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| back fire https://slantsix.org/forum/viewtopic.php?t=23893 |
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| Author: | Watercraft 6 [ Wed Jul 04, 2007 3:26 pm ] |
| Post subject: | back fire |
Engine runs but backfiring through carb. (sounds like somebodies playing a Cow Bell in rythm with motor). Also, what is the proper dwell, and procedure for setting the carb. screws. It is a 1970 225", freshly rebuilt carb., I misplaced all the books for it too so I'm not sure of firing order. Does any one know where I might find that online. This engine is in a boat. A Correct Craft ski boat. Thank you for your time and answers. |
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| Author: | SlantSixDan [ Wed Jul 04, 2007 3:55 pm ] |
| Post subject: | |
If it's in rhythm, then you've probably got some spark plug wires attached to the wrong plugs. This needs fixing in a hurry before you break stuff. Firing order is 1-5-3-6-2-4. #1 is frontmost, and the #1 distributor cap tower is at roughly the 4:00 clock position as viewed from above. Dwell is 41-46°, achievable with a points gap of approximately 0.020". Carb adjustment procedure is here . If you are working with a 2bbl carb having two idle mixture screws, make sure they are both adjusted the same number of turns out from the seated position. You didn't mention it, but the valve adjustment procedure is here . |
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| Author: | Watercraft 6 [ Thu Jul 05, 2007 12:23 pm ] |
| Post subject: | |
Mixed up plug wires fits the symptoms. I corrected the wires as per your instructions. Now it will not start at all. There is spark at the first plug (only checked one), the spark looked weak to me but I am no expert. The current plug is a Champion N9YC, they are black/sooty. Could the marine engine have a different firing order? |
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| Author: | SlantSixDan [ Thu Jul 05, 2007 2:33 pm ] |
| Post subject: | |
Firing order is not different on the marine engines, unless you have a reverse-rotation engine, which is not usually found in single-engine installation (only in twin-engine installations). Distributor rotation is clockwise, so make sure that starting from the 4:00 position, your spark plug wires are 1-5-3-6-2-4 as you count around clockwise. N9Y is a really cold plug. Might've been standard for marine applications, but cold-fouling you see suggests it's too cold. You might want to try the NGK ZFR5N spark plugs that work very well in these engines on the street. Remember, remove the metal ring washers from the spark plugs before installing them. Weak spark? Go through the ignition system. Points, condenser, spark plug wires. Maybe now's a good time to put in an electronic ignition conversion. |
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| Author: | GTS225 [ Thu Jul 05, 2007 3:06 pm ] |
| Post subject: | |
Dan.....I suggest we ask if he's had the distributor out. Might it be that it's 180 around on install, and the firing order is thus 180 out? That would throw a wrench into your "4:00 position" for start of order. Roger |
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| Author: | SlantSixDan [ Thu Jul 05, 2007 3:49 pm ] |
| Post subject: | |
Good question, whether he's had the distributor out (How 'bout it, Watercraft 6?), but not sure why you mention the 180° figure. If the distributor were removed and not replaced in the same rotative position, it could be off by almost any number of degrees...remember, it's a slant-6 with a gear-drive distributor, not a V8 with slot-drive. |
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| Author: | GTS225 [ Thu Jul 05, 2007 4:12 pm ] |
| Post subject: | |
Quote: but not sure why you mention the 180° figure. If the distributor were removed and not replaced in the same rotative position, it could be off by almost any number of degrees...remember, it's a slant-6 with a gear-drive distributor, not a V8 with slot-drive.
DOH!!!  Slap me upside the nugget for that one!Roger |
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| Author: | Watercraft 6 [ Fri Jul 06, 2007 8:10 am ] |
| Post subject: | |
the block has been to the machine shop for over boring of the cylinders. It was years ago and the whole motor was delivered to them for tear down. So it is an unknown. How might one ascertain the sequence? |
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| Author: | Doc [ Fri Jul 06, 2007 11:26 am ] |
| Post subject: | |
You need to find TDC compression stroke and set the distributor's position, then confirm correct spark plug wire locations to the distributor. If this is a new (rebuilt) engine being started for the first time, you should double check the valve lash adjustment. A tight intake valve will cause "backfire" out the carb. DD |
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| Author: | Watercraft 6 [ Fri Jul 06, 2007 12:54 pm ] |
| Post subject: | |
Thank you to everyone, here is the latest. #1 piston at top of compression stroke should coincide with the rotor being pointed at the 4 O'clock postion on the distributor (so as to deliver spark). I'm not sure how to tell if #1 is at top of comp. stroke. I should add that this motor ran two years ago but not at full strength. The head warped due to heat (that is the short/kind version of the story). I had the head milled, remounted it, ran it briefly to prove that I hadn't siezed the whole thing, then layed it up for the winter. Today I put in new plugs and inspected and regapped the points to the best of my ability. It started after lots of cranking and holding the throttle open. It shakes way too much and will only remain running if fept above 520 rpm. I read 35 dwell at that rpm. And a knocking can be heard as it runs. I can't tell if it's upper end or lower. My plan is to remove the rocker cover and inspaect for a connecting rod off it's rocker, and to help tell if #1 is on compression srtoke (and waiting for spark). |
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| Author: | Watercraft 6 [ Fri Jul 06, 2007 1:02 pm ] |
| Post subject: | |
I should also note that while it was running (roughly) I removed the hose from the ERG(?) valve, this caused a marked increase in rpm. |
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| Author: | Watercraft 6 [ Sat Jul 07, 2007 7:52 am ] |
| Post subject: | |
I should have said PCV not EGR valve. The hoe that goes from the rocker cover to the base of the carb. |
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