Ron1200 Posted August 20, 2011 Report Share Posted August 20, 2011 Just drove the 620 down to Todd's for a new interior. Strong fuel smell. Looked for an leak, but it was dark. Checked the fuel lines from the filter to the carbs. Nothing obvious found using a flashlight. This 620 has dual Hitachi's on a L16. Any ideas what/where I should check? A question? On the outboard side of each carb, where the fuel lines go (carb floats?), there are some vertical tubes. They look like there should be some hoses that connect to them. Probably to the air filter/box. They are now venting directly to the atmosphere. Could this be the issue? This is how it is set up: Quote Link to comment
Skib Posted August 20, 2011 Report Share Posted August 20, 2011 A question? On the outboard side of each carb, where the fuel lines go (carb floats?), there are some vertical tubes. They look like there should be some hoses that connect to them. Probably to the air filter/box. They are now venting directly to the atmosphere. Could this be the issue? those are over flow tubes. dosent affect anything if their open or hooked up to the airbox one of the floats could be sunk Quote Link to comment
ggzilla Posted August 21, 2011 Report Share Posted August 21, 2011 The factory Hitachis vent to the atmosphere. So yes you will smell fuel. And todays gasoline doesn't smell good like 1970s gasoline. The 620 also has a fuel return line and a tank vent line in the engine compartment. If those aren't connected properly they will put a lot more fumes in the compartment than the carb overflow lines will. You can cap the return line, but the vent line must not be capped. It goes to the Flow Guide valve on early models or to the carbon canister on later models. Quote Link to comment
datzenmike Posted August 21, 2011 Report Share Posted August 21, 2011 I see you are not running a Nissan fuel pump buy a replacement one. The Hitachi puts out 3-3.5 PSI so if this one is much higher it could be overpowering the SU floats. I also see a catch can... so where does the vent hose dump out now. Quote Link to comment
banzai510(hainz) Posted August 21, 2011 Report Share Posted August 21, 2011 mike, those fuel pumps are OK.I ran one before with now proplems Quote Link to comment
Ron1200 Posted August 21, 2011 Author Report Share Posted August 21, 2011 those are over flow tubes. dosent affect anything if their open or hooked up to the airbox one of the floats could be sunk I'm no expert on these carbs. And I'm not being a smart ass. :) But if the float was sunk, wouldn't the gas be coming out the overflow tubes? Don't you want the overflow vent to be filtered - to keep dirt out of the float chambers? The factory Hitachis vent to the atmosphere. So yes you will smell fuel. And todays gasoline doesn't smell good like 1970s gasoline. The 620 also has a fuel return line and a tank vent line in the engine compartment. If those aren't connected properly they will put a lot more fumes in the compartment than the carb overflow lines will. You can cap the return line, but the vent line must not be capped. It goes to the Flow Guide valve on early models or to the carbon canister on later models. I'm going to need to check out the vent line. There is major suckage going on. I noticed this when I removed the gas cap and the tank 'popped' back into shape. I see you are not running a Nissan fuel pump buy a replacement one. The Hitachi puts out 3-3.5 PSI so if this one is much higher it could be overpowering the SU floats. I also see a catch can... so where does the vent hose dump out now. The catch can is a mystery to me, as I have never used one like this before. It connects the valve cover vent and the block vent, via separate hoses to the catch can (top and bottom). It does not appear to vent to the atmosphere. It also does not appear to 'catch' any blow-by oil vapor, as it doesn't fill-up with condensed oil. I would think that the two vents (valve cover and engine block) would use the same top hose (via a 'Y' or 'T' hose connector). The can would be vented to the atmosphere and the bottom hose connector be plugged. But like I said, I haven't used this type and may be off base. Thanks all for the feed back. Quote Link to comment
datzenmike Posted August 21, 2011 Report Share Posted August 21, 2011 hahaha that catch can will never work that way. The PO got it wrong. The block vent hose must go to the PCV valve on the SU intake. The valve cover vent to the catch can and the output hose from the can vented to the outside air. Best would be inside the air filter so the fumes are run through the motor but most likely vented down low on the car so the smell won't get sucked into the car. . Quote Link to comment
zed Posted August 22, 2011 Report Share Posted August 22, 2011 I've had two problems on my Hardbody which caused a fuel smell - one, my gas tank got hit by a stone on an exposed seam. Took me months to realise where the smell of gas was coming from. Two, rubber fuel filler pipe perished Quote Link to comment
ggzilla Posted August 22, 2011 Report Share Posted August 22, 2011 Don't you want the overflow vent to be filtered - to keep dirt out of the float chambers? No need. Dirt is not going to float up the 8" of overflow tube and make the turn to get into the chamber. Anyways, that is the factory setup (unfiltered). They were only sold in non-emission-controlled parts of the world. Quote Link to comment
Ron1200 Posted August 29, 2011 Author Report Share Posted August 29, 2011 one of the floats could be sunk It appears to be a float or float valve. I found gas spewing out the overflow of the rear carb vent today. Actually it was quite a bit, like an ounce of fuel within 30sec. So how do I fix this? I've never worked on this type of carb. Any input would be appreciated. I got to get this fixed as the fuel is dumping on the exhaust header. Quote Link to comment
Skib Posted August 29, 2011 Report Share Posted August 29, 2011 the floats are brass, you can either replace it (call steve at Z therapy) or you can solder the hole. Quote Link to comment
Ron1200 Posted August 29, 2011 Author Report Share Posted August 29, 2011 As the float bowls are external, can I just remove the bowl? Or, does the whole carb need to be removed? Quote Link to comment
Ron1200 Posted August 30, 2011 Author Report Share Posted August 30, 2011 Talked to Bruce at Z-therapy. Ordered a couple of floats and gaskets. Apparently it is common for the brass floats to develop cracks over time. The new floats are made of a composite material. He said the tops come off the float chambers so there's no need to remove the carbs... sounds like they are easy to change. I think I will connect some hoses to the SU float vents and route the hose to the bottom of the truck somewhere. This is similar to how my motorcycle is set up. At least it won't be dumping fuel on the hot exhaust manifold if the floats or float valves fail. As the carbon canister and plumbing have been removed, I wasn't able to find any vent line in the engine compartment. I did however, find a cap (secured with a zip tie) on the vent tube on the fuel filler. So I think I've located the blocked fuel tank vent. I'm not quite sure on how to handel the valve/cam cover vent and engine block vent. There is no PCV valve in place. Any suggestions? Quote Link to comment
ggzilla Posted September 4, 2011 Report Share Posted September 4, 2011 I'm not quite sure on how to handel the valve/cam cover vent and engine block vent. There is no PCV valve in place. Any suggestions? My suggestion is to put the stock stuff back on: PCV valve, carbon canister and tank vent line up to the engine compartment. I did this last month to mine and the fume smells have disappeared. Quote Link to comment
Ron1200 Posted September 4, 2011 Author Report Share Posted September 4, 2011 My suggestion is to put the stock stuff back on: PCV valve, carbon canister and tank vent line up to the engine compartment. I did this last month to mine and the fume smells have disappeared. I've already addressed the vent by uncapping/unblocking the vent line at the fuel tank. Besides the vent line has been cut along the frame. I'm up for the PCV valve and a hose to the block vent. What PCV valve should I use? Quote Link to comment
I'm BLUE Posted September 4, 2011 Report Share Posted September 4, 2011 Talked to Bruce at Z-therapy. Ordered a couple of floats and gaskets. Apparently it is common for the brass floats to develop cracks over time. The new floats are made of a composite material. He said the tops come off the float chambers so there's no need to remove the carbs... sounds like they are easy to change. Good that you have found or at least narrowed the problem down !!! Yup ,,, indeed easy to replace right there and not much hassle!!!,,,, Very light torque on the cover screws ,,, May I suggest you check condition of needle/seat before resealing ? :) Quote Link to comment
yello620 Posted September 4, 2011 Report Share Posted September 4, 2011 How about some pics of Todd's work?? Maybe start a thread for it? :D Quote Link to comment
Ron1200 Posted September 4, 2011 Author Report Share Posted September 4, 2011 May I suggest you check condition of needle/seat before resealing ? :) Sorry to be such a nub... You mean the 'float' needle/seat, right? What should I look for? How about some pics of Todd's work?? Maybe start a thread for it? :D Will do... I'm out of town using the hotel internet. Will post some pics when I get back. Quote Link to comment
510kevin Posted September 4, 2011 Report Share Posted September 4, 2011 I've already addressed the vent by uncapping/unblocking the vent line at the fuel tank. Besides the vent line has been cut along the frame. I'm up for the PCV valve and a hose to the block vent. What PCV valve should I use? theres no pcv on the crossover tube for the carbs? if not, there must be a plug or something in there. pull the plug, take it to napa/autozone/whatever and get a pcv that matches the size of the plug. Quote Link to comment
Ron1200 Posted September 5, 2011 Author Report Share Posted September 5, 2011 New Floats... Installed them today. (New Left, Old Right) "> Quote Link to comment
Ron1200 Posted September 6, 2011 Author Report Share Posted September 6, 2011 Success!!! :) No more fuel smell. Fixed the floats with updated floats (this was the major cause of the fuel smell). Unblocked the fuel tank vent. And ran vent tubing from the float bowls to the right side of the engine compartment (keeps fuel away from exhaust manifold if they spew fuel again). Just need to address block vent and install a PCV and this part is done. :) Quote Link to comment
Ron1200 Posted September 7, 2011 Author Report Share Posted September 7, 2011 PCV installed Look what I got... circa 1983... $7 Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.