Very slow crank when spark plug is fitted

[Per Björklund]

Hello, so this question is regarding a powerski Jetboard engine. It is a single cylinder 2 stroke at about 45hp

Anyway, I just swapped the piston and rings aswell as head gasket and bottom gasket. Compression after the swap is about 110 PSI, not alot but i think it´s sufficiant. Never tried the compression on it before the piston broke and then it was ofcourse 0

Anyway it cranks really slowly when the spark plug is fitted, It is not the battery... tried with my car battery.
With the spark plug out it cranks ok. Could it be the starter going bad? It´s pretty hard to turn by hand, it was easier before but on the other hand that piston and ring was really worn and the ski had been hard to start since i bought it so it´s really hard to compare.

 

[DAG]

It´s pretty hard to turn by hand.

With spark plug out or in? with plug out you should have very little resistance

 

[clouse22]

starter

 

[Per Björklund]

It cranks ok without the spark plug. Yeah I am suspecting the starter aswell. Could it be something else to be honest?

 

[Bobert540]

starter

X2 had similar issue this summer.

 

[Blue]

Take the starter apart its probably a stuck brush.

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[Per Björklund]

Thanks for the help guys. Looks like I am going for the starter. Good suggestion, will check the brushes. Otherwise it looks like a Yama starter model so it shouldn't be to hard getting a new one since powerski seems to be out of business

 

[Per Björklund]

Changed the starter and it didn't get better. It cranks easily 3 Times and then just seizes up. You hear the click from starter and then nothing.
Any suggestions to this

 

[clouse22]

Check your flywheel key...timing could be off...could be why it cranks fine quick and then "locks" up

 

[Blue]

Have u tried another battery just as a test? If so is it any better if you remove the spark plugs? I just want to make sure ur wear rings not swelled up and the motors not seized. If all that is good possibly u have a bad battery cable. I have seen the negative cables go bad in the center of the cable but look fine.

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[Per Björklund]

I have not touched the timing belt but you think it might have slipped or something like that? Will check that, thanks
Blue : tried with a good car battery, also have a nice battery charger and the battery is new for this season but same issue there. Battery cable sounds like a very possible reason for sure.
Thanks, will start checking the battery cable for cracks
Had a bad positive cable on The superjet, issue was similar although the cable got really hot and cracked after a couple of cranks. Then it was dead. This craft manages to crank 3 or 4 times every time it's been sitting for a while

 

[Per Björklund]

Forgot to say, it cranks fine without the spark plug.... Which perhaps is an argument against bad wires

 

[Lumpy]

Hit up @OCD Solutions for a new set of power and ground cables. His products and support are top notch in every way.

 

[OCD Solutions]

Possible culprits, in the order I would check;
- cable connections,
- cables,
- battery,
- impeller for binding on wear ring/pump bearings,
- starter,
- solenoid,
- midshaft bearing,
- engine.

Compression adds a great deal of load to the starter so removing the plugs will allow it to crank much easier, even if it does have bad wires.

 

[Quinc]

did you check the ring gap?

 

[Per Björklund]

Thanks for all the answers
Havn´t checked the piston ring gap, although i meassured it with the old ring... didn´t have any issues at all inserting the new piston in the cylinder either. Same manufacturer on both piston and rings as the original one

Engine is loose currenty, so no driveshaft or impeller attached.

Will try and remove the old cables as soon as possible.

 

[Per Björklund]

So ended up removing everything electric. The issue is in the ignition box, which also has the starter relay. Problem is that it is not possible to open. Have you ever seen something like this? I got like 2 volts at the starter.... 2 cranks later it completely died. 0 volts. First though it was the start button but it isn't, does not getting any power pass this box

 

[Per Björklund]

 

[Vumad]

Did you check all of your battery cables. Bad cables rob voltage. Using a good car battery wont rule out bad cables.

The ski cranks fine without plugs because their is no resistance. Think of how easy it is to turn by hand both in and out.

A solenoid engaging is not sufficient. It must allow proper flow through the system. Test the solenoid by removing it from the ski. Trigger it by connecting the low voltage leads to the battery or a 12-volt drill battery. Then ohm the two positive cables in and out of the solenoid.

 

[OCD Solutions]

That is an interesting little solenoid pack. My bet is that it's a standard solenoid sealed in a potting compound to make it waterproof. Sealing it like that may trap too much heat and burn out the contacts.

Is it exposed in the hull or does it fit into the ebox? If you had enough room, I would build a replacement into a compact waterproof case that could be inspected and serviced.