91’ sj650 won’t start

[KIDbilly]

Hey guys and gals. I have been working on a Superjet 650 1991 for a while, at first it was getting no spark so I replaced the CDI ignition coil and stator which all had seen it’s 30 years of service. Finally got spark to the plugs so decided it must be a fuel problem, replaced 20 feet of fuel line put a new fuel filter and water separator, still have a fuel check valve that I’ve not put in because I don’t know where to put it yet. Now it smells like it wants to start and sounds like it wants to start and it’s getting spark but it just won’t start. I have both the carb jets out one and an eighth turn. Pulled the carb apart and everything seems to look clean inside, not sure if it’s the factory carb but I just don’t know where to go next. Any suggestions will help,
thanks to all, William

 

[KIDbilly]

What is the Cranking Compression in each Cylinder?

Need at least 90 psi on both for ignition.

So I did a compression test and the cylinder closer the the rear has 115psi. The other cylinder on the stator side only had 35psi. Does that seem to be a top end or the stator side main seal? Thanks again.

 

[DylanS]

So I did a compression test and the cylinder closer the the rear has 115psi. The other cylinder on the stator side only had 35psi. Does that seem to be a top end or the stator side main seal? Thanks again.

Top end issue, either head gasket or piston/cyl issue. Pop the head off

 

[KIDbilly]

Top end issue, either head gasket or piston/cyl issue. Pop the head off

Not to sure what this means but it doesn’t look good.?

 

[KIDbilly]

Not to sure what this means but it doesn’t look good.?

Could it potentially just be a head gasket?..

 

[KIDbilly]

Yes, it could be just the Head Gasket.

That's definitely a blown Head Gasket.

Install a new one and read the Compression on both Cylinders again.

But at 115 psi it's time for a Top End Rebuild at the minimum.

If you keep running that Engine, the Piston Skirts can break-off and totally destroy the Engine.

So while I was cleaning off the head and removing the old gasket I noticed These two pieces which I assume used to be one piece floating around in the inner chamber between the two cylinders. Do you know what it is and if it’s worth replacing? There are old thread marks on the innards of them and I’m assuming it went on the little Phillips in the center.?

 

[DylanS]

it’s a anode, helps keep corrosion at bay, yes it goes there. Some people run them and most toss them or never replace them.

 

[KIDbilly]

it’s a anode, helps keep corrosion at bay, yes it goes there. Some people run them and most toss them or never replace them.

OK so I put a new head gasket in and bolted it all back together just to see what my compression would be and cylinder one in the rear went from 115 before the new head gasket to 90. And cylinder two in the front of the unit went from 30 previously to 90 as well.. plan on doing a top end before getting it on the water but wanted to see if it would at least fire up as I’ve never heard it run. It’s cranking a lot better and sounds like it really wants to start but I am stumped, any suggestions?

 

[DylanS]

OK so I put a new head gasket in and bolted it all back together just to see what my compression would be and cylinder one in the rear went from 115 before the new head gasket to 90. And cylinder two in the front of the unit went from 30 previously to 90 as well.. plan on doing a top end before getting it on the water but wanted to see if it would at least fire up as I’ve never heard it run. It’s cranking a lot better and sounds like it really wants to start but I am stumped, any suggestions?

Compression is too low at 90 psi brotha

 

[KIDbilly]

Yes, it could be just the Head Gasket.

That's definitely a blown Head Gasket.

Install a new one and read the Compression on both Cylinders again.

But at 115 psi it's time for a Top End Rebuild at the minimum.

If you keep running that Engine, the Piston Skirts can break-off and totally destroy the Engine.

OK so I put a new head gasket in and bolted it all back together just to see what my compression would be and cylinder one in the rear went from 115 before the new head gasket to 90. And cylinder two in the front of the unit went from 30 previously to 90 as well.. plan on doing a top end before getting it on the water but wanted to see if it would at least fire up as I’ve never heard it run. It’s cranking a lot better and sounds like it really wants to start but I am stumped, any suggestions?

 

[KIDbilly]

Compression is too low at 90 psi brotha

Ok thank you. Should I start with top end rebuild or main crank seals?

 

[DylanS]

Are you sure your compression gauge is good ?
Odd to me that your engine has 90psi even in both holes.
Static compression wouldn’t be affected by crank seals that drastically.
Also odd you went from 115 to 90 unless that cyl was wet.

 

[KIDbilly]

Are you sure your compression gauge is good ?
Odd to me that your engine has 90psi even in both holes.
Static compression wouldn’t be affected by crank seals that drastically.
Also odd you went from 115 to 90 unless that cyl was wet.

I’ll make sure the gaugu is accurate. It’s brand new but a cheap harbor freight one. My bud has a Matco one I’ll use to compare. I did finger in a small amount of two cycle oil on the cylinder walls before putting head and gasket back on. What do you mean by wet cylinder?

 

[DylanS]

I’d be willing to bet your gauge is off, it’s highly unlikely you’d be down evenly to 90psi on both cyls.
When you originally read 115 (assuming you tested properly both times with a good charged battery) was there splash of oil in that cyl? That could have caused your 115 to 90 deviance.
Even compression is a good sign, try your buddies gauge, full throttle and crank till gauge stops moving.

If you do end up with lower than acceptable compression you can order .5 over pistons and have your cyls machined to match.