40 IDF vent/jet choice

[Mark]

Bear with me for a moment, IDF-inclined folks...

After combing through numerous searches here, STF, & several other forums I'm still unclear on a way ahead with the lousy mileage our Westy has been getting. That, and she seems to just run out of steam towards the upper RPMs on the highway. CHT's can get up around 375, slightly higher if crosswinds or uphill is encountered. Plugs consistently check light black soot, and can't seem to shake the rich condition. Throttle shafts nice & tight with no slop. Carb floats as per Lord Harney's recommendations.

Some specs of the current setup:
1800 type IV (compression 7.4:1, all cylinders 130 psi compression test)
39.3mm Intake Vv's
New Bosch SVDA set @ 30 BTDC (vac advance tee'd to both carbs, but not timed with vac connected) Dwell ~47, plugs gapped @ .024
Carbs - 28 vents, 115 main, 50 idle, 200 air, F11 tubes
CB 2202 cam
Exhaust - Thunderbird "type" 4-1, (Bugpack)
...anything I'm missing?!

I'm getting conflicting reports from my searches, as it seems some folks are running 28 vents & similar jetting with good results. Then again, others seem to be fine running 32 vents & appropriate jetting.

Apart from that, and from what I gather, 28 vents are too small with the intake valves these heads use, and would stand to benefit at least in the upper RPMs by switching to 32 vents & some jetting changes. That, and the increase in vents would aid torque in a bus engine application.

Can anyone with practical experience in the matter chime in with your recommendations? I know bang-on jetting is going to take a few tries (if I'm lucky) but would like to know a good starting point here. TIA.
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[krusher]

Bang on jetting will require some test equipment like a air fuel ratio meter/gauge
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[madmike]

I would try the 32's,If they don't work out u can alway sell them on here
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"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"

[dan97019]

I dont know how a type 4 1800 compares to my type 1 1835 but my IDF's w/28 mm vents originally came with 115 mains and the motor would barely run so I changed to 125 mains which made it drivable but still had a big flat spot went to 130's and now it runs good and gets around 25mpg so I am running, 28 vents, 130 main, 50 idle, 200 air, F11 tubes on a 1835w/ engle 120 and 40x35.5 valves 8.5:1 ratio.

[Mark]

Thanks for the replies. Here's where my head is at for the carbs' baseline:

Vents 32
Mains 135
Idle 50
Air 200
Vent F11

I figure from all the possible combos on the road, there must be someone running a comparable setup as mine in a breadloaf bus that is happy with his mileage.
When I say bad mileage, I'm talking 12-14 mpg city/highway here. That's even after exercising a lot of restraint with the Go pedal and driving conservatively. I need to do better than that.
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[udidwht]

It's about finding a happy medium. What do you drive mostly? City or Hwy or a combination of both? With the 32 vents you'll pick up your top end but drop some on your low end. ACVW engines love velocity which you'll lose some with the 32's given your intake valve size. I'd go up on the mains to 120 see how that feels.

Remember one thing...Torque, with the 32's you'll be sacraficing some with the change in vent size. (If it's a bus)Buses rely on torque due to their weight.

I'm running a 2056cc with 40 idf's and they're set up using 28vents, 50 idles, 120 mains, F11 tubes, 1.75 needles, 200 airs and it runs just the way I want it considering my driving style.

[Mark]

Actually I ran 120 mains months ago, bought from ACN so I know they were the right size. After running them for a couple tank fulls, I noticed no difference with all variables being the same. Pump squirts kick in when they should, with no leaking. There is the slightest of flat spots, but only when starting cold.
For driving style, about 70/30 highway/city.
I've checked the usual suspects like tire pressure & brakes dragging, but no problems there.
Carbs are synced with the snail, linkage is setup equal, idles well @ 950 RPM.
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[udidwht]

What kind of mileage are you getting? With the Webers you should be getting at least 20 hwy. As long as your not heavy footed. I'm getting 24 on the highway and 18 around town.

[Mark]

[udidwht]

Are you certain the carb floats are set right (10-11mm w gasket in place) Also check your accel pump squirt. What I do is back it off until you feel it stumble then ease it in until you only feel a slight stumble when stomping on the pedal.

Be sure you have no fuel dumping down the carbs during idle and after shutdown.

How far off the seats are your A/F mixture screws? Anything more than 1.5-2 turns suggests it's lean anything less than 1 turn is rich. Verify your fuel pump pressure before anything 3-3.5 is good for Webers.

[Mark]

[udidwht]

I'm running a Web 73 so the profile is different then the CB cam. As for the enrichment circuits mine are still in place with no issues. I've never ran into any issues with them on Webers. But with the Empi copies or USA made Webers anythings possible. Mine are Italian that I purchased back in 88. I'm leaning to your cam profile/valve size at this point. FWIW I'm running big 42x36mm heads.

[Mark]

Thanks.
CB2202 cam specs: 278 deg duration, .410" lift.

Just to compare against your Web 73 grind, 262 deg duration, .426" lift

I recall when I was choosing a cam, I was told by several folks this was a good choice for my application. I'm REALLY don't want to go down that road and split the case unless absolutely necessary.
If that's the case, I know Mr. Raby can expect a call from me in the near future.
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[krusher]

I wonder how well your igniting that charge, played with, timing, points gap and plug gap?

taken a plug out to see what colour they are?
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(06:31:07) RoachGhia: "i drink dick way too fast"

[Mark]

[WVbugman]

30 vents may be a good compromise between rpms and torque. They will flow 15% more air than your 28's. Your mains and possibly your airs will need to be changed
Hotter plugs may be necessary if you take short trips that don't allow your engine to warm up.
40 idf's don't come with velocity stacks. I added them to mine and feel the torque comes on earlier in the rpm range.

[udidwht]

[Mark]

I took the carbs apart, and these popped out. Nice.

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[udidwht]

Have you had these carbs long? Are they made in USA?

[Mark]

I've had them for about 2 years now, and got them from the classifieds here. When I disassembled them to inspect & clean them they checked out fine. I'm not sure why the spring, tophat & retainer would pop out like that.

The carbs both have stamped on them:
Made in Spain
40 IDF 70 00
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