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21/28 engine / carb differences


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mick

 
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21/28 engine / carb differences

Fri Aug 04, 2006 4:59 pm » Post: #1 » Download Post

Are the 21 and 28 engines the same or not? and whats the difference in the carbs and are they interchangeable as I may have dropped a clanger if not.
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StephenRC45
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Fri Aug 04, 2006 5:47 pm » Post: #2 » Download Post

::clang::

Honestly though, the '28 is much teh same as the '21 but with even lower exhaust ports.

The carbs however are 100% different.
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mick

 
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Fri Aug 04, 2006 6:10 pm » Post: #3 » Download Post

are the carbs interchangeable with no ill effects?

And is there a way to easily identify a motor?
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mick

 
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Sun Aug 06, 2006 8:58 am » Post: #4 » Download Post

So my next question is, do 21 carbs work on a 28 motor with no trouble?

Bearing in mind the bike is a 21 with just a 28 motor in.
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Andy
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Mon Aug 07, 2006 2:10 pm » Post: #5 » Download Post

For ease of working on, MC18/21 carbs are certainly preferable to MC28, in my opinion.

Apparently, so I once heard, the MC28 carbs flow a little better, but I've personally yet to see an MC28 make as much power as an MC18 or MC21.
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fontyyy

 
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Tue Aug 08, 2006 11:34 am » Post: #6 » Download Post

mick wrote:Bearing in mind the bike is a 21 with just a 28 motor in.

A whole '28 motor?
Flywheel included?

Get ready for a stunning 50 bhp then Laughing
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Tue Aug 08, 2006 11:45 am » Post: #7 » Download Post

lol thats unfair. Leighs is making 55bhp, and it feels like it too lol Sorry Leigh.
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fontyyy

 
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Tue Aug 08, 2006 11:56 am » Post: #8 » Download Post

Yeah, but Leigh's got a '21 flywheel, JHA pipes and has been set up.

What we need is Andy's motor with my PGM4, HRC card and '28 carbs to see if anything from the '28 is worth having.
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watfordhorn
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Tue Aug 08, 2006 12:21 pm » Post: #9 » Download Post

Maybe we should have a look at Keiths 28, hasnt that got 70+ bhp???

Also like stephen said, my bikes engine has not been apart for more than 8 years, so a ring change is probably well over due, and its running a little rich to be on the safe side. Then again I still maintain my bike is quick enough considering how reliable its been and how limited the mods are....still standard air box!

Stephen said a ring change would get me a few horses on their own, I have some in the garage so maybe I will give it a go and see what happens.
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mick

 
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Tue Aug 08, 2006 12:34 pm » Post: #10 » Download Post

fontyyy wrote:
mick wrote:Bearing in mind the bike is a 21 with just a 28 motor in.

A whole '28 motor?
Flywheel included?

Get ready for a stunning 50 bhp then Laughing


Yes a whole 28 motor as far as I'm aware, is there any way I can find out for sure?
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watfordhorn
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Tue Aug 08, 2006 12:41 pm » Post: #11 » Download Post

do you know the part number on the flywheel? It has a different number to the 21.

I have my old 28 flywheel at home, i could get you the number off it and you could compare it?
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watfordhorn
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Tue Aug 08, 2006 12:46 pm » Post: #12 » Download Post

28 flywheel will have the following numbers on it (you can see without removing it?):-

037000-3321
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mick

 
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Tue Aug 08, 2006 2:50 pm » Post: #13 » Download Post

If I do have a 28 flywheel whats the difference with a 21 because I've got a 21 one too
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watfordhorn
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Tue Aug 08, 2006 2:53 pm » Post: #14 » Download Post

different advance on the ignition, I am guessing with the 28 one on the 21 bike with PGM III your ignition will be retarded.

When I put the 21 flywheel on the 28 I got advanced timing, not sure how the rest of the ignition will affect it on the 21. Maybe if you have complete 28 it will be fine?????

Personally if you have it available I would swap the flywheel and pickup coils etc from a 21 back into the 28 engine, then everything should be matched to your PGM.
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mick

 
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Tue Aug 08, 2006 2:59 pm » Post: #15 » Download Post

I'll check it out, cheers for the help mate.
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