High RPM lean out

[josh_t]

Well i've been driving my B around a little. (illegally, its more fun that way.) It pulls a little better than i thought considering its an auto. It does great until above 4500 rpms. It starts to weaken a little and as if by magic, it cuts out at 5k. I can pump the gas once real fast and it starts working again. There are no problems at any other point in the RPM range or at any other throttle position. Timing is at 20 BTDC (tested thoroughly for detonation, none). Valves are at .014 like the chilton's manual states. The temperature is where it should be. Fuel pump is brand new.

[datzenmike]

They are cheap so cut to the chase and replace the fuel filter. Probably time to be replaced anyway and if it doesn't help, it's only $5.

 

Set your timing to the correct amount. If it needs to be that high then something else may be wrong. Perhaps the mechanical advance is stuck.

[josh_t]

thats done. its a cleanable one and its clean.

[metalmonkey47]

They are cheap so cut to the chase and replace the fuel filter. Probably time to be replaced anyway and if it doesn't help, it's only $5.

 

Not even $5 anymore. We carry an awesome quality cheapo filter for the 1/4 fuel line. I cut one open to check out the material and it seemed to be some pretty quality product for the price. I keep one in the glovebox since I have a rusty tank.

 

http://www.autozone.com/autozone/accessories/Performance/Universal-Fuel-Filter/_/N-25ek

 

 

 

 

[josh_t]

Not even $5 anymore. We carry an awesome quality cheapo filter for the 1/4 fuel line. I cut one open to check out the material and it seemed to be some pretty quality product for the price. I keep one in the glovebox since I have a rusty tank.

 

http://www.autozone....Filter/_/N-25ek

 

 

 

 

 

me and my friend picked one up for his duster but it was the cone shaped one. it works pretty well.

[datzenmike]

Timing is at 20 BTDC (tested thoroughly for detonation, none). Valves are at .014 like the chilton's manual states. The temperature is where it should be. Fuel pump is brand new.

 

First set it to stock timing and see if the problem goes away.

[josh_t]

First set it to stock timing and see if the problem goes away.

 

i'll try that tomorrow.

[metalmonkey47]

Holy crap, you're really running 20 degrees advance? Is that at idle?

 

 

My A15 ran like crap @ 20 degrees. I made a ton more power around 5-7 btdc

[josh_t]

Holy crap, you're really running 20 degrees advance? Is that at idle?

 

 

My A15 ran like crap @ 20 degrees. I made a ton more power around 5-7 btdc

 

i've tested mine at 5, 10, 15, and 20 and it has run by far the best at all rpm ranges and had the most response at 20. and there is no detonation. even the idle is very smooth and quiet at 20 much more so than at any other timing. this issue just started happening too. it used to pull all the way to just above 5k and then i would shift.

[datzenmike]

All engines will idle better if you add 8-10 degrees of advance. This is because they are actually retarded this amount at idle. They run with no vacuum advance at idle and as soon as you step on the gas vacuum is applied and it jumps up.

[josh_t]

i have done a lot with the timing and points gap to see what works best and the timing where its at worked fine until about a week ago. i have driven it up and down hills WOT for a while and this is the first time it has shown any trouble. maybe the points need to be set. it has been a while. i should probably read the plugs too while i'm at it. why did i even post this?

[Jester]

If your running 20 deg timing at an idle, you have other issues. When you get to 4500 you are so far out of time it's no wonder it doesn't want to run. TOTAL timing should not exceed about 35 deg. Start setting things back to FACTORY settings and keep going till you find the problem.

 

Not knowing anything about your car makes it a little tuff to help. Have you done a compression check? What carb are you running? Done anything with the carb? Rebuild or changed the getting?

[datzenmike]

There'a an old saying that 90% of carb problems are ignition. If you have points check the gap, check that the wires are firmly tightened and the distributor tightly mounted so it is well grounded. Check the coil connections. Does the dizzy shaft move if you push sideways on it... is there enough play to say that it wobbles? This will affect the points opening and closing.

[josh_t]

Well i checked some things out recently and it was at 15 BTDC instead of 20 so from what I've tested, thats optimum. It is very shaky and much weaker at 10 degrees for some reason. But i noticed that at the coil i'm only getting 6 volts. I'm almost positive that i'm supposed to get more like 7.5 or 8. It now has a new points distributor so the timing is a little more consistent as well as all the other stuff being new on it too. I dont have the cut out at 5k like before but it seems to miss slightly at idle if it sits idling for a little bit. It also now has a not so bright orange spark instead of a blue one.