Datsun Roadster Forum-311s.org

sunbeam590 wrote:Take your Air filter off and go for a drive..

I've driven with and without the filters. But now you have me thinking, I have velocity stacks with individual foam filters for each, could they just be drawing too much air so the car has a hard time adding enough fuel? I would think the restriction would be the butterfly and the chambers only allowing so much air as long as you have it tuned right with the right needle it should be able to handle the fuel.. right? I may put the stock air filter back on but I started sand blasting off the powder coat so I need to re coat it.

Last night I adjusted the float levels so they were set to both .55" from arm to the base, went for a drive and still cutting out. I took the tops off and put them in an separate empty bowls and cranked it over and the rear carb actually got more fuel, where I was thinking it was getting less since the float was lower than the front when I checked before. It makes me think that when it's fuel starved the front carb gets fuel and not enough is left for the rear but under normal conditions it looks to be working as it should. I'll test my fuel pressure and maybe pull the tank.

I did not read that you tried changing the fuel/air mixture.
What do your plugs look like after a ride without the choke and with it stumbling?
Don't let it idle any before checking them.
Are they a good brown color or white or black?
If white it is probably running too lean, try enriching the mixture a bit in 1/4 increments.

I doubt the foam filters are the issue... I run them without problems on Dellortos, highly modified engine, etc.
Here again, a wide band O2 air/fuel meter would tell you instantly where to look for the problem... If it goes lean then you know it's fuel, rich and one would suspect spark misfire.
Install new plugs and take her out and hold it where it's missing for some time, then do a "clean cut" where you turn off the ignition THEN immediatley let off the gas and coast to the side of the road, then read the plugs (that's what I used to have to do before the wide band). Bring a thick glove so you can handle the hot plugs.

I think I figured it out. I took my fuel pump off and I noticed the the rocker arm was broken, just the last little bit was broken off and at a slight angle so it was barely noticeable. I took off the oil pan to get the piece out and now just have to wait for the new pump to arrive. I kind of remember starting to put the pump on without the spacer and then noticed it it wasn't going to seat properly, I must have broken it or cracked it then. I hope this is it, so I don't have to drain and pull the tank.

The new fuel pump did not fix my problem. I took my tank off because that was the last piece I hadn't looked at and it was really clean. No sign of anything inside, like it was cleaned just recently. I still ran some water and soap into it and dumped it out to see if anything would come out but the water was clean. I let it drain out of the fuel pickup line it it poured out of there no problem. I blew the hard lines out with my air compressor into a bucket to see if any debris would come out and nothing. Is there an in-tank filter or something in the tank that could still be restricting the flow?

I know I am having a fuel starvation problem, after I installed my pump I went for a drive and when it started acting like it was running out of gas, I shut the car off and pulled over, open both float bowls and the front had gas but the rear carb was dry. I've tested the fuel pressure and I had 4 psi. I've put on 3 different fuels filters. I'm at a loss here. I might just start replacing all the fuel lines, I don't know what else to try.

You have to be sure there are no leaks in the system otherwise it is like trying to use a straw with a hole in it. Fuel hoses at the clamps may show wear. If the fuel valve is stuck then flow is wonky might need to check and clean.

Linda

"Front had gas, rear did not.." I would start there as clearly fuel is able to reach the carbs through the lines etc. I suspect some kind of float bowl valve problem... something is stopping fuel from entering that carb.

Do you have the return valve on the rear carb? It may be the source of your problem.

spl310 wrote:Do you have the return valve on the rear carb? It may be the source of your problem.

I don't think so, my rear carb has a Tee banjo bolt that has the line from the front and the return line on it, no valve. What does it look like?

Gregs672000 wrote:"Front had gas, rear did not.." I would start there as clearly fuel is able to reach the carbs through the lines etc. I suspect some kind of float bowl valve problem... something is stopping fuel from entering that carb.

I will recheck this, it does pump gas to the rear but eventually it runs out. It had a new float valve I put in but put the old one back in when I was having problems. Maybe they both are clogged or not working.

Linda wrote:You have to be sure there are no leaks in the system otherwise it is like trying to use a straw with a hole in it. Fuel hoses at the clamps may show wear. If the fuel valve is stuck then flow is wonky might need to check and clean.

Linda

Right now it's a mix of new and old lines so maybe I should take it all off and start over, it should be easy enough.

I've struggled with this exact same issue for years and have tried everything suggested with no luck. Hopefully you'll figure it out.

If you don't have the valve on the rear carb, the fuel will take the path of least resistance - into the return line to the tank likely since that is a larger diameter tube. I have a spare on the bench if you need one. Dann at Rallye has a photograph of the return valve here:

http://datsunroadster.com/PIC_PAGES/NEW ... 161-B2.htm

spl310 wrote:If you don't have the valve on the rear carb, the fuel will take the path of least resistance - into the return line to the tank likely since that is a larger diameter tube. I have a spare on the bench if you need one. Dann at Rallye has a photograph of the return valve here:

http://datsunroadster.com/PIC_PAGES/NEW ... 161-B2.htm

It's funny I thought of this when testing fuel pressure, I just assumed there had to be something that restricted the fuel farther down the line or at the tank, I did notice the fitting for return line on the tank was smaller.

Yes, I do need one if you are willing to sell it. I can pay your through pay pal or whatever is easiest. Thanks for your help!

Sure, I'll part with it. I'll shoot you a PM