Vintage Dirt Bike Q & A

Hello all. I have recently aquired this great bike. My dad has owned for a few years in Dallas, Texas and it ran like the scalded ape that it is. I now have the bike in Lubbock (Elevation 3300 ft). I am unable to start the bike now. Referring to the manual I pulled the main jet (152) on the Kehein Carb. The book recommended a 7% drop so I replaced it with a 142. I left the pilot at 60 as it was before. Filled the tank back with fresh klotz 40 to 1 and could not get it to kick. Good spark, relatively fresh plug. I noticed some binding in the throttle and opened it up to find it was pretty shredded. I now wonder if the throttle was open partially and resulted in the flooding/ not starting troubles. The bike has fired a few times, but will not start. Any help would be greatly aprreciated, especially referring to jetting. Before Dallas, the bike was set up in Houston and Florida. I am also considering a proform pipe and silenecer because the stock pipe doesnt seal well (it may not be the stock one, but its dinged up and painted black) Thanks in advance!!

Awesome Website BTW... keep up the great work.

What does your manual say is stock for the 1980 CR250R with a 36mm carb? I have jetting specs for the 1979 and 1980 models using a 36mm Mikuni and they are practically the same. If this holds true for the Keihin as well, it might be that it was marginally lean previously and it has got worse with your changes at 3'000 feet. This would not help with starting. Maybe go back to stock and start from there?

Stock settings for 36mm Keihin PE01 on a 1979 CR250R:

Main 185
Air 200
Pilot 60
Slide 2.5
Needle 28A
Clip #3
Air screw 1.5 turns out

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

i could not find the stock jet sizes anywhere in the manual. I was pretty sure that the air here is less dense that at sea level, therefore the bike is getting too much gas due to rich jetting for denser air. any other opinions would be great, especially pertaining to the Kehein. Thanks

First things first. If the jetting worked in Dallas, it should work where you are know i.e. the bike should start and run even if it is a little rich. I am guessing the 60 pilot jet is stock. So before you worry about fine-tuning the jetting, pull the carb off and make sure you don't have any blocked jets/air passages. Check the float is working OK and set the float height at 19mm. Go back to the 152 main (at least or bigger if you have it.) Confirm you have a spark and then bump start the bike and get it warmed up. Then see if you can re-start it by kicking it. If have found sometimes it helps to stand on the left-hand side of the bike and kick it with your right foot while it is leaned over. While you have the carb apart confirm the needle is a 28A and the slide has 2.5 stamped on it. Good luck!

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I looked around a partsfish website and it didn't list any main jets smaller than 160. What main jet do you run on your '79 redrocket? I pulled the fouled up throttle tube and cable, and a new one should be here in a few days. Seems like the throttle may have been partially open while i was attempting to start it. I've got spark, but I don't see a big blue kernel every time. The plug is a little old but not fouled. Have a fresh plug to try tomorrow. Thanks for the help. On kickstarting, you're spot on about standing off the machine to kick it. I guess I am rightfooted like most.

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1980 CR250R Elsinore

I generally start mine with the throttle a little open and crack it as it fires up. So while your throttle might have been making life difficult I don't suspect it as root cause of why the bike won't start. I switched to a new Mikuni VM36 round-slide that I got from Vintage Elsinores. Their jetting was near perfect and cured a lot of problems I had with the original Keihin running rich and wet-fouling plugs. With experience I now do not blame the Keihin, I think it was jetted too rich - 178-180 main - for the Southern California ambient temperature (up to 100F) and altitude (up to 3,000'). I did re-build the Keihin and put in a new float valve, needle jet, needle, and jets to make sure it wasn't running rich due to wear. I'll bet if you clean the carb out, put in a new plug, and then bump it to clean it out, it will run.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Pulled the slide apart, and while the barrel is a 2.5, the needle is a 28G on the 2nd clip from the top. When I opened it, is was running a 152 main. http://www.sudco.com says that stock main jet on PE carbs is 160. Earlier you said a 79 runs a 185 stock. Also, what is the difference in the taper between A and G? The float needle is just closed at 3/4 inch (19mm). Next time I go to work on it (at a friend's garage) I will try the fresh plug and clean carb with 152 main again. Thanks.
BTW... my clymer elsinore manual says the stock carb is a 28mm.... must be a typo, just really confused me at first....

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1980 CR250R Elsinore

The stock Keihin PE01 carb on a (1979) Honda CR250R is 36mm and comes with a 185 main and a 28A needle. Option needles are available 31A (richer) through 31J (leaner) with the 31E being equivalent to the stock 28A. It is but a hunch but I would say you have a leaner needle than stock from perhaps another Honda/Keihin combination. The Honda manual lays out the taper and thickness for each of the 31A-J range, you would need to measure your needle to know exactly how it compared. Note the needles available via Sudco do not necessarily match up exactly by thickness and taper, and the codes are completely different. Send me an email if you want me to cut a copy of the parts list and manual...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

I think I've got it figured out. After thorough cleaning and a new throttle tube and cable, I've got it running with the 152 main. I think my problem is that the previous owner had a rich needle(28G) with a lean jet (152). I'm going to try to find a 28A and I already have a 172 main (manual recomend this for my altitude) and that should put me right at stock for 3200 ft. This would explain why it ran well with a 152 main since the taper was richer. Thanks for helping me solve this thing. If you could email me those or post em, that'd be great too.

Ryan

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1980 CR250R Elsinore

Once the original documents are scanned at a reasonable quality to preserve the photos, you get very large PDF files that need to go on a CD. Contact me on my email address and we'll get something worked out...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

They have internet access in Miami?

J

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

carb parts warehouse (carbparts.com) has a part number for the 28A. I'm going to give them a call and see what they can send my way. thanks

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1980 CR250R Elsinore

Called a few places and most couldn't cross reference it. Since the gaskets are old and I'd rather have the satisfaction of a new carb, I think I am going to purchase a Mikuni VM36 jetted carb from vintage elsinores. It is a direct replacement, correct?
Thanks ryan

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1980 CR250R Elsinore

I have a 74 CR250M. I was having problems with the original carb. I called Vintage Elsinore, and they hooked me up with a new pipe, and a new Mikuni carb. They jetted the carb to match the pipe. It was a direct bolt on application.

Good Luck.

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74 CR250M, bought new in 74, still stock, except for the new 36mm Carb, and proform exhaust.

Called today and went ahead and ordered a mikuni VM36 and a Proform pipe and silencer. The mikuni is backordered for another week or so but will be set up for the pipe. The old pipe on the bike now is not sealed very well against the port, and in fact someone has actually used rtv silicone to try to seal it up. Of course it still spews burnt premix onto the cylinder and frame. I've decided its now or never and the weather is getting ridable. I'll let you guys know how it works out for me and the elsie....

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1980 CR250R Elsinore