Engine won't plane off at first

[Waternut]

I've started noticing some wierd stuff with my SJ. I rebuilt it over the winter with Wiseco pistons and it runs great once it's warmed up. However, for the first 3-4 minutes it will barely idle and if I give it gas, it won't even plane off. After about 2 minutes it's got enough juice to plane off but then it takes another minute or two to actually develop full power. I never noticed it before because I always left the ski on the trailer to warm up while I was breaking in the engine.

I know Wiseco's need to be warmed up a bit but my 750 has Wiseco's and it will pull strong after a short idle out of the no wake zone which is about a minute.

Is it just the Wiseco pistons warming up or am I looking at another problem entirely?

 

[steveyz250fpilot]

another problem

 

[redsxr800]

sounds like it might lein on low side

 

[Waternut]

You guys think that maybe when I first start the engines, it takes a little bit of extra time to work the air bubbles out of the fuel lines? I usually pump the primer 2-3 times once fuel starts pumping and it typically takes 3-4 pumps to get fuel to start.

The problem will completely go away for the rest of the day once it gets through that initial craptacular state and it will run great. Piston wash is good as well.

 

[ger87410]

Does it feel like bubbles?

U may want to thoroughly check your fuel system for any cracks or leaks.

Sounds to me like a tuning issue.

When you say the problem goes away for the rest of the day, what's the longest your ski's been sitting unused during this "rest of the day"? It may not have a chance to fully cool down.

 

[Waternut]

Typically it only sits for 30-60 minutes but it's been hours before and I've had to reprime the engine to get it to start.

 

[cmeripper26]

I would check the fuel pump side of the carb, to check for clogged filter or busted seal, o-ring, etc.. Do you run a remote fuel pump?

 

[Waternut]

Both ski's have standard fuel pumps. The SJ has a Mikuni and the 750 has a keihin.

 

[SUPERTUNE]

How do you have fuel lines run and where is the supply for the primer hooked up?

 

[Freakrider]

How do you have fuel lines run and where is the supply for the primer hooked up?

Not to thread jack but maybe related:

Chuck, engine builder Bob that u know in St.Pete says that primer lines cause potential lean conditions ? I have noticed this when the primer lines have lots of air in them and hooked up to a carb supply line (ON or Reserve). I have seen a motor surge because of this condition ?

 

[Waternut]

On the SJ, the fuel lines are run like stock (return on top, supply on bottom, and pulse in the middle) and the primer is connected to the supply line just before the on,off,res switch.

Jump On It, you may have hit something with the primer. I usually have to pump both primers 4-5 times (sometimes more) before fuel will actually start pumping. The SJ primer is the worst of the two. Then I'll give the carb 2-3 pumps of fuel. Maybe there is still air in the primers for a short time after the engine has started.

 

[Cliff]

try hooking the primer to the return line

 

[cookerq62]

do you turn th fuel off when you put them away?

 

[Freakrider]

On the SJ, the fuel lines are run like stock (return on top, supply on bottom, and pulse in the middle) and the primer is connected to the supply line just before the on,off,res switch.

Jump On It, you may have hit something with the primer. I usually have to pump both primers 4-5 times (sometimes more) before fuel will actually start pumping. The SJ primer is the worst of the two. Then I'll give the carb 2-3 pumps of fuel. Maybe there is still air in the primers for a short time after the engine has started.

on my blaster, the primer line is tee'd into the reserve line just after the pick up...the primer is bad and I tried WD 40 in it like "Crammit" has found to restore some of them....anyways the line is full of air and when I start the ski up on reserve it idles with a fuel starved surge, but when I switch to ON position it stops right away because the empty primer lines are not in the fuel path to the carbs...again engine builder Bob in St.Pete states primer lines can cause lean conditions and he is against using them period ! food for thought...

 

[Waternut]

try hooking the primer to the return line

Will that actually work?

do you turn the fuel off when you put them away?

No I typically leave the fuel on. Could that be causing problems?

 

[Cliff]

Will that actually work?



No I typically leave the fuel on. Could that be causing problems?

thats how we all around here run them. no problems

 

[FreestyleFreak]

Will that actually work?



No I typically leave the fuel on. Could that be causing problems?

Yeah that wont cause i problem,i dont even run a gas on/off switch.

 

[Waternut]

I'll try swapping the primer onto the return line and see if the problem goes away. I'll let you know how it goes.

 

[SUPERTUNE]

Put the primer supply on the reserve line from the tank then use the on when riding and starting out, this way when you prime you don't steal the fuel that the engine needs to run on...

 

[cookerq62]

Yeah that wont cause i problem,i dont even run a gas on/off switch.

It's a good way to flood the out of your motor or get air in the lines. Sounds like air in the fuel lines. Like everyone else said. I run my primers from the reserve but I put a loop in the fuel line and put the primer t at the bottom of the loop so there is always some fuel trapped in there to get her going.