Carb help please

[Chuck78]

FANTASTIC!!! CONGRATULATIONS!!!! What did you do to it this time to get it going right? Float height, slide needle position, & dialing the fuel screws on the bottom in to around 7/8 to 1-1/16 turns out?

55 degrees here, great for late November in Ohio. wow I wish I were riding dirt bikes today... got roped into doing side jobs though... $$$$

[BurtyMcSquirt]

FANTASTIC!!! CONGRATULATIONS!!!! What did you do to it this time to get it going right? Float height, slide needle position, & dialing the fuel screws on the bottom in to around 7/8 to 1-1/16 turns out?

55 degrees here, great for late November in Ohio. wow I wish I were riding dirt bikes today... got roped into doing side jobs though... $$$$

I took the carbs out and cleaned them again, did a very particular bench synch, put 115 mains in with the 17.5 pilots, really took the time to dial in the air and fuel mix screws, and took the mods i made out of the pods. Now I've got a problem where carb #1 is pumping fuel out of the overflow tube with the bike on or off. Its a steady pump of fuel for 1 second and then a pause for 3-4 seconds and then repeat.

[CrazyCloud]

Your float needle is probably sticking. Try gently tapping on that bowl with a screwdriver handle or rubber mallet. If that doesn't do it, you can take that bowl off (with the carbs on the bike) and shoot some carb cleaner up there to try and dislodge/clean out what is hanging it up.

[Ohuami]

I took the carbs out and cleaned them again, did a very particular bench synch, put 115 mains in with the 17.5 pilots, really took the time to dial in the air and fuel mix screws, and took the mods i made out of the pods. Now I've got a problem where carb #1 is pumping fuel out of the overflow tube with the bike on or off. Its a steady pump of fuel for 1 second and then a pause for 3-4 seconds and then repeat.

Could be a sticking needle jet, leaky petcock, or the theres a leak around or on the brass overflow tube like I had on mine. It was a hairline crack, but it would dump fuel through the crack. I just jb weld the crack, how long will it last? i dont know, but it worked for me.

Also i pretty much have the same setup as you right now, do you mind telling me what your settings are turn wise and where your jet needle clip is on? im running 115 mains and 17.5 pilots too. I keep bogging after 4500 or so.

Edit: my bad i meant float needle lol (thanks chuck)

[Chuck78]

Could be a sticking needle jet,

^ ^ ^ I believe he meant to say a sticking float needle or sticking float. The needle jets do not stick, they are fixed to the slide which moves with the throttle cable action

or the theres a leak around or on the brass overflow tube like I had on mine. It was a hairline crack, but it would dump fuel through the crack. I just jb weld the crack, how long will it last? i dont know, but it worked for me.

YES... this is definitely a possibility, as this is very common. I probably have 7 or 10 fuel bowls here that have cracks in that overflow tube, which always tricks you into thinking your carb is overflowing. Really, the fuel is just leaving through a crack and may already be at or near the proper level, and not actually overflowing.
J-B Weld is not gasoline resistant unless you let it cure for a long period of time, several days or a week. Knowing this, the last time I ran across this for a friend's bike, we got a small plumbing torch and soldered the entire exterior of the overflow tube that is in contact with fuel, after sanding it down substantially to clean it.

You could still have a sticking float or float needle, or just misadjusted float. Checking the actual fuel height while the bike is running using a small clear hose shaved down to a point to jam into the drain screw hole of the fuel bowl will tell you if your carb is actually overflowing or if the overflow tube is just leaking.

If you have an air compressor, what do you want to do is take a blow gun air nozzle with a rubber tip, remove the fuel bowl off of the carb, fill it with water, put your finger over the top of the overflow tube, and put the blow gun rubber tip nozzle on the bottom outlet of the overflow tube. Hold your finger capping off the tube really well and blow high pressure air through the tube. Look for bubbles anywhere on the tube where it would be submerged in fuel. I do this as a standard test on every single set of VM carbs that I work on now, since I have ran into so many that are cracked. It seems to correlate with bikes that live in cold climates or have a lot of extreme temperature swings, hot to cold.



Hope this helps ya, Burty.






Let me know if you ever make any riding trips West or Southwest of Pennsylvania. I know an immense amount of incredible twisty roads in Southeast Ohio and West Virginia, learning more in Eastern Kentucky. I love getting down that way as much as possible. The Appalachian Hills lend themselves to a lot tighter twisty roads once you get south of Pennsylvania. Most of Ohio is really flat, but I can show you some of the best roads in the east in Southeast Ohio! I don't think the stuff in Pennsylvania compares whatsoever to the stuff bordering in West Virginia or Southeast Ohio

[Chuck78]

Just for future reference, from a KZ forum, THIS picture illustrates one of the biggest distinguishing features of VM29 smoothbores vs OEM VM26/28 carbs, VM22 and VM24 have rows of ribs on them on the slide towers so they look similar but notably differentiated.
The little square casting on the right sides of the carbs gives away the smoothbores. Most all but the first year have large hex plugs on the bottom for quick change main jet access. and they are clearly made of solid aluminum alloy, not the cheap zinc-aluminum pot metal alloy that all the OEM VM's and most other older OEM carbs are made out of, so the smoothbore VM29's are 1/3 the weight of OEM, as are Keihin CR Special smoothbores.
Looking at the inlet sides of the carbs is also notably different from stock Mikuni VM##SS carbs



The biggest and most important difference is the jet block/hollow slide construction, which can only be seen looking through the venturi (throat). The slide is hollow, and slips right over the jet block. the jet block bolts into the center of the carb and it IS the venturi for the center, sort of like a removeable center section of the throat of the carb. So that the slide just has a tiny round vertical slice of a channel that it moves up and down in, instead of the entire center of the carb being interrupted by a large vertical bored out round section the size of the outside of the slide, which on normal carbs, you see when carbs are at Wide Open Throttle and there is a big recess on the left and right where the slide formerly occupied. a rather large recess. On smoothbores, you just see a little sliver of a slide taken out of the left and right where the perimeter of the hollow smoothbore slide runs. This creates much better jet signal and much smoother airflow, as there isn't a big void on the left and right sides of the throat of the carb right where all the atomization of fuel occurs. constant velocity of airflow, not a disruption of velocity.


Sorry for side tracking your thread, but since you were confused about misinformation about your bike having smoothbores, I thought I'd take the opportunity to point out what they really were, since so many people have the same confusion.

Hollow smoothbore slide:



and the bolt-in jet block center section of the carb that the slide makes up the "smooth bore" center of the venturi:

basically... on a non-smoothbore VM carb, OEM style VM, almost NONE of the metal you see in the lower picture of the jet block would be there, so that the center throat of the carb has a big bulging void here the solid slide travels. the smoothbore uses the jet block and hollow slide to eliminate almost all of the disruption of that big hollowing bulging void.

illustrating the different look up front for the air jet boss areas:



On a built bike that is 750cc or more, the 29mm VM smoothbores are a big performance upgrade. for 550's and 650's that have a lot of mods, head work, bigger cams, Keihin makes a CR Special in 26mm as well. Mikuni only made 29's and 33's and they are long out of production. Keihin still makes the CR Specials in 26, 29, 31,33,35, and I believe another size or two larger. 33 is about as big as you want to go for even a monster built 1100cc street engine. 26/29/31 is the range for hot rod street bikes. 35+ is for racing only, poor low end response, only good for high rpm use

I will stop hijacking your thread now...







Let us know about your fuel dripping issue, if it is a cracked overflow tube, or in fact sticking float or float needle.

[limeex2]

Yes, I am overwhelmed. Be careful what you ask for... Just kiddin Chuck! Thank you for the info and good reading. Mr Burty, If you are getting a new pipe in the future why try jetting now? It will probably change again. Get all the variables mentioned here done over the winter. Nothing has been mentioned about ignition system. Points or electronic? Sonic cleaning, if not using the proper chemicals does not always remove stale fuel residue. Even the smallest bit changes everything and all work will be for not. Many a carb issue has come from "clean" carbs. I believe most people use Berrymans for full soaking with very good results. There has been others who have the same set up as you are attempting and if all of the variables are done and done correctly you will be very close.

[limeex2]

Sorry for not reading all the posts before responding. Seems Like I've done that before...

[BurtyMcSquirt]

I haven't forgotten about you guys I'm just having too much fun riding around on these bonus afternoons. For an update....She's running like a dream with the exception of High idle in second gear when gearing down. I put the APE filter pods on it and rebuilt the back brake tonight a few more rids and I want to start taking it apart for a complete makeover during the winter. It starts up right away no problem every day and it will even kick start with just a few tries. Keep looking in on me from time to time because I'm sure I will have lots of questions over the next couple of months and yes Lime thank you for the suggestion I will be checking points and ignition soon.

[BurtyMcSquirt]

Let us know about your fuel dripping issue, if it is a cracked overflow tube, or in fact sticking float or float needle.

I think the needle spring side (the small metal spring loaded part was catching on the smallest little scratch on the float brass not allowing the float to rise all the way. I fine grit sanded it and It hasn't happened since. I'm getting quite the education and thoroughly enjoying the small successes.

[Chuck78]

You say high idle in second gear. You must mean just when you are revved up and you decelerate, the idle does not settle down. It should do this in any lower gear or neutral if it does it in one... hanging idle always means lean condition, your air screws probably aren't set quite right. Or the fuel screws need to back out maybe 1/16 turn more. a tiny bit makes a big difference on the fuel screws

[Chuck78]

I'm getting quite the education and thoroughly enjoying the small successes.

AWESOME! This is a really great attitude/outlook to have!
If you are not riding a brand new bike or something made within the last 8 years or 10 years, especially something that potentially could have had 40 years worth of neglected maintenance skipped on it, it is definitely important to understand how your machine works! And important to learn how you need to catch up on decades of skipped maintenance!

[Big T]

As to the points/condensors, if you don't know how old they are, it's best to just replace them. However, OEM parts are expensive and most just upgrade to a Dyna S ignition

[allojohn]

If you decide to go with a pointless ignition be aware there two Dyna S ignitions for your bike - you must buy the right one, for either KD or ND. Take a look and see what you have.

[BurtyMcSquirt]

Hey Everyone! I haven't forgotten about how helpful you all have been, I've been very busy on my bike rebuild over the winter and spring and good things are happening. Pictures coming soon.