951 break in problems

[csmelone]

so i just finished up rebuilding a 951. went to break it in today and have had some problems. the first being after its first heat cycle, i pulled the plugs and they were grey and had deposits built up on the plug. only had a few tiny specs that were shiny. towards the end of the heat cycle it started to run rough and would die at idle. Let it cool down, replaced the plugs, went for the second heat cycle, ran better but not great, could sort of tell something wasn't right. Was headed back to the ram then it started to run great, (was only going to 50% throttle) but was accelerating a lot better and wouldn't die when it came back down to idle. then all of a sudden it started bogging and died on me and wouldn't restart. Pulled it out of the water and got it to run on the trailer and idle just fine. The plugs didnt have anything built up but for some reason they still seam pretty grey and the front one seemed dry. I am going to tear down the carbs off tomorrow and see whats going on but does anyone know what else I should be looking at or can someone tell me if its ok for the plugs to look like that. The picture shown is after it died on me during the second heat cycle.

 

[mikidymac]

Those look super rich. Did you rebuild the carbs correctly?

 

[csmelone]

Those look super rich. Did you rebuild the carbs correctly?

I rebuilt them with genuine mikuni kits but the needle and seat might be viton i believe

 

[csmelone]

I rebuilt them with genuine mikuni kits but the needle and seat might be viton i believe

The only thing I didnt replace was the two plastic check valves because I lost the tool for it and Ive tried replacing them without the tool before and cant seem to do it without ripping the grommet. They looked fine. The carbs were pretty much spotless before I rebuilt them.

 

[mikidymac]

You can use dental floss for the check valve grommets.

 

[csmelone]

You can use dental floss for the check valve grommets.

Can those be a reason as to why its running rich? The pictures dont do it justice but its pretty grey, not black. Im thinking there might be some water in the gas. I pumped out as much as I could and put 93 in it with 32:1

 

[mikidymac]

Are you just running premix or premix and oil injection?

The check valves would typically cause it to run lean.
Did you confirm pop-off and leak down when you rebuilt the carbs?

 

[etemplet]

Those are the intial spark plugs? The initial set up plugs usually go out pretty quick on break-in. I use engine assembly lube and put a few ounces of oil in the engine case before start up. That can build up on the plugs quickly and foul them. I'd also check the oil pump setting. That is a lot of funk for a short run. I'd replace the plugs and ride it. That might be your problem.

 

[csmelone]

Those are the intial spark plugs? The initial set up plugs usually go out pretty quick on break-in. I use engine assembly lube and put a few ounces of oil in the engine case before start up. That can build up on the plugs quickly and foul them. I'd also check the oil pump setting. That is a lot of funk for a short run. I'd replace the plugs and ride it. That might be your problem.

Those are the second set of plugs as I mentioned. The first set was gunked up. The second set which is the picture shown was just wet and grey like water was in the gas or something

 

[csmelone]

It

Are you just running premix or premix and oil injection?

The check valves would typically cause it to run lean.
Did you confirm pop-off and leak down when you rebuilt the carbs?

Its running premix. Did not confirm

 

[etemplet]

32:1..... man that's a lot of oil. I"d expect it to run like crap in short order. I think 40:1 is a bit much for oil but that's what I run. If the engine ran well initially that would make me think the carbs were OK unless the ingested some funk. Good Luck !

 

[csmelone]

So after double and triple checking the carbs it kept giving me issue and would not start. Took the head off to check inside before pulling the motor again because I had a hunch something was wrong internally. Sure enough... what would cause this? Small metal chunks that look like pieces of the rings damaged the piston and head. Only the piston on the pto side has this. Pistons were facing the right direction. Cylinder walls are perfectly fine, couldnt feel any gouges along the walls or on any of the ports. What did I do wrong here and what caused this?

 

[andy.262]

I would check the RAVE valve on that side. If your pistons are over bored and you didn't trim the RAVE, it might have contacted and broke apart, leaving chunks of metal bouncing around in the cylinder

 

[csmelone]

I would check the RAVE valve on that side. If your pistons are over bored and you didn't trim the RAVE, it might have contacted and broke apart, leaving chunks of metal bouncing around in the cylinder

Its stock bore

 

[andy.262]

It still could happen, I lost a whole engine that way (also stock bore). I only mentioned over bore because it's much more likely to happen that way

 

[mikidymac]

How did you rebuild the engine and not have it bored and new oversized pistons installed?

 

[csmelone]

How did you rebuild the engine and not have it bored and new oversized pistons installed?

I bought jugs off a friend who had a shop hone them out and make sure they were in spec. They were stock bore. The original jugs from the motor were shot.

 

[csmelone]

It still could happen, I lost a whole engine that way (also stock bore). I only mentioned over bore because it's much more likely to happen that way

I checked the rave valves, they didn't hit the rings, the rings are still intact. you can see a tiny chip out of the rave valve and a gouge in the piston where a small piece of metal made its way through

 

[WhiskeyD]

Did you pressure test the motor before and after the top end rebuild?

 

[csmelone]

Did you pressure test the motor before and after the top end rebuild?

I didn’t. I did a full rebuild with new crank and all new gaskets and seals.

 

[mikidymac]

I would be suspicious of a used set of cylinders not needing more than a hone to get the proper clearance.

Never put a rebuilt engine in service without pressure testing it, ever.

 

[csmelone]

I would be suspicious of a used set of cylinders not needing more than a hone to get the proper clearance.

Never put a rebuilt engine in service without pressure testing it, ever.

Do you need special block off plates? Or if I can make some what material do I use?

 

[mikidymac]

I use sheets of neoprene rubber cut to size and the carbs and exhaust to squish them air tight.

 

[csmelone]

I use sheets of neoprene rubber cut to size and the carbs and exhaust to squish them air tight.

Thanks I’ll see if I can find some. Do I need a special pump as well?

 

[andy.262]

Silly as it sounds, when I did mine I used shower pan liner from Lowes to seal it, since that was all they had. Squished it between the carbs/manifold and the engine like Miki said. For the air pump I used a regular bike pump with some adapters that accept the schrader valve (1-way, so air can flow in but not out), and adapt it into a hose barb. Then just a hose from the barb to the engine.