225 upper rpm limit?

So...

I have been thinking it might be because of the span too.

So The only thing to do is go to 4.56's

this wont hurt trail riding just helps I think and maybe find a good engine speed for around town.
Top speed I dont care about.

I have a buddy who has a 5 with225, t90 and 4.88's and 33's he says for driving home ect. it 4000 rpm alot so all things being equal 4.56's should split the differance...

Anybody with the sm420 can chime in please...

bought new plug wire's too tired to put in tonight

 

The problem in this is that your 4th gear is the same as all the other 3 speeds that are pulling fine and lugging down the road with no problems with 3.73 gears. I might understand a small loss for the 3rd gear in this tranmission compared to some other 3 speeds but it isn't much. The t86 has even a steeper 2nd gear when compared to the sm420. I till think you havea problem somewhere.

 

Update.
I dragged my beatup self out to the garage and swaped in the new wires.

Took a short drive.
it feels like I gained about 10 or 15 horsepower.
And it goes flat at 3950 rpm which is a gain.
Smoother also.

Its masking the low rpm's in 3rd but only because theres more power now still around 1000 rpm at 30, 35 mph.

 

It's always a bit of a guess, the commando has run flawlessly for 3 years, after new cap,rotor,wires, points etc.
The 3B needs tinkering every month or so, guessing most of it is worn dist and H2O in the carb.
3.73 in c101 and 5.38 w OD in hte B, either will run 15 mph to too fast for me smoothly in high gear.
Both are 225's.
My first guess is dist, but it doesn't take much change in the carb mains to screw things up too, even a thousanth or 3.

 

With 3.73 gears and 32" tires you should be doing 1200rpm at 30mph. If your motor is flattening out at 3900 rpm there is still a problem somewhere. Mine will tach up to more than 5 grand pretty easily in 1st and 2nd.
In fact years ago when the motor was old and tired (166K) miles on it, I tached it several times to well over 5000rpm figuring I had nothing to loose.

Your gears while tall for trail running are quite good on the street and you should have no complaints, heck most modern trucks with v6's run 3.55-3.73 gears.

 

Thanks for the encouragment guy's.

Will work on the timing next.

The good news is It keeps getting smoother and more powerful nice suprise.

 

Yea, you might try advancing your timing a little, just listen carefully for any pinging. If you hear it, back off the timing.
Stock timing marks are kind of based on a best guess, meaning that they aren’t necessarily an exact representation of TDC (Top Dead Center) unless you’ve had your cam and crank degreed and marked true TDC on the timing marks.
Many a crusty old mechanic I’ve talked to will tune timing by ear then use a timing light to make note of where the timing settled for future reference.