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View Full Version : Gas and Oil (mileage and leak)



printjunky
12-03-2010, 12:06 PM
I know this has been addressed plenty before, and I went back to re-read some of the related posts ... But because "oil" and "gas" were removed from my search terms (words too short - does anyone else thinks this is kooky? Should just filter common "the" and "a" type words) ... anyway, I could not get good search results.

We're talking about: 74 SIII, 2.25 petrol, no mods, no overdrive, "fixed" Zenith carb, on 16s (7.5x16s or something).

I appear to be getting unexpectedly bad gas mileage (in the 7mpg range). My speedo's not hooked up, but I did a little fill/refill/google mapped about 30 miles of driving to get mileage, and did the calculation (about 4.4 gallons for that 30 miles (which was about 50/50 highway/town)). I understand there might be some flaws in google's mileage calculation and one fill/refill is probably not an adequate sample, but it still seems pretty low. (confirming a suspicion) It is probably relevant that I am getting carbon-fouled plugs after 10 or so hours of driving - and I'm still messing with the idle/idle mix adjustments, but if it's not running rich at idle, it means it's probably a non-adjustable jet problem or a more general vacuum or internal carb problem. I will be putting a vacuum gauge on it this weekend, see if I can find out more. But what does everyone get from their stock 2.25?

(Again, I know this is also a repetitive question - but stupid search fail ....)

And does anyone think something like 2 or 3 tablespoons of oil left wherever I stop is excessive? I haven't had the thing on the road for even a few weeks, so I haven't done any kind of long-range calculation, but if I had to guess I'd say half a quart a week. My previous SIII (a 73 2.25 I owned in the late 80s/early 90s) barely leaked anything (until the rear main blew on the way from Owl's Head back to Orono), so that's not any kind of normal frame of reference! A non-leaking Rover? Freaky.

gudjeon
12-03-2010, 01:16 PM
Check that the Zenith float level is spot on or about a mm under. If this runs rich, it will guzzle like a pig. Consumption of gasoline like that will dilute the oil and cannot lead to a correct determination of oil use. Mine was at 10mpg and cause gas in the oil and made it stink and thinner. I get around 22 US gal with 7:1, Zenithed engine at 60mph no overdrive. Took some tuning to get there.:thumb-up:

printjunky
12-03-2010, 07:00 PM
22? MPG? Wow! Anything approaching 20 would be great! (or how about just better than 7!

I have the float adjusted down below spec a touch already ... I guess I could try getting it a bit lower. Not much harm if it's on the lean side in the short term.

Because the carb rebuild got stopped mid-task and picked up weeks later, I've always wondered if everything was 100% with that. Also the "proline" kit looked somewhat more janky than I would have liked, though not having seen an oem kit, I can't compare. I do know switching back to the idle mix adjuster that was in the carb (as opposed to the one that came with the kit) made a huge difference. The profile of the "cone" end was way different. I've said it before (recently), the carb might need another rebuild using the good kit (though I got scant corroboration from the brethren here on the actual, specific differences between the kits).

LaneRover
12-03-2010, 09:12 PM
I get about 15 in my 88, got 16 or 17 in my 109 P-up with a Rochester

and briefly got 18 in my 109 SW with a Solex before it dropped to 11 (wish I checked the head gasket then of course). I have since fixed the head and have not driven it enough to determine the new gas mileage.

Tim Smith
12-04-2010, 11:58 AM
I had an SU which was thirsty at about 10 mpg. Running a Weber single barrel with tires that are way over pressure and can squeeze about 18 mpg out of it. If I had road tires instead of off road tires, I wonder what the difference would be.

LaneRover
12-04-2010, 12:22 PM
I had an SU which was thirsty at about 10 mpg. Running a Weber single barrel with tires that are way over pressure and can squeeze about 18 mpg out of it. If I had road tires instead of off road tires, I wonder what the difference would be.

road tires pfffft

Tim Smith
12-04-2010, 12:29 PM
road tires pfffft
You're right. I'm not thinking hard enough. Maybe if I put some bicycle tires on, I could get the rolling resistance down to that of maybe... a bicycle?

Okay. Maybe two bicycles. :D

LaneRover
12-04-2010, 01:26 PM
You're right. I'm not thinking hard enough. Maybe if I put some bicycle tires on, I could get the rolling resistance down to that of maybe... a bicycle?

Okay. Maybe two bicycles. :D

With a fat guy riding the bike (not you, the weight of the truck)

And a winch to help him up hills

Tim Smith
12-04-2010, 01:37 PM
This sounds like a hypermiling set up for sure. What could possibly go wrong!
;)