Powerstroke 3500 blowing flames out of tailpipe - Power Equipment Forum : Power Equipment Forums
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post #1 of 5 (permalink) Old 06-17-2019, 11:24 AM Thread Starter
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Powerstroke 3500 blowing flames out of tailpipe

Hi all,

I have a Powerstroke 3500 generator that I acquired as part of heap of tired equipment I bought as a package. Previous owner said he had no knowledge of what condition the generator was in. When I first tried starting it, I would choke it, give it a pull, and it would pop a few times like it was starting, but as soon as I took the choke off, it would die. Removed and cleaned the carb, replaced the fuel filter and fuel shutoff valve, but no improvement. Finally concluded that the carb must be the culprit, so replaced with a new one. Same exact issue.

I noticed that at the end of the aborted starts, a puff of exhaust would usually come out of the carb, so I decided to pull the muffler off next. Sure enough, the spark arresting screens on the muffler were quite jammed up with soot, and with the muffler removed, the engine was able to start right up and run. Now the issue was that a 4-6" blue flame was seen shooting from the engine exhaust port. I did some reading around the internet, and the prevailing wisdom was that the timing could be off, the valves could be out of adjustment or shot, or the engine might just be running too lean. This generator came without an air filter, so I got a proper air filter for it, thinking this might be all that is needed to change the mixture. No dice, it still shot flames from the exhaust. I made sure the flywheel key was intact and that the timing was correct, and my next step was to look at the valves.

At TDC, the rockers seemed to be putting quite a firm pressure on the valves. Based on rule-o-thumb internet wisdom, I adjusted the valves to .006 on the exhaust valve, and .003 on the intake at TDC. Well, now the pull starting is extremely hard (high compression), and it still just pops a couple of times but won't start. So no doubt, my valve adjustment did more harm than good.

At this point, I have run out of ideas--any advice?
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post #2 of 5 (permalink) Old 06-17-2019, 04:21 PM
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Forgive the silly question, but just to make sure: the engine was at TDC of the compression stroke, right?

I would have done basically what you did, take a reasonable guess at common valve clearances.

Does a valve (typically exhaust) still get nudged open sightly as the piston comes up on the compression stroke? That's the compression release being able to do its job.

If this is maybe a Honda-clone engine, you might be able to go by Honda valve clearances.

However, let's assume you gave at least enough valve clearance (maybe too much, but that's ok). The engine should be able to function, though it will be difficult to pull-start. If you add a spray of starting fluid, carb cleaner, etc, into the carb's intake (air filter removed), will it run on that briefly?

You need fuel, compression, and spark. You checked spark timing, so if the spark is bright blue, that should be ok. You have compression. So let's be sure of fuel.
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post #3 of 5 (permalink) Old 06-17-2019, 05:13 PM Thread Starter
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Thanks for the reply!

Well, there are no silly questions when troubleshooting! I thought I was at TDC of the compression stroke but now that you ask, I can't help feeling like I need to double check that. Like I said, the pressure of the lifters on the valves was quite firm, and I was thinking at the time that it was quite counterintuitive that it would be tight rather than loose.

But yes, if I give it a squirt of starting fluid and a hard yank, it will pop a few times but not continue to run. The fuel I am using came from the same fill can that I routinely fill my lawnmower with, so is reasonably fresh.

I think I'll revisit my valve adjustment and report back.
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post #4 of 5 (permalink) Old 06-18-2019, 09:34 AM Thread Starter
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Definitely no silly questions. I had another look at the valve adjustment, and not only had I not set the valves at TDC on the compression stroke, but I didn't bother to rotate the crank a couple times and watch the valves, or I would have caught my own mistake. So I readjusted the valves, and the engine is now behaving as it had earlier. Pulls with a normal amount of force, will start up and run if I leave it mostly choked, but if I take the choke off, it dies. Watching the flames shooting out of the exhaust port, it is also interesting to see that as the mix gets leaner (taking the choke off), the flames do indeed increase. I haven't figured out why it works like this...

So I am a bit stumped. I suppose the next thing to do would be to pull the head and have a look at the valves and valve seats, but as high as the compression seemed to be when the valves were misadjusted, I find it hard to believe I am getting that much leakage from the exhaust valve.
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post #5 of 5 (permalink) Old 06-19-2019, 06:46 PM
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You may also have an intake gasket leak somewhere along the intake AFTER the carb that's what I would check
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