Bog Off Of Idle

[grumpy56]

Hello all. T350 is running better, but still have a bog right off of idle. If I rev the crap out of it, it will pull, at least after it is well-warmed up. Otherwise, the dreaded boggggggggg. Did have to get a new battery as the old one would not charge, strange in that it was only 1.5 years old. Hope I don't have a charging issue also. Anyway, do you think I should try and raise the needle one notch (clip lower) to richen it up a bit? It idles fine, at least at a fast idle, so I am thinking maybe I have a jet problem. Wide open is fine. Thanks.

[tricky1962]

My T500 used to bog pulling away. In the end I tracked it down to ignition timing.

I would suggest you check all the mechanical stuff first - timing, plug gap, points gap etc before playing with mixture.

[Alan H]

Higher revs = main jet. Pulling away = pilot jet/ throttle slide and bottom of main jet/ needle.
Pilot jets perfectly clean?
Are the throttle slides in the right way? Cutaway, to the filters.
Timing +1. 24°/2.88mm BTDC.

There should be plenty of power to pull away from standstill unless you're setting off in a high gear or weigh 200lbs + !
What sprockets do you have? 14/38 standard.

Figures according to my service manual for all models 1972 era. If you haven't a copy, pm me your email address for a copy FOC.

[grumpy56]

Appreciate the input. I did re-check the timing and I've had those carbs apart too many times and I think everything is OK. I do weigh about 215 so I'm sure that doesn't help, but another problem still exists. Am running stock gearing.

[Vintageman]

The T350 should be perfect. I am 220# The ones I own pull the front tire off ground, 1st gear coming off idle.

Bog off Idle usually means those circuits in carb too lean or not atomizing fuel with incoming air.

few things I would check.

1) Do you still have the second Pilot jet installed?. You may want to clean that hole in it. it's very small. its a 0.7 mm opening if I recall. I think the early were 0.6mm

2) The needle Jet. Is is pitted inside? If so you can clean all you want, but it won't fix that. Simply buy new ones. If they are not shinny inside the metering area buy new ones. I think they are 188 series and if obsolete or can't find any get the 192 series.

3) Is the jet needle OEM or aftermarket? I have never seen a proper aftermarket for the later t350. OEM has Mikuni symbol and lettering. What does it say on it?

4) Do you have the correct size pilot jet. Do you have the correct series pilot jet?

Aren't dicking with those carbs fun.

Oh each time you remove and install carbs. make sure the slides are re-synced and Idle speed sync at least initially.

If you top end is in good shape ( is it noisy ... piston rattling at low speeds) and seals good, no vacuum leaks, timed correctly, good batt, all brass shinny new and NOS good to go!

[grumpy56]

Appreciate all the input. Per comments: (1) Secondary pilots installed and as clean as I can get them. Wasn't able to locate any new ones, so am re-using what was there. (2) New needle jets installed. After market variety. (3) Will need to check the jet needles. Not sure if they are Mikuni or some other after-market variety. (4) Pilot jet is correct. And YES YES YES these carbs are "slots o fun"!!!!! I don't know how many times I've had them off and re-installing the stock air filter and boot just adds to the pleasure!!!

[tz375]

It sounds like it's lean coming off idle. To test that theory, you could wind the air screws in 1/4 turn at a time and see what difference (if any) the change makes.

If it is best with the air screws completely closed, that tells us that either a drilling is still partially blocked or that it just needs a larger pilot jet.

[Vintageman]

as clean as I can get them

I am talking sending a wire or correct size drill through the secondary Pilot Jet By clean what do you mean... for example just an Ultrasonic cleaner or did you run a wire or proper bit as just stated? Same with carb body holes. Need to be sure open just checmical or vibration cleaning won't do it


Are we mixing Jet Needle and Needle Jet?

Needle Jet is the brass like tube/cylinder. You said aftermarket? Never heard of aftermarket on these type. Should be using Mikuni. So are your Needle Jets new and shiny inside where it counts? Please advise what you me by Needle Jet so we are on the same page.


Jet Needle. Now these I have seen aftermarket and Keysters are for the early T350 (1969) or T305 only if I recall. So this may be an issue. Never tried older Jet Needle with newer carb Needle Jet - Main Jet. Do you still have OEM Jet Needles?

[tz375]

Lots of good ideas from, but please do not force hard pieces of metal through jets - it changes the flow rates and then they do not flow the same as stock and that makes jetting really difficult.

As Vintageman suggested, needle jets and needles do tend to wear and corrode over time and that increases fuel flow as a rule. That's why the suggestion was to determine what happens ( if anything) when you make one simple series of changes.

[grumpy56]

In addition to cleaning with carb cleaner, I ran thin wires through all the holes as well as the secondary pilot jet. You are correct, my needle jets (always get those mixed up) is the original and the jet needles from a Keyster re-build kit. I still have the original jet needles so putting those back in there may be an option. I removed the needle jets, and from what I recall, they were looked pretty good. I will also try screwing in the pilot jet to see if that might help. Thank you!

[Vintageman]

o not force hard pieces of metal through jets

If that secondary pilot is clogged this is the only way to clean it properly. If you could get it new no worries but you can't. After a few times of non abrasive cleaning you have to resort to some machining (that rhymes )

I even stated the drill size. You won't ruin it unless you shake or bit dull. The only issue is you will snap off drill bit if not careful. Done that.

I doubt a small wire opens it up enough if sent through a couple times. Been here. That jet hangs low in the bowl so tend to get real messed up inside. If you do run the drill bit by hand you will most likely make it a bit egged shaped, but a tad larger won't hurt this particular jet. You could go one size smaller. I use the correct size and go easy. I always wonder how much it matters, that jet being there, but if it there it needs to be opened to size. If not maybe pilot needs to be a size smaller. well you have secondary pilot I would use it

As far as passages in carb body like the pilot holes I run a small wire to punch it through initially (if plugged after cleaning), but of course if you go back forth enough times you will enlarge hole. Common sense must be used.

Just be sure all the hole are open and to there ~proper size. Air passage too. To me it sure seams like you are not getting pilot flow. Or

When needle jets are just beginning to corrode they reduce fuel flow due to added turbulence. Once they wear/erode even more the fuel flow will increase and not atomize well. So that is why a lightly eroded needle jet might be yoru issue (probably just part of it based on your problem description)

Now If the after market jet needle is larger Dia than OEM than that of course kills flow. being as bad a you state you may have stack up of problems.

Verify your secondary pilot, replace all jet you can with new OEM and put the stock jet needle back in if OK.

[Vintageman]

o not force hard pieces of metal through jets

If that secondary pilot is clogged this is the only way to clean it properly. If you could get it new no worries but you can't. After a few times of non abrasive cleaning you have to resort to some machining (that rhymes )

I even stated the drill size. You won't ruin it unless you shake or bit dull. The only issue is you will snap off drill bit if not careful. Done that.

Maybe that secondary pilot jet is nice inside (good eyes to see that). Else, I doubt a small wire opens it up enough if sent through a couple times. Been here. That jet hangs low in the bowl so tend to get real messed up inside. If you do run the drill bit by hand you will most likely make it a bit egged shaped, but a tad larger won't hurt this particular jet. You could go one size smaller. I use the correct size and go easy. I always wonder how much it matters, that jet being there, but if it there it needs to be opened to size. If not maybe pilot needs to be a size smaller. well you have secondary pilot I would use it

As far as passages in carb body like the pilot holes I run a small wire to punch it through initially (if plugged after cleaning), but of course if you go back forth enough times you will enlarge hole. Common sense must be used.

Just be sure all the hole are open and to there ~proper size. Air passage too. To me it sure seams like you are not getting pilot flow. Or

When needle jets are just beginning to corrode they reduce fuel flow due to added turbulence. Once they wear/erode even more the fuel flow will increase and not atomize well. So that is why a lightly eroded needle jet might be yoru issue (probably just part of it based on your problem description)

Now If the after market jet needle is larger Dia than OEM than that of course kills flow. being as bad a you state you may have stack up of problems.

Verify your secondary pilot, replace all jet you can with new OEM and put the stock jet needle back in if OK.

If these ain't it must be something else ?

[grumpy56]

Thanks for all the info Vintageman. Need to get out in the garage and find my problem!!!!