Topic: Handling and carb issues

[scfire]

 Today I took my first long ride (170 miles) some of which we were in the mountains and noticed two things in particular that need attention and want to pick the minds of the masses.  First off  the bike has a horrible push in the corners.  I can come out hard but have to slow considerably to keep her in the lane going in.  Would lowering the pressure in the front from 38 psi help this?  Also the front forks seem real mushy and I have been wondering about adding preload with a spacer as well as changing to fork oil instead of ATF.  I am also hoping to purchase some new rear shocks ASAP.  Secondly is some carb issues.  I have gone through them and bench synched them but have yet to vacuum synch them.  Between 5800-6200 RPM there is some spitting and sputtering going on and it comes back a little after the 7 grand mark too.  I believe I am running stock mains, but cannot remember 100%.  Should I go up two sizes due to the exhaust?  Thanks in advance for any advice.

Specs are as follows

72 CB350four
Stock size Bridgestone Spitfires 38psi front and rear
Stock Airbox
air/fuel mixture screw 1 turn out
4 to 1 Kerker with baffle

[phil71]

38 psi! that'll feel like riding on basketballs. The 350/4 is harder than most to tune, once moidified. I'd bring the needles up one notch. (
 Spacers might improve stiffness, but probably not a real fix for soggy 42 year old springs.
If you're the kind of rider I think you are, you're going to want to put tapered steering head bearings and new swingarm bushings in. Then it'll come out of those corners without trying to put you in the ditch.

[Untold]

This may be dumb, but are you saying that 38psi is high or low?  I think I'm right around there with my Spitfires as well.

[Bankerdanny]

He's saying it's too high.

[vames]

Factory manual for the CB350F says 26 psi front and 28 psi rear. You're running more than 35%-45% higher than the recommended factory pressure.

I used to go by what it says on the side of the tire for my 400f and I always felt like the tires were way too hard. Running 25-26 psi makes for a much better ride.

[Untold]

Search around, and there are other threads saying 30 is too low, and to start at mid 30psi and go up from there.  So that's how I ended up at 38 on my CB550.  Just sayin

[flybox1]

tiny changes on those smaller carbs make big performance differences.
sync them first....see if there is a change in that mid-rpm flat spot.
if its still there...suggestions:
78 or 80 mains(75 is stock)  -  with your less restrictive exhaust, this is needed.
no need to change needle clip position or (#35) pilot jets.  it should pull hard all the way to redline.
keep the air screw at 1 to 1.25 turns out.
I ran 28psi on my avon roadriders.  front and rear.  handled great.

[TwoTired]

Stock size tires should go by manufacturer guidelines rather than internet guidelines.  IMO.

[vames]

Search around, and there are other threads saying 30 is too low, and to start at mid 30psi and go up from there.  So that's how I ended up at 38 on my CB550.  Just sayin

Just sayin' that those are the numbers from the Honda Factory Service Manual for the CB350F. Take 'em or leave 'em.

Out of curiosity, when you "started at 30 and went up from there" what was the criteria that you used to stop at 38?

[Untold]

I was originally running 42, because that's what I thought the the number on the side of the tire meant.  I had some front end wobble (ended up being other things), so I started searching around for what could be causing the wobble, and came across a tire pressure thread.  That's when I discovered that the number on the tire was the maximum, so I dropped some pressure.  Low-mid 30s just felt bad.  Swishy in low speed corners.  That's how I got back up to 38

[Untold]

And I totally agree with the manufacturer recommendation over the internet recommendation (although, by your logic, I shouldn't listen to you either).  But the original Honda specs were for original tires, and I've read that new tires go by different standards, so I'm not sure how accurate the psi in the manual is, if I'm running modern tires in slightly different sizes than stock.

[Untold]

Here's one of the threads I'm referring to

http://forums.sohc4.net/index.php?topic=118724.0

[phil71]

ok, this is starting to make sense. You put a fatter tire on than stock.  The rim is still orig, so you get 'swish', which is dangerous.  You add air, and that helps rigidity, but that's treating the symptom and not the disease, and there are diminishing returns.. Plus it'll feel like a basketball. Not good.
 PSI determinations have everything to do with how much air a tire needs to keep the weight of the bike up.
Think of it like this. PSI is literally how many pounds a sq/in of your tire can hold up. i.e. :if you had 6 sq" of tire contacting the groun,d inflated to 25psi, it would support 150 lbs.

SO, a larger tire (having more surface area) on the same bike would actually require LESS air than the original skinny ones to feel right. BUT, having not changed rims, you add side to side 'swish', and jacked the air pressure to overcome that..
 You have 2 problems, and you're moving away from the solution in both directions. Either go back to original size tires, or get custom wheels.

[TwoTired]

so I'm not sure how accurate the psi in the manual is, if I'm running modern tires in slightly different sizes than stock.

Then you aren't running stock size tires as you originally told us.
Of course oversize tires need higher pressures because they weren't made to go on the stock narrow rims.  Over-inflatltion is then needed to stiffen the sidewall.

Overinflation also makes the tires wear faster, which is part of the reason why dealers like to sell "bigger tires".  The other reason is that bigger tires are more expensive, increasing their profits.

What size rim did the tire manufacturer specify for you tires?


Or.... what Phil71 said.   

[Untold]

I never said I was running stock sizes. OP did, but I hijacked his thread (sorry). 
I'm running Bridgestone S11 tires on a 550K.  110/90 x 18 Rear  and 100/19 x 19 Front.  Stock rim size. 

The tires were on the bike when I bought it, but I've also seen a number of posts about this size being fine for these bikes, as OEM sizes are harder to find?

[phil71]

never been hard for me. Those sizes you have are suitable replacements for a considerably bigger bike, like a cb750

[Untold]

The thread that lead me to this idea:
http://forums.sohc4.net/index.php?topic=89729.0

[phil71]

that thread is about bigger bikes. Are you still talking about a CB350F?

[Untold]

Nope, sorry.  Like I said, I'm talking about a 550.  Kind of took the thread on a tangent.  I had chimed in that I also ran 38psi, and people asked for specifics.

[flybox1]

Ignore my post above as it refers to 350f carb tuning and tire pressure.
Just figuring out this thread has been derailed for 550 info 
Respect the OP and their topic/thread.
Out.

[phil71]

Yeah, sorry same for me. Also, 38psi is still completely nuts on a 550

[TwoTired]

... as OEM sizes are harder to find?

Only for those that require instant gratification.  Ordering stock sizes isn't much of an issue, just a day or two time delay.  The rear 3.75 replacement is usually increased to a 4.00, though.  But, 4.00 sizes are designed to fit the stock narrow rims.

A 100 front is too big. imo.  If you MUST use metric, a 90 is a better match for this bike on front.  However, the correct 3.25 is still a available, though not often stocked locally.  But, the warehouses have them.

[Retro Rocket]

Stock size tires should go by manufacturer guidelines rather than internet guidelines.  IMO.

Thats not correct at all, those pressures were for old Tires made with different construction methods, newer tires need to have 30-34 PSI or there abouts and usually about 2 psi more in the rear.... Under inflated tires are the main cause of poor wearing tires and bad handling.  1800 gold wing  Honda's run 40 front and 46 psi rear in their tires...  Your soggy front springs will be the cause of your poor handling {pushing at the front} as said earlier, tapered rollers in the steering head, new front springs and swing arm bushes and it will handle well....

From Dunlop...

http://www.dunlopmotorcycle.com/fitment-guide/search?type=fitment&make=12&model=394&year=459&submit=

[TwoTired]

Stock size tires should go by manufacturer guidelines rather than internet guidelines.  IMO.

Thats not correct at all, those pressures were for old Tires made with different construction methods, newer tires need to have 32-34 PSI or there abouts and usually about 2 psi more in the rear.... Under inflated tires are the main cause of poor wearing tires and bad handling.  1800 gold wing  Honda's run 40 front and 46 psi rear in their tires...  Your soggy front springs will be the cause of your poor handling {pushing at the front} as said earlier, tapered rollers in the steering head, new front springs and swing arm bushes and it will handle well....

"Manufacterers" include tire manufacturers.  If the tire manufacturer says to run a pressure in their tire, believe them.  It's not the number on the sidewall, though, unless you are at max load.

[Retro Rocket]

I'm not arguing with you LLoyd, i'm telling you, the old tire pressures of the 70's are long gone, look at any tire manufacturers site and you'll see for yourself...

Here's a chart that may help, and i posted a link to a dunlop page in my last post....

http://www.drivegreen.com/Motorcycle_Tire_Pressure_honda.htm