Please help - Grubee GT5 80/66cc will not accelerate running rich

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nexgen91

New Member
Oct 13, 2011
11
0
0
New Mexico
Just got my GT5 a few weeks ago (used) an have been trying to get it to run right ever since. It was running really rich when I got it, I swapped out the CNS carb for an NT carb (that did nothing except stop the horrible gas leak from the drain tube). I swapped the plug for a champion L86C and later a NGK B6HS. Re sized the main jet to .065mm and have moved the needle into various positions, to alleviate the running rich. After all of this without a load the engine revs high, but as soon as I put a load on it it bogs down and is not accelerating past 5-10 mph (and still running rich), to go any faster I have to peddle to desired speed (somewhere between 15-18 mph as I cannot pedal any faster) and kind of try to cruise it to maintain speed (sometimes it will actually decelerate) I have also re torqued the head bolts as well. I'm at about 4500ft and the ambient temps are 65-85 degrees F. I'm at a loss here and don't know what else to try.

http://motorbicycling.com/images/smilies/Waa.gif
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
I am sorry, let me please start from the beginning. :)

I do not know how your engine is mounted. I do not know how you have the intake tract installed. I do not know how much experience you have with building and repairing engines. I do not know you. I am trying to help you blindly over a keyboard instead of being there with your engine at my fingertips.

I first suggested an extremely common problem with new builds on these engines.

To answer your last question and more:
Yes. It can also make an engine idle or rev high while not under a load (the idle speed screw will not be able to work correctly) which is why I ask.
The possibility of an air leak is often overlooked and folks will try to tune the carburetor to correct for the additional air instead of repairing the actual problem.
Doing so always results in bad performance.

I am not trying to assume that you are doing this, it's just that I do not know how knowledgeable you are with troubleshooting and tuning.

If you have no air leaks, have not tried to enrichen the mixture to tune out an air leak, and you are still running too rich then it's time to check the carb for proper float height adjustment.

Another thing, I do not know how your engine is mounted nor do I know if your carburetor is installed upright, and level as it should be, or is it is rotated at an angle on the manifold or perhaps is is pointed up or down.

The best way to observe this is the seam between the carburetor body and float bowl needs to be level in relation to the ground both front to back and right to left.
The carburetors can tolerate a little bit of an angle but not much.
 
N

nexgen91

New Member
Oct 13, 2011
11
0
0
New Mexico
GearNut said:
I am sorry, let me please start from the beginning. :)

I do not know how your engine is mounted. I do not know how you have the intake tract installed. I do not know how much experience you have with building and repairing engines. I do not know you. I am trying to help you blindly over a keyboard instead of being there with your engine at my fingertips.

I first suggested an extremely common problem with new builds on these engines.

To answer your last question and more:
Yes. It can also make an engine idle or rev high while not under a load (the idle speed screw will not be able to work correctly) which is why I ask.
The possibility of an air leak is often overlooked and folks will try to tune the carburetor to correct for the additional air instead of repairing the actual problem.
Doing so always results in bad performance.

I am not trying to assume that you are doing this, it's just that I do not know how knowledgeable you are with troubleshooting and tuning.

If you have no air leaks, have not tried to enrichen the mixture to tune out an air leak, and you are still running too rich then it's time to check the carb for proper float height adjustment.

Another thing, I do not know how your engine is mounted nor do I know if your carburetor is installed upright, and level as it should be, or is it is rotated at an angle on the manifold or perhaps is is pointed up or down.

The best way to observe this is the seam between the carburetor body and float bowl needs to be level in relation to the ground both front to back and right to left.
The carburetors can tolerate a little bit of an angle but not much.
Click to expand...


Sorry I was not trying to come accross as rude. I dont have alot of 2 stroke experiance, but I am pretty well versed in auto mechanics. I took the advise you gave and checked out the level of the carb, it is actually sitting with a slight forward angle (the top is of the carb is a little more forward on the bike than the bottom) however due to space constriants I have no idea how to remey this situation. Would this in fact cause it to not accelerate? Maybe I am just thinking the operation of the bike is wrong. Am I suposed to pedal up to speeds of 20-30 mph with assistance from the motor, or is the motor suposed to propel the bike to those speeds after I get the bike going? Thank you for your help
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
It's all good! You were not being rude, and I hope I did not come across that way either.

A slight angle on the carb, like 10 degrees maximum, should not affect it enough to cause probems.

Pedal the bike up to 5+ MPH then let the clutch out. The engine should be able to take you up to speed all on it's own after that.

How many miles are on the engine? I know you got it used so that might be a tough question to answer.
Do bear in mind that a brand new engine will not have a whole lot of power. The piston rings and other parts need to marry to each other before the engine can reach it's full potential. How much power depends on the individual engine and how well it was put together by the factory. Some engines seem to double their power after break in is done which takes approximately 500 miles or 2 gallons of fuel.

Keeping the choke lever in the choke-on position will cause what you are experiencing.
On NT carbs, the retaining nut on the choke shaft can get loose and the choke will drop to the closed position all by itself.
Tightening the nut a little bit will stop that. Some folks even use a rubber band to hold the choke in the open position.

Another possibility is that the exhaust is plugged up.
You can remove the exhaust and run the engine just long enough to take a short test ride without doing any damage. Leave it off for a few miles and serious damage can occur.

Too tight of a drive chain can also cause what you are experiencing.

The list of possibilities is long and I will continue to lengthen it if you like.
Hopefully one of these low buck problems is it and you can enjoy the ride!
 
N

nexgen91

New Member
Oct 13, 2011
11
0
0
New Mexico
GearNut said:
It's all good! You were not being rude, and I hope I did not come across that way either.

A slight angle on the carb, like 10 degrees maximum, should not affect it enough to cause probems.

Pedal the bike up to 5+ MPH then let the clutch out. The engine should be able to take you up to speed all on it's own after that.

How many miles are on the engine? I know you got it used so that might be a tough question to answer.
Do bear in mind that a brand new engine will not have a whole lot of power. The piston rings and other parts need to marry to each other before the engine can reach it's full potential. How much power depends on the individual engine and how well it was put together by the factory. Some engines seem to double their power after break in is done which takes approximately 500 miles or 2 gallons of fuel.

Keeping the choke lever in the choke-on position will cause what you are experiencing.
On NT carbs, the retaining nut on the choke shaft can get loose and the choke will drop to the closed position all by itself.
Tightening the nut a little bit will stop that. Some folks even use a rubber band to hold the choke in the open position.

Another possibility is that the exhaust is plugged up.
You can remove the exhaust and run the engine just long enough to take a short test ride without doing any damage. Leave it off for a few miles and serious damage can occur.

Too tight of a drive chain can also cause what you are experiencing.

The list of possibilities is long and I will continue to lengthen it if you like.
Hopefully one of these low buck problems is it and you can enjoy the ride!
Click to expand...

I'm not sure on the miles, the previous owner said he had already broke it in. I will check the things you have listed tomorrow when i have some light to work with. For the choke on the NT carb down is choke off? I have noticed that if I am riding and move the lever up the engine will stall. I am thinking the drive chain may be to tight, will definitely loosen it a bit and try that first, followed by exhaust removal as suggested. Again thanks for the tips.
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
The choke lever works like you think it does, just like a light switch. Up is on and down is off.
The drive chain should have 1/2" up and down free play as measured in the middle between the sprockets. Too tight and you can have what you are experiencing. Too loose and all h*ll can happen. It can bind up on the engine sprocket or jump off of the rear sprocket and tear up your rear spokes if it jumps inwards.

You are very welcome!
 
N

nexgen91

New Member
Oct 13, 2011
11
0
0
New Mexico
Ok checked the chain and it has plenty of slack, I replaced the throttle cable as well (it was stretched and finally snapped) have not tried running without the exhaust yet. I did have someone hold the bike off the ground and it looked like it was spinning the rear wheel pretty fast. Heated up the engine good (312 degree F at the plug) a little to hot I think but it didnt go boom, and still runs.
 
Wm Holden

Wm Holden

New Member
Jun 1, 2011
358
2
0
Ventura California
did you lower the float level?
I find...if it starts easy without too much choking...it's too rich for high speed running.
I'm starting to think the tickler is on there for a reason...imagine that!

Turn off the gas at speed and it runs better for 20 seconds?
 
Last edited:
Wm Holden

Wm Holden

New Member
Jun 1, 2011
358
2
0
Ventura California
nexgen91 said:
I put the float level at 21mm from the gasket seating surface as specified here: NT Carb Tuning Basics
Click to expand...
ok....I don't measure.... I wing it and have had good results...i've finally got mine screamin' to 32mph..
it was a juggling act of fuel filter resriction, needle valve placement, float level, fuel/oil ratio, clean air filter, carb sealing at neck....God only knows what other black magic made it work right...good luck man.
I found my carb...while not technicaly "loose" was errr....not as tight as it could be...when I would get o about 25...the thing would start shaking pretty bad....put my hand on it...and it would even out the run. turn off the fuel..it would pick up speed....so I used the intel to make some changes...and well...it worked for me...again...good luck!cvlt1
 
N

nexgen91

New Member
Oct 13, 2011
11
0
0
New Mexico
Wm Holden said:
ok....I don't measure.... I wing it and have had good results...i've finally got mine screamin' to 32mph..
it was a juggling act of fuel filter resriction, needle valve placement, float level, fuel/oil ratio, clean air filter, carb sealing at neck....God only knows what other black magic made it work right...good luck man.
I found my carb...while not technicaly "loose" was errr....not as tight as it could be...when I would get o about 25...the thing would start shaking pretty bad....put my hand on it...and it would even out the run. turn off the fuel..it would pick up speed....so I used the intel to make some changes...and well...it worked for me...again...good luck!cvlt1
Click to expand...
I got it running a little better now, it accelerated up to about 10 and will hold at around 15-18 mph but wont go any higher. I tried playing with turning off the fuel and that didnt help. Im going to mess with the needle/float a little more.
 
Wm Holden

Wm Holden

New Member
Jun 1, 2011
358
2
0
Ventura California
rich is 4 stroking....it is only firing every other stroke because of too much fuel....4 stroking is how it runs when the choke is on too long....
How do you know it's rich..? (just trying to figure out your trouble shooting method..so i can help...maybe)


you know....did you add oil directly to the tank?
I made mine run poor by doing that once...never again.
 
N

nexgen91

New Member
Oct 13, 2011
11
0
0
New Mexico
ok I got it running sort of ok (it will accelerate to about 17.5-18mph but wont climb any higher and if I pedal to a faster speed it will not maintain it. Moving the choke does not help and neither does closing the petcock.
 
Wm Holden

Wm Holden

New Member
Jun 1, 2011
358
2
0
Ventura California
are your brakes scrubbing?
do you weigh alot?
what method of deduction did you use to make whatever (plz outline) changes you made to get it running better?
Let us know.


This one only gets up to 20mph....turn off the petcock...wait a little (with throttle pinned) then it speeds up to 28mph...then turn the petcock back on before it starves...and it stays at 28mph..
just trying to help you man.
I'll mess with the carb more when i get it finished....
in the mean time...it runs great at low throttle and i don't need to blast around anyhow. and when i do...i know how to get it to go...


 
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