Engine upgrades and mileage dropped? : V-Twin Forum: Harley Davidson Forums

jtmurph00 · 11-01-2009, 01:46 AM

Ok here's the background, bought a 99 NightTrain last year w/ 20,000 miles +/-. Original owner changed to a 42mm CV carb, a screaming eagle cam (he didnt know which one), Kuryakyn hyper charger, and samson rip saw exhaust. It ran rough from day one but I averaged about mid 40's mileage.
After 10,000 miles I changed out the kury hyperharger for a ness big sucker w/ a new K&N, the kury filter probably had more oil on it than the engine did so it couldnt have been breathing too good. Also cleaned & tuned the carb and the BIG change was a Baker 6 speed. Well after all that now Im only getting in the mid 30's mileage.
Whats the deal with that, it actually runs perfect now, smooth as can be, but it is guzzling the gas down. I was hoping the rpm drop from the 6 speed would push me into the 50's mpg.
Im planning on checking the engine out real soon to make the sure the cam bearing was changed to a Torrington. What else should I check to bump up my mileage? Would "downsizing" back to a 38mm CV carb help?
My riding is probably 90% highway @ 65-75 mph down here on the hot & humid Texas coast. Thanks for any help.

jerry34208 · 11-01-2009, 05:38 AM

How much are you willing to spend?

Hillside · 11-01-2009, 06:48 AM

Bring the compression to 9.75, and run a Wood 6.
It WILL be smoother, and it WILL gain power/fuel economy.

Scott

springer- · 11-01-2009, 08:21 AM

First I would figure out what cam and ignition you have before throwing more money at it. Depending on the cam it should do better than 30's for mileage. The ignition module is a big factor in tuning, if you still have a stock module or a fixed curve module, that could be a factor as well. A good adjustable ignition and a proper tune on the carb and you should be in the 40's easily. Also do a compression check and see where you are at. The 42 CV on a relatively stock 80" bike might cost you a few MPG's but it really depends on tuning and how you ride. The 38 CV might be fine for you if it you are just riding it and you aren't always up against the rev limiter.

strokerjlk · 11-01-2009, 08:26 AM

Quote:

Also cleaned & tuned the carb

always go back and check the last change you made.
what was the (tune ) you are referencing?
with the changes you describe a/c and tranny you shouldn't experience any mpg drop.
the tune and cleaning is what I would reevaluate

Coolmaker · 11-01-2009, 08:30 AM

Try riding a tankful and not using 6th gear. If the mileage goes up, than you have it over geared. Had that happen to me, changed the gearing and presto, gained about 8 mpg..

jerry34208 · 11-01-2009, 08:34 AM

Quote:

Originally Posted by Coolmaker

Try riding a tankful and not using 6th gear. If the mileage goes up, than you have it over geared. Had that happen to me, changed the gearing and presto, gained about 8 mpg..

I was thinking the same thing. Provided it's tuned correctly (determine that first), either change the gearing or change the cam. With tall gearing a guy needs to use a cam that produces peak torque down low at the same rpm as when doing the speed limit in top gear.

springer- · 11-01-2009, 08:36 AM

Quote:

Originally Posted by Coolmaker

Try riding a tankful and not using 6th gear. If the mileage goes up, than you have it over geared. Had that happen to me, changed the gearing and presto, gained about 8 mpg..

Yep, 6th gear can actually require more throttle to maintain speed. Depends if it is an overdrive gear or a 1:1. If it is 1:1 then it should be no different than the 5 speed 1:1.

Coolmaker · 11-01-2009, 09:32 AM

Quote:

Originally Posted by springer-

Yep, 6th gear can actually require more throttle to maintain speed. Depends if it is an overdrive gear or a 1:1. If it is 1:1 then it should be no different than the 5 speed 1:1.

You are correct with one exception, Baker DD6 overdrives the primary with a 28 tooth compensator. So even with the 1 to 1 out it is geared taller..

I changed my Baker back to a 27 tooth compensator, and it made a large difference. It is not too tall now and 6th is allot more usable... MPG went from 34 to 42.5... Of course the bike accelerates much better too. The RPM'S are still dropped by about 300-350 when on the interstate too..

jtmurph00 · 11-01-2009, 08:56 PM

Yep, Baker DD6 is what I went with. I'll try as was suggested and ride a tank worth in 5th and see what I get for mileage there. The 27 tooth compensator sounds like a good idea also.

As far as the carb the shop that did the trans swap cleaned up the carb also. I feel confident that the tune is right on just because it runs so good now compared to how rough it was before.

I was considering doing something with the ignition also when I do the cam so I'll definately do it now.