Winter fixes

All things general in here
The Spook
Posts: 198
Joined: 20 Jun 2009, 15:49

Re: Winter fixes

Postby The Spook » 27 Aug 2015, 22:34

Hi all

I have continued to work on The Spook over the last few weeks and have completed the following:

1/ Installed a proper marine heat exchanger. We'll see how it works.

2/ Installed a taller set of gears in the gearbox, now 32% step up.

3/ Pulled the carby off and gave it a complete inspection. Researched jet sizes and have come to the conclusion that the jet sizes that came in the 870 are way too big. In the 750 I was only running 79 pri/80 sec size main jets without power valves. The jet sizes that came in the 870 were size 80 with a power valve front and rear which is equivalent to 87 size jets when the power valves open (when a power valve opens it provides approximately the equivalent of seven jet sizes of fuel to the carby throats), there is no way that this engine will burn that amount of fuel. The jet that was clogged wasn't helping but the other three throats were so rich that the engine was basically drowning in fuel. I have reduced the main jet sizes to 75's which gives an approximate equivalent main jet size of 82 when you add the enrichment of the power valve.

4/ I have installed a wide band oxygen sensor and air/fuel ratio gauge as well as an EGT pyrometer temperature gauge so that I can get a handle on the tune of the carburetor.

Bob

Reklaw
Posts: 199
Joined: 17 Nov 2014, 14:35

Re: Winter fixes

Postby Reklaw » 28 Aug 2015, 07:20

Hi Bob,
Is that why you had black stains on the deck, near the exhaust, running too rich?
BobW

The Spook
Posts: 198
Joined: 20 Jun 2009, 15:49

Re: Winter fixes

Postby The Spook » 29 Aug 2015, 04:54

Bob

I started out in this new boat using 98 octane from the bowser with an octane booster as the comp ratio of the engine is 11.5 to 1, but the octane booster makes it burn very black. Even when using the 750 carb which was jetted very close to perfect it left those black stains on the deck. I have since sourced a 102+ octane fuel from Power Plus Fuels which is good enough to run in the engine without octane booster and I have been mixing the last of the octane booster fuel with that to get rid of it. When I get down to the new fuel by itself and get the jet sizes down I have an expectation that it will be a lot cleaner burn.

Originally I used to run this engine on avgas which is a very clean fuel, but it is getting harder and harder to get so I decided to go with unleaded with the new boat. Unleaded appears to be a bit more difficult to deal with and changing carbs hasn't helped.

Bob

The Spook
Posts: 198
Joined: 20 Jun 2009, 15:49

Re: Winter fixes

Postby The Spook » 26 Sep 2015, 04:12

Here's the latest.

After much gnashing of teeth and tearing my hair out I now have the engine idling at 1000 rpm. The 870 carb comes with a power valve in the primary (45 power valve) and secondary (35 power valve) metering blocks. Although these power valves are of lower values than other Holley carbs they were still to big to work properly with this engine and were flopping open at low revs and pouring fuel into the engine stopping it from idling. I have now gone down to a 35 power valve in the front metering block and a 25 power valve in the secondary metering block, this has cured the raw fuel problem at low revs which means that the engine can run on the carby's idle circuits, a little trickery with a 2.5 mm drill through the primary butterflies to get the relationship of the butterflies to the idle slots right, some playing with the idle mixtures to get them right (used a Gunsons colour plug) and hallelujah it idles like a bought one. All of this has been done with the prop shaft disconnected. Before Neranderah I will reconnect the prop shaft.

I have also found out why I can't get the air/fuel ratio gauge to give me a reading. The exhaust is supposed to have a seal welded into the gap that exists between the four pipes where the collector welds onto the pipes. This gap between the pipes is a four cornered star shape and the exhaust pipe maker is supposed to make a piece of metal that matches and weld that into the gap so that the collector and pipe joint is sealed. They have conveniently chosen to not do that and the exhaust system is sucking air into the collector via that air gap. Hence the air/fuel ratio gauge reads a full lean condition at all times. The good news is that the EGT gauge and pyrometer works great.

The new heat exchanger works well on the trailer with the hose connected to it. I had the engine running on the trailer for over an hour while I warmed it up and went through the idle tuning procedure and it sat at a constant 170 degrees F. Next step is to test it on the water under load and revs.

Bob

Doc
Posts: 256
Joined: 18 Jul 2009, 07:28

Re: Winter fixes

Postby Doc » 26 Sep 2015, 07:58

Hi Bob,
Holley 4150 850cmf carby, you will find all butterfies are open on idle .Linkage which connects front and back can be flatten to close rear on idle or you buy a adjustable one. The biggest problem i had was idling the boat on water for a long time , plugs would fowl up. These carbies were made to dump a heap of fuel for take in a car.
Cheers Leigh.

The Spook
Posts: 198
Joined: 20 Jun 2009, 15:49

Re: Winter fixes

Postby The Spook » 26 Sep 2015, 10:35

Hi Doc

The carby is a vacuum secondary as I prefer them for the application I have it in (vintage rear seat hydro) because the secondaries don't open as aggressively as they do in a mechanical secondary under initial acceleration away from the bank and up onto the plane.

The idle setup and tuning is purely academic as the gearbox doesn't have a dog clutch and cannot be disengaged and the engine won't idle under load in the water. I just like to get it to idle without the prop shaft connected so that I know the base tune of the carby is right. With the previous 750 cfm carby I had actually removed the power valve (it only had one in the primaries) from the carby altogether. When running the boat the engine rpm never gets below 3000 rpm which is above the effective rpm level that a power valve is designed to work. I still have not ruled out the possibility of taking both of the power valves out of this carby and just running it on the main jets.

The next stage is to get the top end jetting sorted out.

For those who may not know, a power valve in a Holley carb is designed so that under mild load and rpm situations (off idle to 2500 or so) it reduces the engines fuel input to give fuel economy, when you put your foot on the floor (Wide Open Throttle) it opens and adds fuel to suit the full power fuel requirements of the engine, hence the term power valve. When you tune the engine for wide open throttle (WOT) you need to get the main jets and the power valve to provide the right amount of fuel to get the
WOT mixture right when the engine is running in the upper end of its rpm range. If you take the power valves out you then need to re jet the metering blocks (read: up the main jet sizes) to make up for the fuel that the power valve (approximately equal to seven Jet sizes) would add to the engine at WOT. For example a drag car would not require power valves as the engine would only ever operate under WOT conditions and the jets would be set accordingly. In the case of my hydro when out on the course the rpm range is from 3500 to 7500 rpm which is also above the need for power valves.

When tuning Holley carbs to idle especially in modified engines a common mistake that people make is not to change the value of the power valve to suit the vacuum levels of the modified engine. Holley provides a range of power valves and it is common that a standard carb is fitted with a 65 power valve. This is fine if the engine is standard and producing 12 to 13 inches of vacuum at idle. The more highly modified the engine is the less vacuum the engine will have at idle. It is this lack of vacuum at idle that causes a high value power valve to flop open at idle, this causes raw fuel to be introduced to the engine at idle through the power valve which will cause rough idle (rich and untunable) and plug fouling. My 870 comes with a 45 power valve in the primaries and this still wasn't low enough to suit my engine, I had to go even further down in primary power valve to a 35 to eliminate the problem of the power valve flopping open at idle. I have also gone down in the secondary power valve to 25 to maintain the Holley power valve difference between the primary and secondary throats.

Bob

The Spook
Posts: 198
Joined: 20 Jun 2009, 15:49

Re: Winter fixes

Postby The Spook » 18 Oct 2015, 04:32

Hi all

Just some info about the EGT pyrometer and temp gauge. It has been a problem to find out what temperatures I should be looking for at WOT and maximum power RPM.

I now think that I am onto it. I found a reference to an EGT gauge in a document about drag racing on the internet. What the document said in a nutshell was that if you have a EGT Gauge and pyrometer installed in your exhaust you should hold your foot at WOT until you are out of the quarter and then look at the EGT gauge, if it has reached 1350 degrees F then the jetting is too lean and you should jet back up at least one jet size, possibly two. Information I have from a drag racing fan is that the drag racing boys like to get them pretty lean as this helps their terminal velocity.

Since then I have also discovered a hydro racer who has in the past used an EGT pyrometer and gauge to tune his hydro engine. He has advised that he used to run his jetting to achieve a EGT up to about 1300 degrees F.

Armed with this information I am looking forward to Naranderah and an opportunity to see how the old girl goes.

Bob

User avatar
bootlegger
Posts: 1472
Joined: 09 Mar 2009, 20:18

Re: Winter fixes

Postby bootlegger » 18 Oct 2015, 08:56

Good luck with the tuning Bob. Just remember we are just muckng around at nerranderra.

The Spook
Posts: 198
Joined: 20 Jun 2009, 15:49

Re: Winter fixes

Postby The Spook » 18 Oct 2015, 23:56

Dave

That's what I intend to do is muck around with the tune of the engine at Naranderah. I come from a technical background so I'm trying to use technology to achieve said tune and getting information out of so called experts is like getting blood out of a stone, so I have to research it and figure it all out myself.

I will probably only require a couple of sessions on the water each day to get a handle on where its at. Seeing that the engine will get through a 40 liter tank of fuel in about 15 minutes or so, that's at most about 30 minutes on the water per day each day. I have no intention of commandeering the lake if that's what people are thinking.

Bob

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WoodRay
Posts: 1006
Joined: 12 Feb 2014, 15:19

Re: Winter fixes

Postby WoodRay » 19 Oct 2015, 08:10

Hi Bob,

I'm watching this post with much interest. I am of the same background and am dealing with similar issues with my boat regarding mixture control. I've been trying to work a way to run an oxygen sensor with regards to the wet exhaust which in my case is not possible unless I risk doing runs with the manifold water flow turned off. Heat and wood, we all know the result.
I read with interest the Gunson Colour Tune. I never new they existed. Excited this could be a possibility but realistically no good for persistent full throttle runs.
As my current engine will be replaced with the original grey (worked), I've worked out that I can reverse the headers by bolting them on with the engine pipe flanges exiting vertical. With that I could fit dry engine pipes and O2 sensor. Noise will be the only short term issue. Hopefully this will sort it.
I have noted though in your writings the influence of air/leaks in the exhaust causing lean mixture readings.
Good luck with your efforts.


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