I have a 4k I built up. It has a Weber , port matched intake and exhaust manifolds . Cam with overlap around 266 duration. Head ported. Double valve springs. Accuspark ignition conversion with gt 40 coil.

Pulls really brutal from as bout 3000 to 5500 then at 6000 just dies in the ass. Any suggestions ? Cheers guys

Your cam is generally mild in the scheme of things. A 2.5k-5.5k peak is realistic for 260-270 advertised camshafts depending on the LSA. It's likely your engine is performing correctly but your expectations have eclipsed its capabilities.

Edited April 10, 201610 yr by GJM85

That's a possibility .

Are you running a 32/36 Weber? What jet sizes are you using? Maybe when the secondaries open it's not optimal.

Yeah 32 36 . 140 secondary and I think 120 primary . Have a 2 inch dodgy exhaust I made on it.

Could it be fuel related ? The mechanical pump out of duty ?

Nah, mechanical pump should be fine. My stock mech pump feeds my worked 5k with a 40mm sidedraft. I'd be looking more at maybe the motor is leaning out above 6000rpm. Or GJM is correct, in my experience 4ks will only pull savagely within the power range of their cam. Still check pressure from the pump, or maybe just replace it in case, bout 50 bucks. Couldnt hurt?

http://www.camtechcams.com.au/toy_4cyl_3k4k.html

 

Camtech 621 has about 260 degrees of duration and is only rated to 6500rpm. I reckon you're just expecting a bit much.

I reckon its as good as you can expect. I have a slightly hotter cam than you with twin SUs carbs and I don't worry about anything over 5500rpm.

 

In the end its a non-crossflow pushrod ancient 1.3L, so don't expect much. You can make it fun around town, but its nothing going up hills at 100kph.

 

You can get a DCOE carb and a hotter cam for 7000rpm, but it will be harder to drive around town in the 2000-3000rpm range. I've put your cam on the bottom of this chart, I have the Crow one marked. The important figures are the durations at 50thou, the lifts max out at 0.4" as they reckon you need new valves springs with more lift than that. I don't think any of these cams would rev easily to 6500, but other things like carbs and port design would make a big difference.

 

You should have a dyno run with an oxy sensor to see if it is rich or lean in the rev range. Then again, you could go for a drive with a plug spanner, run it up to whatever revs with wide open throttle then turn the key off & push in the clutch. Pop the plugs out and they will show you what it is running like at those revs.

 

Check the maximum advance too, maybe a bit more advance will allow it to rev further. What fuel do you use?? 95 or 98?

 

Using a 4.3 diff wakes it up a little over the 4.1, and don't rush for larger tyres on 15" rims... The smaller the tyre diameter the quicker the acceleration.

Yeah I still have original pizza cutters on it. Stock diff . Well it's probably going alright then by the General consensus here. I should stop complaining I guess. It is fun little rust bucket and it's all I ever wanted from it .

Look at your ignition curve, is your ignition recurved / remapped?

Edited April 12, 201610 yr by styler

No it's not , I want to get programmable ignition module but jaycar stop making them

Nooo ..!! Banjo has made a complete programmable igntion system for the K dizzy, but it used one of those as its core!

 

That was on my long-term list!

I reckon you need to look at optimising your ignition curve. That is how you make power.

 

You could track down a cheap aftermarket ECU and use it to run just the ignition.

 

I got an old haltech e8 for $200 and ran it on my g13a Suzuki Sierra engine. Still used the carby but the e8 ran the ignition and I could program it on a 32*32 table at whatever rpm intervals I wanted. Used a GM ignition module and the stock electronic distributor.

 

I also made some diy knock headphones using a knock sensor from a nissan sr20de and plugged it straight into the mic input on my laptop.

 

You could also plug a wideband into the ECU and view or log the data too.

Edited April 12, 201610 yr by ke70dave

You can change your ignition curve either by recurving the mechanical dizzy which is easy to do for a basic curve or

you can get an aftermarket ignition ecu, lock the dizzy and use an electronic pickup sensor to remap. Both methods

change the ignition curve, one is mechanical and one is electronic. Those aftermarket ignition modules can be used in

the mechanical advance setup to replace points and as a pickup for the ecu setup from what I remember. I would suggest

researching ignition advance, its not rocket science but there's definitely some stuff to learn, ie base timing, advance, total

and "all in" rpm. Then you go to a dizzy shop and ask them if its possible to modify your dizzy to suit. Check out altezzaclubs

writeup on recurving a dizzy and see how much the curve changes.

Edited April 12, 201610 yr by styler

http://www.accuspark.co.uk/Blackbox.htm

 

^^These are good, and easy to install/setup.