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AQ151 revs on starting from cold

M

Mikebr

Member
Hi from a new member
My gas AQ151 starts OK but I often rev out to nearly 4k before bringing it back to around 2k to warm up -its quite hard to get that initial rpm right. Am I likely to damage the engine with such a high rpm? Do I need to adjust the mixture to hold the revs at a lower rpm maybe. Thanks
 
Not the mixture... possible sloppy linkage/weak return spring.. When warmed up, what RPMs? And my usual questions... Was it always like this while you've owned it? ... or did this behavior just start recently?
 
sandkicker said:
Not the mixture... possible sloppy linkage/weak return spring.. When warmed up, what RPMs? And my usual questions... Was it always like this while you've owned it? ... or did this behavior just start recently?
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Thanks sandkicker - The engine has just been rebuilt and I have been fiddling with things a bit so although I have had the boat for a few years I am still learning. I suspect you are right about the linkage - its hard to find the right spot for starting and there seems to be too much tension on the throttle lever for it to hold easily.
Worried about damage from excessive rpm when cold more than anything as the engine starts and runs OK when warm and idles at aroung 900/1000 rpm. I thought maybe a richer fuel mix may make for easier starting without the need to keep the revs up?
 
Are you setting the points with a dwell meter? Get as close to 62 degrees dwell with the point gap and then confirm 6 degrees BTDC base timing at 900rpms. There are two types of the PA1 idle air settings depending on the needle The small needle head is preset at 9 1/2 turns out from lightly seated and the large needle is 2 turns out preset. Make sure both carbs open exactly the same time then back off the idle speed screw so it is not touching the body then screw it in until it touches and then add another 1 1/2 turns. Keep the throttle cable disconnected until you get the carbs dialed in then adjust the cable to fit with the control locked in neutral.
 
I had an AQ110 with twin Zenith downdrafts in my first boat. Had a manual choke on the front carb, but it was a florida built boat and they never hooked anything up to the mechanism. Engine was a real pain to start early and late season here in NJ. I eventually installed a manual choke cable. My current engine is chokeless but it has an "enrichment" circuit that does the same thing and it works better than the old heater style chokes. Depending on year you might have an enrichment system. I'm not familiar with that setup so perhaps someone who is will chime in.
 
kimcrwbr1 said:
Are you setting the points with a dwell meter? Get as close to 62 degrees dwell with the point gap and then confirm 6 degrees BTDC base timing at 900rpms. There are two types of the PA1 idle air settings depending on the needle The small needle head is preset at 9 1/2 turns out from lightly seated and the large needle is 2 turns out preset. Make sure both carbs open exactly the same time then back off the idle speed screw so it is not touching the body then screw it in until it touches and then add another 1 1/2 turns. Keep the throttle cable disconnected until you get the carbs dialed in then adjust the cable to fit with the control locked in neutral.
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Thanks Kim - blowing a gale here in West Australia - will go through the timing and carb tuning when I can as you suggest. I have the older two turns out Solex mixture screw and the engine now has electronic ignition which helps. I suspect my base time may be out tho. and I need to adjust the linkages. Will post how I go:)
 
sandkicker said:
I had an AQ110 with twin Zenith downdrafts in my first boat. Had a manual choke on the front carb, but it was a florida built boat and they never hooked anything up to the mechanism. Engine was a real pain to start early and late season here in NJ. I eventually installed a manual choke cable. My current engine is chokeless but it has an "enrichment" circuit that does the same thing and it works better than the old heater style chokes. Depending on year you might have an enrichment system. I'm not familiar with that setup so perhaps someone who is will chime in.[/QUOTE

Thanks Sandkicker. The only enrichment on my engine is from the accellerator pump which gives a few squirts into the throttle on starting - no choke is fitted and I have read the AQ gas Pentas are notoriously difficult to start when cold even if all the stars are aligned properly with engine tuning. Fortuneatly here in Australia it is warm more often than not (well it used to be before global cooling!) and its not so bad.
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Mikebr said:
no choke is fitted and I have read the AQ gas Pentas are notoriously difficult to start when cold even if all the stars are aligned properly with engine tuning. Fortuneatly here in Australia it is warm more often than not (well it used to be before global cooling!) and its not so bad.
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Very true... I'm on the "Jersey Shore" and when I had that boat, I used to try to get out for the "Winter Flounder" season, which back then started mid March. Temps barely above 40 F were not uncommon. Not fun... Where we are, we've had snow accumulations some years the first week of April.

And... yesterday it was 64F here... today we are forecasted to get up to 6 inches of snow.
 
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sandkicker said:
Very true... I'm on the "Jersey Shore" and when I had that boat, I used to try to get out for the "Winter Flounder" season, which back then started mid March. Temps barely above 40 F were not uncommon. Not fun... Where we are, we've had snow accumulations some years the first week of April.

And... yesterday it was 64F here... today we are forecasted to get up to 6 inches of snow.
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bit off topic - coldest day on record here yesterday (and not much different today) in mid-summer Perth on the West Coast of Australia at 17C - we often get 40C+ at this time of the year and our averages are in the 30Cs. Rain, cooler weather - our farmers love it and boating is often too hot in summer here. Global cooling - I'm all for it! Our print and other media can't cope tho' after many years of global warming drama.:D
 
Just wanted to say a belated thanks Kim - advice v helpfull. Starts OK now but suspect my tacho is a bit wobbly at the 800-900 mark but it sounds good at idle and runs OK at about 2500rpm which is flat out for me :)
 
Some tach needles are a bit "wobbly" @ low RPMs on 4 bangers... only 2 ignition pulses per revolution on a 4 cyl vs 4 pulses per revolution on a V8.s

Re: 2500 rpm as "flat out for me".... Is this by choice/useage? Or is engine limited to this @ WOT?
 
sandkicker said:
Some tach needles are a bit "wobbly" @ low RPMs on 4 bangers... only 2 ignition pulses per revolution on a 4 cyl vs 4 pulses per revolution on a V8.s

Re: 2500 rpm as "flat out for me".... Is this by choice/useage? Or is engine limited to this @ WOT?
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Its the original tach from the late 70s I think but the engine seems to be idling happily which is good enough for me. At 2500 rpm my old and fairly heavy timber 25fter gets along fine anywhere between 7-9knots (no satnav quite often) and just feels right in terms of hull speed and noise and strain on the motor and at my age I'm trying to slow things down anyway! Must have a fairly bit prop? Those guages sound interesting - my temp. oil and amps are a bit wobbly too so will look into an upgrade. Is it all a straight swap with the senders?
 
Thanks Kim - always something new to put in. Did put in an "Engine Watchdog" - digital readout- wired to a cheap strobe -also has a high pitched alarm that I often cant hear - that has a sender on the bolt attaching the thermostat housing. I can see this from all over the boat and its always interesting :) - Will post temps around the engine with my infrared gun as the engine fires up when I find it (thats if someone hasn't nicked it)
 
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Mikebr said:
Hi from a new member
My gas AQ151 starts OK but I often rev out to nearly 4k before bringing it back to around 2k to warm up-its quite hard to get that initial rpm right.
Not good!

Am I likely to damage the engine with such a high rpm?
The high RPM is not the issue........ it's the high RPM upon initial start-up while not yet warmed up, and the potential for slipping into gear while at high RPM!

Do I need to adjust the mixture to hold the revs at a lower rpm maybe?
The only external mixture adjustments will be for low speed fuel/air metering.
However, you will have idle "stop" adjustments that must be correct.
However #2........ if it idles correctly once warmed up, these adjustments are likely OK.

Vacuum leaks (around the carburetor base or intake manifold mating surfaces) will cause higher than normal low speed RPM.
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I agree with Kim....... set your ignition point dwell by using a dwell meter. Setting point "gap" is an estimately ONLY of correct dwell angle.

Make sure that when you place the throttle control lever into idle position, that the cable is not holding the throttle plates open at all.
In fact, make the adjustment so that if anything, the cable sets the throttle plates more closed than need be.
You can make a final adjustment later on.

Also look closely at the distributor's flyweight system. These systems are somewhat prone to becoming rusted/corroded and will not provide a consistant advance curve.
Excessive ignition advance may also cause higher than normal engine speeds...... but 4,000 RPM ????? ....... that is rather odd!

Any chance of a vacuum leak at/neat the carburetor base, or at/near the intake manifold mating surfaces?
Is the camshaft indexed correctly?
What ignition advance are you seeing at idle speed?
What does the progressive advance look like? (i.e., plot out the curve and post it)
What is the total advance and at what RPM?

These are a few things that you'll want to look into!


.

 
And Bob....... it's RPM, not RPMs! Revolutions is already plural, and Minute remains singular! :D :)


(oh boy........ I'd better duck!) ;)

.
 
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