Too Much Carbs? 5k In Need Of Lower Carb Diet Perhaps?

[Sidewinder]

Hi all,

 

PRE-EMPTIVE CLIFFNOTES: worked 5k motor is slow, thinking stupid amount of carbs may be the issue. want lump idle back ,and am worried i wont be able to engineer with webers on

 

Looooong time lurker, rare poster here, looking for a little bit of advice

 

I have recently put a worked 5k into my corolla, with the following mods as told by the previous owner:

 

5k engine, (ex rally car )

balanced, blueprinted,

flat top pistons,

lots of head work,

wild cam ( can't remember all specs but 500thou lift )

custom made valves, pushrods and rocker gear.

twin 40mm dcoe webers.

Extractors.

 

this was all copied and pasted from a thread on the motor's previous car, so forgive me if the cam specs seem a little wierd. Now with something like this id be hoping for something a little bit quick, but to be honest its only a small power upgrade from the old 4k in my ke70.

 

I know alot of this would be due to still running the standard exhaust welded on to the extractors. its obviously the big bottleneck in the setup, but how much of a difference would we be talking here?

 

After a fair bit of research, the general consensus around the K motor nuts is that 2 40mm carbies is a bit big, and i seem to think it may be half my problem. the car bogs down if you try to accelerate too quickly, and its almost like its being flooded (no proof to back this up, just thinking theories. highly likely its caused by lack of exhaust instead).

 

the ke10 the motor used to be in felt like a rocket ship in comparison to the motor in my car, and the only 2 differences between the motor now and the motor then is the exhaust, and the carby setup. the motor has a huge cam in it and once upon a time it would lump idle like the toughest little K motor that would ever make me proud! this was with a pair of dellorto carbies on it, though I am unsure of the size. since putting the 40mm webers on, the motor now has no lump at all. I'm wondering if this may be a sign the carbies are too big?

 

I'm also planning a sc14 setup soon, and am wondering if these carbs would be worth having at all for a drawthrough setup?

 

also, the webers have no provisions for polution gear, should i be worried about trying to get this engineered in QLD?

 

sorry for the long post, hopefully someone can help

Edited September 8, 2008 by Sidewinder

[Redwarf]

One word: Dyno.

 

If you put the Webers on and haven't dyno'd it, I've found your problem. I ran twin 40's on a 3K sucessfully, 5K shouldn't be an issue.

[Trev]

As Red has already said the 40's are fine but its the jet size and venturies that matter.

[Sidewinder]

So more of a tuning problem? I just found out they have actually been set up to run as a 32mm instead of the full 40mm? sorry i don't know much about carbies. will i ever be able to get my lump back with these?

[SeptemberSquall]

the 32 mm is the choke size

32 should be about right for 1500cc

 

the reason the engine felt much stronger in the ke10 is that a ke10 weighs about as much as an anorexic 15yr old girl compared with the fat ugly american heffer of your ke70 - seriously must be 200+ kg difference. 5k however modified will not be a powerhouse so weight is an important issue.

 

i agree that if you have added new carbs without tuning on dyno you should dyno first and make sure fuelling is right

the bogging down on throttle opening could be accel jetting too large etc so afr goes too rich on throttle opening

[Sidewinder]

excellent, i don't need to spend money on chokes then :D

 

that leaves my other 2 questions then. without provisions for polution gear, how will i ever get it engineered? or will that need different carbies again?

 

i really miss the lump idle, and I'm seriously considering changing to a carby that will bring it back and allow me to engineer my car

[philbey]

yeh, get them tuned. Also, try changing the exhaust though that might not be that big a difference.

 

dunno what k motor nuts told you 40s are too big, there's plenty of people around the place running them with great success.

 

Also, I wouldnt bother putting a good set of twins on a blower setup for drawthrough. The money you could sell the twins for would fund a weber downdraft blowthrough turbo setup!

[beerhead]

Go spend $250 at an exhaust shop before you try and have it tuned. Did it come with the dizzy that the original motor ran? Or are you running your 4K dizzy? Could be a lack of timing advance too.

[Sidewinder]

Go spend $250 at an exhaust shop before you try and have it tuned. Did it come with the dizzy that the original motor ran? Or are you running your 4K dizzy? Could be a lack of timing advance too.

 

 

for some reason or another, the person who built the motor has done away with the elec. dissy put a 4k points one in. its high up on my list of plans though. points dissy is currently advanced as far as I could take it without pinging

[Felix]

Probably because the advance curve on the electronic dizzy's suck. A points dizzy will give better performance.

 

You should get the dizzy recurved to suit the motor, and get the carbs tuned by someone with a dyno.

[Sidewinder]

what exactly does getting it recurved involve? ive heard it mentioned heaps here in the forum and in the FAQ but i still have no idea?

 

id love to get it tuned on a dyno, but i don't have any carby specialists up here with a dyno. the only people here with a dyno all want nothing to do with carby cars...full sik pretend "performance" shops (I'm sure you know the type)

[philbey]

yeh the old stick in a chip and go fully sick performance shops haha.

 

Inside your dizzy there is a set of counterweights and a guide plate. Recurving it basically means you are modifying the springs and your guide plate to change how the carb advances.

 

Take a look at this

 

The pic just past half way shows the 2 counterweights (cam like) and the spring loaded guide plate. The spring sets how fast the timing advances - lighter equals full advance faster, firmer means slower advance. The slots with the tabs on the outside of the guide plate set the maximum advance.

 

I have a pdf on how to set your own advance curve at home, by using a file and bunch of springs etc. I'll see if I can find it, it's a good read even if you're not doing it yourself.

[Sidewinder]

Good read that!

 

i was a bit worried as my weber manifold doesent have provisions for vacuum advance or emissions..at least the guide answers my questions as to wether or not the vacuum advance is neccesary