I have been working on my 1980 80" FLT and it runs pretty well for the most part, but I have some questions about what the operational RPM range of the engine should be.

Pretty much the engine doesn't seem to be happy if I run it below 2000RPM. There is a very noticeable vibration from around 1300-1900 RPM. Anything above 2000, and it fades, the engine is very smooth around 2500. I have not taken it above 4000RPM.

This is not drive-line related, as I observe the vibration in that RPM range in neutral parked, or with the clutch in coasting.

The best way to describe it is that if I am around 1500RPM putting through my subdivsion, and apply any throttle to accelerate, the bike shudders and shakes as it accelerates. It shudders bad, shakes the footboards and shifters, mirrors are blurred so bad you cannot see anything in them.

Once at or above 2000, it smooths out. The idle is perfect.

-rebuilt top end, all S&S parts
-reman CV Carb (but had the same issue with the stock carb)
-new front motor mount, in the right way.
-Top engine mount is good.

This is my first Harley, I have no other Harley to compare it to. The answer simply may be, 'don't run it with a load below 2000 RPM' But it sure seems to me that something is wrong for it to shake like this at that RPM.

Thoughts and Thanks in advance!

 

Not sure if it could be related, but have you aligned motor, frame and wheels?

 

You answered your own question under 2000rpm vibrates and shutters. Over 2000 rpm it smooths out. You should not be in any gear under 2000rpm. Except in first when starting from a stop. 2000 rpm seem to be the Magic number. Other then that shift at any rpm you want above 2000. I usually shift at about 3000. And don't let the bike go under 2000rpm any less and my bike luggs. Unless I give it just the slightest amount of throttle and slowly bring it up to 2000rpm then I can crank the throttle. Other then that no problem no lugging in any gear as long as I'm over 2000rpm

 

lugging the shovel motor will knock the rods right out of a good motor that has 30,000 miles left in it - if you want to hear it go - bob bob bob in gear dust off your wallet

 

Certainly damage to Bottom end will result...
Even too low of an Idle speed can decrease Lifespan.

 

Stock shovels live in the 2000 to 4500 rpm range and most people set the idle way to low to get that low lope and as has been mentioned it knock's the rods right out of them. May seem like she'd screaming and wants to come apart but pushing past 4k while shifting or passing won't hurt the old girl if everything's torqued down and adjusted properly. Shovels shake just the nature of the beast.

 

That right there says it All!!!

 

Gotta love 'em . They sound like no other.

 

Thanks for all the input.

I should probably clarify a bit - I do not lug the bike and the idle is 800-900RPM. The tach is not very accurate and tends to bounce. I set it so the needle is just under the 1000 mark.

I know what lugging is and understand why it is bad for these engines. The vibration that concerns me becomes very noticeable when decelerating and allowing the revs to drop below 2000 prior to downshifting, or when coasting through my subdivision at 10-15MPH with very, very little load.

I just thought something was off being that I would have to run the engine as high as 2200-2300 RPM in order to basically coast through my subdivision without it shaking like crazy.

If the general opinion is that it is normal, then I will just keep it spinning faster.

Thanks again.

 

your 3 rubber mounts - front lower on the engine and the 2 on the swing arm should be replaced as they are 45 years old possibly - and the top and front lower heim joints might be frozen - they are supposed to move with the engine not hold it fast -- all of this can cause excessive vibes in the bike, my T is smooth at all engine speeds because i did all of it