1989 351W Hesitation Backfire

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Hi,
I recently repaired a broken rocker stud, see here:
http://https://www.correctcraftfan.com/forum/forum_posts.asp?TID=51766&PN=1&title=1989-351w-engine-knock

I used the boat for a few days after the repair, and it ran well. Only small issue that I noticed was an occasional "miss" or two will under load (pulling a wakeboarder). But it cleared up and didn't happen again.

Using the boat again recently, the issue seems worse.

The symptoms are as follows:
- Only occurs after idling for a long time (teaching someone to wakeboard)
- When accelerating, after long idle, the engine will miss / pop / hesitate / splutter and even backfire.
- If I nurse it up to speed with a few pops along the way, it will start running smoothly.
- Once I have run it at speed for a while, it runs smoothly and I can accelerate hard from stand still without any issues.

Any advice on what I can test? I am thinking:
- Idle mixture too rich, fouling plugs? I did notice some black soot on the bottom our our wakeboards.
- Timing issue? My distributor is still original (just with electronic module). Springs are a bit rusty.
- Bad power valve? It is a M600 carb (about 6 years old), so should not be sensitive to backfires.

Any other ideas or advice on how to test?

Thanks,
Greg

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Greg_SA Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: April-19-2007 Location: South Africa Status: Offline Points: 187	Post Options Post Reply Quote Greg_SA Report Post Thanks(0) Quote Reply Topic: 1989 351W Hesitation Backfire Posted: April-14-2025 at 6:22am
	Hi, I recently repaired a broken rocker stud, see here: http://https://www.correctcraftfan.com/forum/forum_posts.asp?TID=51766&PN=1&title=1989-351w-engine-knock I used the boat for a few days after the repair, and it ran well. Only small issue that I noticed was an occasional "miss" or two will under load (pulling a wakeboarder). But it cleared up and didn't happen again. Using the boat again recently, the issue seems worse. The symptoms are as follows: - Only occurs after idling for a long time (teaching someone to wakeboard) - When accelerating, after long idle, the engine will miss / pop / hesitate / splutter and even backfire. - If I nurse it up to speed with a few pops along the way, it will start running smoothly. - Once I have run it at speed for a while, it runs smoothly and I can accelerate hard from stand still without any issues. Any advice on what I can test? I am thinking: - Idle mixture too rich, fouling plugs? I did notice some black soot on the bottom our our wakeboards. - Timing issue? My distributor is still original (just with electronic module). Springs are a bit rusty. - Bad power valve? It is a M600 carb (about 6 years old), so should not be sensitive to backfires. Any other ideas or advice on how to test? Thanks, Greg
	1989 Ski Nautique (SN2001)

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11247	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: April-14-2025 at 7:15pm
	Sounds to me like it's too lean when accelerating. Is your accelerator pump adjusted so it's shooting gas as soon you move the throttle? No slop at all at idle and a little clearance at full throttle (around 10 thousandths of an inch or 0.254 mm in your part of the world) Or maybe richen up the idle a little And check timing around 10 ish at idle smoothly going up to the 30 to 34 range at 4000 rpm

Greg_SA Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: April-19-2007 Location: South Africa Status: Offline Points: 187	Post Options Post Reply Quote Greg_SA Report Post Thanks(0) Quote Reply Posted: April-15-2025 at 1:08am
	Thanks Keno. At idle, the boat revs up instantly - doesn't that mean the accelerator pump is working? I'll look for the squirts, but I think it is good. I'll check the timing.
	1989 Ski Nautique (SN2001)

1989 351W Hesitation Backfire

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