Help with IDAs needed...!

[Stoo the worm Simpson]

Hi guys...this is very similar to turbo-hippy's post before...but didnt want to high jack his thread.

Basically i need some advice on my carb jetting...it runs great on full throttle...but the idle circuit is very lumpy...and judging buy the amount of fuel that it uses...and the way it smell...i presume that i am flooding it on the idle circuit.

the engine is 2017, engle 130 cam, stock ratio rockers...street eliminator heads...with 42 inlet and 37.5 outlet.

the carb manifolds arent match ported as yet...but these are going on at the weekend.

and at the moment the carbs have 37 vents, F7 emulsion tubes, 160 mains, 55 idles and 190 air correctors.

any advice on getting me running smoother lower down the revs would be great, as driving it on the street at the moment is horrible...and i cant drive it on full throttle everywhere i go...can i 

cheers in advance

Stoo

[Jim Ratto]

Hi guys...this is very similar to turbo-hippy's post before...but didnt want to high jack his thread.

Basically i need some advice on my carb jetting...it runs great on full throttle...but the idle circuit is very lumpy...and judging buy the amount of fuel that it uses...and the way it smell...i presume that i am flooding it on the idle circuit.

the engine is 2017, engle 130 cam, stock ratio rockers...street eliminator heads...with 42 inlet and 37.5 outlet.

the carb manifolds arent match ported as yet...but these are going on at the weekend.

and at the moment the carbs have 37 vents, F7 emulsion tubes, 160 mains, 55 idles and 190 air correctors.

any advice on getting me running smoother lower down the revs would be great, as driving it on the street at the moment is horrible...and i cant drive it on full throttle everywhere i go...can i 

cheers in advance

Stoo

Hi Stoo... I doubt a 55 idle is flooding the idle. I've never been able to get a 48IDA engine to run well on a 55.
I'm not saying you do not have an over rich condition. If you do I don't think it is the idle jet.
Don't skip the other things that need to be dialed in and just blame jets.
Fuel pressure, float level, initial timing, valve adjust... all can cause what you're seeing (or smelling)

for instance, even  though your idle jet is small (in my opinion) if fuel pressure is too high, the fuel will run down from main circuit dumps in aux vents and make idle circuit way too rich.

I think people need to stop using their noses for air fuel ratio meters too.

[jamiep_jamiep]

Stoo, I pm'd you some info I collected from here that may help you. Good luck, I'm tuning mine next week so maybe we could share IDA stories...

[ESH]

There are different views on carb modifications and some people seem to have no problem running IDAs as they come but it may be something worth considering. Stick with it though, getting it sorted shouldn't be insurmountable, once sorted IDAs make for a great drive. It may be worth getting an LM1 and driving a few miles with that stuck in the pipe, gives you some real information on what's going on and can save on months of crappy driving.

 

[Sarge]

I have the same engine combo as you.  I had the same problems, too.  I helped my cause by increasing venturi size to 40mm.  After consulting Art Thraen, I changed to f11 emulsion tubes, 160 mains, 200 airs, 115 idle air and 60 idle fuel.... no more problems.  The idle air's are the secret for a smooth transition (street cruising).  Don't overlook the basic engine tuning stuff Jim mentioned... tight valves and ignition problems will lead you down the wrong path.  Hope this helps.

[Stoo the worm Simpson]

thank for all the imput guys...i will double check all that jim has mentioned...as it may well need the rockers re-setting...and my fuel pump isnt regulated at the moment as its only pushing out 3.5psi....maybe time to upgrade.

cheers matt...i have heard great things about LM1s, and ur right it might save alot of time scratching my head
it also may be worth getting a good selection of jets etc and trying Sarges combo.

Thanks again

Stoo

[Jim Ratto]

thank for all the imput guys...i will double check all that jim has mentioned...as it may well need the rockers re-setting...and my fuel pump isnt regulated at the moment as its only pushing out 3.5psi....maybe time to upgrade.

cheers matt...i have heard great things about LM1s, and ur right it might save alot of time scratching my head
it also may be worth getting a good selection of jets etc and trying Sarges combo.

Thanks again

Stoo

3.5psi is more than enough pressure. It is probably the threshold for the needle valve to control. When your pump is on but engine isn't running, look down throttle bores... if you see fuel dribbling over and dripping onto top of butterfiles, you found your overrich condition.

[Stoo the worm Simpson]

Thanks again jim, looks like i have some investigating to do tonight....

[ESH]

... my fuel pump isnt regulated at the moment as its only pushing out 3.5psi ...

... 3.5psi is more than enough pressure ...

Good point on the fuel pressure, definitely don't need any more than that though one thing that may be worth looking into for the future is a return line to the tank. Though usually used in high pressure fuel injected applications it seems it can help smooth the flow to the carbs but this isn't necessary and wont be the source of your issue. I'm by no means an expert on this but just a couple of obeservations we've come accross on my (48DRLA - 48IDA) motor over the years.  On that note the information Sarge has posted based on consulting Art Thraen is likely pretty much exactly what you need to do, I had some good info off Art a few years back too.

Good luck with it. 

[Sarge]

Of all the jet changes, the 115 idle air holders (120 is what comes with the carbs usually) was what helped the most in my case.  No matter what else I did, I had a stumble at cruising speed whenever I tried to accellerate which would seem to indicate a lean transition from idle to main circuit.  The holders are hard to come by... I had Art make me some up.

[Jim Ratto]

Of all the jet changes, the 115 idle air holders (120 is what comes with the carbs usually) was what helped the most in my case.  No matter what else I did, I had a stumble at cruising speed whenever I tried to accellerate which would seem to indicate a lean transition from idle to main circuit.  The holders are hard to come by... I had Art make me some up.

I totally agree. Sarge and Rayburn both turned me onto getting away from the 120 drilling. I tired going larger and my car developed a big lean hole. I don't want to bore you with all the testing I did, but I ended up drilling a set of 060 holders to 110. Bingo, car pulled like a train all the way up. Remember this hole is for air... so like mains, the relationship to fuel hole is not linear. I think the 120 holder was setup for Cobra guys who run 70 idle jets.

[Tobi/DFL]

Good point on the fuel pressure, definitely don't need any more than that though one thing that may be worth looking into for the future is a return line to the tank.

Hi,

I´ve read about a return lone to the gas tank very often but I don´t really know how/where to fit it. I´ve seen that there are double banjo fittings available. Would they work for a return line?
I have a #06 hose from gas tank to the "T-fitting". From there a #06 hose goes to each carb. So where would I have to connect the return line?
I hope it´s understandable what I mean as it´s quite hard to explain in english...
Bye,

Tobi

[Lids]

what regulator are you running, some come with a take off to return to the top of the fuel tank.

What you want is the excess fuel to go back to the tank from the regulator.

[Stoo the worm Simpson]

ok....had a quick look at the carbs last night and i have discovered that the accelerator pump jets on one carb are not delivering any fuel until one third throttle....the other carg delivers all the way though...resulting in the car running on cylinders 1 & 2 at low speeds, then as i crack the throttle wide open im running on all four again.

[ESH]

... I´ve read about a return lone to the gas tank very often but I don´t really know how/where to fit it. I´ve seen that there are double banjo fittings available. Would they work for a return line?
I have a #06 hose from gas tank to the "T-fitting". From there a #06 hose goes to each carb. So where would I have to connect the return line? ...

I'm running a regulator which requires a return line so there's a line off that. When I had a Holley regulator I didn't run a return, I thought about running one but couldn't work out a good place to put it / them in the system. The only thing I did consider was taking it off the feed just before the regulator on the basis that in running the regulator at a relatively low pressure in relation to the pump that it'd help smooth flow between the two but I wasn't conviced. Hope that was of some use?

 

By the way, looking at your car running I'd hazard a guess that your fuel system is fine!

 

[ESH]

... had a quick look at the carbs last night and i have discovered that the accelerator pump jets on one carb are not delivering any fuel until one third throttle....the other carg delivers all the way though ...

I guess that could be a problem! 

[Stoo the worm Simpson]

yeah...i need to sort this first before i even think about the jets...my first thoughts are...float bowl adjustment...accelerator pump jet either blocked or failng in some way...but thats doughtfull as it does deliver fuel, just later on in the circuit...or even dirt in the idle jets..?

[Jim Ratto]

ok....had a quick look at the carbs last night and i have discovered that the accelerator pump jets on one carb are not delivering any fuel until one third throttle....the other carg delivers all the way though...resulting in the car running on cylinders 1 & 2 at low speeds, then as i crack the throttle wide open im running on all four again.

check cam and roller (on throttle shaft between throats) for wear. If either wears (and they do) the accelerator pump delivery will be delayed.
if the'ye ok, check piston and rod that do the pumping
make sure nozzles are tight and have copper washers to seal them

[Stoo the worm Simpson]

Will do jim...i cant c the cam or roller being worn as they are quite new...but i will have a check of everything this weekend..thanks again

[Peter Roberts]

Of all the jet changes, the 115 idle air holders (120 is what comes with the carbs usually) was what helped the most in my case.  No matter what else I did, I had a stumble at cruising speed whenever I tried to accelerate which would seem to indicate a lean transition from idle to main circuit.  The holders are hard to come by... I had Art make me some up.

On an old article that I've read that Art did , he said ...

" The Idle Air Jet Holder is TIG welded closed, so that it can be re-drilled to the size needed. In Art's experience, the Idle Air Jet Holder is one of the keys to unleashing the IDA's tunability. The Idle Air Jet Holder should be sized to the application and engine size. Sizing makes a HUGE difference in idle and off idle performance. Try a 110-115 on small engines, and 130-135 on large ones (they come with a 120). "

Here is the article ...

http://www.aircooled.net/gnrlsite/resource/articles/48idarebuild.htm

I followed his instructions on bigger engines , enlarging the idle air jet holder to 130 , and it made a hell of a dirrerence

I've not tried going smaller though , so may try this on the next car .

[Tobi/DFL]

I'm running a regulator which requires a return line so there's a line off that. When I had a Holley regulator I didn't run a return, I thought about running one but couldn't work out a good place to put it / them in the system. The only thing I did consider was taking it off the feed just before the regulator on the basis that in running the regulator at a relatively low pressure in relation to the pump that it'd help smooth flow between the two but I wasn't conviced. Hope that was of some use? 

By the way, looking at your car running I'd hazard a guess that your fuel system is fine!

Thanks, Mat!

The last season I discovered that the engine seemed to get not enough fuel when accellerating in 1st and 2nd gear. At first I thought I would already be in the rev limiter but I´m not quite sure. Maybe a good working rev counter would help (I have a 914 unit with a "dancing" needle).

As I´m upgrading the fuel lines anyway (aluminium hardline) it would be no problem to fit a return line as I could use the old braided hose which is still in the tunnel.

@Lids: I will use a 95gph Summit Racing fuel pump (http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G3136-1&N=700+0&autoview=sku) and a Filter King regulator which unfortunately doesn´t have a return line.
Bye,

Tobi

[ESH]

... The last season I discovered that the engine seemed to get not enough fuel when accellerating in 1st and 2nd gear. At first I thought I would already be in the rev limiter but I´m not quite sure. Maybe a good working rev counter would help (I have a 914 unit with a "dancing" needle).

As I´m upgrading the fuel lines anyway (aluminium hardline) it would be no problem to fit a return line as I could use the old braided hose which is still in the tunnel ...

Have fun with the upgrade. I had a fueling problem a while back which turned out to be a fuel filter which would clog after a period of running, as soon as a car's good something else comes up.

 

[Lids]

Tobi think about changing your fuel pump!  You can get them which have a return valve built in, this would be easier to plumb in.

http://www.magnafuel.com/products/carb/pumps/MP-4550.htm just use with normal regulator and problem solved

[Tobi/DFL]

Okay, thanks for your help, Mat and Lids!

Tobi

[Stoo the worm Simpson]

Right i had a look again over the weekend, and i have sorted the problem of one carb not getting any fuel...this was due to me routing the ignition leads through the manifold...like alot of people do...but one of the leads had got wedged behind the accelerator pump arm on the bottom of the carb, causing it not to travel as far back as it should..hence the fuel at full throttle and not on idle....!
Now i will go back over and double check the rest off the fuel system before changing my jets