Switched from Pro-Pipe to CS slip-ons & mileage dropped 5 mpg

[Azgunner]

Has anyone ever seen such a mileage drop from just a pipe change, I know most people go from the CSs to a Pro-Pipe rather than the other way around?  It smells pretty rich at start-up & when the engine's hot it doesn't fire right up, it seems like it's too rich & takes a couple of turn before it fires.
I'd like some opinions before I change any more jets or do a Dyno tune.

Thanks.

[FLTRI]

Since you have completely changed the fuel requirements by changing from a 2into1 system to a 2into2 system it makes perfect sense that the bike will need complete retune.
Same goes for the other way around.
Hope this helps,
Bob

[blk-betty]

You say change jets so I assume you have a carb?

What is you set up now?

I've had great luck with the stock CV 40 by just replacing the stock low speed jet with a 46, keeping the main at 190 (stock on my carbs) and raising the needle with two #4 brass washers.  Although I never had the bikes dynoed, this setup seemed to do well regardless of the pipes I used and mileage never really varied more than 1-2 mpgs and I couldn't tell any drivability differences to suggest too rich or too lean. 

Of course a proper tune with a/f reading as Bob suggested would answer your question much better than my seat of the pants anecdotal experience.

[Azgunner]

I run a 44CV with a 50 slow, 110 reamed to about 115 main, & L needle. 95" with Dewey's heads, 37G cams.

[FLTRI]

"110 reamed to about 115 main"
Did you mean 210 reamed to about 215?
Then the question is how and WHEN was it determined to ream out the main to a larger size?

[Azgunner]

Oops, yep that's supposed to be 215 main. I had the bike dyno tuned when I put the Pro-Pipe on. The tuner opened up the 210 jet to what he figured was 215. I know that is not an actual jet size. At the time it was being tune I also had a Woods KT-3 needle in the carb.

[FLTRI]

"At the time it was being tune I also had a Woods KT-3 needle in the carb."
Maybe BINGO!
Was the KT-3 needle removed? And now you are getting poor mileage?
If so, you need to know the needle actually resides in the main jet's bore so if you put a skinnier needle in than you removed it could run a bunch richer.
Also, was the jet tube/emulsion tube replaced also?
If it were me I would return the carb to stock parts thoughout and put a 46pilot, shim the stock needle with 2 #4 washers (.035-.040) with the stock main jet, what ever it was as they are usually plenty big/rich from the factory.

[mayor]

I'd just try running the L needle with a 210 or a 220 main.  I would be leary of running a jet that someone reamed unless they used a specific sized (2.15mm) drill bit. 

[Azgunner]

Was the KT-3 needle removed? And now you are getting poor mileage?

Actually I went to the L-needle hoping it would help my MPG. The emulsion tube is stock. I think going back to stock is a good idea at this point. Stock needle N9ED (what ever that tells ya), 50 slow, & a 210 main.

The profile of the KT-3 needle is a lot smaller dia. than the stock needle for the 1st .275" from the tip of the needle. It also has 3 tapered profiles while the stock needle only has 2.

- KT-3= Ø.05 for about .275" from the tip of the needle to its 1st taper.
- Stock N9ED needle= Ø.064 at the tip & tapers to about Ø.079 within the same .275" length from the tip of the needle.

If I remember correctly, before I installed the L-needle I did compare it to the stock needle & there was only a couple of thou difference in the dias. & I can't remember which one was lightly larger, not sure on the angle of the tapers.

Thanks for the help.



[attachment removed after 60 days by system]

[Don D]

Bob
Are you confusing CV40?
CV44 a good start is a 48 pilot and stock needle and main IME. Just that switch and you may see some good mileage jump. Do some plug cuts.

[FLTRI]

Bob
Are you confusing CV40?
CV44 a good start is a 48 pilot and stock needle and main IME. Just that switch and you may see some good mileage jump. Do some plug cuts.

OOOOOPs, yep, sorry. The basic stock 44mm carb out of the box should be a good starting point, maybe a bit rich on the main.

[mayor]

Actually I went to the L-needle hoping it would help my MPG. The emulsion tube is stock. I think going back to stock is a good idea at this point. Stock needle N9ED (what ever that tells ya), 50 slow, & a 210 main.

the N9Ed is the stock needle in the street legal CV44.  Here's a chart that I made on the CV44 needles:



I measured the needles using a dial caliper so +/- a thousand is likely.  Needles are hard to measure exactly (because of taper), so use the information as a guide. 

[Azgunner]

Good stuff Wannabmayor, thanks. I'm going back to stock & I'll work my way up on jetting as needed. I prefer to run a little on the rich side especially in the Phx. summer heat, but not as rich as I think I am now.

[mayor]

Keep in mind when reading the needle sizes, larger diameter is leaner.  I would start with the main jet.  Try a 210 and see what that does.  have you adjusted the a/f screw since changing the pipes?  a 50 pilot may be a bit much.