full throttle brap, half throttle blah

[Shrivel]

at the start of the season i installed a b pipe on my basically stock RN. i rejetted the carbs with the factory jets (135) and set the screws at fp's recommended starting points. i have been chasing a problem ever since. it appears to run fine at high speeds, there's no hesitation going from half to wot, but it bogs down at the bottom and often won't start after it gets warm without choke. choke it and it starts okay. here's what i've tried:

- messed with the high speed and low speed screws. has some effect but no remedy.
- replaced the crusty, streched carb diaphragms.
- cleaned the carbs.
- blew out all the fuel lines
- sealed up the intake gaskets really well

nothing's fixed it. any other ideas? the ski ran great before i installed the pipe.

 

[Waternut]

Sounds lean and mostly likely caused by an air leak in the crank case or carb.

Do a pressure test on your engine. If you don't know how, I did a quick and simple write up on how to make a tester and how to test the engine. http://www.pwctoday.com/showthread.php?t=166854&highlight=pressure+check

 

[Mike W]

I'm assuming you didn't change the 70 pilots so try 72.5 or 75 pilots.

 

[Shrivel]

Sounds lean and mostly likely caused by an air leak in the crank case or carb.

Do a pressure test on your engine. If you don't know how, I did a quick and simple write up on how to make a tester and how to test the engine. http://www.pwctoday.com/showthread.php?t=166854&highlight=pressure+check

I will have to give this a shot. Thanks for the nice write up. I assume I'll need 3 of the 1.5 inch test plugs - two for the intake and one for the exhaust mani, correct?

 

[Shrivel]

Update: I put together jfw's pressure test setup and found my engine was leaking (the factory pipe manifold hole takes a 1 3/4 expansion plug btw. 3 bucks at Autozone). Sprayed soapy water around the case and head and didn't see anything. Then I hit the exhaust manifold and bubble city! I have two tiny cracks at the top corners that are nearly invisible, but definitely there. I have a feeling I know how it happened, but I'm too embarrassed to say, so we'll just leave it at the fact that I'm an idiot. So now I'm looking for a manifold, but my season may be over, since I don't think I can afford it... crap....

This thing's been nothing but trouble since I put this pipe on...

 

[Shrivel]

I'm assuming you didn't change the 70 pilots so try 72.5 or 75 pilots.

Thank you so much for this suggestion. I changed the jets to 75 and this seems to have completely eliminated my bottom end problems. I still have a small air leak in my manifold, but my patch job appears to be holding enough to get me through the rest of the season.

 

[Mike W]

Thank you so much for this suggestion. I changed the jets to 75 and this seems to have completely eliminated my bottom end problems. I still have a small air leak in my manifold, but my patch job appears to be holding enough to get me through the rest of the season.

Sweet!!!