Wideband Results

[Paul.H]

The 40mm butterfly will flow more air at full throttle than the venturi above so full throttle may not produce more power unless there is some turbulance issue with the butterfly at an angle. In some cases the slight angle may produce better flow but this mainly depends on the type of manifold and the T4 manifolds are pretty straight and large under the carb. I wouldn't waste money on dyno time to find out

[Zed999]

Apologies all round.
Just found after I switched mains on thhe side of the road when 140's pinked, I failed to screw one of the main stacks back in, it was just plonked in the hole.

I'm going camping/walking for a few days.

[Zed999]

...as I drove to the camp site I took more note of my pedal position.

70mph is more like1/4 pedal, 1/3 up the motorway hills.

But up steeper hills I need full throttle to get from 3rd to 4th.

[kaiisons]

just wanted to add my bit to this thread as it has helped me out a bit recently.

stock 1800cc type 4 in 1973 bus.

twin 40 HPMXs
CSP bellcrank linkage (easiest adjustment ever but need to re route the accelerator cable)
vintage speed single tip exhaust
60 idle
200 air
120 main
f7 emulsion

I was having a hard time getting rid of the hesitation in the transition range around 2500rpm. The best I had it running was with 220 air, 130 main and (edit: F11 emulsions). which still had a little hesitation but mostly it was super rich at WOT. The only way I could get rid of the hesitation was to remove the air jet all together.

Did some reading on various forums and saw that some recommended the f7 in the buses. Well what do you know it completely solved my problem so much so that I am now down to 200 air and 120 mains. I think I still have a bit of room for improvement in the idle jet, maybe a 57 will work, but for now 60 is good to monitor the AFR gauge.

It may be that my engine is tired and not producing enough vacuum to get the mains in when required but for the price of 4 emulsion tubes the gamble was worth it.

[[email protected]]

I recommend F11s, using F7s initially is a huge mistake. For 1% of people they will be the right choice, but 99% of the time NOT.
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[kaiisons]

[kaiisons]

I also forgot to mention I have been using a wideband to tune. Innovate MTX-L.

[Wreck]

A question for John , first you are one patient person and thanks for passing on your knowledge . I have read the whole almost 100 page thread .It would be only be a third of that some people would not ask the same questions over and over again .

What I can't find mentioned is power jets in a Tri-jet 48 DRLA ,
Ive a 2600 type 4 , 47 in 40 ex. 10.5 to 1 with a scat 55 . a stepped header up to 1 7/8 done to pipemax specs . with a megajolt ignition . 40deg total 28 WOT.

42mm vents , 62 idles ,185mains ,195 airs and 50 power jets . with holes in the gaskets to let the power jets function. plus .2 emulsions

the jetting is pretty close , I understand where the progression /mains/airs function and power jets function . All the people so far Ive read listing tri-jets, don't mention the power jets . Is there a correct procedure for tuning them . I got the carbs secondhand and they had 120 power jets that were off the scale rich but have been told that was the original jet supplied with the tri-jet.
cheers Derek

[Wreck]

Does anyone have any new feedback on what the various emulsion tubes have on Dellortos .
I have .2's which are the ones listed for twins but I'm trying to get rid of a lean midrange (high 14's to low 15s) at half throttle over 4000 rpm .

, I've tried bigger mains but that has richened up the area after the progression finishes which I don't want .

[Paul.H]

[Wreck]

It's the hottest. CHT and EGT range , my exhaust port walls are not real thick so I'd like to get it down to mid 12s low 13s as I'll be driving in tropical heat .

[Paul.H]

[modok]

If you decrease the middle diameter of the emulsion tube I think it will richen up your area of interest. This -could- delay and lean when the mains kick in, but should be richer in the middle. The difference between #2 and #3, is #3 the middle diameter is 7mm instead of 7.3mm (If I remember right)

What happens if you reduce the air jet??

[Wreck]

the top end goes too rich with a smaller air corrector , I started with a 180 air , 175mains even dropping the power jets to 25's ,the smallest available it was rich . with 175 main

I've gone up to a 205main with a 210 air in various stages but ended up with too fat at the end of the progressions , I think the progression and mains were overlapping .

I haven't got a 1.90mm jet drill ,hopefully I can borrow one during the week , I want to try opening the mains out to 190 which I haven't been able to try yet .

I'd like to be able to get main circuit to richen up the midrange then plateau so the power jets take over and I can fit bigger jets (less likely to block ) .

I'll order some .3s and post the results .

Paul the venturis /chokes are the correct size for the engine according to all the webber /dellorto information I could source . 2600cc peak HP should be at 6300 according to pipemax and Wallace racing calculators ,because of mach airspeed at the inlet valve and yes I agree injection would be nice and would've been a better path . These Dellortos have been a headache but on the plus side I now know how to fix the dellorto drip !

[[email protected]]

It appears to me you are a thinker and know what you are doing. I have very limited experience with the Tri-Jets, though I know they are fantastic carbs.
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[modok]

sharp guy
yes i think the #3 tubes are worth trying, or perhaps reduce the diameter even further below 7mm

Very little is known about the DRLA emulsion tubes and auxiliary venturies.
There are only four kinds of emulsion tube, but there could have been many more.

[norris]

I getting ready to begin tuning my 2276 with a wideband. The car runs fantastic now but all of the jetting has been done by the seat of the pants dyno. I'm almost positive I'll find that my current jetting is way off when I hook up the wideband.
I've read this thread more than once.

John C has stated more than once that the mistake most people make when tuning with a wideband is that they "tune to the existing timing". My question is, would it be better to start with a lower timing? In other words, should I begin my wideband tuning a couple of degrees less that what I've been running? I'm at 30* all in with my .010....should I begin tuning at 28* instead? Or, do I need to lean the jetting out first...back off of the timing...then lean it out more....then back off of the timing...etc.?

My thinking on this may be all wrong, and I realize that. But please correct me if needed.

n

[[email protected]]

the jetting will be different for 34 degrees of timing, compared to 32, 30, or 28 total.

So set the ignition first.

But understand the proper timing is going to depend on engine specs. Squishies use very different than flat top, and semi hemi is very different from quench chambers.
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[norris]

Ok...thanks John.
I'll be back!

[303epps]

Made the decision some time ago to change from 32mm vents to 30s on a stock type 4 engine. Heads are new as a valve seat sunk in number 1 chamber. Specs are below. It's been a long winter up here so that's why I'm updating my results 6 months later.

First of all thanks John for the help sizing the jets, the recommendation was perfect.

And thanks to Modok for details on how to machine vents, my friend made them perfectly.

WOT pulls range from 12.7 through 13.3 starting leaner going richer. At 4000 rpm starts to go a little rich (12.3) so tried a 210 air jet but didn't like the result, too lean in the cruising range. The van really pulls from 2400 to 3800 rpm.

1/4 throttle ranges from 15.5 to 16.2.
55 mph cruise mid 13s to low thirteens when some load shows up. Flat terrain cruise. Head temps under 350* Engine is in its happy place at 55 mph.

Only issue I seem to have is when I shift I hit a lean hole at about 10% throttle and 2200 rpm. Set timing at 10* and that helped somewhat. When I hit the throttle harder and get more accelerator pump volume I hardly notice it. I don't know the size of the accelerator pump jets yet but will find out, whatever stock factory size is I'm guessing. Right now the jet stream is of long duration.

John's Recommendation "If THAT doesn't do it, we'll have to modify the F11s, or try 30mm venturis if the engine is milder (and start over with the main/air combo, something like F11/50/125/200"



Previous results: 303epps wrote:

Type 4 motor - IDF 40s/70 series
Local elevation 2200'
IDF 40s - 32 vents, emulsion F11,50/130/220
SVDA
timing 8*/28*
vacuum at light throttle 2"-3"
exhaust: bug pack "performance header" & muffler

Installed the 220 airs:

WOT: 12.9-13.5 AFR pulls good except could be crisper from 2200 - 2600 rpm. at 2200 AFR spikes to 16 before catching. turned pumps in 3 turns and lag improved somewhat.

Cruise:

40 mph - throttle 15%, rpm 2400, AFR 15.5 - 16.5
45 mph - throttle 20%, rpm 2600, AFR 15 - 16
50 mph - throttle 25%, rpm 2800, AFR 14.5 - 15.2 adding a little throttle 14.7

Will a 230 air jet richen up the main circuit or should I try a 135 main? since I have 230s I guess I should try and find out. Any benefit in consider 30 a venturi?

Eric