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gfallon

tuning newly rebuilt engine

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I have a few questions about getting my newly rebuilt engine tuned right.  this my first go with dellorto  carbs ( lots of experience on su and stromberg ) and a first carb turbo setup.

so what I have is a 1983 us car but the pervious owner removed all the emissions. so no cat, no smog pump, no air rails.

also the last time he rebuilt the engine he put the pistons and liners from the 88 spec car, so it has the 8:1 pistons and nikasil liners. also a port n polished head and he set the boost at 10psi.  it also has an msd timing computer  

 

because all the emissions have been removed  I have it set up for the euro specs. so the cam timing and ignition timing

you can see in the pic I have been working on getting it right and I have it pretty close but cannot seem to get it just right

I have ignition timing at 10 deg @ idle and 28 deg @ 4,000rpm  ( book said 12deg @ idle )

was able to get the idle down to 1,000 rpm ( had been at 1,800 I found the linkage needed to be re adj)

you can see in the pic I have the carbs kind of balanced.  does it need to be at a specific number or just level?

problem is I still have a hesitation at light throttle inputs and the idle is not perfectly smooth  ( so while driving after you let off throttle and when you first go to throttle the rpm will drop for a half second. really only a problem when pulling from a stop)  would this be a carb problem or a timing problem?

also I installed an afr gauge  anyone know what numbers I should be looking for?  at idle, cruzing rpm and at wot?    right now I have 14.2 - 14.6 at idle.  I think it was 10:1 at half throttle and 5psi.  have not pushed any more than that  

 

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I would try & get the balances a little closer, there is no specific number, just as close as possible.

Have you correctly set the idle mixture using something like a Colortune

If one or more of the cylinders are running lean that will cause hesitation. :thumbup:


Cheers,

John W

http://jonwatkins.co.uk

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have not done that yet.  I do have one so will take a look

thanks

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1 hour ago, jonwat said:

I would try & get the balances a little closer, there is no specific number, just as close as possible.

Have you correctly set the idle mixture using something like a Colortune

If one or more of the cylinders are running lean that will cause hesitation. :thumbup:

The spark plugs can tell you if its rich or lean or when you have a blocked carb.So its worth to have a look at them

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Brian, You will get there.

First thing to control is the float level of the two carbs.Have a look how to do that:

http://sideways-technologies.co.uk/forums/index.php?/topic/1048-setting-dhla-dellorto-dellorto-float-fuel-level/

Proceed from there with the following:

https://www.theapplebyclan.com/Richard/Tiger Super6/Useful info/Dellorto/

Hesitation when going on throttle can also be caused by a faulty accelerator pump /injector.

When pushing the throttle there should be a squirt from the pump to enrichen the mixture directly.

This is what Tim Engel says about the matter : The accelerator pump's affect is felt when the throttle is opened quickly. After the idle jets and air correctors are set, any stumble on rapid acceleration probably involves the accelerator pump, and should be dealt with by adjusting the pump jet and pump stroke (volume). On the Dellortos, you can also adjust the preload of the spring in the accelerator pump linkage to determine if that volume of fuel is squirted in quickly, or over a longer period of time.
 

http://www.lotuselan.net/forums/lotus-carbs-f40/adjusting-the-squirt-dellortos-t13117-15.html

http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/390698-dhla40-accelerator-pump-adjustment.html

greets

Geert

Edited by gvy

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Not sure if either of the pics are hot idle, but they indicate that neither the linkage is balanced or the air bleeds are balanced?   Is this because they wont balance or its not yet been done?    Without this you are not going to get a super smooth idle. 

I would agree on the float heights, worth putting the time & effort on getting them right.

As the engine is newly rebuilt, may also be worth running it in a little before you try to fine tune. 

Presumably a 10:1 AFR is significantly rich, but I wouldn't really know what to expect as I have no way of measuring mine

Your spec sounds similar to mine and I need to run slightly larger 42 pilot jets.   Do you know what you have fitted?

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Of course pic 1 is idle as its got more vacuum.   So tubes 1 & 4 should be adjusted to match via the central linkage adjustment and the bleed screws should then be opened on 2 & 3,  until they drop down to match 1 & 4 (assuming that 1 & 4 bleeds are already closed) 

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you can see the ruff idle in the video 

I checked the color tune and they are all blue in color so should be good

will look into the accelerator  pump

I also changed timing to 15 degrees at idel. (was 10)

  It did seem to help but not much 

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Brian, leave the accelerator pumps alone for now. They have no impact on idling. They add fuel on acceleration. If the engine stumbles when you add open the throttle then you might want to look at them. For now, focus on the balancing screws and get all the 4 barrels equalised as good as you can.


Ad initium

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The accelerator pumps only add fuel when you depress the gas pedal a bit faster but they do nothing when the pedal will be depressed very very smooth.As said above they do nothing on idling.

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This is a quote from an older post in another thread but it still applies.

Follow the carbtune procedure systematically. It's a process that improves the running in repetitive cycles. Here is a good file link that describes the process well. http://www.mlmparts.com/media/pdf/carbtune/using-carbtune-ii.pdf

Changes on the vacuum screws are more or less immediately noticeable and that's what you should work with primarily. I can also recommend you the Des Hammil book on dellorto carbs. It's very comprehensive and full of insight. 
https://www.amazon.com/Build-Power-Dellorto-Carburettors-SpeedPro/dp/1903706750

Keep going, you'll get there. Once you do, it'll feel real good and give you a lot of insight into the carbs functioning and how you can maintain them going forward

My timing on a ROW 84 Turbo is 12 degrees before TDC at idle btw. As per manual


Ad initium

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1 hour ago, gfallon said:

I also changed timing to 15 degrees at idel. (was 10)

Although its tempting to adjust the timing for the 'best' idle, its far more critical to the engine's health at max advance.   I'd therefore avoid dialling in more advance at idle.   

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US cars were jetted as lean as they could possibly get away with to squeeze through US emissions regs. So the idle jets (which affect low end as well as idle) may well need increasing in size.

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I richened up the idle jets and it did get better, it still does the same thing just not as pronounced.  cly 1 and 3 will fluctuate together, 1 goes down and 3 goes up, so 1 loses some vacuum and 3 adds some vacuum.  I can here the engine pop out the exhaust each time it happens.  

i will look at the color tune tonight (easier to see when its dark)  but my afr reads 12 and 13's ( it was in the 14's)

i looked at the notes the previous owned made, he changed some jets,  not the idle jet's.  idle jet is a 52

changed the main jet from a 165 to a 170

changed the main air correction jet from a 230 to a 210 

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Gis

i red your link on the carbtune and one thing i noticed is about the restrictors. one of my restrictors was broken (mine screw into the top of an extension, one had the screw broke off) so that may cause some of the fluctuation i see.  it is weird that the engine pops at the same time. number 1 is the one with no restrictor but cyl 2 also reacts at the same time

also i have the how to power tune book.  i am also helping a friend restore a 1959 alfa romeo giulietta veloce. i got the book to help with his webbers 

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Ahh, I'd assumed you were on DHLA40, but seems you are on DHLA45, which should be good for your setup.   If it were me, I'd probaly try a full stock set up for the HC spec DHLA45 and take it from there.   But the fluctuation in vacuum is more likely to be mechanical, not the carbs  (assuming they have been correctly rebuilt).  Do you have euro spec cams & timing? 

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GOT IT RIGHT!

used the color tune again and was able to richen up a little more but it was # 4 the last one it looked more lean then the others so richen it and smoothed right out.

I did count the number of turns out and I am at 9, the how to power tune book said any more then 7 and you can step up. so yes I can get the next step up on the jet at some point.

its been raining a lot so have not gotten to drive it yet but I am sure it will be good

thanks to everyone for all the help 

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Great news, it's always worth perservering to get the idle mixture correct as it's surprising how much effect it has on driveability.

The Colortune really are worth the money, well done. :thumbup:

Edited by jonwat

Cheers,

John W

http://jonwatkins.co.uk

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