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Discussion Starter · #1 ·
Help
I have rebuilt a 1972 Oly 399 and can not get it to idle. It was not running when I got it. I put new pistons in sealed the bottom half put new seals in and rebuilt the carb. It takes a bit to get it running (spray) but when it is running its got good top end. sounds like its got a lot of power but as soon as I let it idle down it dies?
Bill
 

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Go back into the carb and pull the pilot jet (up the tub)
Then the air screw and spray all the passages
Floss the pilot jet to clear it then spray it too!
 

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Discussion Starter · #3 ·
Welcome
Go back into the carb and pull the pilot jet (up the tub)
Then the air screw and spray all the passages
Floss the pilot jet to clear it then spray it too!
Hello kccats
I have a Tillotson carb HR76A I believe is the number. I have flossed the holes under the welsh plugs twice and I not see any issues with them. I don't see any thing on the carb diagram that says pilot jet, not sure what you mean. Today I hade it idling for a bit than it died and its really hard to get started. I believe its a carb problem but she has me scratching my head.
Bill
 

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On that carb there isn't a pilot jet, as you've noted.

It has a mixture screw, which basically does the same thing as the pilot jet and air screw.
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Discussion Starter · #8 ·
Thanks for all the help so far. Well after waiting forever a new gasket kit, I have checked everything in the carb again and replaced the welsh plugs and new intake gaskets. It's getting better but still will not idle. Getting better meaning, I can get it to start faster with spray and it will stay running close to a idle but I still have to hold the throttle open a bit to keep it running. It still feels to me like not enough fuel. Could the spring on the needle be to strong? Thank again Bill
 

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Replace the fuel pump who knows when the last time it was replaced with it being that old. Along with the fuel filter also in the tank there should be a tygon fuel line and at the end of it a weighted fuel filter as well I would replace that also as those usually are in the most shallow part of the tank to ensure you can get every last bit of fuel out of it.
 

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Discussion Starter · #10 ·
Replace the fuel pump who knows when the last time it was replaced with it being that old. Along with the fuel filter also in the tank there should be a tygon fuel line and at the end of it a weighted fuel filter as well I would replace that also as those usually are in the most shallow part of the tank to ensure you can get every last bit of fuel out of it.
Lines are new, fuel filter new. I'm getting a lot of air coming out of the return line after opening it up again. I am ordering another new carb kit I'm guessing gaskets must be bad.
 

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Discussion Starter · #12 ·
I'd be leary of crank seals on something this old. But carb gaskets and pump diaphragms are in order too especially with the gas these days vs what was used back then. On my 72 Skidoo Nordic 440E I was blessed with electric start. That made the hard starting engine much easier I'll say.
[/QUOTE I put new pistons in, sealed the bottom half and put new seals in. Just ordered a carb kit, I will find out next week 🤞
 

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Replace the fuel pump as well. Those can go bad at any time and as I said who knows when it was replaced. Make sure the line in the tank is there with the weighted fuel filter on the end of it.
 

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Discussion Starter · #14 ·
Well I found the pistons were in backwards even though I put them in with the arrow to the exhaust, Like Wisco said. I found this out by seeing the ring gap in the exhaust port. It runs and sounds better on the high end and binging it down to an idle but guess what. The pain in my ass still will not idle. I even put another carb kit in it.
 

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Sometimes a high idle is caused by a lean condition. Check the crank seals and the carb adapters into the engine for leaks. With the engine running, spray some carb cleaner or WD40 around those areas. If you get a change in idle, that would indicate a leak.
 

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Discussion Starter · #16 ·
Thanks everyone for your help. I found the problem. She run like a million bucks. The left piston was in the right and the in the left. The arrows do point to the exhaust. Thanks again.
 

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What? I've never seen a left and right piston?? New one to me. Something to keep in mind if I ever work on a 1972 Oly.
 
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