10mpg with dual solexes...how is this even possible?!

[guitarman63mm]

I started a (hopefully) long road trip last week, and I'm getting really, really dismal mileage, and I'm hoping to figure out what I can do to fix it (buying new carbs or going to FI is, at the moment, probably not going to be an option, unless I can find a known good system on the way.) When I logged my first all-highway miles last week, I got 16.4, then 13.46, and then 9.16. From watching my gas gauge, it appears it's on track to get 10-11 on my next fill-up. My odometer is accurate and it isn't skipping, according to my GPS.

-Partially rebuilt 1700 out of a 914. I lowered the static CR (it still has domed pistons) to around 8.2 or 8.7, I can't find my notes. I was warned that fiddling with my deck (0.060" iirc) might make this a bitch to tune. I reused the cam because it appeared to be fine (and the 1.7L had a much more low-torque cam than the later 914s, so it seems to work.) I'm running a 205 series distributor (from the 914), timed at 27-28˚ BTDC at full advance, hoses off. I'm considering getting a Pertronix SVDA and trying that instead, but I'm not sure an SVDA will work correctly.

-I rebuilt a pair of dual solexes, and put in PTFE bushings. I set them up per Bentley/Colin's instructions. They work fine, no leaks, smooth actuation. I did not change out the jets from whatever was in there stock. I have the accelerator pumps set up to engage immediately with the throttle. I have not measured how many CCs they pump out. I have an electric Carter pump going to a Holley regulator, so I don't think my bowls are overfilling. That being said, I generally have to hold the throttle open and crank for a few seconds to get the engine to start, so I'm not ruling this out yet. For whatever reason, the base idle adjustment per the Bentley was not working for me, so I had to lean out the lower mix screws and richen the central idling circuit to get it to agree with me. This may also be the source of my problem.

-This is a hightop, with a solar panel installed, and lots of tools and parts loaded into my bus - my curb weight (per a weigh station) is about ~4050lbs, without me in it. I suspect this is what's really killing my mileage, but I'm not certain. Tires are inflated to 37 rear, ~35 front. I was running my tires lower in the front, but with the extra load, I pumped them up.

-Lastly, the exhaust smells rich to me, but I don't have a exhaust gas analyzer to double-check. I'm planning to check the plugs tomorrow, but with only ~400 miles on the engine, I'm not sure it can tell me much. I'm going to check for burnt points as well, but I doubt they're damaged.

-CHTs around town are between 300ish at an idle, to 350 at around 45mph, and it can get up to 375 if I'm going 55-60 or so on a hot day, but I try to keep things around 50-55 max. It's definitely not running hot.

I tried to anticipate any questions, I know it looks like a brain dump in here...thanks for any assistance! Given that this trip will wind up being about 2500 to 3000 miles round-trip, the difference between 10 and 20 mpg is somewhat significant, at around $450...I'd rather spend that on my bus, rather than fuel!
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Jimmy

- 1974 Safaré Custom Camper. 091 trans + Dual Weber 34 ICTs + Pertronix SVDA + 1.7L 914 T4 engine.

[busdaddy]

How are you calculating miles travelled?, using the odometer or actual point A to B distances?
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[guitarman63mm]

The odometer isn't perfectly accurate - my speedo says I'm going 55 while my GPS says I'm going 50 - but it isn't skipping, from what I can tell. Adjusting for this would actually make the mileage worse, to boot.

I checked my log, and on my first highway miles, the odometer said the two gas stations were 147 miles apart. Google maps says that they are 145 miles apart. The discrepancy could be the odometer, or just a rounding error on my part, but it's certainly not enough to get it that far out of whack.

My owner's manual from the Safaré company claims that it gets 18mpg, so that's what I'm shooting for.
_________________
Jimmy

- 1974 Safaré Custom Camper. 091 trans + Dual Weber 34 ICTs + Pertronix SVDA + 1.7L 914 T4 engine.

[busdaddy]

OK, so the odometer isn't skipping.......
Idle adjustment alone won't eat 10 MPG no matter how hard you try, I'm guessing you didn't write down the jet numbers that were installed when you did the rebuild?
How do your plugs look?
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[timvw7476]

Check what you didn't check, like a seized caliper or slipping clutch.
Find one of those and your back at 13-15mpg!

[guitarman63mm]

No, I didn't write them down. I'm going to pull the plugs tomorrow and post some photos.

What else could it be? Chokes always on? My choke elements warm up and appear to work as intended...should I try holding wire-locking them wide open and seeing how my highway miles end up? I did all of this carb work over a year ago, so my memory is failing me. I'm 99.9% positive that I correctly indexed everything on the bench, but I have to second-guess myself with this kind of mileage.
_________________
Jimmy

- 1974 Safaré Custom Camper. 091 trans + Dual Weber 34 ICTs + Pertronix SVDA + 1.7L 914 T4 engine.

[busdaddy]

I've had choke heaters make intermittant contact where the terminal is riveted to the little porcelain insulator, usually loose and wiggly, the chokes would close up at random times even in hot weather.
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[mnskmobi]

[richparker]

Not that I have any experience with your set up. I was getting shitty milage on my engine at 28*, I bumped the timing up to 32* and gained 7 mpg on the highway. I feel you pain, good luck.
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[SGKent]

10 MPG is low but floored into a 50 mph headwind burns fuel like crazy in a bus.

Another issue is could your timing be changing slowly?

Last - we keep records on all our cars. We try to use the best gasoline in whatever octane works best for that car. Cheap gas can be watered down. The alcohol in the fuel can hold water so sometimes unscrupulous stations add water because it is absorbed into the alcohol in the fuel.

Bus tanks can be hard to fill so you can have times where you fill completely on one fill-up and then under-fill the next, then fill-up completely. That under-fill will really make the math bounce. To eliminate that, check it over 3 or 4 tanks and see what the average is.

[Wildthings]

How are you timing your engine? Through the hole in the top of the fan shroud or using the bus timing scale. If using the bus timing scale are you 100% sure you have the pulley correctly marked? Running puke rich would certainly kill you mileage, but to get down to 10 mpg it should be noticeably boggy at times I would think. Have you run with this jetting before and gotten okay mileage? If not then pull one of the carbs and get the jet size and then buy four jets that are 1, 2, and 3 steps smaller and try them one step smaller at a time.

Unless it just runs like crap when you change to a smaller jet, run each set for at least one full tank of gas and preferable two before trying the next set.

[guitarman63mm]

I've been driving up and down a lot of hills, but it still seems low to me. Were I going up and down mountains, maybe, but in Tallahassee? I don't think it should be killing it this badly.

I thought about the tank over and under-filling issue by letting the pump stop it, but it's still funky. That should have made the whole thing a wash, and it appears to be trending downwards instead.

I'm timing it through the hole in the top of the fan shroud, and an advance timing light. I haven't checked it in ~400 miles, so I'll check it again tomorrow.

I've never run this jetting 'before', because I only started driving it last week. I'll figure out the sizes. (it's hidden behind the carb drain plug, right? I need to pull out my Bentley...)
_________________
Jimmy

- 1974 Safaré Custom Camper. 091 trans + Dual Weber 34 ICTs + Pertronix SVDA + 1.7L 914 T4 engine.

[Wildthings]

[1967250s]

Wildthings, do you have the part numbers for the different fans? I have a similiar conundrum: I have a previously 914 1700 engine and forget if I used the 914 fan or the OG bus fan and am not really sure of the timing, (even with the original metal timing scale) though it seems to run pretty well. Would you recommend using the "I"timing mark or the metal scale and what timing for a 1700?
Thanks for any help.

[Wildthings]

[Dansux]

Check all the wires and connections to both the chokes. I had a bad wire to my right carb once and the choke would not open. The wire looked fine but did not conduct electricity.

[guitarman63mm]

Got delayed a few days with other things. I pulled the plugs on #1, #2, and #4 (same order in the photo, left to right), and it's quite clear that the right side of the engine is running rather rich. If it were just rings taking longer than usual to seal, I would imagine it would be on all of them, correct? I also suspect that it's not my jetting - unless some hack was in there, trying to compensate for the right side of their engine being weak, why would anyone run different mains? I'll check that in a bit, I need to find something to drain the bowl into...

I checked the choke operations and wires. On the driver's side, this is the initial setting. It opens fully at 3 minutes and 30 seconds. I also noticed some fuel dribbling on to the throttle plate while I watched - I think I should reduce my fuel pressure or double-check the float level. This certainly isn't helping my economy, but it doesn't seem to be causing any fouling on this side.

The choke on the right side opens fully in 2 minutes, from a much more closed position. There is no fuel dribbling on the throttle plate.

Points are still at 0.016". Haven't bothered to check the timing yet, because I wanted to ask about this first before putting the plugs back in.
I think the chokes are operating correctly - I've pulled the cleaners off before while on a trip, and they were always wide open.

So, inductively...Fouling means a) unburned fuel, or b) burning oil. Now, given that my mpg sucks,and the plug was just a dry carbon, we can safely assume it's fuel. So, if the chokes work, and the jetting is correct, then the only other thing is that my accelerator pump is putting out too much fuel, or that the idle solenoid on the right is going haywire, correct? What else could it be, other than these, or jetting?
_________________
Jimmy

- 1974 Safaré Custom Camper. 091 trans + Dual Weber 34 ICTs + Pertronix SVDA + 1.7L 914 T4 engine.

[busdaddy]

[Dansux]

If you are in Florida the chokes probably don’t need to stay on that long. I would consider turning them back a mm or two.

[guitarman63mm]

That's a 1/2" nylon barb on the CIS, going into the K&N air cleaner above it.

I spent about a week cleaning out all of these passages, methodically soaking and scrubbing everything in acetone/gasoline/brake cleaner, each as needed, so I really don't think it will be clogged. It wasn't a rush job. That being said, nothing's impossible, but it's just really frustrating to have to start from scratch when I was almost sure I did everything right.

I tried to pull the main jet on the passenger side carb, but I couldn't get it out once it was unscrewed. I took a photo and it's a 130 main. I tried the same on the driver's side, but there's no room. I'm really baffled. It's like there's nothing to be done unless I pull the entire thing apart (and that's not really an option unless I can find someone who has spare parts/jets for these things in person.)

The only thing I found when going over everything is that the cut-off on the passenger side was totally loose, and the rubber washer was cut and not sealing. I made a new seal under that special washer with Dirko for the time being. I don't think this is relevant to the issue, because, to my understanding, if it were loose and not grounding, it would just cause it to shut off, not to keep going?

I'm wondering if it was just a whole lot of short trips or something, combined with the chokes being on longer than needed. Once I get back on the road (tomorrow?), it'll become quite clear if it can manage, or if it needs to be pulled apart.
_________________
Jimmy

- 1974 Safaré Custom Camper. 091 trans + Dual Weber 34 ICTs + Pertronix SVDA + 1.7L 914 T4 engine.