Perfect DOHC carb set up

[ksqrly]

Ok so I have straight pipes and pod filter. Tuning my carbs with different setups. Right now I have a 135 main. stock is 127.5 and 117.5. Please dont worry about the stock jets sizes being different this has been well debated on other threads. The pilot is the stock size I realize this needs to be bumped up so ordered one size up and two sizes up. I have the needle bumped up one space. It still seems to be running a bit lean, but as far as power goes it is smooth through all revs.

So does anyone have a similar air flow set up if so what are your tune specs. looking to get this thing perfect any input would be much appreciated.

 

[16VGTIDave]

I have a similar setup. Pods and mufflers, but little restriction. 147.5 main, needle raised 1 notch, 45 pilot. It is running a bit rich now that the warm weather has arrived. Going to reduce the mains to 145 and lean out the idle and see how that works.

Changing to a different brand of gas also had a noticeable effect when riding that the plugs also confirm. I usually run Shell Gold which is ethanol free here, and today I tried Esso regular with ethanol (because I was on reserve and no Shell stations close). The bike was still rich just off idle, but crisper at part and full throttle. Plugs are much cleaner. It was also noticeably cooler this evening, so that is another factor... Oh how I wish for fuel injection!

 

[ksqrly]

Did you do incremental bumps up to 147.5. What was the smallest one you tried?

Ya I have been looking at fuel injection. Not that I will be buying one for this bike or anything but there are a few pretty neat little units out there. I think Ictrg, not sure if thats his name but the guy attempting to build the turbo xs, is trying a microsquirt on his bike.

 

[16VGTIDave]

I did. I started with 137.5's last October and went up to 155's by December. I was trying to cure a misfire that started around 7k RPM. Turns out the needles were too low with the clips in the middle groove, so I wasn't able to rev high enough to even get fully on the main jets. And the carbs weren't clean enough, and the mufflers had no back pressure at all, and the valves were shimmed too tight...

Once the valves were set to the largest clearance (too noisy, going to redo them slightly tighter), and the mufflers had some baffling and packing, and the carbs were actually clean, I was able to get the jetting over rich. Now I'm trying to get it leaned out a bit for the warm weather. It takes time and tinkering.

I've been thinking of mega or microsquirt as well. But a 2 into 1 exhaust will come first so an O2 sensor can be used. It's only money...

 

[ksqrly]

Ya I was wondering about the o2 sensor. Do you know if its possible to get two o2 sensors on a micro or mega?

 

[16VGTIDave]

Micro only has one O2 input. The last Mega system I worked on also only had one, but that was a few years ago...

I'm also wondering if an oil temp reading could replace coolant temp? Or where to mount a cylinder head temp sensor to have an engine temp input?

 

[ksqrly]

I dont see why the coolant temp reading wouldnt work as an oil temp reading(but im not an expert). I am completely foreign to fuel injection and until about 5 months ago I didnt know to much about carbs but the idea has really caught my attention.

I really want to see how Icgtr does it on his xs250 bigbore turbo

 

[16VGTIDave]

I just had a thought - on the DOHC engine, there is the screw on the right side of the head that goes directly into an oil galley. That would be a perfect place to measure oil temp. A plan is forming!