77 Maico need help!

brentl

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#1
I've had this 77 400 AW since it was new. Done a couple overbores and crank seals.

Problem: Lately been running progressively worse ....needs more throttle just to keep running ( won't run below half).

Not a compression problem or crank seals.

My suspicion...could wear on the throttle slide cause this? The throttle slide is kinda loose.
 
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#2
Is you 1977 carb stock too? You may want to take off your carb and put on a different one that works the same size to fit the connections. If the temp carb works then you need to rebuild your original carb or replace it due to normal wear and tear.
 

brentl

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#3
Carb is a spare that I had with the little saw cut taat was needed for off idle richness correction. Question is can slop between slide and carb body cause it to not run at less than half throttle? Is this what happens?

I do have a spare mikuni to test with ,got a bing on it now.

Unfortunately I live in the city and need to load up and drive just to crank the bike!
 

IAN P

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#4
the slide cutaway could be wrong i had the same problem with my 1981 440 tried every thing else like you and changed the slide and hey presto ran like a dream.
 

AjayMike

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#5
I hesitate to give advice here, since I'm not all that familiar with Maicos or -- if I remember rightly-- Bing carburetors, but in my experience a loose slide will usually cause an erratic idle (since there is excess air leaking around the slide, upsetting the idle mixture.) This is a frequent problem with vintage Amal concentrics, which have a pot metal slide and carb body that wears fairly rapidly.

A loose slide is not the first thing I would suspect for your problem.

Mike
 

TVRider

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#6
Brent,

How about a little more info? Has the bike been sitting or do you ride it regularly? When was the last time you cleaned the filter? The bings are notorious for wearing out a slide, but I agree that would make it run erratic, not just poor on the bottom. If it cleans out on top I would suspect a jetting problem or slide cutaway problem with the spare carb.
 

sdm

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#7
I agree with everyone above in that we need more info. Some things to eliminate
in addition to what has been mentioned above are.
1. make sure you are using fresh premix
2. make sure the air filter is clean and also the fuel filter (if it has one)
3. install a fresh spark plug
Something to think about might be that if the slide is worn to the point of being loose,
the needle jet and needle itself may be worn also and causing an overly rich issue.
The pilot jet could also be plugged..
These things might be some places to start anyway.
Hope this helps
Sam
 

sdm

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#8
sdm said:
I agree with everyone above in that we need more info. Some things to eliminate
in addition to what has been mentioned above are.
1. make sure you are using fresh premix
2. make sure the air filter is clean and also the fuel filter (if it has one)
3. install a fresh spark plug
Something to think about might be that if the slide is worn to the point of being loose,
the needle jet and needle itself may be worn also and causing an overly rich issue.
The pilot jet could also be plugged..
These things might be some places to start anyway.
Hope this helps
Sam
Something else I forgot is that the float needle and seat
could be worn and not shutting off the the fuel causing flooding. This happened to me on an old IT 175 but mine
puked gas all over.
Just another thing to check....
 
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#9
Sounds just what was happening to my buddy's 81 490, the problem was the carb, it really got bad when it warmed up. He ended up using another Bing he had but with all his new jets, he thought it was a jetting problem at first, and it solved the problem. The only thing we can think of is there must be a hair line crack somewhere on the carb, because the slide was fine, no extra play at all. :think: