Thanks Alan. This matches my experience so far. The pinch is pretty tight from my little experience with smaller engines. I'm glad to hear that this should smooth out.

I am in the initial tuning phase of brake-in and less than a 1/2 gallon through the engine so far. I am running 30% MK (Brazilian blend) fuel with an OS P4 plug, 2035 Pipe and the two small head shims that came installed on the engine. The local rep in Brazil has helped me a lot with the details of tuning this engine and has been running them for the past 3+ years. Currently my engine is running fairly well but I think it is on little rich HSN and a little lean on LSN. I am getting good smoke and crisp response in all throttle positions and the idle seems OK only. I was tuning idle yesterday expecting a high speed for a few seconds and then settle to a lower speed indicating rich. I would run at higher RPM to clear out the crankcase before entering idle. What was strange was after I dialed it in stable with little droop and smooth low idle I would get a higher speed surge for a short time. I would run high and enter idle smooth and after a few seconds the idle would increase for a second or two and then settle again. I am thinking that my HSN is rich loading up the crankcase such that the idle is good to start and then leans out until stabilizing. I need to run it more this weekend to adjust the tune further. My HSN is at 3 3/4 and my LSN is 1 3/4 right now.

Head Shims:
My local rep stated that 0.55mm is what he found as the best thickness for 30% fuel running the OS P3 plug. I am getting a dail caliper to measure the shims provided with the engine to select shims to get close to this. Has anyone else measure head shims to determine their best selection for a OS P4 plug? I only have P4, RT4, RT3 and colder plugs right now.

I hope to finialize break-in this weekend and burn through most of the MK fuel I have. I hope to switch to Byron or O'donell 30% Race blend fuel.

I have found that the idle on these engines will not settle in the way you want until after about a gallon of running. Then it will be very stable to where you can fine tune it nice and low without stalls.

Also this engine is very easy to have the low needle too lean because it will mask it very well. It will idle ok and bottom end will seem ok but that is because you top end is too rich... but the engine will run hot... Once you get used to tuning them it becomes easy but every brand tunes a bit different.

But all in all I am VERY happy with the power these produce! My truggy has never been happier :-)

This past weekend I was struggling with tune during practice and qualifying, running a 6.5 restrictor and the stock .4 head shim, and 97T plug. The smaller restrictor will narrow up the tuning window, but was needed in order to make 10 minutes in highly competitive field and everyone pitting at 10.

I switched from the .4 to .5 shimming and the tune got easier and no more flames the rest of the weekend. The engine was smoother with just a slight loss of power. I believe in more humid condition that higher head shimming seams to work better. I also recommend the break the engine in on the 8mm, because it widens the tune window and makes for easier break in, lots of power too :-).

I have found the same result with the 8mm insert for break-in gives a much better tuning window and makes the break-in process go smoother.

I will play around with shimming next time the heat and humidity go up.

I am running the 8mm insert and plan to test with the 7mm for racing most likely. I have ordered a dial caliper so I can really measure the shims well and tune even more. I will keep posting my results here as I progress. I expect to go to the track this weekend, most likely Sunday.

Seriously? I'm having a few issues getting a strong idle. When I just saw your needle setting I'm a little blown away. That's so different than where I'm at that I'm questioning wether I'm that far off or not.

My needles are closer to 2 1/2 HSN, 3 1/4 LSN which is completely different.

I personally think you are pretty close to a good tun with those settings. If anything you may be a little fat on the bottom with a bit too wide airgap... Just my guess but that may be why the idle is not good.

Ok, thanks for the insight on it. I'll give it a try and see how it goes .

I do have the idle gap around .5mm so I'm thinking it's got to be pretty close? Like you said..maybe it is just fat on bottom and leaning it slowly will yield a stronger idle.

When I pinch the line I get a nice solid 4-5 seconds with very slight increase in rpm before the engine dies so I "think" the idle gap is set already.

Thanks for the help.

I did state that I think I am rich on HSN and lean on LSN. The pinch test for me is only about 1 second pinching at about 2 inches from the port. I am at my first real settings that work on my starter box. I have not measured my throttle opening yet.

I will post my final settings after a full gallon of fuel. What fuel and plug are you using?

My lsn needles are usually right in the area of 2 3/4 to 2 1/2.

Cool, thanks for sharing that info. I'll likely work my way more towards 3 turns and leaner to see how she goes. What is your HSN setting around?

I'm definitely going to go to the track and test it a bit leaner on the bottom, just want to confirm if the HSN is close to what most see.

I do notice that the lsn tune seems to have an effect the hsn tune a little bit due to the carb using a long low speed needle that stays in the way at wide open throttle.

Are y'all talking about needle turns from bottomed out or from flush?

From bottomed out, flush is too hard to judge.

By the way I went to the track today and messed with the settings a bit and am getting closer. I think you guys have pointed me in the right direction and I'll have it idling good soon. Definitely have a slightly wide idle gap to make up for a rich lsn. Only thing is with the long needle carb like these I have to remember to richen the HSN after getting the LSN\idle gap leaned properly.

It's a delicate dance compared to the short LSN carbs and I'm not used to it......not quite yet.

Thanks for the help

I am not quite used to it yet as well. That is why I am tuning the HSN first which sets the inlet flow for all speeds. Then the idle air and fuel are based on the HSN settings.

The manual describes the break in process and then tuning after of the HSN. The process is a little flawed. I think they need to change this process. The HSN should be tunied first.

OK. I got my dial caliper and finally tuned the engine fully. I have about 1/2 gallon of 30% fuel through the engine at this point. I have the following settings:

1) 8mm insert
2) 0.49mm head shims
3) Reedy 2035 pipe
4) HSN = 3.0 turns
5) LSN = 2 3/4 turns
6) OS P3 Plug

The engine performed OK. The HSN seemed to be rich a little. If I increased fuel it ran a little rough at high speed. I am assuming this is too rich. The heat temp was at 130degC after about 6 minutes of hard running. The tune changed a lot as I broke in. I would like to learn how to measure the idle air setting. I had to add air and idle fuel each tank.

I plan to try 0.59mm of shims to see if the performance is smoother. I would like to get to 0.55mm since I was told this is an optima. I would need to sand down a shim to get there without new shims. I hope to improve more at the next test and tune session. First race is planned for 30 Sept!!