Gentlemen,
need some ideas/stats on the HSR42 pilot jetting please!

Here's the story: brand new stock evo, almost straight pipes (baffle is around but straight through, cigar shaped, think of springer stock with the divider in the middle punched out - not sure if it works exactly as straight pipes), stock airbox, no "baffle".

So, the main jet turned out to be 165 (what it comes with), very easy to establish, straight forward. But I'm not sure on the pilot jet, tried bigger and smaller, still feels not right. The starting is very hard, and the mileage is terrible (31 - 32 !). Now I lowered the needle one notch (2nd from the top now), will see about the mileage, but the bike feels better at mid-range.

I did have some minor air leak issue before (there's a whole thread on that), but it seems I fixed it. Also, I checked that there is play in the enricher cable, so it means it closing properly. Judging by the plugs, I'm still slightly on a lean side.

So, I'd like to know what doe the pilot jet usually comes to, esp on nearly stock engines with straight/ free breathing pipes...

 

The needle taper really doesn't do much until you are above(1/8th throttle) 2,500-3,000 RPM's. Most of the normal riding is basically done with the idle/low speed circuit and the needle jet/needle diameter. So moving the needle up or down it is still in the straight part of the needle and has little affect on mileage. the pilot jet , idle mixture screw and Enrichner can affect mileage the most. The enrichner must have the Mikuni enrichner/starter plunger and spring and must have slack in it. Too large a pilot jet will obviously affect mileage. When adjusting the idle mixture most people turn the screw in until the engine stumbles, then turn it out until it stumbles, then set it in the middle. The screw on a Mikuni is an air bleed, so if you turn it out till it stumbles then torn it in until it stops, this will leave it on the lean side and gain a little mileage. If you have it set at more than two and a half turns the the jet is too large go one step smaller and repeat. Lastly go to Lowe's etc and get some metric allen nead set screws for the float bowl, they will make life a lot easier. Just don't overtorque them they aren't head bolts!!
Hope this helps
John

 

Thanx MiaCycles, actually a friend of mine suggested the hex screws yesterday - since I've already stripped two! Very good idea!

Now, you say pilot jet works at 1/8 turn, but my mileage measurements were done at highway speeds - around 65, which is a 1/4 to 1/3 turn. So, can we say at that point the needle taper is already working?
My pilot then was 27.5 - and still somehow hard starting. The screw ended up slightly above 1 turn out. I wonder why so big (the "stock" is 25), while the main is just normal?
Would straight pipes do that?
I ran these pipes before with S&S stock jetting, bored Evo, EV27, and my mileage was way better

 

Pilot should be in the 25-30 range.....usually they are correct right outta the box but had one in here last month that came with a 12 pilot jet.....ran like ***** until we fixed that.

 

I'd be willing to bet you don't have the throttle open as far as you think you do. Take a piece of tape and wrap it around the throttle and put a wark on the stationary part and a matching mark on the moving part of the throttle. Next open the throttle all the way and put a second mark. Then take a good ruler and put a mark half way between the two, this gives you half throttle. Repeat the process until you have marks at 1/8, 1/4, 3/8, 1/2, etc. Now go out and ride the bike and you will see where you are riding throttle wise.
If you end up below 1 turn out(which you are close) then your pilot jet is too small, more than 2 1/2 the your jet is too large. Your idle should be around 950 RPM's any slower and you can get hard starting. Set the accelerator pump to at least .080" and try to go larger unless you get a hesitation, then go back. The straight portion of the needle is in the needle jet from 1/8 to 1/4 throttle so if you are too rich or lean in this range you need to change the needle for a larger or smaller one.
John

 

So I guess there will be nothing wrong if I end up with 30, given kinda straight pipes?
Would this actually contribute badly to the mileage?

 

Idle jetting has minimal impact on MPG, needle, main and ign timing will affect that as well as pipes and air cleaner.

Straight pipes without lollipop baffles are not the best option on a Harley....you have to jet so rich to minimise the mid-range power dip that consumption goes up alarmingly.

 

Oh yeah....my experience with HSR42's is that they are pretty juicy compared to a CV so you may not get that gas mileage back to where you want it.

 

Jokenroll, the adjustable nut behind the throttle also plays a big part in mileage. Usually for a while after any performance modifications mileage drops until the rider settles down, pluss there are the throttle runs to check mileage too. Don't forget to check the accelerator pump setting, if you have it set too tight mileage wiil drop a lot.
John

 

You're right about this. Compared to the stock CV carb, I find the Mikuni to be very sensitive to how much right hand you apply. With the CV I used to get 48-52 MPG under any conditions, With the Mikuni, my mileage varies from 38-48 depending on, well, everything. At the end of the day, the Mikuni, great carb that it is, will never, in my experience, match the efficiency of the CV carb.

I have my Mikuni set up with the "mileage" kit developed by Joe Minton. It works great for me, but since the settings seem contrary to what you guys are saying, and are NOT recommended for straight pipes, I won't go into them here.