64 250 with possible cam issues.

[Motorelic]

Hi gang! This is my first post so lets see how it goes
I have recently rebuilt a 64 250nc engine. Model unknow because it was brought to me as a basket case. The engine was together but there were signs of it being apart at some point. All of my timing marks are lined up and im at 8 degrees btdc. New 74.5 Lacey piston and vm26. All bearings are new. It runs great! My issue is the idle. Its very high then it will come down to somewhat normal then cough thru the carb and stall. It acts lean but its not. No vac leaks and my jetting is a stupid 55 pilot air screw 1/2 turn out and 120 main. Just to get a crappy idle. My concern is maybe the cam. Heres a pic of the profile of the cam that came out. It measures 10mm on both lobes. Im noticing that theres a puff of compression that comes thru the carb while kicking. Even though the engine starts very easily.




Heres a pic of a cam I could try. Intake is 10.5mm and exhaust is 9.9 but the profile is drastically different.



Im at my wit's end with this lil lady and any light you can shed would be amazing. Thanks- Sean

[Motorelic]

Heres what she looks like. Nothing like the original but still fun! If it would idle..........
Yes I took the Dellorto off and put the mikuni on thinking that was my issue. It wasn't.

[Bevel bob]

Cam looks a bit sporty with a high lift and duration, you are getting some reversion as its designed to work well at high-ish revs. It may also be that you need to back off the ignition a few degrees, also you may have an AAU thats not the best type or working well. Where are you?. if you want a milder cam I have a couple to swap and you may get some cash (most unusual!) out of me as well. AAU will have a number stamped on it,what ignition system?.

[Eldert]

Hi Sean

the camshaft in the first picture looks like it is hardfaced . when Megacycle took over Norris camshafts they made some cams witn the Norris N390 profile . something went wrong with the indexing of the lobes because when timing the camshaft you land up with lobecentres around the 89 or 90 degree mark . your camshaft could be 1 of those . are there marking or scribings on the cam ?

the 2nd camshaft looks like a Mach 1 camshaft . very nice cam . i would put that in the cilinderhead and see how it goes .

i never hurts to take readings of the camshaft timing anyway . specialy aftermarked cams you never know if the keyway is in the correct place regarding the lobes .

Eldert

[Bevel bob]

Eldert has looked more carefully than me!, yes the first cam is an odd one. What is the intended use? ,if you are going to plod around like a trials bike then a Mach1 cam may not be the best choice also you would need to lower the CR and fit a better pump for low rpm oiling. Tyres look more off road ? or is that just image/pose value!. You could try increasing the inlet tappet clearance to reduce the duration a bit. Any off road use would need a shield for the carb filter.

[Motorelic]

Thanks for the replys! The bike will be used for around town and some dirt roads. Nothing too sporty. I just want the thing to idle haha! The cam does appear to be hard faced. I put the mach1 cam in just to see if the the puff of compression went away. It did not. I should also say, At perfect tdc the ignition marks line up perfectly. The cam marks have to have the piston about 20 degrees advanced of tdc to line up straight. The crank keyway is straight up and down at tdc and the mark on the crank bevel gear is one tooth counterclockwise of the keyway. The cam shaft drive marks are straight down so when i install the crankshaft bevel it has to be moved to fit on the keyway. I have a degree wheel to check valve timing but the book i have is confusing. at tdc im supposed to rotate the crank clockwise. Is this looking at the left side of the bike where the degree wheel is? That would turn the engine in reverse. I set the rockers at .012 and used the .001 feeler and cant get a reading anywhere close to the numbers in the book. And it says to check the intake first but the exhaust is the next to open when turning the engine the correct way. Im so lost

[Bevel bob]

Where are you based?. I would be interested in the Mach1 cam if you want a more managable idle and would do a swap with some extra cash in your favour.I have a couple of Monza type cams.

[Motorelic]

Hi Bob, im in Virginia USA. Im concerned about the angle of the cam vs angle of ignition timing and crank. Is this just due to the "racey" setup of this cam? Or is something else wrong.

[Motorelic]

My AAU is AA359. Im running points with a 12v conversion from Lacey. The AAU is in great shape with new springs

[Bevel bob]

That AAU should be fine ,points and battery are also no trouble, Your 2 cams have long durations which can be ok for sporty riding but are not usually best for stop start traffic situations ,if they are set up to the marks all you can do is check that they are correct , its possible to re-time them (off the marks) to get the correct timing but you can't really alter the nature of the cam much. You may also have a bigger than ideal carb (for easy use!) and those cams do not work well with a restrictive silencer. I have a similar problem with my 250 which is a pain unless hammering around a race track leaving me deaf with the noise. If you overtune a bike (for its intended use) you usually loose more that you gain, and the bike gets left in the garage for something easy to use.What size carbs have you?, I would go for something around 27mm for town use. The Dianna managed 100mph on one of these .With your style of bike 80/90 would be more realistic.