WOT woes part II - the whole story - UPDATE: Manifold vac test done

[Don S]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Have you done the vacuum tests (under load)?

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Nope did the aux tank run before work; didn't have time for the manifold vac test. I can just use my compound meter that I was using for the fuel test, right? ...and when haulnazz says "one of the ports on the intake manifold"... what is it I'm looking for?

Of the conditions shown in your attachment, what should I be looking for that would contribute to low WOT? ....or is the answer "all"?

Thanks!

 

[Don S]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

You should find a pipe plug on the back of the intake manifold (aft of the carb). Remove it and get a fitting with a hose barb for your size hose. Then do a run and see what you get. Compare it to the chart and see what's wrong.

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Ok... i can figure it out.... Let me ask 2 questions:

1. Based on what you've seen so far do you suspect that the vac test is going to reveal something or is the test more of a "gotta check it to make sure" thing?

2. Assuming vac test is ok, whats next?

3. I can extend the hose on the vac gauge so i csn read it grom the console, right? Its a very tiny hose, so im thinking that it will easily be able to conveythe vac over a 10' length no problem.

 

[haulnazz15]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

1. It is a "gotta check it" thing, but there are a lot of things that can be seen based off of the readings from the vac gauge.

3. You could probably extend it that far, but there's really no need to. Just extend it far enough to read while you're standing at the engine. No reason to be at the controls while you're sitting at idle speed.

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Based on Don's attachment, I was thinking I would need to also

1. goose it,
2. slowly bring it up to WOT

Not necessary? Just idle?

 

[Failproof]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Gauge reading and needle actions are what you are looking for. Take notes as to the reading and what the needle is doing at various rpms, in particular atsafe idle and the rpm at which the problem you are having occurs. A vacuum gauge when used properly can help show bad valves, incorrect timing, lean or rich running, vacuum leaks, and overall engine health. As noted before, you need to note needle action. ( steady, bouncing, fluctuating, erractic, etc).

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

OK failproof.... that was the reason I wanted to extend the gauge tube to the controls... so that I could do all that while safely keeping my eye out.

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Can I use the port that's in front of the carb, port side on the #1 runner? See picture:


That plug looks like it's 3/8"... anyone know for sure?

 

[haulnazz15]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Yes, you can use that as long as it's a manifold air port and not a coolant passage. Should be evident when you pull the plug out to install the adapter. You can goose the throttle by simply moving the throttle arm on the carb, no need to be at the helm to do it. You want to see a brief drop in vacuum upon acceleration, but then it should restabilize fairly quickly.

You do not want to go to WOT. There's no reason to ever go WOT (or even above 3K rpms) when in neutral. It doesn't prove anything and can overspeed the engine.

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

ok, I think I'm getting two stories mixed.

haul, you're talking about doing this in neutral, but Don S, in #21, indicated this should be done under load (presumably because I only see the problem under load). I'll goose it in neutral, but do slow accel (1/2 throttle), rapid accel (full throttle), reading at my bogging point, and WOT all with it under load.

 

[haulnazz15]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

The only part I could see doing under load would be an in-water WOT run. But if you have proper vacuum at idle, and it performs correctly upon accelerating the throttle (in neutral), it shouldn't make much difference when under load. However, if there is an anomaly that only shows up at high rpm/high load situations, it would be worth it to check.

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

Youtube video of manifold vac.

Under way: http://youtube.com/watch?v=sBcEF6pSvyA
at idle in neutral: http://youtube.com/watch?v=JjFxjJ4qF08

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

So, generally running about 14" to 15" at idle and a little jumpy. Running up to the bog point, steady needle, steadily declining to 0" at the bog at 2500 rpm. This occurs at about 1/2 to 2/3 throttle. Pushing up to WOT, bog maintains, and rpm lowers a little.

When goosing the throttle, quickly drops to 0" when done hard, then recovers to about 25" and then comes back to about 15". Multiple gooses resulted in backfire through carb.

SO, based on Don S's attachment, my totally inexperienced conclusion is... that I have no freakin' idea. Maybe restricted exhaust combined with bad valves?

 

[Don S]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

And you still haven't pulled the drive and checked the exhaust passages for restrictions? Why not?

 

[dkellogg3]

Re: WOT woes part II - the whole story

Re: WOT woes part II - the whole story

And you still haven't pulled the drive and checked the exhaust passages for restrictions? Why not?

Well... mostly because this is my first time getting this deep into engine troubleshooting, and I've not yet developed too much confidence in my diagnostic skills.

Based on those vids, do you come to a similar conclusion.?

 

[dkellogg3]

Re: WOT woes part II - the whole story - UPDATE: Manifold vac test done

SOLVED... see first post. Mixed up #3 and #5 plug wires.

 

[pcweber]

Re: WOT woes part II - the whole story - UPDATE: Manifold vac test done

Did this engine with the wires mixed start and idle fine/ smooth?

 

[dkellogg3]

Re: WOT woes part II - the whole story - UPDATE: Manifold vac test done

It sure did. Was able to time it and everything.

 

[Don S]

Re: WOT woes part II - the whole story - UPDATE: Manifold vac test done

I can't count the times that a customer told me his engine sounded fine, only problem is, it didn't.