backfire then big miss
- Thread starter Doc
- Start date
Thanks for the info Fred. I thought a good compression check eliminated that but ...now we have something else to check if the carbs don't fix it.
waybomb
I'd rather be blown
If he has a wiped cam lobe, or a bent pushrod, or abad lifter, the intake valve or exhaust valve will still open enough to let the air in and out easily during a compression check. The cylinder with the bad valvetrain may even have higher indicated compression.
A compression check is only good for things affecting compression - like rings, bad valves, bad headgaskets, cracked head, cracked block, etc.
A compression check is only good for things affecting compression - like rings, bad valves, bad headgaskets, cracked head, cracked block, etc.
Doc, do this test and let us know
Remove the dist cap ,use some way to SLOWLY rotate the motor to "0" mark on the timing tab. .Using some form of an indicator mark the position of the rotor. (closepin, coathanger, welding rod, pipe cleaner etc.).
Leave this in place. rotate motor in reverse rotation and see how many degrees of rotation untill the rotor moves.
A good timing chain and or gears will have very little degree difference.
if you move it 1-3 inches of harmonic balancer rotation before the rotor moves ,suspect timing chain and sprockets are badly worn.
Remove the dist cap ,use some way to SLOWLY rotate the motor to "0" mark on the timing tab. .Using some form of an indicator mark the position of the rotor. (closepin, coathanger, welding rod, pipe cleaner etc.).
Leave this in place. rotate motor in reverse rotation and see how many degrees of rotation untill the rotor moves.
A good timing chain and or gears will have very little degree difference.
if you move it 1-3 inches of harmonic balancer rotation before the rotor moves ,suspect timing chain and sprockets are badly worn.
dreamseeker
New member
dumb question
are you sure you have the correct dis cap
seems things got worse since you replaced.
are you sure you have the correct dis cap
seems things got worse since you replaced.
I don`t see it mentioned but did this develop AFTER you worked on the dist cap?
What rotation is the affected motor. could you have used the firing order of a standard rotation on a rev rotation motor? I know, I know, but is the firing order correct for the motors rotation?
What rotation is the affected motor. could you have used the firing order of a standard rotation on a rev rotation motor? I know, I know, but is the firing order correct for the motors rotation?
Good thoughts Bt Doctur!!!
But this started before we touched anything. It had ran fine last season, but had trouble at the end of the season when I was taking out. It had sat for 45 days at that point. Then when I launched in late May I had trouble starting. Played with points and got er going. She ran semi okay but he backfire started when I gave it a little throttle. 1800 rpm. Changed plugs and she fired right up. All seemed good, then when under load running down river and reved up she backfires. But I could idle okay. Changed points. Again, all seemed okay. But under load she still backfired. We idled most of the 15 miles upriver to Marietta for the sternwheeler festival. After turning off up there I could not get her started back up. If I held the throttle up at 15 to 1800 rpm it would keep running but it was backfiring and sputtering so bad that I shut it down. Hitched a ride back with a friends houseboat and got to work on her. That's how we got to the point of where I started this thread.
Long way of saying I don't see how the plug wires could have been switched for the firing ......we didn't mess with those.
But this started before we touched anything. It had ran fine last season, but had trouble at the end of the season when I was taking out. It had sat for 45 days at that point. Then when I launched in late May I had trouble starting. Played with points and got er going. She ran semi okay but he backfire started when I gave it a little throttle. 1800 rpm. Changed plugs and she fired right up. All seemed good, then when under load running down river and reved up she backfires. But I could idle okay. Changed points. Again, all seemed okay. But under load she still backfired. We idled most of the 15 miles upriver to Marietta for the sternwheeler festival. After turning off up there I could not get her started back up. If I held the throttle up at 15 to 1800 rpm it would keep running but it was backfiring and sputtering so bad that I shut it down. Hitched a ride back with a friends houseboat and got to work on her. That's how we got to the point of where I started this thread.
Long way of saying I don't see how the plug wires could have been switched for the firing ......we didn't mess with those.
pull the valve covers and inspect. maybe you hung a valve from storage, or cracked a valve spring. Had something similiar with a V6. turned out we had decent compression readings but the inner spring of an exaust valve was busted, caused the valve to float a bit sucking in water mist from the exaust.
dreamseeker
New member
doc from all you discribe brings me back to timing advance
idles fine and smooth and your timeing is dead on put at rpms it backfires and runs rough
run the engine at idle and check your timing then raise your rpm as you raise your timing should also increase or advance till it is about 27 to 30 degrees avanced. You should be able to see this easy with a timing light
you avance is mechanical and not vancume in most cases on a boat engine and the linkage in the bottom of the distributer could be rusted and broken
idles fine and smooth and your timeing is dead on put at rpms it backfires and runs rough
run the engine at idle and check your timing then raise your rpm as you raise your timing should also increase or advance till it is about 27 to 30 degrees avanced. You should be able to see this easy with a timing light
you avance is mechanical and not vancume in most cases on a boat engine and the linkage in the bottom of the distributer could be rusted and broken
Update:
Reinstalled the carbs: no joy.
Swapped carbs from starboard motor "just in case": no joy.
Checked all valves: no problems there
physically checked timing chain no problem there.
[FONT=verdana, arial, helvetica]Checked and found out we could swap distributors with the starboard motor to try. Dang if the starboard motor which had been running fine now had the backfire and popping problem. So it appears it's the distributor.
Ordering one today and should have it installed by Monday or Tuesday. I feel better already. What a dilemma.[/FONT]
Reinstalled the carbs: no joy.
Swapped carbs from starboard motor "just in case": no joy.
Checked all valves: no problems there
physically checked timing chain no problem there.
[FONT=verdana, arial, helvetica]Checked and found out we could swap distributors with the starboard motor to try. Dang if the starboard motor which had been running fine now had the backfire and popping problem. So it appears it's the distributor.
Ordering one today and should have it installed by Monday or Tuesday. I feel better already. What a dilemma.[/FONT]
Less than 2 weeks.........tap tap tap...........:waiting:
Just teasing ya
Sorry I know you're frustrated.
Whew! Told ya we'd be ready. Now we just have to get a new distributor in.
ME TOO!!!!!!!!
dreamseeker
New member
glad you found the trouble and will be back in the water soon
wayne:fishing:
wayne:fishing:
You know,Doc,this has brought back a problem I had w/ a Dodge 318 in a p/u. It had points and if I set them @.017" like the book said it would do the same thing you described w/ your engine. If I just closed the points a few thousandths,.013" IIRC, it would never skip a beat. I always attributed that to wear in the shaft bushings. It's been 30 yrs so I guess that's why I didn't recall it when your problem started.
Mike
Mike
Thanks guys!
Had the test drive today. All is GREAT.
The mechanic put in the new distributor and made the port engine purr. GREAT!
Then he puts the old good distributor back in the starboard motor. Trouble. It would not run right. It appears both distributors where wore out. The old distributor did not want to work with the electronic ignition we had put in hoping to fix the original problem. So now we have two new distributors and both run perfect. Whew. What an ordeal.
Like you said Mike. We could tinker with the points and keep it going, sometimes. From last summer through this past summer that's how I kept it running until it died the begining of Sept. It was done until the distributor was upgraded.
On the way I got new plugs, electronic ignition, wires, cap, rotor, and had the compression checked, timing belt checked, valves checked ........ All is good but but it was a long way to get there.
Had the test drive today. All is GREAT.
The mechanic put in the new distributor and made the port engine purr. GREAT!
Then he puts the old good distributor back in the starboard motor. Trouble. It would not run right. It appears both distributors where wore out. The old distributor did not want to work with the electronic ignition we had put in hoping to fix the original problem. So now we have two new distributors and both run perfect. Whew. What an ordeal.
Like you said Mike. We could tinker with the points and keep it going, sometimes. From last summer through this past summer that's how I kept it running until it died the begining of Sept. It was done until the distributor was upgraded.
On the way I got new plugs, electronic ignition, wires, cap, rotor, and had the compression checked, timing belt checked, valves checked ........ All is good but but it was a long way to get there.