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gas in crankcase - SB Chevy/carb problem

Vance

Vance

Member
Hey all,

I've heard of this problem lots of times but ignored it 'cause it was never me...

Today I found that I had fuel in the crankcase of my 283 SBC in my Tucker. Okay, it hadn't been started for 5 months or so and is sitting on a small slope with the nose downhill. Kinda interesting how it all came about. The first thing I noticed after starting it was the front crank seal leaking out oil at a fairly good drip rate.. hmmm, never noticed that before. Then I noticed that the oil pressure was a bit lower than I remembered (around 10-20psi). When I noticed the low oil pressure I shut her down and checked the oil level. Hmmm again - it is about a quart HIGH. Hmmm... I was back checking the drip at the main seal and did the scratch and sniff test - wow, this smells like gas!! Back to the dipstick and check there - this smells like gas, too.

Okay, I know it's coming in the Rochester 2bbl carb (could see gas inside)and the slope is probably helping matters 'cause the fuel can gravity feed from the cab-mounted tank. I pulled the carb to do a rebuild and check it out.

But, what exactly is the problem??

Is it just worn float valves or is this something inherent in the Rochester 2bbl??

Is it a certain seal or ??

I was going to search all over but figured all you smart guys could help me out.

thanks,

Vance
 
The last time that happened to me it was a ruptured diaphram on the mechanical fuel pump mounted to the engine block. It leaked gas right into the crankcase.
 
I have seen it many times, check your fuel pump if it is a mechanical one.


murph
 
I'll check out the fuel pump, too. But, I'm pretty sure this one is in the carb as I could see fuel in the intake manifold. I also noticed a little dripping out the shaft plug for the butterfly in the base of the carb(hmmm). As a result, here was also a puddle of fuel on the top of the manifold.

Vance

Edit: Yes, it is a mech fuel pump.
 
There should be two welch plugs in the bottom of the carb body. You'll have to remove the base plate to see them. These notoriously leak. You can seal them with JBweld or Epoxy. It will often drain the bowl after sitting for a long time, causing long cranking time. In your case with the tank gravity feeding the bowl, it would have continued until the tank was dry. Just another thing to look at.
 
I did have a Volvo years ago that I put a Weber conversion in place of the twin SU carb's and when I was going down steep hills it would drip gas down the throat and speed up like you had put your foot on the accelerator.

The Weber carb had a brass tube that went from the top of the float bowl into the throat of the carb, I do not know if it was an air vent or what.

Check your carb and see if a nose down attitude might allow the float to let enough fuel in to overflow the float chamber and see if there is a path from the float chamber into the throat.

Did it start differently than normal?

Makes you wonder about the gas leaking into cylinder(s) then past piston(s) and into the crankcase.

I think I would pull the spark plugs and put some lubrication into each cylinder just in case.

You probably already decided that a shut-off on the fuel tank for long periods of inactivity might be a good idea.

My Imp has an electric solenoid valve with a glass contamination inspection bowl (where you can't see it) that shuts the fuel off when the key is turned off.
 
On a snow cat the fuel tank is usually higher than the carb on the engine. A small piece of dirt under the needle can cause gas to leak direct into the engine when shut off. Many of the Thiokol's DMC's and LMC's used the electric fuel shut off solenoid to prevent this from happening. You may want to consider installing an electric 12 volt fuel shut off wired to the ignition switch to prevent future possible problems along with fixing whatever is causing your current problem. The shut off is just added insurance to prevent major problems if this problem should happen again.
 
mtntopper said:
On a snow cat the fuel tank is usually higher than the carb on the engine. A small piece of dirt under the needle can cause gas to leak direct into the engine when shut off. Many of the Thiokol's DMC's and LMC's used the electric fuel shut off solenoid to prevent this from happening. You may want to consider installing an electric 12 volt fuel shut off wired to the ignition switch to prevent future possible problems along with fixing whatever is causing your current problem. The shut off is just added insurance to prevent major problems if this problem should happen again.
Click to expand...



I have to agree with MTNTOPPER. Another problem it might be but not sure what you have. I once had a toyota Land Cruiser and the fuel pump somehow was left on. Electrical. Anyway it filled my engine completely full. I drained the oil/fuel and flushed her with about 10 quarts of oil. I then drained her again. Filled her up with 5 quarts and started her ran it till she warmed up. Then shut her down and changed the oil one more time. No problems with the engine. Changed fuel pump and wired it correctly (bought the toyota used about 1 month before). BUT Petersons stocks a fuel shut off valve and fuel filter for about $80 bucks. I will be adding one of these to my Thiokol 6 passenger for added security. MTNTOPPER suggested that awhile ago and its a good idea on anything the has the fuel higher than the carb.
 
I'm wondering if it would be possible to install a manual external fuel shut off valve on the line going from the tank? If this is possible, it would stop the fuel in the tank from continuing to drain into the carb if there's a leakage problem in the carb itself. I know a snowcat is allot bigger and more complex but I keep picturing a type of setup like on my snowblower where theres a fuel shutoff on the line going from the tank to the carb. I never used to have any problems with it and always filled it up with gas before putting it away till one day I came to use it and the tank was dry. Turns out there was infact a needle stuck in the carb that allowed the gas to keep flowing till the tank was dry. Just a suggestion.
 
Yes they do have them. I had one on my cat but man the brainyache that ran the hoses was about as smart as Hillary Clinton is on Immigration! Im guessing the fittings were 3/8" and the moron forced the 1/4" fuel line over it and then didnt clamp it. Anyway I was running the cat in my yard and parked her so I could work on her. Man I about shit when I saw that! If that would have cut loose which it was ready to since the hose was all split it would have created a fire storm in the cab! SCARY!
 
One thing to think about with a manual shut-off valve is that unless you put a placard somewhere like next to the key, it is sometimes easy to forget to turn it back on and crank for a long time before you remember why it will not start.
 
GSSD06 said:
One thing to think about with a manual shut-off valve is that unless you put a placard somewhere like next to the key, it is sometimes easy to forget to turn it back on and crank for a long time before you remember why it will not start.
Click to expand...

Been there, done that! I once had my axe in hand ready to go aborad of my snowmachine after pulling on it for 1/2 hour before I remembered that damn fuel shutoff.:smileywac
 
had this problem gas tank was full sitting in sun built up pressure and filled crank case full of gas came up with easy solution got a fuel tank selector valve for 76 Chevy truck with twin tanks it has three hose fittings on it one from each tank and one to the carb valve is open to one port with no power the other has to have power to it to open put plug on side open with no power and put power side in fuel line i run a power feed to the + side of coil then with key on valve opens this way you don't have to remember to turn on a switch
 
Thanks for all the help, guys!!

I haven't got back to dig into this yet as I was beating myself up trying to hang onto a DitchWitch most of the weekend...

I'll be adding an elec fuel cutoff as suggested. Any other suggestions for the elec solenoid? I'll check Napa and the ones suggested from Petersens and the 76 Chevy one. Anyone have a favorite?

I'll have to mount it in the hardline between the tank/engine compartment(under the cab) or in the soft fuel line right at the pump (lower rt. side of engine).

Vance
 
Most motorcycle petcocks are now vacuum operated. One of these might work for you (and give you the "reserve" feature as well).
 
Snowcat Operations said:
Petersons stocks a fuel shut off valve and fuel filter for about $80 bucks.
Click to expand...

Any p/n on this? I sent an email to Jeremy at Petersens asking for availability of elec fuel solenoids with/without a filter. I mentioned I was putting it on a Tucker since I figured he would ask the application.

Well.... his response was:

SORRY, BUT WE ONLY DEAL WITH LMC'S AND PISTEN BULLYS.

JEREMY​

I replied to clarify that I wasn't looking for a Tucker OEM part and asked for LMC/PB apps. I haven't heard back... :confused:

I have found lots of solenoinds for the ricer NOS systems in the $60 range. Might have to go that route if the NAPA guys can't help.

Vance
 
mtntopper said:
Just tell him you need one for a 1200 Spryte. To much detail for small minds stalls the project.
Click to expand...

I agree. Most people cant understand beyond what a parts book says in front of them. I cringe everytime the guy asks me at the parts store what make and model. OK Napa guy its a 1969 Thiokol 1202B 6 passenger snowcat. The look I get is funny as hell. LOOK I just need a 1970 Ford 200 Inline 6 exhaust manifold gasket. OK Its for a Ford 1970 F100 with a 200 CI 6 cylinder. OOHHHHH Yah I have those.

Anyway I belive I was quated about $80 bucks the last time I asked Peterson's.
 
Just buy them from McMaster they are about 40.00 bucks

If you need the number I can look it up we just ordered 3 a couple of weeks ago



Vance said:
Any p/n on this? I sent an email to Jeremy at Petersens asking for availability of elec fuel solenoids with/without a filter. I mentioned I was putting it on a Tucker since I figured he would ask the application.

Well.... his response was:

SORRY, BUT WE ONLY DEAL WITH LMC'S AND PISTEN BULLYS.

JEREMY​

I replied to clarify that I wasn't looking for a Tucker OEM part and asked for LMC/PB apps. I haven't heard back... :confused:

I have found lots of solenoinds for the ricer NOS systems in the $60 range. Might have to go that route if the NAPA guys can't help.

Vance
Click to expand...
 
Snowcat Operations said:
Boggie. Would you look up the number? I need one for my 1202. as well. Thanks.
Click to expand...



Here you go For outside locations use # 5077T13 Stainless Submersible selonoid you have to tell them 12VDC coil



For Inside you can get by with # 7876K11 Delrin selenoid valve comes ether with leads or 1/4" quick disconnect the 1/4" nimber is 7876K13 these are both 1/4" pipe threads


Be sure to add a filter before the valve to prevent it from getting pluged.
just a small inline is all you need.

McMaster Phone # 630-833-0300

or

http://www.mcmaster.com
 
Last edited:
Thanks, Boggie!!! Why didn't I think about McMaster... lots of great stuff there - and the best search feature I know of on a website...

Vance
 
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