Mmb80 not running good

#1
Hi there,
I have an mmb80 that my kids have been riding but then the centrifugal clutch went out and I just finally ordered one. It's been about three months but before I put it away I made sure and run the fuel out. Today I went and started it up because the clutch will be here soon and it's running choppy. It takes a sec when you slam it to rev up and when you let off it goes really low idle then comes back up. Also at full rev it doesn't stay at a constant rpm it sorta is like waves.
When I use the govenor arm instead of the throttle it works fine so is the govenor broke and how can I fix it?I
 

I74

Active Member
#3
Sounds like you might have some issues with the springs ect. for the governor arm & or throttle linkage.
I would check & make sure none are missing, or hooked up wrong.
You can reference where they belong, off of You tube vids,, where they are showing how to adjust the throttle stop linkage screw.

Could also have a dirty carb …..

I
 
#4
Sounds like you might have some issues with the springs ect. for the governor arm & or throttle linkage.
I would check & make sure none are missing, or hooked up wrong.
You can reference where they belong, off of You tube vids,, where they are showing how to adjust the throttle stop linkage screw.
I
It ran great before I put it away for three months but I'll check anyway. It wasn't messed with when if was put away.
 

I74

Active Member
#5
I would drop the float bowl on the carb, if all the springs check out.
The jet holes & passageways in that carb are very small,, & can get restricted very easy, even with the slightest bit of dirt ect.
MM has a vid on cleaning the main jet & emulsion tube ect.
There is also a pilot jet tube, which is under the idle speed screw on top of the carb.
You just unscrew the idle screw all the way out, & then use a small flat blade screwdriver ect. under the pilot jet top, & then just carefully pry it up & out.
It is just a friction fit with an O-ring.
I would use a small bit of non chlorinated brake cleaner, to spray out the tubes, jets,, & carb passageways ect.
Hope this helps.
 

SAT

Active Member
#7
I would pull the tank, lines and filter. Clean the tank, replace the lines and filter. It only takes a bit of cobweb and flash rust to weaken the governor response. I would replace the spark plug as well.
If the carb bowl is ugly, I would re-vamp my fuel, additives, and gas can.
 

I74

Active Member
#10
Sat has added good points there...
I don't even use pump gas in mine, & never have.
Instead,, I use 4 cycle -''ethanol free''- 92 octane ''Tru fuel'', or the Briggs & Stratton stuff, that you find @ Lowes or Menards ect.
The stuff burns super clean, has a shelf life of up to 3 years,, & also has cleaners, stabilizers, & friction modifiers in it., ect.
You can pretty much leave it in & not have to worry about draining it out when the seasons over ect.
Menards had the B&S stuff on sale the other day, for around 3 bucks a Qt.
You might think it's a bit spendy, but it's well worth every penny.;)
 
#12
Sat has added good points there...
I don't even use pump gas in mine, & never have.
Instead,, I use 4 cycle -''ethanol free''- 92 octane ''Tru fuel'', or the Briggs & Stratton stuff, that you find @ Lowes or Menards ect.
The stuff burns super clean, has a shelf life of up to 3 years,, & also has cleaners, stabilizers, & friction modifiers in it., ect.
You can pretty much leave it in & not have to worry about draining it out when the seasons over ect.
Menards had the B&S stuff on sale the other day, for around 3 bucks a Qt.
You might think it's a bit spendy, but it's well worth every penny.;)
I just use pump ethanol free gas.
 
#13
Sat has added good points there...
I don't even use pump gas in mine, & never have.
Instead,, I use 4 cycle -''ethanol free''- 92 octane ''Tru fuel'', or the Briggs & Stratton stuff, that you find @ Lowes or Menards ect.
The stuff burns super clean, has a shelf life of up to 3 years,, & also has cleaners, stabilizers, & friction modifiers in it., ect.
You can pretty much leave it in & not have to worry about draining it out when the seasons over ect.
Menards had the B&S stuff on sale the other day, for around 3 bucks a Qt.
You might think it's a bit spendy, but it's well worth every penny.;)
It's running 6 bucks a quart here.
 
#19
So I took everything apart, I haven't done anything yet besides change the spark plug but I was wondering how I'm supposed to clean the tank? It seems pretty clean and I changed the gas which was dirty and im going to install a filter. I am also going to take the carb apart.
 

Rapidrob

Well-Known Member
#20
Four months ago my engine just started to run like crap.
It was not the gas,not the fuel being old,not the fuel having a slight amount of ethanol in it. The tank was clean as was the fuel line and filter.
The ignition system was dead-bolts on producing a bright spark.
Cleaning and even new jet did not help. I bought a new carb off of Ebay for ten bucks out of Texas and the engine is running better than when it was new.
The new carb has an adjustable idle jet,unlike the orginal which was not.
 

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