help with vac advance, fuel economy, EGT and all things related to distributors on modified, low vacuum engines

[kpr]

combo of slightly too rich at cruise and lack of vac advance will be doing it.   if you could get the afr too around to 15-15.5 at cruise maybe enough to bring temps down.   ideally you'd want the timing at cruise in the high 30's with vac advance. but a max mechanical advance of about 30degree should be ok.  wouldn't want to go much more than 30 as will be too much for full throttle.

 

 

re lean mix being hotter,  think of a gas torch. not enough oxy - rich and colder burn,  perfect mix - pretty much hottest.    too much oxy  - lean and temp starts to drop off 

[BlownCorona]

hmm thats a good way to put it, but how come too lean for too long = melted pistons and stuff. 

 

and 15.5 isnt too lean then? pretty much just dont want to damage the engine, but im having trouble actualy finding what ratios are dangerous, with everyone just saying every engine is different. 

[kpr]

its mostly too much advance that  melts stuff.   but the wrong afr will make it worse.    say if you had an engine tuned to  12 afr at full load, and the timing was set just below knock.(detonation)  then you were to lean it out to 14afr bad stuff is going to happen. same  deal but lean it out to 16fr  bad stuff may still happen, but possibly get away with it. 

 

low load (cruise etc)  you can get away with a lot more. plus you generally need more advance for the leaner mix.

 

ballpark figures  would be

12.5-13afr  full load, for best power

15-15.5afr cruise, for best economy and cooler running temps  (maybe closer to 15 being an old engine - only real drama going too lean is nasty shit starts coming out exhaust and it will get gutless)
25-30degrees advance full load*  (again probably closer to 30 being old engine) 

cruise 35-40degrees*  (as above)

* after 3000rpm, and yeah you will just have to go with the full load timing if you cant run vac advance

 

the most important thing when tuning is keep the timing lowish till you have afr correct, then advance the timing.   can get away with all sorts of  horrible afr's when the timing is low.

[BlownCorona]

thats great info, cheers for that, will have a play tomorrow and report back

[Ned]

The pilot just is the one you wanna mess with at 1/8th throttle, not so much the needle. Depending on if its fuel or air depends on turning it in or out. Front of the carb is air, so turn it in a bit for less air, richer mixture, back of carb turn out for more fuel.

I know you got rid of them, but the hole you used for vac doesnt look like a vac place to me...? Butni could be wrong/doesnt matter anymore

[BlownCorona]

those are the holes that are used for balancing the carbs i believe, there are no other ports on the carb bodys, seems to give a pretty good vac signal, but just drops off. 

 

the mixture screw is the first thing im gonna play with, but i have a suspicion its the cross over of two circuits since its such a precise point in the throttle position, 

 

ill also try to grab a video aswell

[BlownCorona]

KPR - just re reading your ballpark figures, with the timing, how am i meant to get the timing more advanced at cruise than at full throttle? am i misinterpreting that, because it seems like something isnt quite right? or is that assuming that vac advance was still working?

[peteretep]

timing will be more advanced at cruise becuase low throttle open creates lots of vac, full throttle there is no vac so no advance

[BlownCorona]

i reset the idle mixture screws using the wideband now, they are now at 2 3/4 turns out now as opposed to about 4 from memory. this apears to have cured the lean spot so thats pretty sweet. 

 

under full load, the afr is around 11.5-13 depending on conditions. probably getting a bit rich at some points. but this may be fixed by my next point

 

at cruise, the afr can be between 12-14 depending on the condions, revs/gear etc etc, and i can notice its really quite thirsty, this may also be a symptom of not enough advance, it could also be because ive upped the performance, but its really quite bad on fuel at the moment and im sure i can lean it out a little more at cruise and probably dial in a bit more advance, so ill look into all this, leaning it out at cruise may also have a small affect on full load and lean it out just that little bit that id like. 

 

other than that, its running beautifully, i took a video to try show the afr throughout the range, but it didnt show the dials well at all. ill try again next time, i really need to buy some gopro mounts

[kpr]

i just posted those cruise numbers to give you an idea what the engine would likely work best at.   if you managed to get the vac advance working, probably be seeing around those numbers    

 

its using a good 20% more fuel than needed at cruise with those afr's.   plus without the vac advance you  will have to give it more throttle to hold the same speed. which makes it worse again.    but yeah even leaning it out will use alot less fuel.

 

11.5-13  for full load isn't  that bad.  ideally you'll want it to flatline closer to that 13 somewhere.  but don't expect it to go a huge amount better if you manage to  get it there.  most of the power is in the timing.

 

i still think you should check those vac ports don't open up to the filter side of the throttle plate, if you haven't already. 

[Spencer]

yea agree that you need to figure out that those ports are actually legit. Maybe just a tap some new ports in he runners.

[BlownCorona]

i will double check the ports, though its where youre meant to balance the carbs from so surely its right? 

 

anyway, quite a good result from round 2 of tuning today, after fidling with the mixture screw and getting it quite close, i had a good think about what circuits needed adjusting and how ect. and came up with an idea, that lifting the needle circlip 1 position (its now on position 2 from the bottom) should help, and its pretty much got it dead on now, 

 

cruise sees around 14.5 - 15

full load sees about 12.5-13 

and idle is around the 14 mark too. 

 

i didnt feel any power difference as you say, but the ratioes are certainly alot more steady. and as you say, now playing with the timing will yeid more results. 

 

as for the vac advance saga, at 100kmh i actualy sometimes have about 3InHg of vacuum and at 50kmh about 5. not exactly alot, but it is there again (it used to be dead 0)

[Frosty]

Find a Fiat 850 dizzy & mod it to suit.

Full 22 deg mechanical advance and no vacume advance/retard fitted in any form on these engines it's all mechanical.

Advance curve can be modified with different springs and weights.

Only problem is cold stating will be a bit harder due to a bit more static advance.

32 deg is considered as ideal total advance so you run 10 deg static with 22 deg mechanical giving a total of 32, but I'm sure you already knew that.

Merry Christmas.

[BlownCorona]

its more than im trying to find a way to get low engine load advance to gain a bit of fuel economy back. im not 100% certain if its even possible, and if not so be it. but it would be nice. 

 

in my internet travels i have come across units like this 

 

http://www.cbperformance.com/ProductDetails.asp?ProductCode=2013

 

in which you lock out your factory dizzy at full mechanical advance, then this unit is wired in and interrupts the signal between the points and the coil firing, this gives a fully programmable ignition timing against RPM. which sounds like it would be a pretty sweet thing to have, im just yet to find out if there is any way to get it to recognize low engine load with the type of low vacuum engine im running. 

 

any thoughts on units like these? figured id just keep it in this thread rather than start a new one. 

[downtrail]

Be no good if your vaccum is low as it relys on a map vs rpm reading for your load points youd be better off adding a tps and using something similar that'll use alfa n insted of speed density to create a tunable map for your motor

[BlownCorona]

ive emailed to ask them about the 'resoultion' of its map sensor, but i have 1-3inHG of vacuum at 100kph cruise, and if i can get it to recognize variations of vacuum that low, then i should be able to program in proper 'vac advance' aswell as the rest of the benefits that come with a fully map-able ignition table. 

 

but we will see how it goes. 

 

im not sure how i would adapt a TPS onto it, but ill have a look at this alpha n stuff too, cheers downtrail. 

cant wait to actually get back to the car and have a good tinker/get a wof

[eke_zetec_RWD]

Just an idea.... And it's a pretty shit one. But you could remove the vac diaphragm unit off the side of the unit and install a 12v solenoid to push or pull on the arm. Then use a switch on your throttle to activate it.

Actually fuck that put a link on it to run all the timing and be done with it haha

[downtrail]

3" of mercury is around 90kpa so you have 10kpa to play with. Even if you set the map up from 80 - 100kpa in 2kpa spacings to give you 10 load rows it would be so erratic and unstable that running it like that would be pointless as youll be jumping huge timing numbers to try get a good wot timing vs a cruise timing. You will be much better hunting pick a part for a tps you can make a bracket for and easily adapt to be driven from the throttle shaft or pulley or where ever works best for your set up. This will give you a much smoother transition through the timing range from low load to wot

[BlownCorona]

Good info, I wasn't that confident it would work unfortunately. I haven't had much luck finding anything stand alone alpha n for a reasonable price either.

I had considered linkage controlled advance, like pre war motorcycles but decided that was a little archaic for my liking haha

[downtrail]

Megasquirt will work fine if you want a cheep solution. Only thing is you will need to run some sort of triggering to give the megasquirt a reasionable rpm reading. In the way of a toothed wheel etc. You can then lock dizzy and re wire coil to megasquirt add a tps and set up to run it alpha n. Ignore all the fueling and trims etc maby just use some resistors to clamp the temp readings at what ever value Probably done need to tho.

This way will let you tune ignition timing whilst still leaving your fuel controlled via carbs.