Air fuel ratio for direct drive

[kwanjangnihm]

A spark plug magnifier is an inexpensive tool to have at the track. They are lighted and have a typical 10x magnification that allows you to look closely for the slightest bit of coloring on the insulator and to easily inspect heat patterns.

https://www.enginelabs.com/engine-tech/ignition-electronics-efi/yes-spark-plug-tuning-critical-carb-cam-selection/

 

[keys2pines]

A spark plug magnifier is an inexpensive tool to have at the track. They are lighted and have a typical 10x magnification that allows you to look closely for the slightest bit of coloring on the insulator and to easily inspect heat patterns.

https://www.enginelabs.com/engine-tech/ignition-electronics-efi/yes-spark-plug-tuning-critical-carb-cam-selection/

Got it! Thanks!

 

[OneBFC]

Heat range appears good. Can tell by the color change on the ground strap. Once you get used to reading plugs you will gain a lot of confidence in tuning your engine.

I think you are on the right track.

 

[CarMotorBarge]

A spark plug magnifier is an inexpensive tool to have at the track. They are lighted and have a typical 10x magnification that allows you to look closely for the slightest bit of coloring on the insulator and to easily inspect heat patterns.

https://www.enginelabs.com/engine-tech/ignition-electronics-efi/yes-spark-plug-tuning-critical-carb-cam-selection/

Got it! Thanks!

http://www.jetsrus.com/FAQs/FAQ_spark_plugs.htm

Here is another link. You need to look at the picture that shows where you read different parts on the insulator to determine rich/lean at idle, mid range, and WOT.

You need a magnify glass to look inside the threads to read the rich/lean on the insulator for WOT or you need to chop a couple of plugs. The white insulator in the pictures above gives you no info about rich/lean at WOT.

 

[keys2pines]

Heat range appears good. Can tell by the color change on the ground strap. Once you get used to reading plugs you will gain a lot of confidence in tuning your engine.

I think you are on the right track.

Thanks! I was confident when I had my turbo camaro, airboat has me second guessing myself because of the low rpm. After doing more reading, the AFR at WOT is just way too lean because of the load on the engine. The AFR should be 12.3-12.8 or 13 max under full load, which at 3000rpm I'm at full load. I was emailing holley to see about tuning this carb, and basically I'm stuck to changing main jets only. The rear metering plate is not able to be changed, and can't be converted to a metering block. This carb was meant to be on a two-carb setup, not used alone. If I change the main jet, then I'm going to be richer all around, and my mpg is going to go down. I honestly think I'm going to convert to EFI and be done with it. I can play with the AFR instantly and see how the boat responds and I won't have to second guess myseslf.

http://www.jetsrus.com/FAQs/FAQ_spark_plugs.htm

Here is another link. You need to look at the picture that shows where you read different parts on the insulator to determine rich/lean at idle, mid range, and WOT.

You need a magnify glass to look inside the threads to read the rich/lean on the insulator for WOT or you need to chop a couple of plugs. The white insulator in the pictures above gives you no info about rich/lean at WOT.

Thanks, I ran across another similar article when I was reading. I'll still end up reading the plugs again, but I'm going to follow the wideband and see what happens.

 

[One Eyed Gator]

Can't you tune it for WOT and use a piece of Wire in the IFR ( old school trick) to lean it out at idle but will be a little fat at cruise.

Depending on the metering plate you can also drill and tap IFR and emulsion circuit for 6/32 brass blanks and drill them to the size you need.

Just some thoughts

 

[keys2pines]

Can't you tune it for WOT and use a piece of Wire in the IFR ( old school trick) to lean it out at idle but will be a little fat at cruise.

Depending on the metering plate you can also drill and tap IFR and emulsion circuit for 6/32 brass blanks and drill them to the size you need.

Just some thoughts

I was just looking around online about drilling the metering plate and I came across Holley secondary metering block conversion kit 34-6, which says it's for 4160 style carbs with side-hung floats, which is what this carb is. I just emailed the guy at Holley again, asking why this can't be used. He told me there was no conversion kit, or a different metering plate available. I was looking into EFI and it's going to cost an honest $1100 after you add the new fuel pump, lines, etc.

 

[John Fenner]

I have put those kits on many of those carbs.

 

[keys2pines]

I have put those kits on many of those carbs.

Yea, I don't think this guy knows what he's talking about. I ended up finding a quick fuel metering plate that has provisions for jets and comes with a modified float to clear the jets. It was on the Holley website. I emailed the tech back and he said "The 34-6 that you asked about will not work because it is a metering block conversion kit not a metering plate. However the quickfuel 34-2QFT will work on the carb, My mistake." I still think he's wrong because the point of a conversion kit is to get rid of the plate, but anyways I ordered the plate and I'll get more tuning done next week. Thanks again for all the help!

 

[Rich Andrews]

Or... get with Ed MAck or another carb expert do it right and preserve the motor!

 

[Krahammer]

You can't go wrong with Mr.Mack. He is the best carb guy there is.

 

[keys2pines]

Or... get with Ed MAck or another carb expert do it right and preserve the motor!

I hear you, but I put my own engine together at 18 years old. I'm not a newbie by any means, I've just never messed with carbs or the rpms a direct drive airboat runs. I have a wideband and a dyno (prop rpm), I'll get it right, if not, it's going EFI

 

[Rich Andrews]

Yup, and my buddy has been racing cars since he was 18 and thought he knew it all.... go ahead w that efi let us know how that works out

 

[keys2pines]

Yup, and my buddy has been racing cars since he was 18 and thought he knew it all.... go ahead w that efi let us know how that works out

No offense, but if I thought I "knew it all" I wouldn't be here asking questions. As for the EFI, there is a reason new cars don't come with carbs. I'm positive it would make more power and be more efficient with EFI and a coil-per cylinder system than the carb and distributor. Even the aircrafts are rated for more HP with fuel injection. :salute:

 

[SWAMPHUNTER45]

I would agree that EFI is going to be more efficient, the reason that I personally have not crossed over is two fold. First the system is only as good as the system, if that makes sense. It's sensor or sensors ability to read gasses and then transmit data to the ECU to read and adjust is the key. With this being a somewhat new product line to the after market and so many different variations, personally I am waiting for them to work through the process. The other concern is with the technology comes glitches or defects and a EFI failure in the field can not be quickly overcome. If my fuel pump or HEI fails we have a micro pump or module to limp us home. If that ECU or high pressure pump would fail then I don't think I could get home without assistance. Cost is prohibitive on carrying a spare ECU at this point and the systems are auto not marine. When you seal them and encase then heat becomes a concern. At least at this point in the development these are concerns.

I have heard that one of the higher dollar systems is now using 2 pumps and if the primary fails the smaller pump can limp you back. This is an example of the type of advancements that time and market demand will help with the products evolution. With Aircraft almost everything is redundant and that is a hard to beat concept. Until then I am going to run a slightly rich mixture and stay on a carburetor. I would recommend that until you cross over you work to accomplish the same and rely more on reading your plugs and tailpipes. A dark ashen slate grey in the pipes and golden brown on the plugs is a happy and safe engine.

 

[hdsadey]

Swamp they do make a "marine grade" system from FAST EFI. More geared towards a Mercruiser setup.

I been running a Fitech for 2 years with little problem. I now carry a spare pump since finding aluminum shavings in the fuel filter causing the engine to starve for fuel. Thought I had a dying pump. So now I have a spare. Airboats are more auto than marine IMO. They are sealed against the elements in an engine compartment. They surely don't get the heat of being under a hood in an airboat. I don't think I will ever go back.

 

[SWAMPHUNTER45]

I have read about guys who put ECU and ECM in sealed boxes and the self generated heat bakes them. That was my concern. Some will adapt a PC fan but often times it will fail in the marine environment as it was made to be in a controlled climate.
Glad your finding success with it. I'm still old school for now but Mr Branch has put an EFI 520 inch Caddy out on the street. He likes them but I'm not convinced they are built well enough for my application at this time.

 

[hdsadey]

The ecu is built into the throttle body on the Fitech. The hand held controller is clamped in like a cell phone holder. Don't have to have it plugged in for it to operate.

I've had alot of experience with them. In the hotrod world everyone has seen to forgotten how to treat carbs in this day of fuel injected everything driving. Garbage ethanol fuel is not kind to toys that sit for extended periods. It was easier to sell them the stand alone systems so they could enjoy themselves instead of calling me complaining their hotrod won't run right lol. :lol:

 

[keys2pines]

Welp, I changed the jets that were in there (62 mains and secondary metering plate 64) all the way up to 70 mains and 74 secondary, 74 was the highest I had. No change in AFR, or max prop speed. The power valve went bad while I was testing and my AFR went straight to 10.0. I verified the power valve went bad by turning the idle mixture screws all the way in and the engine was still running. I went and got a new power valve, and I'm back to 13.6. Seems like there is a fuel restriction somewhere in the carb, right?

 

[One Eyed Gator]

Have you checked the float drop not float level? If the needle and seat are to far down then the float will never drop far enough to allow the correct amount fuel in. I had it happen when my fuel pressure regulator went bad and spiked the pressure to my carb.

Just a possibility