I set my dwell angle and timing on my 350 chev motor in my boat correctly but when i put the foot down it back fires i check with the timing light it seems to be jumping from advance to ****** by 2-3 degrees while it idles
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Re: problem in timing
On the distributor there is 2 types of advance.Vacuum and mechanical.The vacuum type has the mushroomed shaped bit screwed to the side of the dizzy.you have to pull the small vacuum hose off when you set the timing.Using your timing light,bring the revs up.The timing should not move.Put the small vac. hose on and off and the timing should move up and down.If its a mechanical advance,there is springs inside the dizzy that hold small weights.As the dizzy spins,centrifical force moves the weights outwards creating advance.Check the springs are in place.If you have access to one,try a another dizzy to satisfy your problem.A good shop will have a dizzy tester they can put yours on to check all these thigs.Hope this helps
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dwell angle is the no of degrees rotation between points closed and points open and for example on a 4 cylinder engine ( 4 lobes =90 degrees the dwell would be around 45 degrees available
there is an adverse relationship between point gap and dwell angle
the closer the points the bigger the dwell and conversely the bigger the gap the smaller the dwell angle
in a distributor the point gap of 18 would have a large dwell angle and that affects ignition timing
in your workshop manual there will be a dwell angle specification and if you set the points at .020 " that will put you close to the dwell angle specification
from there you adjust the gap to obtain the dwell setting
after yo have the dwell set , adjust the ignition timing
there is plenty of information on dwell angle, /point gap if you type in ---dwell angle to point gap relationship--
this engine should have an electronic ignition in which case there is no dwell angle
dwell angle was the degrees between the points opening and closing to give maximum saturation for the coil field
as it should be ab EFI engine then ECM makes the adjustment necessary for the correct setting for the fuel in use
as it is a low compression engine , the fuel octane rating that is best suited for it is 91
it will run well on 96 but the advantage gained is outweighed by the cost
the dwell angle and the point gap are closely related and seldom alter unless the point cam is worn or the point rubbing block is worn To go back to 1956 I will have to open some old manuals to get the dwell so if you make a comment I will see what I can get for you. As you can appreciate the dwell angle is the degrees turned that allows maximum saturation of the coil to produce the hottest spark and that is why I mentioned that the point gap is critical to get the correct dwell.
check the ht wires for a crossed set check the firing order as there are two wires that out of sequence will cause this problem. To check firing sequence go to google and type in firing order for chev/gm 350 engine and it will give all the details.
Sounds like its seized.. Checked the oil lately? OR One good possibility is the timing chain broke and is collected in the bottom of the timing case jamming the crank shaft.. Starter will not overcome this.
Here is the firing order diagram for that engine, and the ignition points should have a gap of .025 in. or a 35 degrees dwell angle, and the spark plug gap is .034 in., and the ignition timing should be set at 6 degrees before TDC with a standard transmission, and 12 degrees before TDC with an automatic transmission. If the distributor was removed then it will have to be installed correctly, and let me know if you require any further assistance.
You have a 1986 454 engine with an old style breaker point ignition distributor, GM has not used a breaker point ignition for their V-8 engines since 1974, is that an older distributor or something after-market?
The ignition points dwell angle for that engine should be set at 29-31 degrees dwell (a dwell meter would be the most accurate way to set the ignition points), or a .019 in. point gap.
The spark plug gap for that engine would be .035 in. and the timing should be set at 10 degrees before top dead center.
While looking at the engine from the side or from an overhead view, the #1 cylinder will always protrude slightly further to the front. In other words, the valve cover and head that has less room behind the water pump and sticks out further is #1. Firing order 1-8-4-3-6-5-7-2 is the same.
timing and dwell angle is non adjustable in these later model vehicles. the dwell is simply a reading that might be useful on a scope, while the timing advance is controlled by the systems ecu(computer) by taking readings off the knock sensor(or pre detonation sensor). this is a mazda engine. is there a problem or are you simply trying to keep up on the maintenance?