TBO88

iTrader: (24)

I have a new OS Speed Spec 2 . Leaning out to race settings and the motor will not go back to idle. Stays on high RPM then eventually goes down? I have taken needles out of carp and cleaned, tried different pipes,lengthened both pressure and feed lines. Took carb out and put back made sure all the way down. Big race in < 2 weeks bought this motor for HP and getting real frustrated at this time. Anybody help?

chippy

iTrader: (4)

Sounds like the bottom is to rich with the combination of the Idle to high.

TBO88

iTrader: (24)

I turned the bottom end in and it is worse?

chippy

iTrader: (4)

Ok then go the other way out and see if this settles it down quicker.
Is there excess fuel anywhere around the front of the engine if so the front bearing may be gone and need replacing. This can also make the engine run on.
The OS engines are notorious for that.

TBO88

iTrader: (24)

No fuel around bearing. It is brand new. I did go fatter, very sluggish in ramping up RPM

MaxTech

Your top needle in too Lean backoff 1/4 turn and then try run it hard for 2 mins before tune it again, Spec II has a very sensitive carby so lean it in with small inclement, The Spec II definately dont like to run hot, my engine run best at 95-100C with no shortage of power and runtime. also what pipe you are running with? that is another thing can make the engine ran hot and high idling.

TBO88

iTrader: (24)

I had a RD logics turbo 3 on, tried a IDM 2607, have a skyline vr12+ on now

MaxTech

Dont know about the RD logics but the other 2 is not quite suitable for Spec II which I have tried, and the best suited pipe is OS 1050 and Maxpower 2602The Max pipe is run it cooler then OS pipe but both can give you heaps of power and 5mins of runtime.

TBO88

iTrader: (24)

I do have an OS speed 1040 L52, on our other car. I will try that pipe tomorrow. Did you mean 1040 not 1050? I never heard of a 1050

MaxTech

1050 is the new pipe from OS, I think pipe is same with 1040 but different head

yeh 1040 will works but a bit thustier.

Mazda614

iTrader: (1)

TBO88,

The 1050 is the best pipe for the Spec 2. As for your tuning problems, HSN should be set at approx 2.5 from closed ( factory standard), this is a good start position. Start with the LSN out approx 3.5 turns from closed and run the engine on the starter box until at temp. The high RPM hang up is caused by the LSN needle too lean, slowly start leaning the LSN needle and observe the RPM coming back to idle, you will soon reach a point were the idle will start to hang up again, then back off 5 mins. The HSN needle can then be leaned but usually no more that 1/2 turn otherwise the engine will start exhibiting the same problem. Tuned correctly these engines are a blast especially with the 1050 pipe, good run time and heaps of mid to top end power.

TBO88

iTrader: (24)

I did all that was suggested and still have the problem. The idle seems to come down in steps.If i go out anymore on low end needle engine is flat from low to mid.

afm

This is a very tricky symptom with OS carbs but first of all I suggest you go back to factory settings, specially on the LSN needle, than just work around the HSN needle and the idle screw.

When you run it hard and you come into stop the engine seems to have a very high idle and then starts to drop in increments, it is because you have to much fuel left in chamber and engine has to burn it before idling, so try leaning the HSN needle a little at a time while reducing idle speed opening idle screw. It is very tricky, but just be patient until you find the right balance.

Trust me don't fool aroaund to much with LSN. OS carb is different than Nova and Picco carbs.

AFM

MaxTech

TBO88, your are in the right track now, Do it as per AFM said and you will have 1 of the fastest engine in your track