to cool the bike did restart and I managed to get close to home before going on to free wheel.
 I have rebuilt another engine, new mains, rings, crankcase seals, little end and condenser. The engine was substiuted for the first one and an almost identical running scenario was experienced - sporadic firing etc etc. Changed the plug and the engine fired up. For a few minutes the bike responded perfectly to the throttle and would tick over quite nice - you could rev the engine to spin the rear wheel and then close the throttle and the engine would run down real smooth and the clutch would disengage the engine quite nicely tick tocking away. However after a few minutes the engine died and after that only sporadic firing. Checked the fuel level in the float bowl with the  fuel immediately turned off at the tap the moment that the engine died- Ok and the float floating - no flooding. I've put the bike away and I'll live to fight another day but this problem is a real tickler.I can only conclude that the common factors between the two engine 'trials' are the HT coil nd carb but I'm really not sure.
After reading this latest installment does any body have additional comments.
I don't know why the text reverted to itallics - I'm on a lap top leant to me by one of my daughters and I can at last transmit replies from home. Thanks again - George  

Crankcases expanding when hot allowing in air ?

Seems unlikely but you seem to have explored every other possibilty, would it be worth rigging up a temporary Battery powered Ignition system to prove a point.

I did this on Guys Mosquito but we ended up reverting to standard but with an external condensor.

Its about time Worzel gave us some input, he normally has all the answers

Hi,

I have a couple of Raleighs with the Gurtner carbs. I doubt you will have overlooked this, but these carbs. are very sensitive to even very small particles of whatever in the fuel. Main jet and  tickover jet can both be affected. Sometimes when the motor stops, the muck can drop clear, and all seems OK again - for a while!

I assemble the carb. in almost surgically clean conditions, and always use a paper in-line micro filter to stop muck entering. The nylon mesh type of filter seems to let particles through, so are not so good.

Until I did things this way, both my Wisp and Supermatic drove me 'potty'

Best,

J.

I have been playing with Cyclemaster ignitions to obtain two firings per rev I have found information indicating the time best to fire with mag coils is at maximum flux. Cyclemasters have a key on the flywheel which can shear if the taper is not lapped in. This allows the flywheel to move and whilst timing is not affected the position of maximum flux is and this gives hell. Because the flywheel can then move again and pick up on the sharp remains of the sheared key it resets back to maximum flux position. Is your flywheel moving on its shaft? just another thing to try.  Grumpy

i've had a few of these so here's my advice ,

Have you removed the centre ( pressed in ) diffuser jet from the carb  and gived it a good clean through both the holes and the carb cavity around it , Double check the float for sticking, plastic seem more likely to stick than the old copper ones...

Around the coil mountings on the frame ,scrape the paint off and get a good earth, check the cylinder head mounting brackets are also going to good metal on the frame.

Try another flywheel , you can lose magnetism on these ,my AV32 ran ok ,but a new one transformed it.

I use the briggs and stratton fuel conditioner ,as if standing my P50 up for a while it would need a carb clean, after adding the conditioner it will restart after a long lay off.

New condenser ,I've had a couple of dodgy new ones so try an alternative .

Lastly have a good look at the three wires that fit onto the points themselves ,these can get very close to the coils in the magneto and can arc across.

I know its a big list but its one of these silly things that take the longest time to fix....

good luck.

What plug are you using?

Sorry to sound so basic but my Runabout was just like this. I found the last owner fitted the wrong plug. Went great when I put in an NGK B5HS.

Thanks to everybody who has replied some really good comments.
I like the separate ignition system which uses a battery - if this works then I can concentrate purely on the electrics. The possibility of muck in the pilot jet passageway is another area where I feel quite uncomfortable - is there any way that the jet under the slide can be removed to check that the cross drilling is clear? I was considering tapping the core out to 3mm and extracting it but of course this ruins the jet. The fuel is currently being filtered through a paper type filter but heaven knows what has b gone on previously.
I have just applied a vacuum to the engine via the inlet stub pipe. With everything blanked off I applied a relatively low vacuum (0.2 bar negative) There was a very small gradual decay in vacuum, turning the flywheel with the vacuum applied also indicated that the crankcase seals were in pretty good order.
I'm off home now and I'll start with the easiest things to try i.e. scraping the paint off around the coil fixings to the frame - the bike has been taken back to bare metal, bead blasted and hand painted with coach paint to a thickness that would grace the Forth road bridge! After that test I'll get ready for a coil / battery circuit. 
Thanks again to everybody - I really don't feel alone - thanks.

Hi Happyg,

The brass idle jet can be tapped out from the underside. I use a soft aluminium rod. These jets can be very prone to clogging. There are two small holes on opposite sides of the waisted part of the jet, and these can be almost impossible to find if they are blocked. Just persevere. Obviously the carb housing needs to be clean too.

Make sure you note how the jet sits in the carb before you remove it. The flat goes to the front.

If non of this makes any sense, then your carb is different from mine!

Happy brumming, and hope this helps.

J.

Just to add my Pennorth! I had some similar problems toy yours with my RM9, but my problem was I couldn't get her to run for more than a few minutes, initially I couldn't get her to start at all.
 It all started after I had come home from a run and as I got home I went to turn her off while still running, she started backfiring like mad, and that was the start of my problems which took over 3 months to sort out.
After trying many of the things you have which included substituting the coil for a "known Good one", Brian Aplin finally notified me that he had a new batch of coils in stock,
I sent off for one at a very reasonable cost, fitted it, end of problems! It may nor be the answer to your problems but for about £18 it's got to be a good investment.

Brian

Hi and thanks to everybody's suggestions.
Fender, thanks for replying - I am using exactly that plug that you have listed and without doubt the bike does start easier with it.
The other night I cleaned off all the paint work around the HT coiland engine head to frame brackets. Started the bike on the fourth swing of the pedal, sounded great and the lowest rhythmic tick over to date. Revved up several times on the stand left the throttle alone - bike ran down to speed - engine clutch disengaged - GREAT. Took the bike out for a run up and down the road, everything seemed just fine. took a chance and carried on to Ron's place (about 1.5 miles), pulled up and the bike just sat there popping away. Started to explain what I had done when the engine petered out. Funny - not. Couldn't believe it - it just wouldn't fire up. Fuel checked, plug sparking and noted to be a little sooty.Left the engine to cool, got it going again and made about half a mile before it died again. Fortunately it's all down hill from the half mile stage.
I have now made a platform and fitted a coil and battery and external condenser. I've only just finished.The engine started first pedal and almost immediately settled down to a lovely low tick over and nice throttle response. I'll give the bike a ride out tomorrow and see what happens - anything after approx 25 minute is the current bench mark. 
bhiltonlancia - thanks for the info - it seems like you also went through the same performance. I have been chasing this one around for quite some time. When you look at all of the replies quite a few suggest electrical so tomorrow will be an intereting day.
pottypantherman - I have a carb of the type which you describe and I'm going to  have a go at getting the jet out. However I must say that the carb I am using has a side entry main jet and there is no possibility to tap out the jet from underneath.
Thanks everybody - I dont what I have hit on this keyboard but the itallics have cut in, anyhow I'll let you know the resuts of the ignition mod for anybody who's interested. George
 

Almost sorted. The battery/ coil ignition / new external condenser certainly made a much improved starting and initial running. After setting off for its first trial run on Saturday morning, feeling confident all was going to be OK with the bike, I was gob smacked to find running troubles within 100 yards of setting off which certainly felt to be fuel starvation. Immediately checked the fuel level / flow OK. Tapped the carb with a spanner, started the engine , all seemed fine and continued with the run. The engine ran fine for the next half hour or so but after getting to Ron's palce the poor running returned and difficult starting. Checked the spark etc and then gave a squirt of petrol into carb intake and revved up the engine. With the coil ignition eliminating the electrics all now pointed to either a carburation problem even though two 'side' jetted carbs, ultrasonically cleaned etc hd been tried, or the bike was just not going to run at Ron's place. Using a third but later type of carb and from pottypantherman's and norfiat's info I gently drifted out the cental jet and petrol washed.and air blew the passageways - the jet appeared clear but the wasted part which feeds the pilot jet was covered in gloop (like a clear wallpaper paste). I doubt that fuel would have been able to pass through the passageways. With the later carb fitted and the temporary ignition system in place the bike was given a test run and over the next two hours the bike was stopped / started numerous and never missed a beat. This morning I took it out for around about an 8 mile run without any problems.
The next move is going to be to reinstate the electrics - from the much improved behavour with the temporary ignition arrangement - I will be renewing the low and high tension ignition coils (bhiltonlancia's experience) as I realise that  for reliability everything has to be spot on. 
Thanks to everybody for their great analytical suggestions - the forum is a real good tool. Ther's a wealth of experience out there and I must say that carlsquirell's suggestion about using a battery is
a high ranker when you want to separate electrics from carburation - could have saved a month of my life trying to sort this one!