Newbie help needed!

[Smithy1216]

Hi.

Have ridden off road for years but never had trials bikes before.

Bought an old 05 GG 300 txt pro which needed a bit of tlc to have a play about on.

Only been out once on it and it popped the thermostat out along with all its coolant. Gear oil was milky too so replaced waterpump and put fresh fluids in.

Need advice as it still seems to be overheating.

Fan appears to come on and run as it should, then after pottering about for 5-10 mins it starts to steam and spit coolant out of the breather pipe. All hoses are hot so pretty sure circulation is OK.

Don't know if it's relevant but I'm pretty sure the bike has a 280 top end not a 300. And having checked the plug it's definitely running lean. 

Thinking maybe radiator cap or leaking o rings on cylinder head??

Any advice would be appreciated as these things are totally new to me!

TIA. 

 

[carl ekblom]

"Fan appears to come on and run as it should, then after pottering about for 5-10 mins it starts to steam and spit coolant out of the breather pipe. All hoses are hot so pretty sure circulation is OK."

A leaking barrel/head joint can give those symptoms.The joint must be 100% tight under the gas pressures when the engine is running

If your head is from a smaller engine it might increase the compression. Perhaps not what you want. A GG300 is a hefty bike to ride

My guess is that there was a problem they tried to rectify with an other head while it might be the barrel that was distorted after overheating.

It shoud be very difficult to read a plug with modern fuel and modern 2-stroke oil. I would check the jetting, air filter and the condition of the carb

[Smithy1216]

9 hours ago, carl ekblom said:

"Fan appears to come on and run as it should, then after pottering about for 5-10 mins it starts to steam and spit coolant out of the breather pipe. All hoses are hot so pretty sure circulation is OK."

A leaking barrel/head joint can give those symptoms.The joint must be 100% tight under the gas pressures when the engine is running

If your head is from a smaller engine it might increase the compression. Perhaps not what you want. A GG300 is a hefty bike to ride

My guess is that there was a problem they tried to rectify with an other head while it might be the barrel that was distorted after overheating.

It shoud be very difficult to read a plug with modern fuel and modern 2-stroke oil. I would check the jetting, air filter and the condition of the carb

I agree that changing the o rings first is probably the way to go before delving into anything else. Picking up on your comment about reading the plug, it's almost white which I always understood meant the bike was running lean? I'm thinking that when the barrel and head were changed the jetting and carb settings perhaps weren't touched causing it to run lean?  Is the jetting any different on a 280 compared to a 300? Would the bike running lean contribute to it running hot?

Thanks. Paul

[richt]

Check the mixture screw on the carb. Standard carb is a Delorto and the screw is actually a fuel screw not an air screw and should be 2.1/2 to 3.1/2 turns out.

Sparkplug (NGK) BPR5ES

There are casting or stamped numbers on the head and barrel. The different sizes must be paired as the bore diameter is the only difference between them and the cylinder head inner O-ring size are the only variation. 

In your frame number will give the original engine size example VTRGG 3002 F055 1234

30= Engine size 300cc. or 28= 280cc.  & 25= 250cc 

F= model year 2005

 

Edited September 5, 2021 by richt

[Smithy1216]

27 minutes ago, richt said:

Check the mixture screw on the carb. Standard carb is a Delorto and the screw is actually a fuel screw not an air screw and should be 2.1/2 to 3.1/2 turns out.

Sparkplug (NGK) BPR5ES

There are casting or stamped numbers on the head and barrel. The different sizes must be paired as the bore diameter is the only difference between them and the cylinder head inner O-ring size are the only variation. 

Thanks for that. So presumably the further out the screw is the richer it will run?

[richt]

 

8 hours ago, Smithy1216 said:

Thanks for that. So presumably the further out the screw is the richer it will run?

Yes that's correct.

If you have the owners manual there are some mistakes in it! They quote figures from the pre-pro models like the petrol/oil ratio as 2% (50:1) Pro models run 1.5% (75:1) and  Gear oil quantity as 550cc Pro models have a smaller gearbox and only need 350cc. 

[Smithy1216]

O rings now changed and still steaming through breather hose 🙉

Checked jetting and its actually running a 30 pilot. I've ordered a 36 which I believe is standard?

My question is would it running so lean cause it to overheat?

[richt]

36 is standard, I would wait an see if it still boils when you've fitted it. 

There shouldn't be any great pressure in the system unlees there's a problem like head O-rings or a crack somewhere in the castings.

Carry out a check by filling the rad to the very top and running the engine with the rad cap off while looking for bubbles or even a fountain coming out of the filler neck. Its not easy to see if the head O-ring has dropped out while putting the head on but it is possible.

Here are some engine specs:

Engine size                         250                280               300

CARBURADOR		PHBL26BS	VHST26BS	VHST26BS
Main jet		118	106	106
Jet needle position		D36 - 3ª	D48 - 4ª	D48 - 4ª
Throttle valve		60	55	55
Slow jet		35	S36	S36
Spraying jet		270K	272HH	272HH
Passage jet		200	270	270
Level of the floats		12.3 mm	12,7 mm	12,7 mm
Fuel screw		2.5 turns out	2.5 turns out	2.5 turns out
Spark plug		BPR5ES	BPR5ES	BPR5ES
Gap of electrode		0.9 mm.	0.9 mm.	0.9 mm.

 

[Smithy1216]

13 minutes ago, richt said:

36 is standard, I would wait an see if it still boils when you've fitted it. 

There shouldn't be any great pressure in the system unlees there's a problem like head O-rings or a crack somewhere in the castings.

Carry out a check by filling the rad to the very top and running the engine with the rad cap off while looking for bubbles or even a fountain coming out of the filler neck. Its not easy to see if the head O-ring has dropped out while putting the head on but it is possible.

Here are some engine specs:

Engine size                         250                280               300

CARBURADOR		PHBL26BS	VHST26BS	VHST26BS
Main jet		118	106	106
Jet needle position		D36 - 3ª	D48 - 4ª	D48 - 4ª
Throttle valve		60	55	55
Slow jet		35	S36	S36
Spraying jet		270K	272HH	272HH
Passage jet		200	270	270
Level of the floats		12.3 mm	12,7 mm	12,7 mm
Fuel screw		2.5 turns out	2.5 turns out	2.5 turns out
Spark plug		BPR5ES	BPR5ES	BPR5ES
Gap of electrode		0.9 mm.	0.9 mm.	0.9 mm.

 

That's great info thanks 👍

[Simba]

It seems to me that you may have a cylinder head issue, causing you cooling system to over pressurise. 
If my bike did this I would not be running the engine until I had removed the head. Particularly as it’s an easy job on a 2t trials bike. 
Sorting your carb now, doesn’t change the fact that damage may have already been done.

[Smithy1216]

7 minutes ago, Simba said:

It seems to me that you may have a cylinder head issue, causing you cooling system to over pressurise. 
If my bike did this I would not be running the engine until I had removed the head. Particularly as it’s an easy job on a 2t trials bike. 
Sorting your carb now, doesn’t change the fact that damage may have already been done.

The o rings have been changed this week and the head didn't appear warped when we checked it at the same time.

The jetting has now been corrected but it is still getting ridiculously hot and steaming. 

After testing the fan this morning I'm fairly confident it is actually the culprit. New one should be here in the morning so watch this space! 🤞

[Simba]

Sorry mate I need to put my glasses on.
I know you’ve changed the water pump but are you 100% sure you have good coolant flow and circulation.

[Smithy1216]

12 minutes ago, Simba said:

Sorry mate I need to put my glasses on.
I know you’ve changed the water pump but are you 100% sure you have good coolant flow and circulation.

Yes mate. Fresh coolant. Ran with cap off, can see coolant circulating and all hoses hot. 👍

[richt]

The fan on mine will turn on just as the top of the rad is too hot to touch, from a cold start its about 5-10 mins.

You say Ran with cap off, can see coolant circulating, Were there any sign of bubbles?

note the rad needs to be full to the brim, I've used a piece of clear hose that fits snug in the filer neck then positioned upright. Fill with coolant so you can see any bubbles rising just like when you bleed brakes.