Su Tuning Help Needed

[tojo2]

but have a step out from the carbs to the manifold.

 

 

Not something I know but got a feeling that step could be causing some mischief

[altezzaclub]

Well, last night I had the airbox off and lifted the slides to see how the throttle plates compared in their idle position.

 

There is a small (few mm) distance of freeplay in the dashpots (slides) before the shock absorber works in the oil properly, so the slides jump up quickly to start with.

 

One slide had twice the freeplay of the other, meaning it might flutter up and down quite differently. I played around with them and found it was much more even if I swapped the dampening valves over between the carbs. I'll drive it today and see if that helps.

 

You may be right, but I hope not! :abuse:

 

It would be a lot of work to pull it all apart and match the manifolld & carb with epoxy. Certainly it must be generating swirl vortices at higher air flows, but the problem is only from 2000rpm down to 1000rpm with zero throttle on over-run.

 

At that stage the throttle plate should be on idle and the engine has high manifold vacuum as it sucks hard to pull air through the closed throttle plate. I'm using closed throttle plates, not the newer ones with the relief valve set in them, (44 in the diagram) so there's another thing to look at.

[altezzaclub]

Well, its slowly smoothed out over the last couple of weeks.

 

I opened the tappets out to 16thou, as Crow Cams said in their specs, rather than the Toyota 10/12thou I had them on. Now you can hear them, whereas at 10/12 they were dead quiet. I might take them back and see.

 

...& it was off to John Kane's dyno today where he set the mixtures on the new needles.

 

He said the new needles work fine right up to max throttle, where they're about 2% lean which won't be noticeable.

 

The remnant of the over-run is from the cam as it gets down to 1200rpm, but its hardly noticeable now.

 

So... 'rolla sorted.... next project!

[tojo2]

Good news. Any figures from the last dyno?

[altezzaclub]

nah- he didn't offer any and I didn't ask... ;)

 

It cost me $20 to have him look at it, check the exhaust gas and set the mixture and idle... I think he just ran it up on the dyno to get mixture under load.

 

The first visit he went over the tuning generally, changed the points and said it was lean right through the range... for $110.

 

We did go and check the road dyno we used before we did the work. Not much change going the 'downhill' way if I ran it 2000-4000rpm, but taking it to 5000rpm took it from 19seconds to 14.5seconds. Going the uphill way, same 20kph to 100kph went from infinity (never got to 100 going uphill!) to at least holding 98kph!

 

Its definately much better doing general country driving in the hills around here.