1975 Suzuki GT-250 street bike please help me Compression?

[Zechariah]

Hello all,
My father has a 1975 Suzuki GT250 street bike, this bike is completely stock and it has only 3K miles.
I am wondering how much compression it should have?

Thanks,
Zechariah

[jeffcoslacker]

I don't know specifically...80-140psi is typical for two strokes though...

[Zechariah]

Ok thanks I just went out and checked it and it had 90PSI in either cylinder Should I be able to start it on 90PSI?

Thanks,
Zechariah

[jeffcoslacker]

I would think so...if it's dry and hasn't been started in forever it'll read lower than normal, there's no fuel/oil residue on cylinders and rings to bring it up a bit...

If that's the case, you'd probably see 90-100 if it was "wet"

You can try priming it with WD-40 spray in the carbs...most two strokes like it, they fire on it like starting fluid and it at least gets a little lubrication going internally...

you've got spark, I guess?

[jeffcoslacker]

That's a nice classic bike...make sure it's feeding oil, you don't wanna seize that motor...

If there's any doubt, at least mix some with the fuel at 16:1 or so to give it some lube...

Those were oil injected, right? I don't remember having to add oil to the fuel..thought they had an oil tank and injection system...

[jeffcoslacker]

You get that baby running yet?

I'm excited for you...I'd LOVE to have one...looked at a GT380 last summer...sounded like the dirt bike from hell...love those old smokers...

[Zechariah]

No, I'm charging the battery and then I'm going to try starting it, Hope it works... if not I'll be back for more help

~Zechariah

[Zechariah]

Alright, so it has a strong spark a full battery and what brand new plugs I tried a little WD-40 and it won't start any ideas?

~Zechariah

[jeffcoslacker]

Hmmm.

Nothing at all? No backfire, putt or anything?

I think points were an issue on those sometimes...if it's been stored sometimes the points can get corroded or the lobe they ride on can corrode and grind up the plastic block on the points arm..then the dwell will be totally wrong, it may spark but be so off-time and short duration it won't fire...

It's worth a look in the cover...

If you see nothing there, try mixing some fuel/two cycle oil at 16:1, squirt a little in each plug port and put the plugs back in, see if it fires like that.

If so, the reed valves might be gummed closed...they are in the crankcase and have to be able to be sucked open when there's crancase vacuum in order to inhale fual/oil mix...if they are stuck, nothing can get through from the carbs...

I guess your familiar with 2 stroke basics? If not, a little understanding will help you figure it out...let me know. I'm no whiz, but understand in principle...well enough to get them running, usually...

[jeffcoslacker]

PS if the plugs aren't getting wet with fuel after trying repeatedly to start it, the reeds are probably stuck.

Don't try too much if that's the case...the engine is turning over without lubrication...you don't wanna wreck it before you even get it running...

[MagicRat]

It sounds as if it has not run for a long time. Have you looked at the carb? Unless the carb was drained properly before it was stored, the float could be stuck in the up position, meaning fuel cannot flow or the jets are clogged.

Also have a peek in the gas tank. Is the inside of it full of rust? Rust debris can clog the fuel line and the carb and should be cleaned out.

[jeffcoslacker]

Originally Posted by MagicRat

It sounds as if it has not run for a long time. Have you looked at the carb? Unless the carb was drained properly before it was stored, the float could be stuck in the up position, meaning fuel cannot flow or the jets are clogged.

Also have a peek in the gas tank. Is the inside of it full of rust? Rust debris can clog the fuel line and the carb and should be cleaned out.

If the spark timing and dwell are correct or close, shooting a volatile liquid into it should at least get some reaction from it...but if the reeds are stuck closed, nothing that goes into the carbs will go into the cylinders...

Remember this is a two-stroke motor...it inhales through ports that draw from the crankcase...the reeds control the orifice from the carbs into the crankcase...

And if the reeds aren't stuck, just getting fuel to it will make it start, but if the oil injection is not functional, it will seize after running for a short time..

You are correct that the carbs are probably a mess though...but for the purposes of determining if it will start or not, it's not an issue...

[Zechariah]

Well um I guess I should have told you guys this before,

When we got the bike it had been sitting for about 1 or 2 years without being touched. We have done the following to the bike:

-Taken the gas tank off done the lye treatment to it to remove all the rust and old gas the tank is now almost perfectly clean inside, then we had it sand blasted, filled in a couple of tiny dents and repainted it and the side covers to very close to the original color (a kind of specily golden orange) and now it looks REALLY good (my father was at one time an air brush artist and he used a automotive sprayer and high quality paint)

-We have clean the whole bike and outside of the engine I took the carbs off and cleaned them (I didn't put any new seals or O rings in, should I have??)

-Installed a new clutch cable the clutch is not working though and it wasn't before we put the new cable on either (I read some were that if you start it and warm the engine up and work the clutch it might free it up what do you guys think?)

-Installed a new head gasket (But I am not sure I did this right I took the head off carefully cleaned and dried the surface with some engine cleaner and a paper towel then put the new gasket in place and put the head back on then carefully torqued the head bolt in a pattern like you would when changing a tire. Did I do this right? I didn't know about this site when I did this or I would have asked for some advise on how to do it then)

-The spark plugs look new but I can't remember if we put them in or not (we have been working on this project for about 3 years )

-The battery was new a year ago but it hasn't been used just sitting I put a charge on it the other day and it appears to be holding it

Other than that I can't think of anything else... the compression is 90PSI in both cylinders.

it has gas in it that is about 8 months old (it should start on this right?)

Oh I all so replaced the fuel lines and the gasket in the fuel switch I know that gas is getting in to bowls... but I don't know if it is getting to the cylinders.

Also we replaced the air filter.

I put a fix of 16:1 gas and 2 cycle oil in the cylinders threw the spark plug holes and it didn't even sputter.

Now what should I try?


Thanks for helping me I am still learning as I go, I have been doing automotive work for about 9 years but still the biggest job I ever did was a clutch job on a Geo Metro I have never done a rebuild or any thing major, but thanks to the internet I can learn how to do just about anything.


Thanks again,
~Zechariah

[jeffcoslacker]

I still think your reeds are stuck.

Can you feel any suction at the carbs when the engine is cranked?

[Zechariah]

Is it possible that this bike doesn't have reeds? if not can anyone tell me where they are located? (I can't find them)

Thanks,
~Zechariah