Johnson QD fuel consumption

[Fastwin18]

So I took my Johnson QD19 out for the second time yesterday. It runs very smooth, both at low speed and WOT, but it seems to be consuming heaps of fuel. I’ve been cruising around for 2 hours at mostly 4 knots (I’d guess appr. 20% throttle). Occasionaly I would increase speed for short bursts. The total fuel consumption was just north of  2 gallon. As far as my understanding goes 1 gallon/hour would match WOT, not cruising at very low speed. I would have expected half of that. I could not find any obvious fuel leaks. The motor was rebuild last year, with new rings, head gasket, carb rebuild etc. Compression on both cylinders is on the lower end, 83 and 85 lbs, but I’m hoping this will improve somewhat over time when the rings have set. Any ideas what could be causing this?

[Fastwin18]

On this video you can hear the rpm.

[Fastwin18]

Strange, the .mp4 video is less than 2.4 MB so it should be supported but I cannot get it to upload.

[crosbyman]

2 strokes are  not fuel  efficient &  dirty spitting out 20- 30 % of the incoming fuel-oil out the exhaust .  Other tan tweaking the carb I doubt  you can do much more.

I found trolling with my 9.5 turtle to be a bit much on fuel after a full day.  I switched to a 4hp Merc. for trolling

 

 

Joining AOMCI has priviledges 🙂

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Fastwin18

[billw]

I have to say my ’55 Fastwin is an absolute HOG on gas, compared to my ’56 FD, which is almost the same motor and had the same amount of love given to it, as the Fastwin. I would like to know what the difference is, too. It’s not like I don’t know how to set the mixture screws…

Long live American manufacturing!

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Fastwin18

[Fastwin18]

Nice setup there Crosby man.

I did not expect a gallon an hour for a ten horse motor at such low speeds. If you’re saying it is normal then it just is what it is.

[jeff-register]

Yes nice boat!!! To give you a compairson my friend has a 1957 Johnson 35hp on a small 14 foot old runabout. I was running a 1978 Evinrude 85hp 15 foot tri hull, heavyer boat.

I used much less fuel than Steve did? Better design I guess. My Mercury KG7 used the same fuel consumption as my KF7 both 10hp. The KG7 had twice the reeds too, go figure?

When you reringed did you check for cylinder wall taper? They wear like an ice cream cone, guessing!

When I was mini bike age we would raise the compression by sanding the head using modeling clay on the top of the piston to check clearances. When the clay was thin time to quit sanding! Crude but it was functional. They were lawn mower engines until we found West Bend or Mac go cart 2 stroke motors. Then we went to Honda 305 motors with a 4 speed trans on a go cart. Got pulled over once, no ticket, he just wanted to know what we were running.

P.S. replaced the brake petal for a shift petal. Who needed brakes anyway!! Just downshift to stop!

[Fastwin18]

Hi Jeff,

I did not check for cylinder or piston wear. For one I don’t have the proper tools, and secondly no one over here is willing to bore the cylinders to fit new oversized pistons. So new rings was the best I could do, and hope for the best.

[fleetwin]

Well, I think plenty of unburned fuel is lost overboard through the crankcase drains when run at low speeds on the older engines.  I always seen a “sheen” on the water when I run my old 10hps.

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Fastwin18

[Fastwin18]

O yes, that definitely is the case and did not surprise me. What did surprise me was how much fuel seems to be going overboard this way.

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