Getting very frustrated now. What am I doing wrong??
Some facts: Engine had 170lbs compression (measured with a good guage-checked it using my air compressor). Don't know why it had this much compression I just assume the previous owner shaved head. This is the second time this motor (( Internal Combustion Engine ? )) blew up and both times it only ran about 3 miles. Before running I did a positive pressure check - it held pressure for several days. Then did a vaccum test and after 2hrs it was still holding 10 inchs of vaccum (no drop) so the seals were good. I did these tests with the intake boot in place, I just put a plug in. Wanted to make sure the boot wasn't leaking. New 38mm Mukuni with a 330 main jet. We are about 150ft above sea level here. After the motor (( Internal Combustion Engine ? )) blew up I did another vaccum test. Same result as above so seals are good. When I took the main jet cover off bottom of carb lots of fuel ran out so the float bowl was not dry. Does anyone have an idea why so much damage in just 3 miles?

What type and what octane fuel are you running?

Rand

good question rand if the compression been uped like he thinks he needs to b running racing fuel or prem with octane boost. i used to have a banshee with high compression and had to make sure i was running the good stuff.

Also, are you sure your exhaust side sealing is good?

What Fuel grade are you using? Have you checked the ignition timing and what ratio are you using with the fuel/ oil mix?

I feel for you that is nasty.

if your gas tank clean?
any rust in it ?
also try an different head?
would ask what oct gas and mix but its already been asked?
if i remember 20/1?

also was there any crap in the jet cap when you pulled it out?

I am running premium fuel, 20/1 oil mix, clean gas tank and run filters before and after.
No esxhaust leak because I am a silcone homo and no black oily crap around exit.

carb jetting too lean?

without knowing ur comp ratio no way to know if prem gas is good nuff but if i remember right i believe its after 10.25 to 1 prem isnt good nuff. im sure hoser would know

Thanks for the info.
I think I gona do what you suggust here. Gona run race fuel or maybe lower the compression by adding a spacer under cylinder (1/16th maybe)??
The other suggestion was jetting? So I gona get the biggest ass jet I can get and work down.
The odd part was that my brother said he was watching the pyro gauge and he said it never went over 1100' that's the reason we went out for the first ride after rebuild in the first place.

Got a buddy up here from napa valley. Don't know why he came up here to Canada to go camping.
What a fool, theres fresh snow in the hills. Gota go see him now. Will check for new suggestions on this topic on monday when I get home from work. Thanks for the suggestions.

my intake boot where the carb hooks in had a hole on the bottom of it and my piston looked just like that but the hole was more in the middle

It was an silicone homo job

If you are running 170 pounds of compression in an Ody then more than likely you need to run a lot higher octane fuel or race gas.

1.) What is your squish band measurement? I am currently setting up Ridindirty's top end and I had to put a spacer plate under the cylinder to acheive a squish band of around .060" so he will not have to run race gas.

2.) What thickness is your head gasket? If you are running just the one thin gaskets this will raise your compression by around 10 to 15 pounds.

3.) How thick is your base gasket? Is it the thin .016" Speedchaser gasket? You can run a thicker base gasket such as what comes in the Cometic or Athena gasket sets.


Rand

When I was running my Odyssey, I would jet it rich. I would start by placing a main that had it blubbering when I had throttle wide open at a slow speed say approx 10 mph and then go down in jet size until it would accelerate without a stumble... Yes I was always " rich" and the plug was always dark. I feel that the 350 Engine just needs to be rich, for the just in case issues and the nature on the Engine to begin with.
I have jetted using plug chops, but I truly feel this Engine just needs more gas... I ran my at 50/1 with amsoil I believe interceptor oil... It had a pipe air box mods and 38mm carb and engaged at 4700 rpm approx...
This is what worked for my setup... Always had plenty of power and it is with a friend now and we still run it on his figure 8 track hard... Mostly wide open
If I was racing for money I probably could've gone down on the main quite a bit and made big power.
I'm posting just in case your jetting was lean
Regards G.O.

Looks like detonation to me.

What head gasket were you running how thick is it ?

Do not forget you plug heat range. The timing refered to above is the reatrd and advace. The Engine at idol should be a full retard then advance off idol then about 3k or so it should back to retard. If the CDI (Capacitor Discharge Ignition) is bad it will stay advanced and hole the piston no matter what you do. This leads to preigniton and then detonation and what you have ( blow hole) is a result.

Recap:

jetting
plug temp
Compression Ratio
timing
gas/fuel
porttiming
head shape
rpm

I feel for you man, hang in there.

Not that I know what I am talking about but I was thinking someone maybe did some bad work on the head, what made me think this is the whole in the piston being off center.

Good luck.

Randman: My base gasket is .016 and Head gasket .040
If you all look close at the one photo you will see the piston in the up position. The top of the piston (before the crown starts) was flush with the top of the cylinder so the only gap was the head gasket. I don't know what my squish was because I didn't measure it. I guess I should have done this after the first blow up. I did a vacuum test before I ripped this thing apart like everyone on this site has suggested in past posts (yes I read them - good info at someone elses expense). I left the intake boot on because I wanted to check for leaks here too. It held vaccum for two hrs with no pressure lost so I know for sure everthing was good.
Someone please answer the following for me. Why didn't the pyro go over 1100' ??????
If you get detonation like hoser said would the pyro show it ???????
Thanks for all the suggestions. I now believe it was detonation - poor fuel - posible jetting - and I need .060 so that I don't have to run race fuel. Thanks all but please answer pyro questions if you know.

1.) EGT's can give false readings if not placed in the proper position.

2.) The EGT should be placed from a specific distance from the piston or if you can see it, the wet line within the exhaust pipe.

3.) EGT's are not the definitive way to jet an Ody.

4.) EGT's will basically tell you if the change from a base line that you establish from a history of running the Engine.

If you piston is even with the top of the cylinder then either the top of the cylinder has been decked or the bottom of the cylinder has been shaved down. Can you take some pictures with the piston at its lowest position so we can see what the clearance is from the top of the piston to the bottom of the ports. Just trying to find out visually if it can be determined which has been done.

Thanks, Rand

Your problem was your jetting. 330 is way to small for you mikuni carb. Holed piston is due to a lean condition causing detonation. Combo of high compression with lean jetting. When you rebuild it put in a 460 main jet

Sorry for all who swear by egt's but a plug chop is THE ONLY way to accuratelly read your jetting. I have seen more topends go with egt readings below 1150 degrees. It was your jetting and high compression. Get a vesrah gasket kit and use all 3 head gaskets. Try to get the comp. To 165. At 170 you will need to run closer to 100 octain to slow your burn rate. And your running a stock non watercooled head. That is going to be a hot running Engine

THERE I GO. that's the info I wanted.
Randman: I gona go out n put cylinder on and get pics for ya. Gona b a few minutes though.
I will do it now. Give me fifteen mins.

take a couple photos of the head also if u can

Here are the pics. Sorry BS I went to the shop before I read your post.