cruising in 2nd gear holding throttle study and

[jo jo]

Like i was saaying throtttle study in 2nd and i get a hesatation,is that a flat spot? And i just went thru and cleaned jets and carbs. Bs38 carbs. Needle clip set at manual specs and mix screws set at specs,bike does have pods and open pipes.Any suggestions would be appreiciated.

 

[5twins]

Hmmmmmm, a throtttle study, sounds serious, lol, lol.

 

[Dead Roman]

What do you mean a hesitation? If the throttle is steady the revs will be steady. Are you talking about accelerating after long periods at the same throttle setting?

 

[gggGary]

If you go looking through 5twins posts you will find the "hot set up" for what you got. It will not be a guaranteed run great, but it will be a good place to start. Define "pods and open pipes" neither is ideal for a smooth running engine. If what you want is style and looks you are good now, if you want a great running flexible engine after your mods you will have to earn it by tuning not buy it or luck into it. Plan on buying several sets of main and pilot jets and doing lots of runs and changing as you dial it in. Again you can take 5twins advice to the bank. We would love to hear how this goes for you.

Yeah I am bit harsh above but truth is; tuning is hard work, alter the intake and exhaust and you have to tune. Just looking through all the jetting setups Yamaha used through the years of production will give you an idea of what an art tuning is.

 

[jo jo]

I understand gggary, it take's fine tuning and may not be perfect with my setup.i also had a flat spot in the idle,but i replaced my advancer springs and got that better, im gonna try some main jet upgrades, and i will let u know where she goes.thanks

 

[gggGary]

OK but we don't know which BS38's you have, there were at least three major types and several variations over the years.

Pictures help figure out what you have since they were often swapped.

 

[jo jo]

There linked and have the press chocke. I think there 78, but could be 76 or 77 .yes?

 

[gggGary]

Yes
These are 76-77
View attachment 12424

And these are 78-79

The obvious difference is the float bowl vents were external on the 76-77 and moved to the intake bell so to be inside the filtered air on the 78-79

Here is the jet chart

Note the huge change in main jet size in what is essentially the same carb between the two types.

 

[peanut]

wow awesome post Gary as usual....

Those pictures are sheer porn

 

[gggGary]

I am not sure who did the top set, Oldskool?
I am guilty of the bottom set.
Yeah when they are clean they sure are pretty.
One of my goals this winter is to have an overhauled set of each type on the shelf. I have a 78-79 set that is done, and it is so nice to grab it, throw it on a bike and see how the bike runs knowing any issue are NOT carb related! The herd has been growing again, it is back up to about 8 and the van is headed out to a retired oval trackers "cache" tonight after the slimy crud get together. -2C right now though (5 AM) it will be a chilly 150km run today.

 

[peanut]

sounds like you have a serious habit there Gary hope you manage to pick up some good stuff

I like your thinking re bolting on spares that have a tested and known performance.

if its any consolation its -2 over here in the UK tonight also .

 

[jo jo]

Boy those are nice,makes me want new carbs,that was very helpful.I will take them off and check the float vents.Its getting prettychilli up here by lake erie,dont think i'll be riding anytime soon.t.t.u.l,jojo

 

[Scrambled]

Boy those are nice,makes me want new carbs,that was very helpful.I will take them off and check the float vents.Its getting prettychilli up here by lake erie,dont think i'll be riding anytime soon.t.t.u.l,jojo

You can send your carbies out for a rebuild or you can buy new carbs. There are options. But keep in mind, with a modified exhaust and filters you might have to throw some brass at them anyway.

 

[jo jo]

Oboy, my carbs are 76-77 ,so i set them per manuel, and now my left cylinder isn't as hot as the right and i also notice on the left mix screw isn't doing anything turn it all in and no stall,unlike the other side.....im ready to throw in the towl.

 

[gggGary]

Have you synchronized them?

 

[weekendrider]

Clean the pilot circuit on the left one again. Carb cleaning is just part of owning these.

 

[jo jo]

Ok, i wil try what about float level should i rich up that side?i also noticed some fuel drip from that bowl....

 

[gggGary]

Fuel drip is usually a leaking float valve or bad float. Test your floats with a quick dip in a cup of hot water, bubbles = trash.

 

[jo jo]

Gggary,float foats,no bubbles,but brittle gasget and tore intake was my problems,and i switched them with some ok ones and back in action,but now that you helped me figure out my carbs are77,i set the airmix screw at 1.5 as specs call for, and not good, had to open them up to get that after throttle backfire out.Doe's this mean i need to increase main jet or pilot?

 

[jd750ace]

The main jet size is for wide open throttle. The pilot jet up-size would have helped your original complaint of hesitation at steady state throttle. I believe what you had was lean surge, and since gaskets fixed your original issue, that was the case, but the jetting would have been a band-aid working around the air leak. If you have to use excess mixture screw, that's still your pilot jet needs to go up. Low speed issues will most always be air leaks, or the pilot jet. Your mid-range roll-on performance is needle height and taper, and the WOT is the main jet. That's just general CV carb stuff, and the circuits overlap. For the final word on any of these carbs in particular, 5twins can get you straight.
Also, you can cause yourself a world of headaches by trying to jet when you are not sure you are airtight on the intake side, and/or when the carbs are not synched up.