brucey

Hello to anyone still interested! Just tried it again with fresh fuel with absolutely no difference. However I did notice it blowing a lot though the crankcase breather pipe (Alan Whitton item). There was very little black smoke (even when revved) and compression test results were o.k. This combined with the heavy breathing convinces me there is an internal air leak within the engine. Maybe valve guides of a seal somewhere? I don't mind stripping the engine to rectify the fault, or even giving it to an expert to sort out, but I would like to confirm the actual fault before I remove the engine from the bike. I think I will just put it back in the shed for a while untill I feel enthusiastic enough to start all over again. Bruce.

Just a quick update. I fitted the 110 mainjet (god bless ebay!), checked all the other jets and blew everything though with carb cleaner (it's all new anyway). All appeared to be o.k. It's just possible I didn't have the carb seated in the rubber manifold groove properly the 1st time I tried it as I think it went a bit further on this time. I'll put yet another new plug in and some fresh Shell Vmax tomorrow and see what happens. If that fails, I will have to start with the basics all over again.....................or just give up and buy a Honda! Goudrons, where abouts are you?

looking on the internet, it may be possible I have an air leak. I will fit the 110 main jet, start the bike and give it a squirt of carb cleaner to see if it speeds up. I have noticed a small oil leak which I think is comming from my base gasket. Can I lift the head & barrel slightly, remove the thin gasket and apply some RTV sealer around the cylinder base instead of using a gasket? (I would need to watch the oilways!) Would a slight leak around the cylinder base cause a fuelling problem on a 4 stroke? It must be something fairly simple as the effect is so dramatic. I am now using a Dellorto PHBL 22 Carb. 100 (soon to be 110) Main Jet 35 Pilot Jet 60 Choke Jet D40 needle and 260BZ Needle Jet

Thanks for the comments guys, I just ordered a 110 main jet from e bay. I'm tempted to give my £20 Micuni pit bike carb another go. At least it ran on that one, just not very well!

After stripping and checking my cub engine I was disappointed to find I had much the same running problems with not revving past 1/3 throttle and sooting up plugs on reassembly. Convinced I had a problem with my new 20mm Dellorto carb, I tried a friends 22mm Dellorto carb (from his 250 Serco Cub). This appeared to work much better. The engine revved pretty cleanly and the plug even appeared to go from black to straw colour! I must admit we didn't do an extended test due to time constraints but the bike was vastly improved. Bob at UPB kindly exchanged my carb for the larger one. The only difference is that my new 22mm carb has a 100 main jet and the main jet in my friend’s carb was 110. As my Cub is 200cc, I thought it would be better. Full of anticipation, I fitted my new 22mm carb to find it doesn’t run unless the choke is on! Even though it revs past 1/3 throttle (with a bit of popping and banging), as soon as the choke is turned off, the engine just dies even after running for 10 mins. I tried raising the needle (2nd notch to bottom notch) but it made no difference. The plug is back to it’s usual black/sooty colour. Would 110 to 100 main jet really make that much difference? (I guess it’s fairly easy to prove). I can’t believe I’m having so much trouble getting this engine to run properly and seriously thinking about giving up altogether and getting a modern 4 stroke bike instead. Bruce.

just scroll down a bit from this forum!

There is lots you can do to a Cub with a modest workshop. I did the following to mine (see photo's on pre 65 forum): Widened and lengthened swing arm. Fitted chain tensioner and side stand. Fitted Sammy Miller Swing Arm Bushes Fitted plastic chain rub block to top of swing arm Modified swing arm to fit snail cam adjusters Made detachable front engine mount plates (with adjustable offset) Made Ally Bashplate and mounts. Fitted External Oil Filter (from e bay) as it adds 1/2l oil capacityMade and fitted Top Tube Oil Tank Put inspection hole/push rod fitting hole in top of cyinder head. Varoius rockershaft mods. Put drilled sicencer bush inside exhaust (to create more back pressure and quieten it down a bit) Fitted Taper head bearings with Montesa Yolkes and Forks (best improvement to date!) Electronic ignition and delorto carb (Jury still out on this!) Alloy tank and plastic mudguards And plenty more. My point is you don't need to spend vast sums of money to make significant improvements yourself.................but it helps! Look at as many other bikes as you can for ideas and inspiration. They don't even need to be Cubs! Good luck with the build, Bruce.

Replaced fluids (apart from clutch/primary drive as cover off to check ignition timing). Put fresh fuel in tank and it started 3rd kick quickly settling down to an even tick over. I have fitted a drilled bush (7 x 8mm holes) into the exhaust in an attempt to quiten it down and possibly produce a bit more back pressure but it is still too noisy to rev the bike up in my shed without the misereable guy next door complaining! I ran it for a couple of minutes to make sure the oil was circulating o.k. and cure up the new high temp paint on the barrel. I will sneek out and wizz it up and down the road/path if I get a chance tonight. The problem is trying to get it up to running temperature and rev it up without loading it all up and driving to a practice area. I have just purchased a Gunson Spark Plug Cleaner (Mini Bead Blaster) to recycle the growing collection of sooty plugs I have. It seems to work o.k. especially when combined with a squirt of 'super clean' I also picked up 4 plugs from e bay for less than £6 incl postage (I pay almost that each from Halfrauds!). Fingers crossed! Bruce.

Jack, I just finished putting the engine back in tonight. I had the bore glaze busted and checked ring gaps etc. Everything checked out o.k. While it was apart I loctited the final drive sprocket nut and took the opportunity to do some minor mods to the cylinder head. (replace thackery washers with solid spacers and blank off top of head nuts) I haven't found anything obviously wrong but have left the clutch cover off to check the ignition timing with a strobe. The engine used to smoke a bit on start up and clear after a short while (possibly morgo oil pump and cub valve guides?) With a bit of luckwill have it running tomorrow night (with yet another new plug fitted). Time will tell. I haven't given up hope yet! Bruce

1. Too easy and I thought wire brushing plugs was a bit of a 'no no'. 2. A wire brush may not reach those little crevices! Anyway, I see it's arrived, so I'll unpack it and give it a go!

Looking at my increasing collection of Cub spark plugs that have virtually no wear (less than 8 hours use) but have been removed because they are 'sooted' up, I decided to take the plunge and invest in a Spark Plug Cleaner. Basically it is a mini bead blaster that plugs into a compressor air line. Before you respond, I am also taking steps to resolve my dirty plug habit! I note that the cleaning medium is cast iron balls rather than sand (silicon) and have ordered a spare bag as I have no idea how long it will last. Does anyone have any experience using one of these devices and/or any tips? (not spark plug tips!) If not, I'll let you know how I get on. These tools seem well suited for trials bike applications where wear isn't the issue although I do have a reputation for rash impulse buying things I don't really need (my wife has banned me from Aldi!). Bruce.

Esteve, I can accept the fact that I had to remove the spring from my RH Sammy Miller Footrest and lift it to kickstart the bike. What I hate is when the kick start lever flicks back into its 'stored' position at the bottom of the stroke and gets stuck under the footrest mount! with any luck the engine is now running and you have the hand you need to unhook the kickstart lever on the throttle twist grip! UPB are doing a splined kickstart and ally lever for about £200.... You pay your money......... Just had the barrel glaze busted and will be putting it together again over the weekend. If I put a strobe on the engine whilst its running, what should I mark? The 2 yellow dots (1 on the rotating stator and 1 on the static pick up) were set up to align on tdc. Not sure if I should do the oil return mod while the engine is apart. Bruce.

Just a bit of an update, I have contacted the guy who sold me the ignition and carb and been advised to try retarding the ignition as this has cured similar symptoms on other Cubs. As this costs nothing, I will probably put it back together and try it. Bruce.

Stork, Thanks for the information, your advice is appreciated. I'm not sure what happened to my previous post but I have edited it to make it a bit clearer. I'll contact the guy who sold me the carb and see what jets and needles he would reccomend trying. Now that the engine is out of the bike, I'll pop the barrel off and check the rings, small end (which I made on my lathe), piston and bore. I may also get the bore glaze busted as I didn't do this on first assembly (my first engine build). The bike has run well in the past but always fouled plugs. I can see no reason why I shouldn't be able to get the bike running well at all revs with a plug the proper 'straw' colour. Bruce.

Esteve, Cheers, looks like I may be sending some more money Terry's way! The only thing I hate with his kick start is the way it flicks and gets stuck under my Sammy Miller Footrest Mount. The special splined shaft and alloy kick start UPB offer prevents this but at a price! Alan, My Dellorto Carb is a PHBL 20. The main jet is screwed in the bottom of the float bowel. Although I did have a main jet unscrew itself on a Mikunni carb and had very similar running problems (died when the throttle was opened). Carb setting are as follows: Main Jet: 100 Pilot Jet: 40 Needle D40 (currently set 2nd groove from top out of 4 grooves total) Timing was set as instructions (align yellow marks with piston at TDC) which I believe is an actual static timing of 3mm btdc. Stork995 I have tried a number of plugs with the following results: NGK B6HS (carb needle was in middle position, ran for approx 5 mins from cold) black and wet (Oil?) NGK B5HS (carb needle in 2nd to top position, ran for approx 15 mins) black, not as oily NGK BPR4HS (carb needle in 2nd to top position, ran for approx 1 hour although would not rev past 1/3 throttle) very dark brown, dry. Generaly Mikunni carbs have always resulted in black sooty plugs. I tried a 'pit bike carb' with 'standard' and 'reccomended Cub' jet sizes and a slightly larger Mikunni carb that ran pretty well for several trials. Then I started getting problems with not reving out and bad starting at which point I decided to invest in the Dellorto carb and new ingnition. The last plug (using the dellorto carb) has reduced the 'sootyness' to some extent. The bike does not puff out bellows of black smoke when you rev it as if it were running way too rich but dies above 1/3 throttle opening which makes bigger hills interesting! Bruce.

I refitted the head and pushrods. I get 125 psi on the compression tester. This is kicking the engine over with it attached to an engine stand (a bit slower compared to kicking it over in the bike) and with all the oils drained. I'm also slightly concerned that my splined kickstart shaft splines seem to be disintegrating! This might be a good opportunity to go back to a cotterpin shaft set up.

Thanks Totalshell and Alan, My thoughts are the same about the Delorto rubber connecting hose and this isn't a 'hot only' running problem. The Eletrix ignition looks the same spec (and components) as the ignition I have just fitted from UPB. I guess I could pop the head back on and check the compression. I currently have the engine mounted in a rather handy stand I bought at Kempton Park Autojumble. I acquired a Kawasaki piston and made some gudgeon pin bushes for my engine but couldn't obtain rings and didn't have enough experience (or bottle) to start cutting bits off the skirt and redirect oil return channels to do it myself. This is still an option but I don't want to introduce another set of variables! I fitted the new carb and ignition in an attempt to resolve running problems once and for all but they have only partially cured the problem. It maybe time to take all the bits to someone who knows what they are doing. Now I just have to decide who! Bruce.

Thanks for the ideas and comments guys, Now the head is off, I'll get the valve guides checked out. I'd tend to agree with your thoughts that the bike is running rich but playing with the needle height has made little difference. I'm running a 100 main jet in the 20mm Delorto and i think a 35 pilot jet. I'll also get somebody else take a quick look at the engine while it's apart to get a second opinion. Bruce.

I have recently fitted new UPB PVL type electronic ignition and UPB Delorto Carb to my cub in an attempt to make it run better. I consider these good pieces of kit and already set up to run with my engine. (Bob is very helpful). The engine currently oils plugs and appears to run rich. It dies when the throttle is opened quickly and will not rev above 1/2 throttle. The symptoms get a bit better each time a new plug is fitted but not great. I didn't rebore the barrel when I built it as it seemed o.k. I fitted a good standard piston with new rings (all at +40"). This is my 1st engine build. It seemed to run o.k once the rings bedded in but has got proressivly worse. It smokes a bit on start up but not excessively when hot. I have removed the enginge and head to sort an irritating oil leak from the rocker shaft near the oil feeds. I have a brand new Hepolite +60 piston and rings sitting in my shed. I'm wondering if I should have it rebored to + 60" and fit this for good measure. The engine is running with an Alfa roller big end and Morgo high capacity oil pump, Alan Whitton breather mods and various other goodies. It has a square barrel and head. I'm begining to loose heart with something I have spent so much time and money trying to get right on what should be a simple engine. However, I am not going to let it beat me! What would you do next? Any advice appreciated, Bruce.

Hi, I have dealt with Terry on a number of occasions during my Cub build. His products are second to none and his prices fair. I either see him in person at an Bike Jumble (Kempton Park) or speak to him in person on the phone. Considering he is a legend in Classic Bike circles, he is extremely helpful and always gives advice freely. Just my personal experience. Bruce.

I would just like to add that you can build a really nice Trials Cub which would be more than competitive at pre 65 club level for very reasonable money. Believe me, I've seen them! The trick is (and I may offend some purists here) to get the expensive bits like forks, ally wheels and tank (ty 175) from old twinshock bikes and adapt them to fit a Cub. I have used a set of 1970's Montesa forks on my bike and fitted Taper Headstock Bearings and the Montesa ally billet Yolks at the same time at a total cost of about

I think you need to ask yourself the following questions: What sort of competitions do you want to do? i.e beginners and wobblers club trials to pre 65 championship rounds What mechanical ability and facilities do you have? What sort of budget do you have? Then do some research by attending pre 65 trials like the Talmag (where most people are more than happy to talk about their bikes), look on ebay for parts and complete bike prices and go to Autojumbles (bigger the better) to pick up the bits you need. Personally, I'd get the bike running reliably as it is and ride it to see if you like riding 'classic' bikes before spending too much money. There are some photo's of my recently completed Cub on this forum which cost me in the region of £2K in parts alone! You can buy a really nice modern bike for that sort of money and require a fraction of the fettling and maintenance. Even though I have just swapped my spare cub parts for a modern bike for modern club trials, I still wouldn't part with the Cub for the pre 65 stuff, but then I like playing in my shed!

Jon, Once again, many thanks. That's pretty clear now! Bruce.

O.k. water pump seal replaced and new seals and dust caps in fork cartridges ready for reassembly. I even turned down a location bush to press the new fork seals in! I have a couple of questions: How do you remove the front fork springs to put a longer pre tension spacer on? existing one is 63mm long, I intend to make 2 new plastic sleeves 75mm long. I think you pull the spring down from the top (maybe compress it using strong cable ties) then hold the top nut (the one with the adjuster in) and undo the exposed hex nut under the spring near the top. Is this correct? I'm also a little unclear how I fill it up with oil on reassembly. I was going to reassemble everything apart from the M8 cap head screw that goes in the very bottom. Turn the forks up side down and pour the oil in there. The trouble is I think the solid ally bush at the bottom (that the M8 cap head screw goes into) will stop me filling it from here. Am I missing something obvious? Bruce.

Jon, Many thanks for your quick and concise reply. That's a really useful website. Looks like I'll be busy down the shed tonight! Bruce.