95, 120 jet. OK I'm at a loss, hard start and pop/cough

[ebear]

.I've been through everything I can think of.
Starting, It will what I will best discribe as a backfire out the exhaust [never thru carbs] and stop the motor then turn a couple more times then do it again. I can get it to run by putting the control in full start advance and cupping my hand over one carb for a short 2 seconds while turning it over once it starts it runs but the backfire/pop is still present.Running the boat. at top end the pop is more prevelant and robs power when it happens.
Background. I picked the boat up with #4 blown.

I rebuilt the motor being careful to put everything back exactly as it was before. Now i have to stop there and add that #4 was pretty beat up. I had the block machined 30 over, got a 30 over piston and changed the rings on the other 3. The head was beat also, but after a bit of grinding and sanding, it came out pretty clean so I put it back on. I have heard of chunks getting stuck in the metal and causing detonation so I made an effort to be sure that it was clean.

I went through all the wiring, checked and reset the timing to 32 deg wot cranking. I rebuilt the carbs, floats are level, mix screws 1 1/2 turns, fuel pressure is at 3.5 lbs cranking. I indexed all cyl and it fires on all marks. What am I missing please help I wat to take it out someday.

 

[CharlieB]

Re: 95, 120 jet. OK I'm at a loss, hard start and pop/cough

WOT is way too advanced. If you found that 32 degree number in a book, it was a mis-print and should be more like 23 at WOT cranking.

Idle mixture is probably way too lean, 1 and 1/2 is usually just enough to get the motor started and must be readjusted once IN the water to 'Best Idle Speed' and even from that point you will STILL need to further open each idle mixture screw almost 1/8 turn to provide the additional fuel needed for a two stroke to accelerate without hesitation, lean miss, or bogging. It is most advisable to make this last adjustment just turning the screws the width of the screw-driver blade slot from that Best Idle until you just get to the point there is perfect acceleration opening the throttle rapidly from idle to WOT.

 

[ebear]

Re: 95, 120 jet. OK I'm at a loss, hard start and pop/cough

I have it in a clymer pdf. I don't mean to offend here but another factor here is that before I took it apart, I had locked the timing adjustment in place so I wouldn't fight with it when it went back together. so it sits exactly where it was originally. Also I ran it before I found the problem and it started and idled without any problems( zero compression on 4 and no pieces in block). Now the guy said that he had taken it to the marina for work recently. Is there a possibility that either He blew it and took it to them to make it run so he could dump it on a victim like me. Or is it possible that the popping that it has now is the same thing that blew #4 in the first place and I should be looking for something else causing this issue

 

[ebear]

Re: 95, 120 jet. OK I'm at a loss, hard start and pop/cough

Also, It can't be 180 out, can it

 

[1nebel0]

Re: 95, 120 jet. OK I'm at a loss, hard start and pop/cough

You can't possibly be running 32 degrees or you are going to blow a hole through the other pistons...23 degrees is max and given the wonderful gas we have drop it to 21....You are running LEAN... Charlie nailed it...you will need to double oil to break in all rings as well as follow breakin procedure which you don't mention. You can't do anything to make it run right if it is down a cylinder. It can sound ok on a stand but once under load will always show its ugly face....

 

[ebear]

Re: 95, 120 jet. OK I'm at a loss, hard start and pop/cough

Honestly, I kinda thought 30 was high. But I trust the book. I'll try it tomorrow n let you know.