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| CR250M1 Timing https://vintagedirtbikeforums.alp-sys.com/viewtopic.php?f=21&t=1819 |
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| Author: | go_hercules [ Mon Apr 07, 2008 9:51 pm ] |
| Post subject: | CR250M1 Timing |
Hi, I have a 1975 CR250M1. The book calls for the timing to be 2.3mm before TDC. I have retarded this some to about 1.8mm to try and reduce the kick starter kicking back so bad. I noticed the 1973-1974 book calls for timing of 1.5mm, which is way more retarded than the 1975. It is essentially the same engine, with identical ignitions, so I was wondering why the big difference and was wondering if I could reduce the advance even more down to 1.5mm. Anyone have experience with this or suggestions? The thing is very hard to kick over and when it kicks back it is brutal on the back of my leg!! Thanks a lot. |
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| Author: | mitchie [ Tue Apr 08, 2008 5:51 am ] |
| Post subject: | Re: CR250M1 Timing |
Don't know about setting '75 at 1.5 btdc, but the 75-76 M1s have 4mm longer rod affecting piston speed through the stroke, which may explain timing recommendations. Also, porting is somewhat different, but don't think that would make much difference in timing. |
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| Author: | dogger315 [ Wed Apr 09, 2008 10:03 am ] |
| Post subject: | Re: CR250M1 Timing |
Honda Racing recommends 1.8 to 2.0 mm BTDC for '73 to '75 Elsinores, so at 1.8 mm you should already be there, but I have read in other manuals that Honda recommends 1.5 mm BTDC for all '73 to '75 CR250Ms. So I guess you can try further retarding and see if it helps. If the "kick back" persist, you might want to invest in a compression release. As far as identical ignitions, doesn't your M1 have a CDI? dogger |
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| Author: | mrmikkelsen [ Sat Apr 12, 2008 6:25 pm ] |
| Post subject: | Re: CR250M1 Timing |
You are not doing anything strange like running it without a base gasket, head gasket; or either one of thin material are you? Check some pictures of other heads and see if your's has been shaved for high compression or anything odd. I'd be interested to see a compression check reading to see if you are pumping 200 psi or something crazy. Your timing sure sounds fine, so I am thinking of what else could be roughing up your foot. When you kick it, do you ease the piston up toward the top of the compression stroke then kick it though with commitment? I can't imagine you have an 1/8" of carbon built up in there from neglect. Naw, that can't be it. Does it actually start and run okay after the kicking dance is done? |
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| Author: | go_hercules [ Sun Apr 13, 2008 6:00 pm ] |
| Post subject: | Re: CR250M1 Timing |
This is in response to several of the questions above: The 1975 CR250M1 came with points ignition just like the 73-74, the CDI was optional. This bike is completely stock and unrestored. It has the original piston, stock gaskets, no carbon buildup, etc. I think I will do a compression check just for grins. Once the bike is started it runs great - good idle, good top end, no pinging, no overheating, etc. I have tried kicking it from just past top dead center and in just about every other position. I also tried kicking it with the spark plug in but disconnected and it doesn't kick back which I think sort of confirms that the kick back is ignition related. I think I will also try cutting the advance down to 1.5mm and see what happens. I have tried to find out why Honda advanced the timing so much on the 75-76 but can't find anything in the old magazines, etc. Thanks for all the suggestions, any more would definitely be helpful. It is a fun bike but the bruising is getting aggravating... |
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| Author: | Dave [ Wed Apr 23, 2008 3:05 am ] |
| Post subject: | Re: CR250M1 Timing |
i too have a 75 model,the kick back is part of life with the beast.even with the timing set at the recomended settings.there are worst things to start.i have a 70 model Yamaha RT1M with a webco head.it has downright brutal kick backs.might wear a good boot when starting and build your leg muscles.these bikes were made when men where men.i had a 73 model CR250M and i still have a MT250.those two bikes kick back sometimes too.the timing is static on these bikes and it has no retard for spark,it will kick back no matter what you do,the RT1M has a spark advance on the flywheel,it still kicks back if you give it a half hearted kick.my 79 CR250R kicks back too,harder than the 75 model does,and it has a cdi ignition on it.my 75 runs the points setup. |
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