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Gas Flow Problem 620


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#1 620owner

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Posted 17 July 2017 - 03:50 AM

Trying to figure out why the gas line and carb is going dry.

 

After setting a couple days I have to prime the carb several times to get gas back to the carb and then it runs fine.

 

Can't figure out why the gas is running back into the tank emptying the Cab, filter and line.

 

 

 



#2 datzenmike

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Posted 17 July 2017 - 04:43 AM

Once in the float chamber it's impossible for it to jump upwards and out through the needle valve even if it was still open.

 

For the fuel lines and pump, a loose hose clamp or crack, might let air in. Maybe one of the one way valves in the fuel pump, and fuel could siphon backwards from the higher engine end to the lower tank end.

 

For the carb, maybe one of the jet cover plugs is loose/not sealing or the float chamber front cover not sealing and gas is dripping out slowly enough to evaporate and not be noticed..


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#3 Crashtd420

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Posted 17 July 2017 - 04:46 AM

I could be way off but the first thing that popped into my head was is your gas tank vented properly?.. maybe negative pressure sucking the fuel back the tank....
Or a leak?

#4 620owner

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Posted 17 July 2017 - 06:46 AM

Well no external leaks that I can see. I dropped the tank, all new lines. Everything all hoses replaced Fuel, Return, Vapor and Vent lines. New fuel filter, pump and HItachi Carb. No negative pressure, does it with the gas cap loose. 

 

I'm with you Mike, maybe

A bad fuel pump and it's allowing the gas to flow back to the tank.

 

Is it possible it's going VIA the fuel return line ?



#5 datzenmike

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Posted 17 July 2017 - 06:58 AM

The thing is, is there is (or should be) way more than enough gas in the carb to start your vehicle and drive a block. Once started, the pump would easily suck up the fuel through an empty line and keep going.

 

You have a window on the front of your carb. Next time you shut it down, confirm that the fuel level is in sight on the glass. Next restart take a look and see if the gas level is still there. If it is it should start immediately.

 

If it has gas.... is your choke working??? Without a choke, carb engines can be difficult to start.


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#6 620owner

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Posted 17 July 2017 - 07:51 AM

After it sets a few days the carb is empty, nothing in the bowl, window empty. Fuel lines empty too.

 

To get it to fuel back up it takes awhile, three or four primes and I can see the gas fill the filter and make it's way to the carb.

 

After that it will run fine and re-start all day but leave it sit a few days and everything is dry again.

 

No signs of leaking, has to be going back in the tank. The engine isn't flooding, it does't even try to fire, which it should if it went into the manifold.

Like I said  I have to prime it to get it to fire.

 

I've got an electric pump, I think I'm going to rig it up,  by-pass the mechanical pump and see what happens.

 

I'm thinking that it's gravity siphoning back in the tank. (High Carb - Low Tank)

 

Man I don't know ???



#7 datzenmike

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Posted 17 July 2017 - 11:11 AM

Gas can't climb up out of the fuel bowl through the inlet needle valve.

 

I'm not saying the gas is entering the engine. Use a mirror under the front of the carb and inspect the two 12mm jet covers for signs of leakage stains. Run your hand over them and the bottom of the window in a day's time, you might find one of them is damp. Maybe check tightness of the jet cover plugs and the three screws holding the front cover on.


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#8 620owner

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Posted 18 July 2017 - 05:49 AM

Ok I took some pictures, I know pictures are worth a thousand words.

Last nite after setting 24 hours, Fuel Filter empty and carb very low (Fuel at bottom of window).

 

LuMi1w9.jpg

 

 

Here's the fuel lines and filter:

 

7E2MJCC.jpg

 

 

It started right up and ran fine. Here's the gas level running:

 

 

5cZuPwe.jpg

 

 

I let it run 15 minutes and then checked it 1 hour later, fuel filter full and carb on the Dot. Everything dry.

 

Checked it this morning after setting overnite, fuel filter empty. Didn't check carb I had put things back and was heading out for work. I'm thinking the bowl will low.

 

This is just an over view of the engine bay:

 

1hVhu4q.jpg

 

 

Carb view:

 

PkFy3Qs.jpg

 

 

Over-view of fuel filter and lines:

 

WBe0kcq.jpg

 

Never know what you might see....



#9 datzenmike

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Posted 18 July 2017 - 06:28 AM

Work firewall won't let the pictures through, have to wait till I get home.... 


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#10 heywier427

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Posted 18 July 2017 - 07:11 AM

pinch the gas line shut after it comes out of the tank.  see if it back flows then.

 

Im with mike.  How can the bowl empty if not leaking.

 

Maybe check valve in pump not working, allowing fuel to go back to tank, and that pressure is pushing air into the return line into the carb and flooding/pushing the gas into the engine?

 

But then agian, if it still does it with fuel cap off, that theory is shot.

 

Its got to be leaking out of the bowl cover.


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#11 banzai510(hainz)

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Posted 18 July 2017 - 07:57 AM

if I let my weber sit for a weeek its takes awhile to get the carb to fill up also.


Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#12 datzenmike

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Posted 18 July 2017 - 04:39 PM

You have to looked at the underside front of the carb. The primary/secondary jet covers are under there and can't be seen really without a mirror. 

 

$_1.JPG?set_id=880000500F Underside of carb, front is to the right. The two brass plugs that cover the entrance to the two jets are just to the left of those black wires.


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#13 Rhapakatui

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Posted 18 July 2017 - 05:05 PM

Great thread.

I have this same issue with my 710 goon. 38/38 Weber. I just assume I'm losing fuel somewhere. My redneck solution was to put a boat style hand bubble in line before the fuel pump. I only drive the goon a few times each year, so I prime the pump with the bubble when it's been sitting. The check valve in the bubble holds prime for a week or so.
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#14 620owner

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Posted 19 July 2017 - 10:22 AM

OK, I'm on it.

Here's a pic of my old carb. Thought I'd use it for reference.

 

4sqQA0a.jpg

 

The fuel filter was empty and fuel bowl low today. Had enough gas to start, it picked up the gas from the tank quick and filed filter and bowl so I let it run ten minutes.

Checked the Jet covers and bowl cover after setting fifteen minutes. Everything dry as a bone.

 

Right Jet:

 

v55XD3d.jpg

 

 

Left Jet in the mirror.

 

zZvPhZJ.jpg

 

 

I was able to get a look of both jet covers and bottom of bowl after removing a hose.

 

kPbj7S6.jpg

 

So I guess that eliminates Jet/jet covers and bowl gasket/seal.

 

You say the fuel pump has a check valve to prevent back flow to the tank. It has to the problem.(A BAD new pump)

But there does have to be a way of it getting air to allow it to back flow, right...



#15 datzenmike

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Posted 19 July 2017 - 12:42 PM

Check those plugs after the car has sat for a day and cooled down. Try snugging them and also the three cover screws.


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#16 620owner

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Posted Yesterday, 04:27 AM

I drove the 620 all day yesterday all most 100 miles. It was 90 degrees here in Ohio yesterday and I did a lot of stop and go traffic so ran a little warm at times. I noticed the temp gage running a little past midway at times but it ran great. 

 

I let it set 4 hours and checked the carb. Dry as a bone. The fuel filter was full. 

I checked it this morning fuel filter wasn't full,  down about a quarter of an inch.  The carb still had gas, maybe down a little but close to the Dot.

I'd say that is probably normal levels ?

 

I did gas it up yesterday almost to full tank. The tank is a little above half full right now. 

 

I'll check it when I get home from work today after setting 24 hours.



#17 datzenmike

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Posted Yesterday, 05:11 AM

My 620 ran just below 1/2 in the marked 'run range'. Sounds normal.

 

For good cooling you need good air flow and good coolant flow.

 

Air..

Be sure you have a fan shroud. It increases the fan efficiency

Make sure the rad fins are straight and clear of bugs and debris

Make sure there are few areas around the rad for air to get past without going through it. One is under the hood just above the rad support. If there are gaps seal them up.

Clutch fan should turn by hand but stiffly. If very loose it will not move enough air.

 

Coolant...

If you don't have a coolant recovery system get a later rad cap and a pop bottle. Coolant expelled when hot is recovered and stored. When the engine cools down the coolant is sucked back in. Rad rarely needs topping up.

Always run 50/50 distilled water and anti-freeze mix.

Check for soft rad hoses. They rot from the inside out and may look ok and pump suction will collapse them.

Make sure the heater hoses are not joined together to bypass a leaking heater core.

Cap off and coolant level down enough to expose the top of the core... are the tube openings crusty with deposits from hard water? This will reduce flow.


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#18 620owner

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Posted Yesterday, 08:44 AM

I'm going to check the top of the cores as you suggest. Might need a good flushing.



#19 Jesse C.

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Posted Yesterday, 09:13 AM

http://community.rat...orum/10-trucks/


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