Slowly working through some of the issues with my 1970. Car was running really great one day and I parked it, next day I fired it up and it started to drop gas from the fuel pump...big puddle. Swapped out the fuel pump and the two S lines (frame to pump and vapour return). I had to use bulk fuel line for the line replacement because my new frame to pump S line didn't show up in time. Now have it, haven't put it on yet.

The problem: immediately after starting the car after the pump swap I noticed on the test drive that the car was not idling well, except on high idle from cold. I also have to help it a bit to start it by feathering the gas a little and didn't have to often before. Now the car would probably stall if I let it at idle sometimes, sometimes not...but almost always it will nearly die at a light if I've been driving for a while, especially if it's right after I've given it a good run through the gears, or if I'm coming off the highway for instance at the top of an off-ramp. Heavy acceleration to relatively fast braking for a stop is the worst. It almost seems like the car gets plenty of gas if you give it to the thing, but has a hard time drawing it on its own. The longer I drive the car the worse it seems to get, but is much better when just starting out for the first time in a day (likely because of the high idle it holds until warm, honestly). Under load the engine still seems to pull nice and hard, but it feels pretty weak coming into 1st gear and reverse at normal idle (about 800 I guess). The engine does not seem to miss. This may be unrelated but if I turn the AC on while the car is idling it will kill it almost instantly if I don't give it gas (AC still blows pretty cold but does make a decent amount of noise when engaged). This is an original numbers L46 350 with 59k miles, if that helps. This is a higher compression engine and used to diesel fairly consistently on shut off, but that has also stopped entirely lately...not sure if that's related or a product of my switching fuel to the 94 octane stuff at Petro Canada. Just throwing it out there in case.

Sorry for the long description...but I figure the more detail the better for the experts out there! Thanks in advance. Overall this car is good to me, but the last month or so it has been old and grumpy.

 

Dirt from the pump replacement got into the needle valve in the carb. Gas is pouring into the manifold.

 

So hammer some carb cleaner to it and probably replace the fuel filter? Seafoam spray right into the carb or fuel tank additive or both? Thanks for the help.

 

No Most likely your carb is now full of barnacles and fish heads from the dying fuel pump. Try changing the filter first, but you probably will have to pull the carb, take it apart, and clean it all out. Sorry, buddy.

 

Yes I tried the Sea Foam before I saw your post above and it didn't help at all. Just a smoke show for no gain. I'm going to visit my mechanic next week to work on a couple of other things and it sounds like I'm also going to be asking for a carb rebuild? Or just a cleaning...is there a difference? Sorry I'm in the learning phase here. I've got a fuel filter coming tomorrow and I'll throw that on myself, but I doubt that's going to help at all. Sad face...the thing ran like a top a short few weeks ago. The memories.

Just have to throw this out there, and it might be a very silly thing to suggest...but my engine used to also diesel consistently on shut off (has 11:1 comp) but now it does not ever. Could this be a sign that I've lost some compression? Or should I just chaulk this up in the victory column. Only other change I've made is to 94 octane fuel from 91.

 

No, take the carb apart and clean the fuel bowl/bowls and needle valve.

 

You didn't say what kind of carb you have, but on my Holley, I can just pop the bowls off and clean them out in about 20-30 minutes. It's been a few decades since I have worked on a Rochester that your car came with, so I don't know if it is harder or not.

 

Gee imagine that. You need to do a little more investigation before tearing things apart. A leaking valve and seat is not the most logical or probable cause based on your description.

Remove the air cleaner and look down the carb throat while it's idling. Do you see gas dribbling anywhere? Stop the engine and continue to look into the carb. Any gas dribbling?

If yes- what kind of fuel pump did you install? Stock GM part or shiny Edelbrock ?

If no- do you have an electric anti-diesel solenoid that bumps the carb primaries open when the ignition is on. Is it working? Is the idle speed adjusted properly?

 

Thanks I will look at this tonight and report back. I don't have a lot of confidence around carbs...none basically, ha...so I hope I've described the problem accurately. The problem does seem to be getting worse.

The fuel pump I installed is a correct replacement from NAPA, and the carb is the original QJet that came with the car.

Mike I know Montreal well...went to Bishop's in Lennoxville and played piles of rugby in the city!

 

I had the car over at the local carb expert's place and he did not see anything wrong with my carb that he thought would cause the symptoms the poor thing has. We increased the idle speed slightly and that did seem to help.

The problem was particularly bad tonight afterward however (near stalling at idle after deceleration). I've noticed three additional things that were not occurring before the pump swap...

1. The problem is worse with the headlights up. As soon as those come up the idle drops noticeably, and the idle increases noticeably when I put them down. I'd say a couple hundred RPMs. Vacuum leak?

2. There is a puff of whitish or greyish smoke ONLY on a hot start and not even then on all hot starts. I even saw a puff come out of the air cleaner today when we started the car after fiddling with the carb and there was a lot of fuel and air in it.

3. The car really wants to quit when I pull into the underground parkade where it is living for this month...on the ramp on the way down (good sized grade) it will stumble and die if I don't help it out with the clutch in.

Have also discovered that I have a very slow leak from the 90 degree brass fitting between the fuel pump and the hard fuel line to the carb. It is slow enough that as it comes out it mostly evaporates before it has a chance to puddle. I've got a new line and fitting ordered.

Just to clarify, the car does not miss from what I can tell, and it pulls very, very, strong for a 42 year old original L46 with 59k miles. I don't drive it hard, but it had no issues on the highway today, and I stepped into it in 2nd and 3rd tonight and it still goes no problem without hesitation. Basically, as long as the car is in gear and under some load, any load, it is fine...just can't idle or handle a rapid deceleration clutched in / in neutral.

 

Yes, you have a serious vacuum leak from the headlight system. You didn't answer my questions about an anti-diesel solenoid or idle speed.

 

Can the light system leak throw off my idle this badly?

I have the idle speed adjusted just slightly higher than stock I believe. The manual calls for 750 warm and mine's probably set in the area of 850 or 900. It doesn't want to hold this always of course.

I have to admit I don't know what to look for in terms of the anti-diesel solenoid. Does anyone have a picture?

 

Track that down and fix it before messing with anything else.

 

Ok, I don't think I see an anti-diesel solenoid, electric anyway. I am going to try to attach some pics for the first time here.

Two things that are not stock for sure that stand out are the gasket stack under the carb. The car came to Canada via Phoenix so maybe they were going for some extra cooling of the fuel there? No sure. The external line fuel filter is going to be gone once my new pump to carb hard line shows up. I'll just be going back to a filter at the carb's fuel inlet. I don't think either of these things are contributing too much to my problem, but feel free to tell me otherwise.

Link to the pics until I figure out how to actually embed them:

http://s1078.photobucket.com/albums/w482/brcmpbl/

 

Well, now the old girl won't start at all. Will hold an idle for a few seconds on cold start and then will die immediately if I even touch the gas pedal. Some bad luck lately with this one.