Modified Gx200

[Whitetrashrocker]

Screw the adaptor to the plug hole and pull like you mean it. Make the engine roll a few times. You'll see the needle bounce up and up. Where it tops out is the reading. There should be a check valve to hold the gauge.

Try the thumb on top first. Your engine tries to run..... Not so sure it's compression, but it's good to learn.

 

[Abtheman28]

Screw the adaptor to the plug hole and pull like you mean it. Make the engine roll a few times. You'll see the needle bounce up and up. Where it tops out is the reading. There should be a check valve to hold the gauge.

Try the thumb on top first. Your engine tries to run..... Not so sure it's compression, but it's good to learn.

Cheers. Yeah I had a look today, I got the motor running good while it was cold on the stock carb managed to get a few revs out of it but could tell it was leaning out to much in the higher rpm as I have a free flowing exhaust header pipe and pod style air filter. I changed back over to my modified carb after the motor was warm and it coughed and splattered and stalled the motor. I then tried using he stock carb with a 36 main jet and E tube to suit and it still ran like crap with the motor warm.

So at this present moment it looks like it runs only while cold.... back to the drawing board. As you said if it's running it shouldn't be a compression issue. I pulled the head the other day and couldn't see anything wrong with the rocker gear or valves

 

[Flyinhillbilly]

Have you checked the phonelic insulator between the carb and head really close for cracks? REALLY CLOSE?

 

[Bbqjoe]

Did you even try the fuel cap?

 

[Abtheman28]

Have you checked the phonelic insulator between the carb and head really close for cracks? REALLY CLOSE?

I have had it off but havent really had a close look. Will do tomorrow

---------- Post added at 04:16 PM ---------- Previous post was at 04:15 PM ----------

Did you even try the fuel cap?

Yes i did try the fuel cap. Had it off the tank and it made no difference

 

[Bbqjoe]

You know, there's not many times in life when you can start all over for $99 bucks.

 

[Randy H]

You know, there's not many times in life when you can start all over for $99 bucks.

True That!

 

[mckutzy]

Hes in New Zealand.

 

[Abtheman28]

So finally got my hands on a engine compression tester. I ran the test to start with and achieved 55psi (the best I could get) then dropped a couple tea spoons of oil in the combustion chamber and achieved 75psi. So guess I could say the motor has seen better days!

What still makes me question this though is I can get the motor idling perfect and it only begins to cough and splutter under light to medium throttle while under load.... and blows a flame or 2 out the exhaust pipe and will stall the motor. (Would an issue with engine compression cause this?) as I mentioned in prior posts I have done "everything" else to the motor regarding checks including changing the carb with another one and gaskets. I also checked the insulator which is that black bit of plastic the carb pushes up against for cracks and it looked perfect. ....have replaced ignition coil, head gasket, spark plug, removed fuel cap when running, changed fuel with new fuel, checked flywheel key, reset valve clearances. Am yet to strip bottom end.....yay!

Any info be great before I strip it down.

 

[KartFab]

oh wow you are still having issues? that sucks, bad.... see if you can put the engine at tdc on the compression stroke, take out the valve breather hose, and put it in the spark plug hole and blow, you shouldnt get any air blowing out of the intake or exhaust at this point.

 

[Abtheman28]

oh wow you are still having issues? that sucks, bad.... see if you can put the engine at tdc on the compression stroke, take out the valve breather hose, and put it in the spark plug hole and blow, you shouldnt get any air blowing out of the intake or exhaust at this point.

Hey mate,

Yeah still having issues. But have stripped the motor down in the mean time. The other day I pulled the side cover checked for anything obvious, (all looked good) inspected cam lobes, gearing , timing, lifters etc, cleaned out cases and resealed the cases again. Pulled head off and am going to remove the valves and inspect each one for possible carbon build up in the chance this may be limiting them from closing properly. At the same time I will lap the valves back in to make sure they seat properly. I also have some valve stem seals on order as thought I may as well do them while I was in there, least then I know there is no chance it could be head related. But thanks for your advice, it's always good to learn this kind of stuff from other people who know better! a good test to follow on with.

 

[Whitetrashrocker]

That's an over head valve right?
You can leak test the valves.
Turn the head upside down with valves and springs still in. Make sure it clean and dry. Install a sparkplug. Fill the combustion chamber with gas or solvent. Wait a while and see if the fluid leaks out around the valves.

I like to do this before removal of valves and again afterwards to see if they lapped properly.

---------- Post added at 06:02 PM ---------- Previous post was at 05:59 PM ----------

Also as kartfab mentioned. A leak down. With piston at TDC pressurize the cylinder via sparkplug hole. Listen where the air escapes from. Remove pressure and move to BDC and do it again this. Will tell you if the bore is wore out.
Just don't turn engine with pressure on it. It will spin fast and can hurt you.

 

[Bbqjoe]

Grasping at straws here.
What if the compression release mechanism is engaging when above idle?

 

[Abtheman28]

That's an over head valve right?
You can leak test the valves.
Turn the head upside down with valves and springs still in. Make sure it clean and dry. Install a sparkplug. Fill the combustion chamber with gas or solvent. Wait a while and see if the fluid leaks out around the valves.

I like to do this before removal of valves and again afterwards to see if they lapped properly.

---------- Post added at 06:02 PM ---------- Previous post was at 05:59 PM ----------

Also as kartfab mentioned. A leak down. With piston at TDC pressurize the cylinder via sparkplug hole. Listen where the air escapes from. Remove pressure and move to BDC and do it again this. Will tell you if the bore is wore out.
Just don't turn engine with pressure on it. It will spin fast and can hurt you.

Yup it's the overhead valve Honda clone motor. Cool thanks for that I will do the test with fluid inside the head to start with before I pull the valves out and see what happens.

Regarding the leak down test once I reassemble the motor. When the motor is at BDC and I have applied pressure to the cylinder, how do I confirm the bore is worn? What am I looking for?

---------- Post added at 09:37 PM ---------- Previous post was at 09:35 PM ----------

Grasping at straws here.
What if the compression release mechanism is engaging when above idle?

I know when I had the cam out of the motor I inspected the cam compression release mechanism and the spring tension was perfect nothing was wrong with it. What would cause it to engage when above idle?

 

[Bbqjoe]

I know when I had the cam out of the motor I inspected the cam compression release mechanism and the spring tension was perfect nothing was wrong with it. What would cause it to engage when above idle?

Beats the crap out of me. Like I said, just grasping at straws.
This one is baffling.

 

[Whitetrashrocker]

Doing a proper leak down requires a pressure regulator and a couple gauges.
Example.
At TDC apply 90psi. The rings will leak a little and show that they are holding say 70 psi.
At BDC at 90psi it sound be about the same as at TDC.

The bore gets wore out and the top pressure will not hold as much.

There is alot of variables but it tells what the ring condition is in.

You can find leaking valves too. Air will either leak out exhaust or carb if a valve is bad.

 

[KartFab]

But thanks for your advice, it's always good to learn this kind of stuff from other people who know better! a good test to follow on with.

ehhh its more like a bunch of people that know very little (at least me), but combined we can finangle something.

Hopefully your bore and rings are in good shape. This has got me baffled. Seems like you eliminated all the easy stuff.

 

[Abtheman28]

I pulled the valves from the head today and found quite a bit of carbon build up on the exhaust Valve stem as per the photos attached. One pic of the cleaner looking intake valve and the other the exhaust. The head seats appear to be ok but as mentioned prior I will lap the valves back in before reassembly. I also checked each valve for straightness just to confirm the stems were not bent from possible valve bouncing and they were both good.

So here's hoping I have found the issue! Time to reassemble it once I come off shift at work.

 

[Whitetrashrocker]

Your gonna need some Prussian blue to check your lap job properly. Be EXTREAMLY sparring with it. A tube will last a full blown rebuild shop for 50 years! Not joking.

https://www.permatex.com/products/s...epair/rebuilders-aids/permatex-prussian-blue/

 

[Bbqjoe]

I pulled the valves from the head today and found quite a bit of carbon build up on the exhaust Valve stem as per the photos attached. One pic of the cleaner looking intake valve and the other the exhaust. The head seats appear to be ok but as mentioned prior I will lap the valves back in before reassembly. I also checked each valve for straightness just to confirm the stems were not bent from possible valve bouncing and they were both good.

So here's hoping I have found the issue! Time to reassemble it once I come off shift at work.

That's not your problem.
It's still something else.

Oh, and where's your breather tube?