bs 34 or 38 ?

chilliwackwestie · Full Member Joined: Sep 26, 2008 Posts: 37

Which setup is better ?
I have a set of each
which should I use ?

Cheers

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

If you don't use the 34's and want to part with them let me know. I have some side covers for a 78 id trade or just buy em. I realy just need the casings , the choke on mine doesn't stay open on its own in 1 and 2 position, and the tube to the pilot jet has a nick on it.

pumps · Posted: June 27, 2009, 9:53 pm Post subject: Re: bs 34 or 38 ?

Use the 38s as the 34s are emission type and not as good for performance. Read this from mikesxs.com

www.mikesxs.net/tech_tips.html

weekendrider · Posted: June 28, 2009, 12:12 am Post subject: Re: bs 34 or 38 ?

For me the 38's are easier to get in and out/off and on.
It's easier to clean the pilot circut on the 34's and checking fuel level in the bowl is easier with the spigot on the 81-83 34's.
I like the choke arrangement on the 80-81 34's better than the cable choke on the 82-83's.
Each has it's merits. So I guess it is individual taste/liking.
There is a difference in the depth between the two so stock airboxes for one will be tough to use with the others. I forget exactly but I think the 34's are 1/4" to 3/8" longer.

yamalama · Full Member Joined: Nov 14, 2008 Posts: 26

In my opinion, the 34's are the best choice. I like the single fuel T, Their also lighter than the 38's. which is nice if your running pod filters. you do have to tweek em a little, take the caps off covering the mixture screws, turn them out about 3 1/2 turns. Its been my experience that the stock pilot and air jet work fine. The stock needle and needle jet. are pretty right on even with pods. up about two main jet sizes and your good with pods. I agree with XS John, the BS34's are superior carbs for the XS650, one of these days Iam going to try a set of his needles.

pamcopete · Posted: June 28, 2009, 12:35 pm Post subject: Re: bs 34 or 38 ?

Well, I also prefer the 34's. I have 38's on my '78/E and 34's on my '81H.

The 34's must have been made with greater precision because they were under the scrutiny of the FEDS for emissions. The result is smoother overall performance, better idling and they hold their settings.

To say that the 38's are better for performance is probably based on the fact that they are richer, but I believe they are richer to compensate for their lack of precision.

I run both with stock everything. Jets, needles, idle mixture, float level etc. and per my comments on another thread, I think the key to successful carb performance is to sync them properly instead of screwing with jets, needles, float level and idle mixture.

As for the 34's being too lean, I have never experienced any pinging, knocking or detonation on my '81/H even on the hottest days using 89 Octane.

PS: Rich mixtures were used in multi cylinder, carbureted engines with a manifold feeding several cylinders. The richer mixture was introduced to satisfy the leanest cylinder at the expense of the not so lean cylinders.

Non of that applies to the XS650 with a carburetor per cylinder, especially with the BS34's that supply a uniform mixture to each cylinder due to their precision metering.

dpmphoto · Posted: June 28, 2009, 12:46 pm Post subject: Re: bs 34 or 38 ?

I have both and really see no difference in performance if both are properly set up,went up one size on main jets and that's it.To be honest I don't see a huge difference with new after market carbs although I have never used delorto''s or whatever there called,just too much money and parts are not cheap either. Now I'm gonna get a boatload of s*** from mikuni guys. Hey I can get the front wheel off the ground with the stock carbs and 17-29 sprocket setup no prob.

xsjohn · Posted: June 28, 2009, 12:47 pm Post subject: Re: bs 34 or 38 ?

BS34's will obviously run on minimum epa fuel settings .........but they will run a bunch better and cooler set up correctly........

xsjohn

pamcopete · Posted: June 28, 2009, 12:50 pm Post subject: Re: bs 34 or 38 ?

xsjohn

I don't think that the EPA ever mandated a mixture other than the ideal of 14.7:1. They just said it had to be consistant.

xsjohn · Posted: June 28, 2009, 1:01 pm Post subject: Re: bs 34 or 38 ?

14.7-1 may be idea for a water cooled engine that maintains 190 or so cylinder temps.......go for it ...........

It is widely accepted that 13:1 is a good safe ratio for normally aspirated engines.......and gas is also a coolant.......

Full rich on airplane engines is about 12-1.......

Overly rich will wash the rings and cylinders if overdone........lean will just fry everthing........

epa should keep their noses out of air cooled engines.............

xsjohn

pamcopete · Posted: June 28, 2009, 1:44 pm Post subject: Re: bs 34 or 38 ?

xsjohn,

Well, yes John. I stand corrected. More like 12.5: 1 to 13.5:1 for an air cooled engine.

The point is that the EPA did not take it upon themselves to redesign the engine and it's fuel requirements. They simply mandated that the fuel mixture had to be more consistant.

The result of this for us was a better carburetor in the BS34. A more precise and better built carburetor.

xsjohn · Posted: June 28, 2009, 2:01 pm Post subject: Re: bs 34 or 38 ?

""""""""better built carburetor""""""""

No doubt in my mind......but the stock BS34 is to lean...all the way across the board......I started with 55 MPH and cylinders temps pushing 275 and some times higher and now I get 55 MPG and have lost over 30 degrees or more...haven't seen 240 yet theis summer and it's been 95 already........and it runs 10 times better.......take it for what it's worth.....but what would I know ....I have only been tuning motorcycle carbs for 40 years....and was trained by Yamaha...............

xsjohn

pamcopete · Posted: June 28, 2009, 2:10 pm Post subject: Re: bs 34 or 38 ?

xsjohn,

Well, I too get 55 MPG with a stock BS34 on my '81/H, so I must be burning the same amount of gas as you are.

xsjohn · Posted: June 28, 2009, 2:15 pm Post subject: Re: bs 34 or 38 ?

Na....you haven't factored in gearing and temperatures or performance.........yours must be scalding...............pushing 270 I bet if ridden over 10 -15 miles.....and squalling the engine on the highway no doubt...........

xsjohn

pamcopete · Posted: June 28, 2009, 2:50 pm Post subject: Re: bs 34 or 38 ?

xsjohn,

Well, none of the above. I was getting 50 MPG until I installed Mikes 17-6822 coil, which has a much longer spark duration. Longer spark duration results in a more complete ignition of the initial "kernel" of flame that in turn produces a more complete combustion of the total mixture in the cylinder.

The latest MPG calculation was after a run on the Interstate at 65 to 70 MPH for 50 miles combined with 50 miles in town. I think that stop and go traffic heats up the engine a lot more than a steady run with lots of air blowing over the heads.

I think that if I was "pushing 270F" the engine would probably sieze up because oil quits working at about 240F. But, I am using Pennzoil 20W50.

John, you probably have a point to be made here, but exagerating isn't helping.

xsjohn · Posted: June 28, 2009, 2:59 pm Post subject: Re: bs 34 or 38 ?

""""""""I think that if I was "pushing 270F" the engine would probably sieze up"""""""""

Spose you measured all the temps after the highway run........I have only measured these things at least a 500 times and countless others have too......what is this exaggerating crap...............

xsjohn

pamcopete · Posted: June 28, 2009, 4:27 pm Post subject: Re: bs 34 or 38 ?

xsjohn,

Well I did exactly as you suggested. I just came back from a two way run on the Interstate for a total of 10 miles. Stopped the bike and read the right side head temperature with an infrared thermometer and the highest reading was 260F right around the spark plug.

This is with an ambient temperature of 94F, so higher than I thought, but not exactly pushing 270F.

There was no evidence of "squalling the engine" whatever in hell that means.

On the plus side, I also removed the "points" cover" on the left side and the temperature of the PAMCO was 200F. Well within the 302F max temp rating.

xsjohn · Posted: June 28, 2009, 4:33 pm Post subject: Re: bs 34 or 38 ?

Run it another 20 miles or so .....like 30-40 total.....you will find your 270.........

And I have found that the side of the cylinder can run hotter than the head...especially the right side...........

xsjohn

pamcopete · Posted: June 28, 2009, 5:46 pm Post subject: Re: bs 34 or 38 ?

xsjohn,

Well john, I may well do that, but probably on a cooler day than today. The reading of 260F was with an ambient temperature of 95F. I had done readings of the PAMCO before with an ambient temperature of 75 to 85F and the PAMCO temperature was below 200F, like in the 180 to 190 range. So, that is about 7% lower. So, I would expect that a 20 mile run at Interstate speeds (65 - 70MPH) with an ambient temperature of 80F would produce a cylinder temperature of 260 - 7% X 260 = 241F.
y main purpose in doing the run today was to see what the PAMCO temperature would be on a 95F day. Well, it's 200F, well below the 302F max operating temperature.

Getting back to exageraiton, just for a moment...are you suggesting that the cylinder head temperature continues to rise and never stabilises? Like a 50 mile run will be hotter than a 20 or 40 mile run? What would the temperature be after a 100 mile run?

xsjohn · Posted: June 28, 2009, 11:26 pm Post subject: Re: bs 34 or 38 ?

10 miles is not enough to find the peak temperatures....... and these running stock can get 260-265 degrees on the cylinders especially the right side after 40 miles even on a 70 degree day........and on a hot day more...

xsjohn

nudude53 · Posted: June 29, 2009, 12:56 am Post subject: Re: bs 34 or 38 ?

Ok now kids, fight nice.

A few of questions....
Before I installed the Pamco I was running the dual lobe single points set up and was getting 55 mpg on the long hauls, I haven't checked the mileage since but it seems to definately run smoother since the switch. I'm running stock '73 BS38's with a 132.5 main jet (up from 130) with the 4JN19 needles clip in the 4th groove, K&N type pods, Autolite 63 plugs, Mobile1 synthetic oil and nearly open pipes. The empty weight is the stock 427 lbs.

Q: If I switched to the BS34's would it increase my mileage, performance, relibility and cooling significantly?

Q: If the failure point of the Pamco is 302F isn't that a little close to the heat window of the engine?

Q: What mods similar to the alternator venting could be done to keep the Pamco cooler without sacrificing the integrity of the unit?

I'm not looking to break the land speed record, just reliability and endurance.

pamcopete · Posted: June 29, 2009, 5:40 am Post subject: Re: bs 34 or 38 ?

nudude53

The measured temperature of the PAMCO was 200F when the cylinder temperature was 260F and the ambient was 95F. The cylinder temperature would have to get as high as 392F in order for the PAMCO to get to 302F, so I don't think the PAMCO operating temperature range is close to the heat window of the engine. This test was done with an '81/H and stock BS34 carbs.

Rather than worry about arranging more cooling for the PAMCO, you can cool the whole engine down by using johns needles. I'm sure that they work, but I can't use them because I have to always relate to a stock setup when talking about the PAMCO.

nudude53 · Posted: June 29, 2009, 9:02 am Post subject: Re: bs 34 or 38 ?

Thanks Pete
John and I have dicussed the earlier 4JN19 needles but so far he hasn't the chance to really spend any time refining them yet. I believe his focus has been directed to the mass numbers of later model bikes that are out there having problems.

Q: Any plans for a Pamco for the BMW bikes?

jerseykat1 · Full Member Joined: May 03, 2009 Posts: 79

i am with john on this one, it's jsut common knowledge that a richer mixure runs cooler and thats the bottom line. Now as for cylinder temperatures go i have no idea what my cylinder temps are or where before i installed johns needles, But i can tell you that the engine runs cooler (based on how hot my right leg used to get, and more so than my left leg), stronger, i don't get ANY popping or backfiring that i would occasionally get with the stock needles.

I can't speak for pamcopete ignition system as i don't have it installed, But generally speaking if his ignition system allows for a more complete burn thus creating more explosive energy (energy=heat), i would think that richening the mixture a bit would be benificial in that it will create more power (powere aka engergy) and thats always a plus.

when tuning an engine for performance or just plain drivability, I and many others believe that cylinder temps should always be monitored, it's a really good indication of whats really going on in an engine, sometimes you can't always hear pinging especially if your going down the highway at 65-70 mph (pinging usually occurs under heavy loads, 65-70 mph is considered a heavy load), but the cylinder temps will tell the complete story.

Not trying to bash anyone. My stock 34's with johns needles made my bike more enjoyable to cruise around with and only took 20 minutes to install.

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