Slows down when throttle is opened. Ignition?

[Z-Luke]

After some HEAVY searching on the forums I have found a lot of information about not revving over a certain RPM (5000) and all the issues that could lead up to that. I think I'm having ignition issues combined with carb issues. The carbs I'm going to get rebuild, but when I look for ignition troubles I can't seem to find what the correct advance is supposed to be. So far I've found that at @700rpm you're upposed to have 17 degrees BTDC of advance. But what is supposed to be at speed?

My car is exhibiting the following symptoms (4-screw dome, 1970 L24)

- hesitation, poor idle, won't ide when cold.

- using more than 1/4 throttle the car loses power

at 70 mph if I push the throttle in the car slows down, if I ease up on it the car speeds up. Engine will not go over 4000 rpm under load, 5000 rpm in neutral. Exhaust note goes very flat and it doesn't sound like its "working". I'm going to tackle ignition first and on Saturday I'm going to check the timing with some help.

On the boards I've noticed mostly the trouble seems to come from spark plugs (new in this car), and rotor/dist cap. Timing is mentioned a lot but is rarely the cause. The car never seems to spew black even with the choke closed so it could be running lean. I think I had gone 20 miles at 70 mph before i noticed my foot was to the floor. It just didn't sound like it was trying.

In street driving, part throttle operating results in STRONG engine performance 1/4 throttle shot to 50mph in second gear, felt great. This is all inconsistent, sometimes its totally flat. Sometimes it just bucks and hesitates not unlike my motorbike when its cold and the choke is open.

[motorman7]

Sounds like two issues to me.

First off; Slowing down when you push the throttle sounds like you are too far advanced. I am guesing you would hear a bit of pinging at mild load, heavy load and you slow.

For the rough idle, check the float bowl level. I adjusted mine the other day and it made a world of difference at idle, and at speed.

Just my thoughts,

Rich

[moritz55]

Here's some settings I used on my car..... I have a 4BL Holley, 390cfm .. but setting the advance and Idle would be the same.

When fully warmed up:

900 RPM normal idle - 16 BTDC advance

900 RPM car pulls 14-14.5psi vacumm.

then set advance ... at 3k RPM.

3000 RPM - 42 BTDC total advance

Note: when my alternator kicks on... my idle RPM drops around 50-80 RPM to 850-820 RPM. This is important... as I had to make my carb(s) slightly richer at low RPM so it maintained power. I had my carb(s) too lean....

Cold Idle Starting:

1500 RPM when started (choke pulled 1/2way)

2000-2100 RPM when choke fully pulled out.

One final comment is you may have your Carbs set Too Lean. If your timing is set correctly, then try making your carbs slightly (1/8 to 1/4 turn richer). Readjust your idle and Advance to the above settings I reference and you may see improved power and acceleration under load.

Here is one link for reference on idle mixture tweaking:

http://www.classiczcars.com/forums/showthread.php?t=30161

Here is one that has a lot of information on ignition settings. Post #79 has my setup:

http://www.classiczcars.com/forums/showthread.php?t=30380&page=4

Just my thoughts.... so keep us posted.

Good luck.

Edited November 19, 2009 by moritz55

[GreenZZZ]

The less obvious stuff:

Vacuum leak in the manifold, carb throttle bushing or could even be the brake booster...

Distributor bearing/bushing shot

[Z-Luke]

Thanks for the responses! I'll be sure to check into it this weekend. I have absolutely no daylight by the time I get home. I've got 8 volts on the coil at idle, 12.9 on the battery. Pretty sure I've got a soggy alternator. The lights on the dash and the headlight that works get brighter with RPM.

I'll probably get a new internally regulated unit at some point. I pulled out some plugs and they were as black as the sky at night, but I did flood the every loving nuts off of it the other day (choke got stuck) so I only just cleared it as it got dark. Couldn't pull them again because I couldn't see.

[beandip]

First off , are we dealing with a stock L-24? Secondly with a original dist and ignition? If both are true set the timing at 10*BTDC with the vacuum advance disconnected and plugged, and at normal RPM 650 to 700. Use 20w oil in the SUs . Believe me the oil does make a difference . No 20w use 10w/30. If you still have the same problems, and you are using NGK plugs, then look to the carbs and set the air balance , then the fuel mixture. Do a search here on the site . there is ample info on this. When using your timing light , pay attention to how steady the line appears . If it is bouncing and erratic , most likely the bushing are shot in the Dist. Check this stuff and get back to us. DON'T start throwing parts and money at the problem. Sounds , at this point to be adjustment and tuning.

Gary

[beandip]

to check if the brake booster is bad, just let the engine idle and step on the brake. If the idle changes , you either have a bad vacuum line or the booster is bad.

Gary

[Walter Moore]

You could also have a bad fuel pump, or a clogged fuel line. Both will cause the engine to lose power under load.

[Z-Luke]

The idle doesnt change with brakes. This evening after I went and pumped some air in the tires, I had it warmed up good and it still accelerates nice and hard at almost no throttle between 1500-3000 rpm. I tried tipping my toe a bit (hard to tell, short throttle travel on this guy) it popped and jerked and slowed down.

I tried to replace the rotor but the jobber bit PartSource sold me is WAY taller and it wouldn't fit, the cap just had no room to go on.

I checked the fuel filter and its only filled to about 1/2 inch up with gas. I can see it getting sucked up by the engine. I thought I read on the forum somewhere that it should be completely submerged in gas but I can't duplicate my search result at all. Is it supposed to be full of gas or just have some pooled in it?

Could be that the fuel aint getting where it needs to be like Walter says. Its a brand new filter by the way, looks like the previous owner was troubleshooting the problem. I bought it from a "farm boy" who said the carbs need rebuilding. I don't disagree with him, but to me it seems like the carbs are doing at least a somewhat capable job considering I flooded the motor the other day playing with the choke too much.

Where is the other inline filter on the gas tank? I haven't had a chance to roll under the car too much lately. Do I have to drop the tank to find it?

I should mention that, given the fuel gauge is operating correctly, the car is getting overly good gas mileage in my opinion. Only used a very small portion of what I poured in coming back from another town (where I bought the car).

Edited November 21, 2009 by Z-Luke

[Nigel1943]

Have you tried lubricating the bob weights in the bottom of the distributor? They could be sticking or you could have a broken spring. Only way to find out is to take it apart.

[Z-Luke]

yeah we lubed the weights, they look clean though. The mechanical advance is working we checked with a timing light. The dist was set at 1 notch to advance, we moved it forward a few notches and that bought the torque on a little sooner but it still had no guts in the mid-to-upper rpm. We can't make the vaccuum advance work but sucking on the tube, it moved a little but not much. Getting about 6 hg's at idle of the advance and it goes up with engine speed. Might be working, hard to tell. I'll replace the vaccuum advance pot.

Still feels like its not getting gas. I'm done for today though I'll get back at it tommorrow. Engine isn't putting out enough power to get past 70 mph still, and if i release the throttle for a second and then just press it slighty it seems to pull hardest. Any more throttle and it just wheezes out. I suspect carb and fuel delivery trouble I think the ignition is mostly okay.

[Walter Moore]

...Engine isn't putting out enough power to get past 70 mph still, ...

Not to belabor the point, but that is the EXACT symptom that my car exhibited when the fuel pump failed.