brucey Posted March 4, 2011 Report Share Posted March 4, 2011 Hi, I am just building the engine for my Trials Cub Project. I am fitting a PVL ignition which I purchased second hand about a year ago. I'm sure Alan Whitton said set the timing 5mm BTDC but the guy who sold me the ignition said 2.0 - 2.5mm BTDC. I'm running a +40" 7:1 piston and 'R' Cam in a Square barrel, side points engine. I know Alan uses a higher compression Kawasaki piston (I've got one but couldn't bear to bore a perfictly good barrel). I can just about get both timings but would like to set the correct timing in the middle of my adjustment. I'll be running the engine on a Mikuni VM22 (26mm) pit bike carb if it makes any difference to the timing as I believe these are the kiddies to fit. Also, what valve clearances do you use for an 'R' cam? I was also going to do the mod that puts a plate in the head to make fitting the push rods easier. Does anyone have any photo's or sketches of this? It's taken me a year on and off to build this bike but I can see the light at the end of the tunnel now! Any help would be appreciated. Bruce. Quote Link to comment Share on other sites More sharing options...
old trials fanatic Posted March 4, 2011 Report Share Posted March 4, 2011 (edited) Hi, I am just building the engine for my Trials Cub Project. I am fitting a PVL ignition which I purchased second hand about a year ago. I'm sure Alan Whitton said set the timing 5mm BTDC but the guy who sold me the ignition said 2.0 - 2.5mm BTDC. I'm running a +40" 7:1 piston and 'R' Cam in a Square barrel, side points engine. I know Alan uses a higher compression Kawasaki piston (I've got one but couldn't bear to bore a perfictly good barrel). I can just about get both timings but would like to set the correct timing in the middle of my adjustment. I'll be running the engine on a Mikuni VM22 (26mm) pit bike carb if it makes any difference to the timing as I believe these are the kiddies to fit. Also, what valve clearances do you use for an 'R' cam? I was also going to do the mod that puts a plate in the head to make fitting the push rods easier. Does anyone have any photo's or sketches of this? It's taken me a year on and off to build this bike but I can see the light at the end of the tunnel now! Any help would be appreciated. Bruce. All i can say is i've known Alan a long time and IMHO he knows more about PVL ignition than anybody else i've come across so i would go by what he told you. He can also help with the mod for the pushrod fitting. I thought a VM22 carb was 22mm which would be normal for a Cub whereas a 26mm would be a VM26 which is a bit larger than most of the people i ride with use. Jack the Lad will probably be along soon with his advice as i know he does work on Cubs for Bob Moore and he also advocates the use of pit bike carbs so can probably advise re those. Ignition timing shouldnt be affected by the carb size or jetting i have found. Good luck with the build BTW Edited March 4, 2011 by Old trials fanatic Quote Link to comment Share on other sites More sharing options...
brucey Posted March 4, 2011 Author Report Share Posted March 4, 2011 OTF, Thanks for the information. I just wasn't sure how much difference the piston and cam make to ignition timing. I guess I can always phone Alan and ask! (he has never been anything but helpful). I have seen the fantastic job Alan does on the push rod inspection hatch but will have to do it myself as I spent the remainder of my budget on one of Alans cnc machined gear change levers instead! I have also recently discovered Classic Dirt Bike Mag and obtained back issue 16 which has an article on the Comerford Cubs. In the Article Donald from Armac reccomends setting the clutch using a DTI. I'm assuming you operate/disengauge the clutch and adjust the 3 springs until the pressure plate runs true (using the DTI to check). Has anyone else done this? The VM22 Mikuni carb advert said the following in reference to its size: "PLEASE NOTE 26mm IS THE WIDTH OF THE OUTLET SIDE. THE SLIDE IS 22mm." Bruce. Quote Link to comment Share on other sites More sharing options...
superhondaman Posted March 5, 2011 Report Share Posted March 5, 2011 OTF, Thanks for the information. I just wasn't sure how much difference the piston and cam make to ignition timing. I guess I can always phone Alan and ask! (he has never been anything but helpful). I have seen the fantastic job Alan does on the push rod inspection hatch but will have to do it myself as I spent the remainder of my budget on one of Alans cnc machined gear change levers instead! I have also recently discovered Classic Dirt Bike Mag and obtained back issue 16 which has an article on the Comerford Cubs. In the Article Donald from Armac reccomends setting the clutch using a DTI. I'm assuming you operate/disengauge the clutch and adjust the 3 springs until the pressure plate runs true (using the DTI to check). Has anyone else done this? The VM22 Mikuni carb advert said the following in reference to its size: "PLEASE NOTE 26mm IS THE WIDTH OF THE OUTLET SIDE. THE SLIDE IS 22mm." Bruce. Get in touch with motocarb and get the VM20 the smaller carb is better suited to the 199 cub. Quote Link to comment Share on other sites More sharing options...
jack_the_lad Posted March 5, 2011 Report Share Posted March 5, 2011 Hi, First thing you need to ask is how good a rider are you? If you set your PVL to five mm BTDC you might find it responds a little too quick. I personaly would not use an R cam. Will let you know about the Mikuni carb just about to try one this afternoon. I would also use the Kawasaki piston.These are not very high compression. Jack I am just building the engine for my Trials Cub Project. I am fitting a PVL ignition which I purchased second hand about a year ago. I'm sure Alan Whitton said set the timing 5mm BTDC but the guy who sold me the ignition said 2.0 - 2.5mm BTDC. I'm running a +40" 7:1 piston and 'R' Cam in a Square barrel, side points engine. I know Alan uses a higher compression Kawasaki piston (I've got one but couldn't bear to bore a perfictly good barrel). I can just about get both timings but would like to set the correct timing in the middle of my adjustment. I'll be running the engine on a Mikuni VM22 (26mm) pit bike carb if it makes any difference to the timing as I believe these are the kiddies to fit. Also, what valve clearances do you use for an 'R' cam? I was also going to do the mod that puts a plate in the head to make fitting the push rods easier. Does anyone have any photo's or sketches of this? It's taken me a year on and off to build this bike but I can see the light at the end of the tunnel now! Any help would be appreciated. Bruce. Quote Link to comment Share on other sites More sharing options...
bobb Posted July 7, 2015 Report Share Posted July 7, 2015 did you got it sorted ? what setting are you running now on the ignition ? i would also like to know what valve clearence you use on the R cam i use whats in the cub manual but that seems very noisy kind regards bob Quote Link to comment Share on other sites More sharing options...
trialsrfun Posted July 15, 2015 Report Share Posted July 15, 2015 (edited) Hi, I am just building the engine for my Trials Cub Project. I am fitting a PVL ignition which I purchased second hand about a year ago. I'm sure Alan Whitton said set the timing 5mm BTDC but the guy who sold me the ignition said 2.0 - 2.5mm BTDC. I'm running a +40" 7:1 piston and and#39;R' Cam in a Square barrel, side points engine. I know Alan uses a higher compression Kawasaki piston (I've got one but couldn't bear to bore a perfictly good barrel). I can just about get both timings but would like to set the correct timing in the middle of my adjustment. I'll be running the engine on a Mikuni VM22 (26mm) pit bike carb if it makes any difference to the timing as I believe these are the kiddies to fit. Also, what valve clearances do you use for an and#39;R' cam? I was also going to do the mod that puts a plate in the head to make fitting the push rods easier. Does anyone have any photo's or sketches of this? It's taken me a year on and off to build this bike but I can see the light at the end of the tunnel now! Any help would be appreciated. Bruce. I set the valve clearance for the R cam to the Triumph recommended settings of 0.002" Inlet, 0.004" Exhaust adjusted when engine is cold, are these settings regarded as the most suitable? Do most of you fellow Cub riders use the R cam or do you prefer the std type for trials. Edited July 15, 2015 by trialsrfun Quote Link to comment Share on other sites More sharing options...
goudrons Posted July 17, 2015 Report Share Posted July 17, 2015 (edited) You needn't both cutting a hole in the head to help locating the push rods. Just wrap an elastic band around both rocker arms, this will lift them up and cause the other ends to protrube enough to make locating the rods very easy. The band will stretch as you push the head down onto the barrel and jobs a good'un! Once on, just remove the band. I always set mine 3mm BTDC and used a 22mm Dellorto direct from Eurocarb. It reved out quite nicely, but because of the R cam it never idled that well, they never do with an R! As already noted, a lot of knock off Mikuni VM22's for pike bikes get listed as 26mm, this 26mm is the airbox end's opening, not the size of the carb. So it sounds like you have the right size at least. Edited July 17, 2015 by goudrons 1 Quote Link to comment Share on other sites More sharing options...
cub Posted September 8, 2022 Report Share Posted September 8, 2022 Ive built a trials cub in Uk and am interested in kawasaki piston mod is it z200 any details ? Apreciated i have r cam and it revs well but is bit tappetty at higher revs 45 mph + Quote Link to comment Share on other sites More sharing options...
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