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Fouling plugs and poor performance at high rpm, what causes this?


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Michigan boarder

I'm having some issues with the boat and ran out of daylight, and am done for the night.  Tomorrow I plan to put a timing light on it.  Here's the story:

Background:

  • '94 Echelon, rebuilt and bored/stroked the engine in 2015
  • 150 hours on it to date  
  • we re-used the original stock Thunderbolt distributor
  • spark plugs are R43TS gapped at .035
  • repropped, 49mph WOT at 4,900rpm consistently
  • rebuilt carb installed last summer - ran perfect.  However, I ran the choke wire from the coil.  This year I relocated the choke wire to the alternator, on the terminal that only provides voltage when the key is on.

The problem:

  • This season it started to top out at 4,400rpm and would not climb

Recent attempts to diagnose:

  • Checked plugs, #7 was black and fouled
  • Installed new plugs.  #7 fouled again. 
  • Installed new wires & new plug #7.  #7 fouled again.  In the course of testing, started to climb no higher than 3,800rpm
  • Installed new cap and rotor and new plug #7.  This time #7 and #8 fouled.  Replaced them, same problem, fouled again.

It starts really well, idles fine at 575rpm, and seems to run smooth and is responsive under low power.  But as I roll forward on the throttle it does not seem to pick up.  Occasionally it will hold at 3800rpm, then pick up to 4400 rpm (like one of those fouled plugs is now firing).  Also, if I get it up to 4400rpm and turn sharply the rpm will drop, down to 3400, then crawl to 3800, and usually hold there.  Also, sometimes when it's stuck at 3800 if I cross a large wake and bounce it gains power (again like one of those cylinders is now firing) and goes back up to 4400rpm.  Then I turn sharp, it drops, and is stuck at 3800rpm or worse.

Again, I have not put a timing light on it but I think my problem is in the distributor, like it's not advancing.  What do you guys think?  Also, when I put the new rotor on there is play, I will try to load that vid or gif from my phone.

 

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Gotta verify still. Take a known good wire and plug(1 maybe if you can) and plop in 7. If it fouls then, injector?, valve? Weird about the choke too. Verify it is completely open.

Steve B. 

edit: Oops no injector thats right. 

Edited by Steve B.
oops
  • Like 1
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Michigan boarder
15 minutes ago, Steve B. said:

Gotta verify still. Take a known good wire and plug(1 maybe if you can) and plop in 7. If it fouls then, injector?, valve? Weird about the choke too. Verify it is completely open.

Steve B. 

edit: Oops no injector thats right. 

Agreed, that was on the list too, to run with the flame arrestor off and see what the butterfly is doing.  But I assume it's open, otherwise it would not run well at idle.  Also I did check all carb linkage, all seems fine.  

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@Michigan boarder - don’t like the rotor play, results in timing scatter.  Can you determine whether it’s the rotor fit on the shaft or is it distributor gear.  How does the distributor cap look?  How old is the coil?

Should also verify choke opening fully with new wiring, try going back and see how that works.

Edited by Woodski
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Michigan boarder
9 hours ago, Woodski said:

@Michigan boarder - don’t like the rotor play, results in timing scatter.  Can you determine whether it’s the rotor fit on the shaft or is it distributor gear.  How does the distributor cap look?  How old is the coil?

Should also verify choke opening fully with new wiring, try going back and see how that works.

It's definitely not the rotor fit, that is tight with a groove that the rotor mates with, no play there.  The play is in the distributor gear.  Cap is new, looks new.  The coil was replaced 7/21/2012.  I was thinking of picking up a coil somewhere today.  I agree on the choke too, it was operating fine in the driveway a month ago but is a good thing to double check.

In an oil analysis a couple of years ago (it's been 3 years since I've done it) they mentioned the presence of bronze, which can indicate distributor gear wear.  I'll certainly check the other things, but do you have a recommendation on a distributor?

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If you are thinking of replacing the distributor, I'd check Summitracings site. Then call them or chat online to find the perfect one. They are awesome. I could see the distributor messing up all the plugs. But just one, and it moves around to another cylinder makes me think it's something else.

Steve B.

  • Like 1
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1 hour ago, Steve B. said:

If you are thinking of replacing the distributor, I'd check Summitracings site. Then call them or chat online to find the perfect one. They are awesome. I could see the distributor messing up all the plugs. But just one, and it moves around to another cylinder makes me think it's something else.

Steve B.

Unless the distributor shaft gets into some sort of harmonic motion.  Given that it is synchronized with the vibrations in the engine, I could see this happening.

@Michigan boarder, it is easy enough to mark and pull the distributor to check the gear and assess the play.  It should also be easy to poke a new bushing in it without replacing the whole unit.

  • Like 1
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Michigan boarder

OK, I'll start with the coil and carb inspection.  I'm traveling and between meetings all day but plan to stop by Napa or Autozone on the way home this afternoon, can you guys recommend a coil part # from those stores?

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Michigan boarder
26 minutes ago, justgary said:

Unless the distributor shaft gets into some sort of harmonic motion.  Given that it is synchronized with the vibrations in the engine, I could see this happening.

@Michigan boarder, it is easy enough to mark and pull the distributor to check the gear and assess the play.  It should also be easy to poke a new bushing in it without replacing the whole unit.

Would it be the bushing or the gears?  It seems like the gear would be worn for it to rotate like in my pic, if it were the bushing wouldn't it have some wobble to it?  I was also wondering if under load, as it's accelerating the play wouldn't matter because one gear would be pushing against the others, but I don't know what happens between those surfaces at that rpm.

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It is either the gear or the roll pin and hopefully not the cam (no bronze there).  The gear is cheap and easy to replace.  It’s standard Chevy.

As for # 7 not firing, perhaps checking spark plug wire resistance to see if that one is way out.  They will all be different based on length assuming resistor wires.

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Michigan boarder
1 hour ago, Woodski said:

It is either the gear or the roll pin and hopefully not the cam (no bronze there).  The gear is cheap and easy to replace.  It’s standard Chevy.

As for # 7 not firing, perhaps checking spark plug wire resistance to see if that one is way out.  They will all be different based on length assuming resistor wires.

OK.  I've got a ski show practice tonight, so won't pull the distributor but would like to pick up a coil.

#7 was fouled before I replaced the plug wires, then fouled again with the new plug wires.

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Michigan boarder
26 minutes ago, Woodski said:

See if distributor cap is corroded.  I would go back to previous choke wiring before too much parts swapping.

New distributor cap.  Old one had some corrosion but not bad (was new last year).  I agree on going back to "what has changed?" as usually the easy answer.

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Take the old coil with you so bolt pattern is the same. Just get the highest voltage one you can.

Steve B.

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martinarcher

Putting the timing light on it is a good thing as well.  I just had a pretty wild experience with that.  We had the boat running a bit off and I decided to do a normal tune up (plugs, wires, rotor, cap, carb fuel filter, clean arrestor, fuel water separator, and a timing check).  After I got everything installed I hit it with the light and couldn't believe the timing mark was WAY off the timing tab at idle.  I was guessing 20 degree too far advanced.  I checked the harmonic balancer's alignment with the timing tab using a piston stop, yep, the mark on the balancer was dead center between my marks using the stop.  Quadruple checked the #1 wire, checked it with a second timing light, checked the plug wires weren't off the by one, everything looks fine.  I put a timing tape on the balancer to get an idea where I was at....28 degrees BTC @ 650 RPM which was 18 degrees too far.  I finally pulled out the 9/16 wrench and moved the distributer to the factory 10 degrees BTC @ 650 RPM.  The engine idled way down.  I readjusted the idle and it revs nice and smooth and idles well.  I've been battling a hard starting issue for a LONG time.  The starter cranks happily (to my surprise after seeing the timing) but it takes a while to get the engine to fire.  After adjusting it the other night it fires up really nice now.  Hoping the lake test results are the same.

 

Long story short, always check the timing!  

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martinarcher

As far as a coil, I have had good luck with the Pertronix coils.  The Accel coils don't last very long under a hot dogbox in my experience.  

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Michigan boarder

My memory was jogged a few minutes ago.  Last year I swapped out plugs in mid season due to them fouling, but I figured that was due to my son (who used the boat a LOT) idling around the lake for hours on end.  I can't recall top end because I was usually behind the boat footing at that point, i never really went WOT when cruising around with my wife with me behind the wheel or pulling my other son wakeboarding.  So I think this problem started last summer, which would rule out the choke wiring issue.  I'll still check it obviously, but I don't think that's the problem now that I add in this info.

Just to double check, when I set the timing there is no bypass or "timing mode" that the distributor goes into with the Thunderbolt distributor, correct?  The last time I set it I simply had the #1 wire to the plug and light and the + and - leads connected to the battery, and set the timing based on the marks on the harmonic balancer.  I do remember the light bouncing around a bit.  I think I set it last year maybe?  Maybe the year prior.

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@Michigan boarder - a clue!  As long as the choke has the correct voltage you should be ok but that is an easy check.  Ignition timing is done straight up, 8-10 deg BTDC at idle and more importantly, 32-33 deg BTDC at 4500 RPM or when it maxes out usually over 2500 depending on the module.  The module could also be the culprit, not advancing properly.  You do need to pull the distributor and check the gear, if the pin shears you stop.

@martinarcher - I always like to mark the flywheel with a punch just in case. They start hard at 28 degrees BTDC!!

  • Like 2
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Michigan boarder
On 7/29/2021 at 1:47 PM, martinarcher said:

As far as a coil, I have had good luck with the Pertronix coils.  The Accel coils don't last very long under a hot dogbox in my experience.  

Internal resistor correct?

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Michigan boarder

I bought some new plugs, gapped two at .035" and replaced #7 and #8.

Started and ran up to temperature, choke opens up fine, carb working as it should.  Shut it down.

I hooked up the timing light, started it back up, pulled the transmission disconnect on the throttle, and found that #1 was WAY off, the 10 degrees mark was about 4 inches below the harmonic balancer mark.  Interesting though, there was not much scatter.  I advanced the timing and got it spot on at 9 degrees.  I gave it throttle up to 2,500 RPM and it was at 34 degrees.  I gave it more throttle to 3,000 RPM and it went completely retarded, again like 4 inches off the mark.  While watching the light, it would occasionally shine once on the 30 degree mark, then back to retarded for 10 rotations, then I'd see the 30 again with one flash.  I throttled down to idle, and at idle it was similarly retarded.  I looked back to the distributor and verified that it did not move.  I know this for a fact because the little vent on the side was normally about 1/8" away from touching the coil.  After my initial adjustment I could fit my thumb in there, and I could still fit my thumb in there.  Still at idle, I went to adjust it again (advance) and felt spinning resistance inside the cap/distributor, so I stopped and shut it down.

Thoughts?

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Wow. Timing sounds so wild I dont think it would run or start well. So, verify that timing light is working well. Then go back and make sure timing marks actually are what you think they are by doing the piston at the top of it's fire stroke thing. 

Again, I'd think if this was a problem at the distributor all plugs would foul or the engine would run awful. Keep us posted,

Steve B.

edit: Do some plugs look perfect?

Edited by Steve B.
added thought
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Michigan boarder
13 minutes ago, Steve B. said:

Wow. Timing sounds so wild I dont think it would run or start well. So, verify that timing light is working well. Then go back and make sure timing marks actually are what you think they are by doing the piston at the top of it's fire stroke thing. 

Again, I'd think if this was a problem at the distributor all plugs would foul or the engine would run awful. Keep us posted,

Steve B.

edit: Do some plugs look perfect?

Yes, some plugs look perfect.

I should probably just buy a new timing light.  I'll do that tomorrow.  There is an adjustment on the back of the light to advance the light, and it was at zero, verified several times.

 

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Just to add another perspective make sure you don't have a pair of plug wires reversed. If your timing ends up testing close, I think my next check would be pulling the valve cover and making sure rockers are happy.

Steve B.

Edited by Steve B.
typing error
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Michigan boarder

I bought a new timing light, one without the degree adjustments.  It also holds the flashing light without having to hold the button down which is a nice feature.  Before starting the engine I put the distributor back to approximately where it was before I ever moved it.  I replaced #7 and #8 plugs (fouled again) and started the engine and timing was off by about 20 degrees.  I moved the distributor and got it to 10-11 deg BTDC, set the idle at 575 RPM, and at full advance 3,000 RPM it reads 32-33 deg BTDC.  Again, no real scatter with the timing, it stays right on the mark.  Water test hit 4922 RPM at 49mph.  Hole shot is ridiculous, I forgot how powerful this boat is.  

So I do not plan to pull the distributor.  I might do that this fall though, when I pull the boat out for the season.  I plan on putting it in the garage for a week or so and removing all of the guages and the dash pod for a winter project.  I'll could remove the distributor at that time if you guys think it's a good idea.

What would cause my timing to change, just wear/seating of parts?  I know for sure the distributor is not where it was when the engine was first installed, because of that vent location on the cap. The engine has exactly 170 hours on it since the rebuild. 

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