I have a 13b out of an 88 with a mikuni carb. I noticed the other day that my dipstick was being pushed out I pulled out and a rush of air came out I'm just wondering what could be the issue. I also changed the oil too and there was no coolant or fuel in the oil.

 

The PCV system usually does the job of venting the 'crankcase' i.e. oil pan pressure. If the pcv system isn't there or clogged for some reason, the pressure is vented from other locations - like the dipstick tube...

 

Mine is a 12A but maybe your 13B is similar? There's a tube running from the oil fill to the charcoal canister that vents the crankcase. Note the red arrows in the photo below, that is the same tube. Has it been capped off? Plugged up?

 

What they both said ^^^ but the charcoal canister actually vents into the oil fill tube and is sucked out with the crankcase gasses (through the smaller hose on the oil tube) over to the intake. On stock cars it goes through the purge valve on the rats nest. If the nest is gone you need to run the hose to your air filter.

 

Awesome thank you for all the tips I'll take a look and let y'all know.

 

Excellent information, thanks!

 

So I looked at my engine and the tube that runs from the oil fill goes straight back Into the block. That's what I'm guessing is causing the over pressure and the run from the charcoal filter just ends by the firewall.

 

So the upper and lower nipples at the oil tube are connected by one tube? Yeah, that won't work.

The gas tank vents vapor up to the charcoal canister. There's a small metal vent line running under the driver's side, right next to the fuel and return lines (3 hard lines total). On the firewall these hard lines stop and convert to rubber lines.

The gas tank vent line is the small tube going to charcoal canister. The charcoal "holds" the vapors until the next time car is started up. Then the engine vacuum pulls from a vac hose to the oil fill tube (small upper hose on oil tube). This serves two purposes:
It pulls vapors from the "crank case" (oil, water, fuel vapors) & pulls that gas tank vapor from the charcoal can. This helps emissions, pulls moisture from oil/crank case, and keeps your garage from smelling of gas.
Many complaints of "lung butter" in the oil fill tube can be cured by routing the "PVC" line properly. Many cases of gas tank pressure or vacuum can be cured by having the lines in/out of the charcoal can routed properly.
On a race car it might not matter, but on a street car, 15' of vacuum line can solve many little issues like these.

 

The nipple on the fill tube does not pull vacuum, the nipple on the center iron does. Fill tube to charcoal canister or catch can, block vent to air cleaner with a pcv inline.

 

Ah, got ya. I wasnt looking at my car when I wrote that. But either way the air flow/vacuum pulls in one nipple and out the other, drawing vapors out of the block and emptying the charcoal can at the same time.
On the stock setup this goes through the purge valve on the rats nest. When I first took the nest off I kept the p.valve per Carl's instructions, but now I just have a parts-store PCV in-line like you do.

 

Yeah, all the emissions were removed from my car, so it took me awhile to figure a system to properly vent the engine.

 

I am working on the same pressure in crankcase issue on my 1980 12a with a stripped Niki. I am not clear on the best way to install a PVC and what has anybody found to be a good part number to get with an after market PVC ( or from what model car). Another question is the gas tank vent line on the fire wall, can this just be a direct connection to the top of the air cleaner? If so will this then solve the pressure in the gas tank to vent so when you open the fill cap you don’t get the pressure release?