Bog Right Off of Idle

[grumpy56]

Hello all. Finally have the 1970 T350 running pretty well. However, have a "bog" right off of idle, therefore I really have to rev it to get it going. Currently have the pilot screw at the "standard" setting (1.75 turns out). Any tuning suggestions? Thanks.

[yeadon_m]

Sounds like it is too rich or too lean just as the throttle slides lift. Therefore, I'd try a fairly extreme change in pilot air screw setting to see whether it helps or makes it worse. Try a whole turn in or a half turn out. My gut (with no experience of this bike) is its too lean and turning the screws in and so richening the off idle mix might help. So long as your float heights are correct then too lean is more likely, often from things like a part-plugged pilot jet or pilot circuit somewhere from pilot air intake through pilot outlet and bypass holes.
Good luck!
Mike

[grumpy56]

Thanks Mike. Will play with the adjustment screw. Just re-built carbs, including setting the float level, so hopefully an air adjustment will fix the problem.

[Vintageman]

is your bike all stock including air box?

What does "... Just re-build carbs..." mean exactly please

Do you have the second pilot jet installed?

Is your only issue coming off idle when starting out only? Otherwise, how's it running?

Usually bog off idle only condition is a lean pilot circuit. In this bikes cas eif you have secon pilot that little passage may be partly plugged.

[grumpy56]

Bike is 100% stock, airbox and carbs. Bought rebuild kits consisting of new jets, gaskets, etc., about everything except for the floats which look OK. Set them to spec and cleaned everything that I could get to with carb cleaner and compressed air. I did not get a new "pilot jet B" in the kit, but cleaned the old one and screwed it back on over the other pilot jet. Only issue is a bog just off of idle. Otherwise runs great up to redline, at least in the lower gears. Have not had it out on the highway where I can see how it runs in the higher gears. Do appreciate your help.

[Vintageman]

Bought rebuild kits consisting of new jets

So we are talking a Keyster kit or the eBay cruzin man himself carb kit?
Did you swap out the OEM Jet Needle for the one in the kit? The t350 had two different needles. If you did swap and still have OEM needle and OK I would use the OEM and not one from kit.

The other issue is the Needle Jet. Looking down into the Needle jet barrel, first ¼” where it does its metering, is it smooth and shiny or rough and pitted looking? Chances are low that it is OK in there.

Your issue sounds like pilot circuit is too lean (if issue is when at very small throttle and blipping it more open quickly). Else all the above ammters too. Did you make sure the two little pilot holes feed holes in the carb body to supply engine were open?

Did you use the kit supplied pilot jet? If so get a true Mikuni pilot jet just to be sure. On Pilot B jet did you ensure the little hole was indeed perfectly open and smooth inside? I have found that these little guys see a lot of moisture (since they are low in the bowl) I think its a 0.7 like Mikuni air jet. At one point I found out what size drill that was and run that through the hole, actually I think I went a tad larger. Be careful for drill bit is small and it can snap. Ask me how I know

[grumpy56]

Appreciate the info Vintageman. Yes, used a Keyster kit and all the stuff that was in there. Going to rip in to it this weekend and see what happens.

[Coyote]

Keyster kits have a bad reputation. Rightfully s0. They earned it. Most everything in the kit is junk. DO NOT use the included main jet, pilot jet and most importantly the slide needle. About the only thing in the kits I've had some OK luck with is the float needle and seat. Bowl gaskets might fit -- might not. It looks like a good deal up front, but in reality it's wasted money.
Vintageman, what you need to keep from breaking small drills is a pin vise. Available at most hobby shops, it comes with 2 reversible collets that handle anything from zilch to 1/8 inch. The unused collet stores in the handle. Yes, you turn it with your fingers.

[Vintageman]

used a Keyster kit

If I recall the Keyster Kit is for the 1969 version of the carb. 70-72 had different jetting


See Specification 6 and 11 ->
http://www.oldjapanesebikes.com/mraxl_G ... ins/page-2" onclick="window.open(this.href);return false;

pin vise

I had this when I got the bits I need from machine shop where I use to work (miss this) Like you said just use hand motion and feed partial turns reverse an repeat. The drill needed is very small and snaps real easy so go slow.

[grumpy56]

Can you purchase other rebuild kits? Any source is appreciated.

[Vintageman]

I only think there is Keyster and Cruzinimage.

I think Keytser has a mark on jet needle -Yxx - if you google you may see what it crosses to in Mikuni (OEM). I think it is the early one like I said, but check since i have seen many things and getting older and forgetting stuff.

The Needle Jet (188 or 182 series forget) is obsolete? you can use the 159 series which is available. That one takes a hex main jet versus large round main and you can "cross" round to hex, but I just use the round for it crossed threads in just fine

My first thought if issue only coming off idle quickly is lean pilot circuit. If issue in the 1/8 to 1/4 throttle range then Needle circuit stuff

[grumpy56]

Fooled around with the old Suzi yesterday and it seems like the "bog" issue has disappeared, at lest for the most part, by enriching the mixture just a bit (1/4 turn on the mixture screw after synchronizing them). However, now I can't get the idle to return to normal. It goes up to about 4 grand and stays there quite a while. Will re-adjust the cables and don't know if a slide or needle jet is hanging up. Can't get slides or springs for these carbs very easily. I was thinking of stretching the spring a bit to see if I can get some additional downward force in case a slide is hanging just a bit. Thoughts? Thanks.

[ConnerVT]

Idle adjusted too lean will make it slow for RPMs to drop.

But hanging at 4000 RPM is something different, I would suspect.

[Vintageman]

If it revs high idle and no starting out bog, it may because the slide is open so much it is not using pilot circuit but, running off needle. So it sounds even more like your pilot circuit is too lean. I don't believe 1/4 turn on pilot air screw would fix as much of a bog as you first explained it to be.

Don't over torque carb mounting nuts, it causes carbs to deform: sticking slides

Make sure the idle adjust rod is not bent, not allowing you to return slide to idle position

Make sure throttle cable not bound up and has slack at idle

I don’t think stretching spring trick works. I have doubled up springs one slightly smaller dia. But if slide is binding or idle rod bent that won’t help. Should work with stock slide springs

[grumpy56]

Thanks guys. Will need to pull the carbs and go through them again.