Low compression

[soupnutz]

My blaster has been getting harder and harder to start lately. I upgraded the carb and the reeds and pretty much had to give it half throttle to start it. Decided to do a compression check and am only getting 60 psi, which is about half what it should be.

The top end is a vitos 240 bbk with cast piston. Its been on for about 4 years but only has about 20 hours on it. I pulled it apart and the cylinder walls look great, the piston has some carbon buildup but looks good otherwise and the rings don't look bad. It had the copper head gasket and I've read that vitos gaskets arent the best, but it looks ok. Right now I'm looking at replacing the rings and gaskets and seeing what it does. As there anything else I should be looking at?

Another question is, with a bbk, should I only get a new piston from that company because of the different ports and piston cut-outs?

 

[blasterdemon7]

Did you hold the throttle wide open and kicked it till the needle stopes rising ? Kicked it about 8-9 times ?

 

[soupnutz]

Lol, held the throttle open and kicked it until my foot hurt. Pobably about 50 times.

 

[Larry's Shee]

Did you also try another gage? Highly doubt it would even start, let alone start hard with that psi. Gage could leak, bad schrader valve, not sealing to plug hole, if schrader is at gage instead of tip, you're adding lots of volume. Not as critical on an auto, but a Blaster has way smaller b/s to start with. Unless you used crappy oil or something should still be good @20hrs. Why do you think it needs a new piston? Have yo measured the bore (six ways) and piston?
Never saw mention of Vito's head gaskets being questionable, got a linc?

 

[soupnutz]

Posted that from my phone so I left some stuff out, but more specifically, after i changed out the reeds and the carb, thats when it took half throttle to start it. Played with the pilot jet and air/idle screw to get it idling good. At that point it was starting first kick. Took it down the street to check the top end and it died a few blocks away, couldn't get it to start. Pushed it home, checked for spark and everything. It felt physically a lot easier to kick it over and with my finger on the hole I wasnt feeling much pressure. Hooked up the guage and got 60 psi, took it off and tried again with the same results. Figured I had the main jet too lean or had an airleak and fried it. Took it all apart, but everything looks good. Only thing I see is there looks like theres more play between the piston and cylinder than there should be, cant find my feeler guage right now to check it. I'm pretty sure my pressure tester is good though, it's been dead nuts on everything I've used it on before.

 

[Blaaster]

Tell your mods and the jetting you were using and we will make an educated guess if it was too lean.

What oil and ratio do you run?

I have known an incorrectly tensioned head gasket to leak when overheated by a lean mixture.

 

[Larry's Shee]

Posted that from my phone so I left some stuff out, but more specifically, after i changed out the reeds and the carb, thats when it took half throttle to start it. Played with the pilot jet and air/idle screw to get it idling good. At that point it was starting first kick. Took it down the street to check the top end and it died a few blocks away, couldn't get it to start. Pushed it home, checked for spark and everything. It felt physically a lot easier to kick it over and with my finger on the hole I wasnt feeling much pressure. Hooked up the guage and got 60 psi, took it off and tried again with the same results. Figured I had the main jet too lean or had an airleak and fried it. Took it all apart, but everything looks good. Only thing I see is there looks like theres more play between the piston and cylinder than there should be, cant find my feeler guage right now to check it. I'm pretty sure my pressure tester is good though, it's been dead nuts on everything I've used it on before.

That right there is the clue to your problem. Bet you had an air leak, or the carb had extremely lean jetting, or was plugged/dirty. For everyones information/benifit, when you have a sudden problem such as this, perform a leakdown test before dissasembly to help find out why. I:I

 

[soupnutz]

Yeah, you're right. I should have done a leakdown check. I pressure tested the carb and the intake manifold together but not everything as a whole. As far as the carb, it was brand new and I jetted it richer than all of the other members that I've seen with the same carb.

Anyway, it will have to wait. I just snapped a control arm in my car and that comes first, plan on getting the forged 240 piston and gaskets from Vitos next payday, so I'll see how that goes.