Yamaha G1 hesitates and won't pull.

[griffo002]

Hi Guys...And thanks for this site.

I not long ago I picked up a G1 in good condition and running well here in Aussie.
Then one day,whilst travelling along it made a sound like a dragging stick...i throttled up and the sound went away...A week later it did it again ,throttling up did not take the sound away but pulling the choke on did.It ..All good again for about a week...Then back came this sound and a loss of power....It now stumbles to take off and won't idle...it stutters to rev out but once it gets high in revs its ok with back wheels jacked up....I have put on a new carby on and set the air screw at the common 1&1/2 out(it makes no diff at any screw setting), new air filter, spark plug,new fuel filter,checked the reeds(perfect)....There is no seeps or weeps around the seals at all....I am burning the exhaust in the fire pit now ....I started it without the muffler on and it ran like a dog....

Any one can help Id greatly appreciated it immensely .

Griff in Aussie.

[JRL]

I'll hazard a guess that you have a fuel delivery problem. Pulling on the choke and improving the running characteristics would generally indicate lack of fuel.
Check fuel tank for fuel level, water incursion, clogged pickup, fuel line kinked or occluded, fuel pump for function.
Another issue might relate to air leaks. Anything that's between the carb and pistons is suspect.
Assuming your replacement carb is correct for your cart?
Run a compression test. Rule out the simple things.

[JRL]

Might also rattle the crank on both ends and check for loose bearings, which would lead to leaking crank seals, and piston scuffing could result. Any oil wetness on the bottom of the engine is a sign of crankcase leak...unless the muffler flange proves to be the culprit.
If it's trying to seize the choke would improve (for short period) running due to cooling effect.
Low compression is a sign. However, that would be an easy fix on a two stroke. Relatively speaking.
U may be able to pull the muffler and view the piston. Should appear smooth and no vertical marking. If you see damage...there's your problem.
You have the two stroke oil correct? Correct ratio and type of oil?

[griffo002]

Thx for the replies JRL....this girl does need a top end rebuild...I put in new rings and its up to 100 psi but still rattles...I can't get over size pistons and rings here at all...i have to import them from the US or China..( the book say there 4 sizes of piston and rings for them) I have drained the tank an put new fuel in using 50:1 ratio....look I used mower oil 2 stroke oil that I had....I can blow in the tank and fuel comes out ok but won't when I crank it...are the vacuum pump very strong to push the fuel through when cranking at all?That choke trick worked once but not the second time or now.

I might get dummy tank and set it high just to test it as in a gravity feed....Ill keep you posted.

[griffo002]

I hung a fuel tank high and gravity fed the carb...No improvement at all,bummer.It just sputters and coughs at the carby with air cleaner off until it finally picks up the revs then off it goes..back the foot off and it just dies....could the timing have moved?.

[cgtech]

Number one! Keep your old carb! The old one might need some love, but it's the good one! If all other options are exhausted for the original carb, get a new "real one". It will bite the pocketbook, but the $35 China carbs are so bad and cheesy, they barely ever have a true "happy customer". Sure, I wish the real carb didn't cost north of $200 usually, but the real one isn't junk right out of the box (or crummy plastic bag). I still suspect crank seals as #1 problem, but worn out 35 year old carburetors might also have a part to play.

[griffo002]

i am with you cgtech... what else is there?
BTW...I am not a blood sucker... I donated to this site...Thx

I have pulled off all the pipes and hoses from the intake ...all looks like new... am otaly confussed

[Lochlin]

I have used a lot of those China carbs on multiple carts. They very much are hit and miss and sometimes take multiple attempts. Twice now I put a new China carb on a cart only to take it off, throw it away and try again with another China carb. In each instance the 2nd China carb worked fine. Don't be afraid to try it again with the carb.

[JRL]

How does it run with the air cleaner on?
Little 2 strokes can be right sensitive to intake "mods"...if it runs worse with the air cleaner in place, it's too rich for some reason. Worn carb parts. .if still runs the same (with your gravity feed fuel tank), that probably ain't the problem
A badly worn engine with poor compression will run as you describe. They go until they don't. If it's rattling, it's going to sel-destruct soon enough.
The piston skirt will break off and make a mess of things. As they wear out, they require more fuel to start and accelerate, but it cannot function well in such a rich environment.
All the wear is global within the engine. If you feel in a diagnostic mood, plug the engine ports (carb mount and exhaust ports, fuel pulse line and spark plug hole.)
Use a small hand vacuum pump with a guage to pull vacuum on the engine fuel pulse line. It should hold the hand pump for a few minutes. If it immediately drops to zero, pull the engine and refresh the thing. Your wallet and the engine will thank you.
You might have a cylinder base gasket leak, but the piston rattle is a sign of impending doom. Rather than replace a piston only, go for a cylinder/piston/ring/crank ball bearings and seals kit. And, if any up and down on the rod, or roughness, a kit with a crank assembly.
I'm assuming that the flywheel or stator is not loose, flywheel key is intact, and all grounds and connections clean and tight.
If the flywheel side bearing fails, the flywheel might contact the the stator causing run issues. And it would rattle too.
Since it once ran ok, we'll rule out electrical components at this time...that said..? Plug cap, plug wire, coil, cdi...wiring issue? Loose or corroded grounds, loose motor mounts... incorrect electrical components, the list is endless. The trick is sort it out and avoid throwing Aussie bucks in a shotgun fashion at it.

[griffo002]

Thx again JRL... it makes no diff with air cleaner on actually... I have ordered a top end rebuild kit from the States plus new reeds And crank seals...In for a penny in for a poond as the poms say......when they arrive i fit and report back....It has me tossed... it has 100 psi , that not brilliant for sure but should still run at idle and pull away when throttling up...weird...It won’t beat me..the bloody sound so of a thing...lol