Recently picked up a euro spec 175 super shifter engine, I opted for the dellorto VHSB 36 RD carb option as the general consensus seems to be the tillotsons did not work as well on these engines.
I’m located in Australia, driving on mainly shorter sprint tracks and it’s currently summer here so we see ambient temps anywhere from 28-36 degrees C close to sea level and running on 98 Ron pump fuel, 4.5% synthetic motul oil mix
There seems to be some conflicting info about as to what min/max EGTs to aim for on these motors, I was told min 500-520C max 680-700C
Although there is many variables involved, would love to hear everyone’s setups and feedback from what you have found running this carb on these engines, there is one app available that covers this engine/carb setup and it recommends a rather different configuration from how the carbs come pre setup, I found my setup to be very rich all round out of the box.
Tuning to a fixed number is always less than ideal, though I try to set an upper limit…
So long as the EGT is climbing the whole longest straight and not falling off, you’re good. You want the highest number you can achieve, which occurs at the ‘perfect’ stoichiometric mix in your upper RPM range. If it starts falling off, you’re lean and seeing detonation. Since most people don’t want to run the ragged edge, they find a ‘close’ upper number and tune to that.
The advantage of the Tillotson is the ability to turn needles while driving instead of being ‘stuck’ with what you chose. If you choose poorly, you either have to pull in and change or risk damage, or tune conservatively.
Definitely agree that tuning to a number is not ideal, however as with any new engine and working out what the normal feeling is having the data is important to do so.
Just for running laps I personally would never aim for the high end of those numbers for safety, but it’s also nice to occasionally get it in that optimal window to see what it feels like and know where it can go if you want it.
the tillotson is definitely convenient, however from what many have said narrow the power band quite a lot, they are also not great on every style of corner for some.
this post was more intended to hear about others that are running the dellorto carbs and their setups/experiences, ie what needles they found worked for them and how the engine responded to it etc etc
Do you run the 20mm header extension that the 175 SSE uses here in the US? That will change your target EGT’s, as it drastically alters the sensor position relative to the bore, not to mention the exhaust length.
Below are some base/starting carb settings for sprint racing that Ashley (Remo Racing, the IAME Australian distributor) uses for his 175 SS (with the 36mm RD)
As to the app, I find it gives me insanely rich settings (like tubes at DQ273 or higher and a main jet at 195).
On EGTs, the IAME factory told me even low 700s (like 710C) were okay, high 600Cs no problem. I’ve also had problems getting my water temperature up above 50C even with the by-pass loop (which comes standard). I don’t think I’ve ever had decent head temperature and have always run too rich with the prospect that fuel is being burnt in the pipe leading to deceptive higher EGTs. The only time I’ve ever seized was using the Tillotson (I couldn’t handle the high speed needle). With the Dellorto I’ve been getting at least 15 hours out of the piston using BP98 and Elf 909 at 4.5%. When testing the engine on long/road circuits, I was using Elf Race 102, but head office at IAME told me it was a “cold fuel” and I was better off just using the 98 even on road circuits (which I’ve done, including Phillip Island with its torturously long main straight and high speed nature - couldn’t be tougher on a kart engine; I’ve done close to 100 laps (like 400 km) there with the 175 running the Dellorto and not had an issue, it’s an engine package with so much potential including, relatively, minimal maintenance requirements and the ease of an electric start).
Interestingly those base settings are very similar to how the carb pre set for my setup with the only differences being the idle atomiser was a CD1 and air screw 1.5 turns otherwise the same.
I have found with the apps recommendations that they are much closer to the money than the out of the box setup, changing the needle from a k19 to a k28 made a big difference and then the bigger jets make much more sense to getting it in the ballpark, that being said I haven’t run the motor up past EGTs min/max 450/650c but even at that it has been on par with speed to other KZs on our local sprint tracks here.
I am able to get the temps where they are meant to be with my setup, however perhaps a coolant heater would benefit your setup, it is something I am considering doing to assist getting it up to temp quicker as it does take some time to get it in the operating window
Would love to hear from anyone that has played around with any mods on these engines to get any improvements out of them, obviously they are detuned for reliability but would have some good potential if your willing to give up some of that, what have you found has worked for you?
