‘79 Invader 440 compression/not starting

[GatheringEagle82]

Hi all,

I have a 1979 invader 440 and am having some trouble getting it running. I believe it to be a compression issue. Here’s what I have done to the sled so far:
— replaced crankshaft seals
— new pistons and rings
— new head gaskets
— cleaned and rebuilt carbs
— new fuel pump

When I initially rebuilt the motor and mounted it back in the sled, I had about 135 psi in both cylinders. In the meantime, I replaced the fuel pump after figuring out it was junk, and cleaned the carbs. I was getting good spark and fuel - but it wouldn’t start. So I checked compression again to only find a reading of 105 psi. I have pulled the plugs and put two stroke oil down both cylinders and let it sit — which brought my compression back to 135psi — only to have it drop back down to 105 psi after pulling on it trying to get it started.

Will the rings eventually loosen up enough to seal? Or is this a cylinder wall issue? I’ve checked the new pistons and have not found any holes. Pistons are installed correctly (arrow pointing towards exhaust port).

Thanks for any insight you can provide.

[Ameritude]

Do you remember what brand of head gaskets you used? Some brands are very finicky and need almost perfect mating surfaces to work good. Its odd to me that your losing and gaining compression with no heat cycle. It also doesn't make sense to me that you aren't even getting a pop out of the engine, even with lower compression. Hopefully one of these guys can help you out, you came to the right place. Good luck.

[GatheringEagle82]

I believe the gasket set came from Parts Reloaded and manufactured by PR4 components.

I am getting a pop out of the engine, on about every 3rd or 4th pull.

[gixxer6]

Putting oil in the cylinders explains the change in compression.  The service limit for these is 90psi, from my experience 105 is quite low (I usually see at least 120 in a healthy engine).  It should run with 105psi, so I don't believe it's the compression causing it not to start. 

Do you have good spark?  Airbox and exhaust free of critter nests?   

[GatheringEagle82]

The exhaust appears to be free of any obstructions, and yes good spark.  No air box on this machine.

I noticed I’m getting smoke coming out where the y-pipe manifold meets the exhaust. Am I loosing back pressure from this?

Thanks for the responses thus far, much appreciated!

[72SSRS]

Try seeing if it will start with pipe unhooked  at the y pipe.  If you get it to fired up that way then pipe is clogged.  Plugs should be wet if pipe is clogged. 

[gixxer6]

Since you just did the crank seals, it might be worth checking your timing. 

[Robodave]

I had the same kind of thing on my 80 Intruder. Try getting a timing light to make sure both spark plugs are firing. If not replace spark plugs and/or ignition module.

[GatheringEagle82]

Just an update. I was able to get it started tonight after pulling on it for what seemed like thousands of times. Glad I decided to try starting it one more night before looking into the timing!

Thanks all for the responses.