Intake air leak?/Run away engine

[racerx143]

WaveBlaster 701 with dual 44 SBN's on Riva intake.

I have been chasing a run away condition. I had a rear seal pushed out a bit so I replaced all the crank seals and "assumed" I was all good. Reinstalled the engine and had an immediate run away again the minute I fired it up in the shop. Pulled the engine and made block off plates and built a set up to pressure test the engine. (lesson learned to always pressure test....) The exhaust plates worked perfect, no leaks. The first set of intake plates leaked massively. The gaskets I had on the engine were from Riva and thick and in good visual condition. They leaked, so I ordered 12 off ebay from somebody in AZ and they leaked... these gaskets were thin. Tried grease on both types and it helped but didn't stop the leak. The plates would rock a little on the intake so I built another set from different material (stop sign) and ended up with the same results. These had a little rock to them also on the intake and I still had massive leaks. I should add, all the block off plates I made seemed to have a little rock even on a glass surface. I ended up going to Advance Auto and getting 1 3/4" expansion plugs which fit perfect in the intake and sealed it off completely. At this point I still had a slow leak and couldn't find it with soap and water so I ended up submerging the engine all the way up to the head in water to test it only to find my PSI gauge had an internal leak when I dipped it underwater. But otherwise the only thing I noticed from the engine was a very very small bubble escaping about every 20 or so seconds from one of the pry points at the base of the rear cylinder. So small that I can't imagine it could suck enough air through to cause a run away.

So all that leads me to my question, has anybody ever had an intake warp to the point it will not seal to the base of the carbs? I don't know what could cause that casting to lose it's flatness but i am running out of ideas. I had this thing underwater for about 5 minutes with no noticeable leaks from the engine or intake so I am now focusing on the intake where the carbs mount. I am going to replace the test gauge today and at this point plan to test it with the carbs on and the top of the carbs plugged but wanted to see if anybody has dealt with a situation like this. Thanks.

 

[mikidymac]

The first engines I have ever had fail a leak down test were my Yamaha 650 and 701 on the intake gaskets even using OEM gaskets so now I always use Threebond 1211 on all Yamaha intake gaskets. To pass the pressure test your engine needs to hold 8 psi for at least 10 minutes after that it is good to go. I would also use 1211 on your carb base gaskets to be safe.

 

[Quinc]

I had a similar issue where I chased an air leak for a season and it ended up being my fuel filters where sucking in air through the plastic. New filters from autozone and she was perfect after that. Check your filters, hoses, fuel tank pick ups etc. Also you might have too lean of a low jet, or need to turn out the bottom screws another 1/2-1 turn. Also do the pressure test with your carbs on. Get the right size freeze plug that fits in the carb.

To check that the intake is flat and the carb bases are flat, use sand paper on a plate of glass to bring down any high spots.

 

[mikidymac]

I had a similar issue where I chased an air leak for a season and it ended up being my fuel filters where sucking in air through the plastic. New filters from autozone and she was perfect after that. Check your filters, hoses, fuel tank pick ups etc. Also you might have too lean of a low jet, or need to turn out the bottom screws another 1/2-1 turn. Also do the pressure test with your carbs on. Get the right size freeze plug that fits in the carb.

To check that the intake is flat and the carb bases are flat, use sand paper on a plate of glass to bring down any high spots.

Are you sure the throttle and choke shafts will hold air? I have never heard of pressure testing with pressure all the way through the carbs, typically you block off at the base of the carbs.

 

[Quinc]

Are you sure the throttle and choke shafts will hold air? I have never heard of pressure testing with pressure all the way through the carbs, typically you block off at the base of the carbs.

That is a good point. I haven't tried it and only heard of others doing it.

 

[mikidymac]

You really shouldn't have to test through the carb since it doesn't hold air pressure. Just block off at the base of the carb to find your air leak and use a good carb base gasket like the thick green ones with some 1211.

 

[racerx143]

The first engines I have ever had fail a leak down test were my Yamaha 650 and 701 on the intake gaskets even using OEM gaskets so now I always use Threebond 1211 on all Yamaha intake gaskets. To pass the pressure test your engine needs to hold 8 psi for at least 10 minutes after that it is good to go. I would also use 1211 on your carb base gaskets to be safe.

That's one of the next steps, I was just using a thick grease with the block off plates. I was trying to avoid making any kind of a mess while testing but I think I'm past that point..

I had a similar issue where I chased an air leak for a season and it ended up being my fuel filters where sucking in air through the plastic. New filters from autozone and she was perfect after that. Check your filters, hoses, fuel tank pick ups etc. Also you might have too lean of a low jet, or need to turn out the bottom screws another 1/2-1 turn. Also do the pressure test with your carbs on. Get the right size freeze plug that fits in the carb.

To check that the intake is flat and the carb bases are flat, use sand paper on a plate of glass to bring down any high spots.

My lean condition is causing a total run away engine. I can't see how to lean of a setting or jet would cause what I am experiencing. The same with a filter issue. But I have been "educated" before by others on things I didn't consider so thanks for the input.

You really shouldn't have to test through the carb since it doesn't hold air pressure. Just block off at the base of the carb to find your air leak and use a good carb base gasket like the thick green ones with some 1211.

The reason I wanted to try with the carbs on is the eliminate the fact that the block off plates I made might not be 100% flat. The expansion plugs work perfect but obviously doesn't tell me if the intake surface is an issue. I made 2 sets and even though the material I used looks flat, so far haven't been able to get any of them to seal. If I can seal up the carbs tight enough I will be able to test to see if there is still a leak at the base with soapy water. Before I found myself knee deep in this issue I thought all run away engines were caused by leaking crank seals.. Urgh...

 

[Roseand]

That's one of the next steps, I was just using a thick grease with the block off plates. I was trying to avoid making any kind of a mess while testing but I think I'm past that point..



My lean condition is causing a total run away engine. I can't see how to lean of a setting or jet would cause what I am experiencing. The same with a filter issue. But I have been "educated" before by others on things I didn't consider so thanks for the input.



The reason I wanted to try with the carbs on is the eliminate the fact that the block off plates I made might not be 100% flat. The expansion plugs work perfect but obviously doesn't tell me if the intake surface is an issue. I made 2 sets and even though the material I used looks flat, so far haven't been able to get any of them to seal. If I can seal up the carbs tight enough I will be able to test to see if there is still a leak at the base with soapy water or sink the bitch again in a tub of water

You're not going to be able to seal the carbs. Seal up your intake mani with some 1211 or similar, let it cure, and test. Unless your manifold and case surface is severely warped 1211 will take care of it. It's easy enough to take a straight edge to the surfaces too. If you don't have a known good straight edge, hold two against each other and shine light between them to see what you're dealing with
No need for the water tank. It's all fun and games until a plumbers plug pops out and swamps your motor. Just soapy water is the golden standard.
I run a very thin layer of 1211 over all base, intake mani and exhaust mani gaskets. Its nice because it basically guarantees you won't have any water or air leaks.. And makes you much less likely to gouge the surface when scraping it off with a razor blade.

 

[fastgtfairlane]

silly question but are you sure the throttle cable wasnt slightly tight causing the engine to run away as soon as you started it? ive seen and had that happen on my own skis as well as others too.

i always use "assembly goo" on the exhaust, base, intake and carb gaskets to ensure no leaks and also will keep the gaskets from tearing if you have to remove something and making them eccentually reusable for the most part

 

[racerx143]

You're not going to be able to seal the carbs. Seal up your intake mani with some 1211 or similar, let it cure, and test. Unless your manifold and case surface is severely warped 1211 will take care of it. It's easy enough to take a straight edge to the surfaces too. If you don't have a known good straight edge, hold two against each other and shine light between them to see what you're dealing with
No need for the water tank. It's all fun and games until a plumbers plug pops out and swamps your motor. Just soapy water is the golden standard.
I run a very thin layer of 1211 over all base, intake mani and exhaust mani gaskets. Its nice because it basically guarantees you won't have any water or air leaks.. And makes you much less likely to gouge the surface when scraping it off with a razor blade.

Got ya on the water tank test, i realized the possibility but was over chasing the leak with soapy water. I had sprayed all my test equipment first and only when I dunked the pressure gauge underwater did I find out it was leaking from inside the gauge itself. Can tell ya though, it's 99.9% air tight! My intake to engine seal is fine so only dealing with the intake to carb at this point. I did eyeball it with a straightedge and there is the slightest of slight gaps. I suppose Ill just take the 1211 advice and try it with my block of plates first. Thanks.

 

[racerx143]

silly question but are you sure the throttle cable wasnt slightly tight causing the engine to run away as soon as you started it? ive seen and had that happen on my own skis as well as others too.

NOOO! This was/is a full on pull the lanyard, hit the stop button still going WFO condition. Had to wide open the throttle to kill it.

 

[racerx143]

On my way to pick up some 1211, pricey isn't it? ($30.00) I know its cheaper online but i want to ride this weekend. I'll report back after I see how this all works out.

 

[Freakrider]

Too much to read above but throttle plates are in sync?

 

[kevbo]

Definitely look for leaks. The bottom adjuster controls idle mixture. You should be able to richen the idle mixture enough even with a small air leak.

 

[Quinc]

On my way to pick up some 1211, pricey isn't it? ($30.00) I know its cheaper online but i want to ride this weekend. I'll report back after I see how this all works out.

1211 is best, but you can use any engine sealant like honda bond etc.

 

[Spike]

Are you sure the fuel is not restricted? Bad needle seat, bad filters? internal carb blockage ?

 

[racerx143]

1211 on the intake, gasket and carbs and all is good. Ran perfect all weekend.

 

[Pro-pulsion]

I have found the easiest way to get a solid seal on your engine for a pressure test is to just hole punch your exhaust bolt pattern onto a sheet of 1/8" rubber, same with your carb side, sandwich the rubber sheet between the exhaust mani and block, sandwich the other rubber sheet between the carb bases and intake mani, apply pressure through the pulse fitting. No need for block off plates and has worked 100% of the time for me. A lean runaway could also be badly worn throttle shaft bushings. You're taking in air from below the throttle plate so you're essentially losing carburetion control with an extra air injection. As Quinc said too, if you believe your intake manifold is not truly flat, get a surface plate which can just be a thicker piece of glass, 1/4" thick would be ideal, a thin layer of contact cement on both glass and 220 grit sand paper sheet, smooth down the manifold until you have a consistent surface finish. That'll be about the easiest way to do it.

 

[racerx143]

I have found the easiest way to get a solid seal on your engine for a pressure test is to just hole punch your exhaust bolt pattern onto a sheet of 1/8" rubber, same with your carb side, sandwich the rubber sheet between the exhaust mani and block, sandwich the other rubber sheet between the carb bases and intake mani, apply pressure through the pulse fitting. No need for block off plates and has worked 100% of the time for me. A lean runaway could also be badly worn throttle shaft bushings. You're taking in air from below the throttle plate so you're essentially losing carburetion control with an extra air injection. As Quinc said too, if you believe your intake manifold is not truly flat, get a surface plate which can just be a thicker piece of glass, 1/4" thick would be ideal, a thin layer of contact cement on both glass and 220 grit sand paper sheet, smooth down the manifold until you have a consistent surface finish. That'll be about the easiest way to do it.

I'll have to try the rubber sheets in the future. The expansion plugs work great for checking anything below the top of the intake but will hide any issues between the base of the carb and top of the intake.