Poor Acceleration

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 11:14 am

My '71 is running "OK" but accelerates poorly, especially at the higher RPMs when I would expect it to start pulling strongly. Acceleration/power seems to plateau 3-4k rpm and starts misfiring. Timing is set to spec 10° BTDC. Stock DHSA 32 carb is suspect. Possibly getting too lean a mix when the secondary opens?
And since I got your attention, how the hell do you get a screwdriver on the slow idle adjust screw? I can't even see it!
Thanks all!
~Steven

seabeelt · Post by **seabeelt** » Mon Jun 24, 2013 11:56 am

If its a 1608, timing I have read elsewhere, should be 5 deg BTDC initial timing advance. Not that this will fix your issue, just an observation
R/

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 12:23 pm

seabeelt wrote:If its a 1608, timing I have read elsewhere, should be 5 deg BTDC initial timing advance. Not that this will fix your issue, just an observation
R/

Thanks. It is a 1608 - I'll double check that. I have also read 12° BTDC many places. I should add I checked the mechanical advance and it seems to working (i.e., not frozen or gummy).

So Cal Mark · Post by **So Cal Mark** » Mon Jun 24, 2013 12:28 pm

if it's a misfire, I'd look closely at the ignition system. It's important to have the points set properly or you will not have any coil saturation time, causing a really weak spark. Those systems are marginal at best, and if not in perfect condition won't work very well

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 12:55 pm

So Cal Mark wrote:if it's a misfire, I'd look closely at the ignition system. It's important to have the points set properly or you not have any coil saturation time, causing a really weak spark. Those systems are marginal at best, and if not in perfect condition won't work very well

Thanks Mark. I can say the new points I installed were funky. I had to twist the moving arm to get the bushing parallel to the cam lobes. I will recheck and reset after it's settled in a little. Tomorrow night I will also check for arching in the plug wires.

majicwrench · Post by **majicwrench** » Mon Jun 24, 2013 1:42 pm

Like Mark said, "missing" is usually an ignition issue. Points can bounce too at higher rpm. Did it do this before the funky points?? If so, can you put old set back in??
Hard to find quality points. Keith

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 2:00 pm

majicwrench wrote:Like Mark said, "missing" is usually an ignition issue. Points can bounce too at higher rpm. Did it do this before the funky points?? If so, can you put old set back in??
Hard to find quality points. Keith

I replaced in sequence the condenser, rotor, and then points. Behavior did not change. That leaves cables or cap...
When I get the misfire to go away, I have a 34 DMS carb I am hoping will help with the plateau. I'll update this thread after I check the cables for arching. Thanks everyone!
~S

So Cal Mark · Post by **So Cal Mark** » Mon Jun 24, 2013 2:11 pm

the stock carb should allow it to rev to 6-7k without any issues. Do you have access to an ignition scope?

majicwrench · Post by **majicwrench** » Mon Jun 24, 2013 2:27 pm

Another thought...(need to quit thinking) it could be running out of fuel. An issue with cap/rotor/wires should "miss" as it is pulling hard, even at low rpms.

Tis easy to "T" a pressure guage in at carb, run long hose so gauge can be hung on wiper arm, then watch as you accel. Any loss of pressure = problem.
Keith

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 2:35 pm

So Cal Mark wrote:the stock carb should allow it to rev to 6-7k without any issues. Do you have access to an ignition scope?

Nope... would be nice though!

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 2:40 pm

majicwrench wrote:Another thought...(need to quit thinking) it could be running out of fuel. An issue with cap/rotor/wires should "miss" as it is pulling hard, even at low rpms.

Tis easy to "T" a pressure guage in at carb, run long hose so gauge can be hung on wiper arm, then watch as you accel. Any loss of pressure = problem.
Keith

T off the vacuum line to the brake booster for example? That would be vacuum not pressure so what am I missing?

majicwrench · Post by **majicwrench** » Mon Jun 24, 2013 2:51 pm

Sorry could have been clearer. "T" into the fuel inlet line at carb. Everyone should have one of those cheapy round vacuum/pressure gauges. If not, go get one. Then buy a "t" fitting, brass plastic whatever, and 4ft of fuel line (1/4"?) then go drive car. Fuel pressue should never drop at all.
Keith

smbaird37 · Post by **smbaird37** » Mon Jun 24, 2013 3:49 pm

majicwrench wrote:Sorry could have been clearer. "T" into the fuel inlet line at carb. Everyone should have one of those cheapy round vacuum/pressure gauges. If not, go get one. Then buy a "t" fitting, brass plastic whatever, and 4ft of fuel line (1/4"?) then go drive car. Fuel pressue should never drop at all.
Keith

Thanks Keith! Yes I have one and have tested fuel pressure near idle (about 4lb). Did not occur to me to test at higher RPM but I will give a look.

majicwrench · Post by **majicwrench** » Mon Jun 24, 2013 4:08 pm

Not just higher rpm but when problem occurs. Need to get it out on the road.

So Cal Mark · Post by **So Cal Mark** » Mon Jun 24, 2013 5:40 pm

fuel issues appear under load, so it's gotta be driven to see what's happenin'.
While ignition issues usually appear under heavy load, especially acceleration, your funky points could be causing the problem

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