Raw fuel smell

[Bowtied13]

Hey guys I'm new on the forum, I was just a lurker for quite a while. So hopefully I'm doing this right. Here's a picture of my truck. It's a 1984 C10 Silverado, sb350 with a 700R4.

Over the last while when I drive my truck it smells like raw fuel really strong in the cab. I could never pinpoint where it was coming from. Well today I jumped in the truck to go somewhere. Before I started it I depressed the brake pedal, as I did it made a hissing noise (like air leaking) and suddenly I was hit with a pretty strong smell of fuel. I took my foot off and did it again. Same thing happened. It's been happening for a long time but I just now was able to connect it with the brake pedal.

I don't know if it's some sort of vacuum leak with the brake booster or something. Has anybody experienced anything like that?

[Dead Parrot]

A booster leak should not cause a gas smell. Booster leaks suck air in, not let gas out. Still worth checking the booster out. Bad brakes can lead to large fuel spills when you smash into the thing in front of you.

A little gas can create a lot of smell. Had a similar issue a while back. Turned out to be a small leak on the mechanical fuel pump. Never enough to drip on to the ground, just enough to make the pump damp when cool.

Other suspects: bad gas tank vent system, slow carb leak(every Q-jet I have owned has leaked out of the fuel filter casting plug after a few years.)

[tucsonjwt]

I would check to see if the gaskets on your Qjet look wet, indicating a carburetor leak. Also, I would also crawl under the truck and check all of the rubber fuel lines and check to see if the vapor recovery canister smells like gas. The recovery tanks load up with fuel after a while and need to be replaced.

[Bowtied13]

Thanks for the input. I'll take a look at it this evening. If it helps I'm running a Holley 650 Cfm street Avenger

[Bowtied13]

Upon further inspection it appears that the vapor recovery canister had been removed from the truck in the past. I did an engine swap on it about 6 years ago (from the original 305 to my built 350) and may have unknowingly taken it off.

From what I have researched the vapor canister should look like the top picture.

What is this ball looking thing that's bolted to the firewall in the second picture?

[tucsonjwt]

That is a vacuum canister (reservoir) which stores up vacuum to assist HVAC and cruise control, etc.

I don't know if the evap system has any vacuum associated with it - I have never had an evap equipped truck.

http://www.classicindustries.com/pro...ts/ap7330.html

[Bowtied13]

Alright. Well it looks like I'll be buying a vapor canister and figuring out how to install it. Hopefully that'll resolve the issue.

[TKCR]

Most people take those canisters out. I took mine out. There must be another reason why your getting the gas smell, unless the PO didn't cap something off right.

[tucsonjwt]

The evaporative canister is a smog requirement, so you might be required to have one. Interestingly, my 83 (and all of my prior year 3/4 ton trucks) did not have an evaporative canister because those were considered "heavy trucks" and did not have an evaporative canister requirement.

Instead, the third port on the sending unit on the fuel tanks just have a one way valve - same valve as on the differential vent. I added fuel line from that third port and routed it to the back of the truck by the spare tire (both tanks - I have dual tanks.) This moves the vented gas odor to the back of the truck so I don't smell it in the cab of the truck. I have two vent cap valves at the ends of those lines.

I think the 3/4 ton and up trucks required an evap canister not long after 83.

Oddly, my 83 has a smog pump has all kinds of smog pipes and valves, but no evap canister. It does not have a catalytic converter either. Seems like the EPA did not go all the way with the earlier heavy trucks.

Before you buy the evap canister, I would check all of your hard and soft fuel lines and the carburetor to make sure that you don't have any leaks. It is not easy to find fuel leaks because the high temperature of the intake manifold vaporizes any leaking fuel before you see it, and a small leak under the engine evaporates quickly. So, your best bet is to check for leaks right after start up with the engine running (make sure to chock the truck well before you get under it and set the parking brake.)