Problem with acceleration from standstill
02-14-2008, 08:55 AM
#1
Thread Starter
Join Date: Feb 2008
Location:
Posts: 8
Problem with acceleration from standstill
Hi all,
Recently installed an MSD ignition in my '66 fastback. Everything is running great except for one thing...when I start from a standstill and put my foot to the floor the engine sputters and backfires. I figured it must be timing so I took it into a shop for a tune up. When I got it back it was running much better but still has this annoying problem. The shop I took it toare a bit old school soI'm not sure they were on top of the MSD. Thought I get some forum advice before taking it somewhere else. Any suggestions?
Thanks,
Jeff
Recently installed an MSD ignition in my '66 fastback. Everything is running great except for one thing...when I start from a standstill and put my foot to the floor the engine sputters and backfires. I figured it must be timing so I took it into a shop for a tune up. When I got it back it was running much better but still has this annoying problem. The shop I took it toare a bit old school soI'm not sure they were on top of the MSD. Thought I get some forum advice before taking it somewhere else. Any suggestions?
Thanks,
Jeff
02-14-2008, 09:58 AM
#3
6th Gear Member
Join Date: Oct 2006
Location: Cork, Ireland
Posts: 6,417
RE: Problem with acceleration from standstill
correct me if I'm wrong, but the big thing with those MSDs (the difference) is that they create longer or multiple sparks.
So from this they work as any distributor does, just enhancing the spark. From this I cannot see how the MSD (if working correctly) could be the issue.
If you have all your timing right my first 2 guesses would be:
a) vacuum advance of distributor shot or not functioning
b) to much or too little petrol from accell pump.
to a) ignore if you have a new distributor:
i have a feeling you have a timing gun as you adjusted yourself.
leave engine running in idle.
Disconnect the advance hose on distributor side and plug.
check initial timing. should be around 8-10 degrees
put the hose back. still 8-10 degrees (should be when connected to ported vacuum on carb)
then disconnect the advance hose on carb side (leave connected on distri side).
the idle might change as it's running lean now. check timing (don't adjust anything, just for reference).
Then suck on the hose that is still connected to the vac advance at one end. (i know it sounds mad).
You should feel the mebrane pulling against your sucktion. You should see the timing advancing.
When you created a lot of vacuum, block the hose with your tongue.
the pressure should hold up and not release. the advance should stay advance and not coming back to where ti was until you release the pressure again (remove tongue)
wash your moth and let us know how you were getting on (if you have a vacuum pump, then you can use that instead your mouth)
to b)
switch engine off, remove air cleaner
look down the carb and when you push the accellerator fullt (you can do that with moving the throttle linkage), you should see a nice solid shot of fuel swushing down the carb.
let us know if that's the case.
If it is the case you might want to try to put the accelleration pump linkage in a different position (in most cases there is 3 positions to choose from).
what engine, what carb ?
So from this they work as any distributor does, just enhancing the spark. From this I cannot see how the MSD (if working correctly) could be the issue.
If you have all your timing right my first 2 guesses would be:
a) vacuum advance of distributor shot or not functioning
b) to much or too little petrol from accell pump.
to a) ignore if you have a new distributor:
i have a feeling you have a timing gun as you adjusted yourself.
leave engine running in idle.
Disconnect the advance hose on distributor side and plug.
check initial timing. should be around 8-10 degrees
put the hose back. still 8-10 degrees (should be when connected to ported vacuum on carb)
then disconnect the advance hose on carb side (leave connected on distri side).
the idle might change as it's running lean now. check timing (don't adjust anything, just for reference).
Then suck on the hose that is still connected to the vac advance at one end. (i know it sounds mad).
You should feel the mebrane pulling against your sucktion. You should see the timing advancing.
When you created a lot of vacuum, block the hose with your tongue.
the pressure should hold up and not release. the advance should stay advance and not coming back to where ti was until you release the pressure again (remove tongue)
wash your moth and let us know how you were getting on (if you have a vacuum pump, then you can use that instead your mouth)
to b)
switch engine off, remove air cleaner
look down the carb and when you push the accellerator fullt (you can do that with moving the throttle linkage), you should see a nice solid shot of fuel swushing down the carb.
let us know if that's the case.
If it is the case you might want to try to put the accelleration pump linkage in a different position (in most cases there is 3 positions to choose from).
what engine, what carb ?
02-14-2008, 02:30 PM
#8
4th Gear Member
Join Date: Jun 2006
Location: Fontana, California
Posts: 1,483
RE: Problem with acceleration from standstill
In order:
Check timing both staticly and dynamically.
Check ignition system for bad plug wires and secondary ( rotor, cap, coil.)
Check for dirty air filter.
Check fuel pump output volume, pressure,
Check fuel filter.
Check accel pump for proper squirt volume.
sputtering and backfiring are sure signs of electrical or fuel delivery problems. its usually electrical. From the fuel perspective it can be too much air, too much fuel or not enough of fuel or air.
Check timing both staticly and dynamically.
Check ignition system for bad plug wires and secondary ( rotor, cap, coil.)
Check for dirty air filter.
Check fuel pump output volume, pressure,
Check fuel filter.
Check accel pump for proper squirt volume.
sputtering and backfiring are sure signs of electrical or fuel delivery problems. its usually electrical. From the fuel perspective it can be too much air, too much fuel or not enough of fuel or air.
02-14-2008, 02:46 PM
#9
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
RE: Problem with acceleration from standstill
Definately check electrical first. 90% of carburetor problems are ignition problems. If the ignition is good then it's most likely the accelerator pump.
Tuning the pump requires changing squirters and pump cams, and fine tuning by adjusting the spring tension on the pump cam arm. You need to buy the cam assortment kit for that, and squirters are sold seperately by size.
Tuning the pump requires changing squirters and pump cams, and fine tuning by adjusting the spring tension on the pump cam arm. You need to buy the cam assortment kit for that, and squirters are sold seperately by size.
02-15-2008, 06:53 AM
#10
1st Gear Member
Join Date: Oct 2007
Posts: 138
RE: Problem with acceleration from standstill
If it ran fine before the MSD, then it ain't the carb. Focus on the MSD.
* Is it securely mounted and not moving? (a mistake i have made
)
* Are the wires secure/good contact? Did you have to 'stretch' the wires to fit? New connections?
* Swap old coil back on- if it runs fine - bad MSD.
*Did you change plugs / wires at the same time? Could be a bad one from the factory (happens occasionally to me[>:]) Are you SURE the firing order didn't get disturbed?
If it is the original plugs wires - remove and inspect. Replace if they are more than 12K miles - the more powerful spark may be breaking a weak wire down. Are the plug wires and coil wires loomed correctly? Are they touching metal directly/shorting a spark?
* Is it securely mounted and not moving? (a mistake i have made
)* Are the wires secure/good contact? Did you have to 'stretch' the wires to fit? New connections?
* Swap old coil back on- if it runs fine - bad MSD.
*Did you change plugs / wires at the same time? Could be a bad one from the factory (happens occasionally to me[>:]) Are you SURE the firing order didn't get disturbed?
If it is the original plugs wires - remove and inspect. Replace if they are more than 12K miles - the more powerful spark may be breaking a weak wire down. Are the plug wires and coil wires loomed correctly? Are they touching metal directly/shorting a spark?