Almost got her tuned juuuuust right

[vincejames]

Wanted to pull the group on this. I think 5twins might be getting annoyed at my constant inbox messages; even though he has helped immensely in getting one of my three XSs' back on the road! I'm thinking he will still probably chime in when he sees this...

1978 XS650, BS38s. Recently, installed a PAMCO, running a shorter 2 to 1 exhaust w/ a baffle, UNIs, PMA from Hughs. My Main jet is at 145, Pilot at 40, needle clip setting on the third slot, mixture screw 1/2 turn out (anything more makes the bike run poor w/ no idle).

The bike idles fine with the current set up. The issue I'm having is there are flat spots out of first gear and the beginning of second between 2000 - 4000 RPMs range. Once I get above 4000, I get a nice surge of power. The rest of the gears are fine and I'm actually pretty content with the power from 60MPH to 80MPH - I'm thinking my larger main helps here...

I've experimented with going down on my pilot jet to a 30 and my main to a 140 while adjusting the mixture screw. I do not have any other size jets, and will have to order if I'm going to try others. The bike ran poorly with a 140 main and a 30 pilot and still poorly with a 145 main and a 30 pilot. I've had some poor experience with moving the needle clip (not to mention I had a semi-bad air leak), but have not ran the bike with a the needle clip moved w/ my new PAMCO. I'm thinking about moving the needle clip to the 4th position to richen my mid-range (see attached)

Please don't forward me to the carb guide. I've read it and others and am still learning how to properly tune these bikes - I'm more looking for an opinion from the group to see if how they fixed their flat spots. My other two XSs don't have any issues and run fine. It's just this one that has more mods than the others that I'm currently having issues with.

 

[TwoManyXS1Bs]

Figure out a way to keep it in that 'flat spot' for awhile, like up a hill, or level in a tall gear. Then, install fresh plugs, immediately ride it in that zone, and only that zone, for awhile, immediately kill the engine. Pull plugs, see if it shows lean or rich...

 

[vincejames]

Figure out a way to keep it in that 'flat spot' for awhile, like up a hill, or level in a tall gear. Then, install fresh plugs, immediately ride it in that zone, and only that zone, for awhile, immediately kill the engine. Pull plugs, see if it shows lean or rich...

Thanks for the reply. I will do this. Just an FYI - last time I pulled the plugs they seemed to be lean (a tad white in color). This was a surprise to me because I always thought I was running too rich (backfire etc)

 

[TwoManyXS1Bs]

Yeah, gotta watch out for 'all around' plug readings. They can tell you that you might have a problem, but that's about it...

 

[grizld1]

Vince, if you keep trying to tune in 4-step jumps, you're going to have nothing but trouble. Open your wallet and do it right.

 

[vincejames]

Vince, if you keep trying to tune in 4-step jumps, you're going to have nothing but trouble. Open your wallet and do it right.

"I do not have any other size jets, and will have to order if I'm going to try others."

Believe I mentioned that "I will order if I'm going to try others."

~ I'm well aware of the jumps I am making. I'm just trying to refrain from buying every jet known to man, when there is clearly only a couple I need. But thank you for chiming in. I see your from Carbondale. IL for the WIN!

 

[5twins]

Now that I see a good picture of your exhaust, I think that may be a big contributing factor to your tuning problems. I mentioned to you that short open pipes can be difficult to tune for. Well, so can 2-1 systems. You have the worst of both - a short open 2-1, lol. The problem with many of the 2-1 systems is they are made mostly to fit (mount to) the bike in question but little regard is given to the performance part of the equation. The header pipe lengths, diameters, and the collector diameter usually aren't ideal. The collector, in particular, is often too large. Some have gotten improvements by sleeving it down, reducing it's I.D. I don't mean just sticking a baffle in it like you've already tried. I mean reducing the outlet diameter, maybe with something like this .....

https://www.ecstuning.com/b-ecs-par...N0p8GSdWT9agXpP0Ze94Q-XOubMaFcjmETRoCEW_w_wcB

 

[vincejames]

Now that I see a good picture of your exhaust, I think that may be a big contributing factor to your tuning problems. I mentioned to you that short open pipes can be difficult to tune for. Well, so can 2-1 systems. You have the worst of both - a short open 2-1, lol. The problem with many of the 2-1 systems is they are made mostly to fit (mount to) the bike in question but little regard is given to the performance part of the equation. The header pipe lengths, diameters, and the collector diameter usually aren't ideal. The collector, in particular, is often too large. Some have gotten improvements by sleeving it down, reducing it's I.D. I don't mean just sticking a baffle in it like you've already tried. I mean reducing the outlet diameter, maybe with something like this .....

https://www.ecstuning.com/b-ecs-par...N0p8GSdWT9agXpP0Ze94Q-XOubMaFcjmETRoCEW_w_wcB

Link does not work, maybe send me the path instead...

 

[5twins]

Hmmm .... works on my computer. This is what I meant, a reducer that has a slotted end to match and clamp on your collector, and a smaller outlet .....



Auto parts stores have lots of them in all different sizes.

 

[weekendrider]

The link worked for me also and now is showing in the pop up ad at the top of the page.

 

[vincejames]

Well I have this in there. But, I straightened all of the little cut outs, so technically it's like a reducer. Ha

 

[vincejames]

Wanted to just jump back on and comment. I took the bike out for a nice ride. Still has great idle and great power from 50 - 60 MPH. The issues continues and this time right off idle in first gear! Cracked the throttle open as I left a red light and the bike was just flat, no power. Once it got going a little, boom, it's like the bike got hit with paddles ( you know those ones docs use for CPR), flew right up to redline.

Waiting on all of my jets to come in. Sure hope I don't have to go up in size on my pilot. Running anything larger than a 40 pilot kind of scares me...

 

[weekendrider]

Maybe it isn't jet size or jet clogging, but obstruction in the pathway. That is something that only be cleaned chemically or with pressure or both?

 

[vincejames]

I've gone through the carbs many times with air and carb cleaner. I've also replaced the throttle shaft seal.

Thanks.
Vince

 

[vincejames]

It's just a pain in the butt. It's the last thing I need to correct to have this thing running perfect. I guess it's going to just mean more and more and more testing!

 

[weekendrider]

You have good "flow" through all the pilot circuit orifices in the throttle body when spraying whatever? Sometimes one or more is plugged.
And you have cleaned both ways, from the bowl side and the throttle body side(by removing the mix screw and covering the outlets with your finger)?

 

[vincejames]

I'll go ahead and give it another thorough cleaning. Thanks, weekend.

 

[B Burdine97]

Sorry not to jump on your thread and change subject vincejames.. But are 2-1 systems that hard to tune? Because Im looking into mikes 2-1 system with a reverse megaphone muffler he sells (17.25", part no. #07-0112) aswell.
Love the look of your bike as well vince!

 

[vincejames]

Well, I'm currently dealing with some pretty terrible flat spots. The engine just falls flat on its face then eventually gets going and there is a nice surge of power. I'm thinking it's mostly because of the 2 to 1.

A little more tuning and I'll get the carb just where it needs to be with that exhaust.

I don't think you should just go and throw a 2 to 1 on your bike and think it's going to run be same. It won't, and you'll be adjusting your tune like I am. By try it out!

 

[mrriggs]

When I had the BS38's on my bike years ago there was a flat spot that no jetting would cure. The issue was the jet needles. I tried a few different needles that I had from other bikes but none of them were right either.

With the CVK34 carbs I was having similar issues until I replaced the dual-taper needles with straight taper needles from an "offroad" carb. The straight taper needles are available in all different tapers, diameters and lengths so I was able to dial it in perfectly.

I'm not sure if there are any straight taper needles available to fit the BS38 carbs but it's worth checking into. Grizld1 was right when he said you are going to have to open your wallet to do it right. I spent hundreds of dollars on jets and needles to get a $50 set of carbs working well.