Deja vous - Rebuild carbs, now tuning questings

[79FiveFifty]

Thanks to all of you and your invaluable wisdom which you have so kindly bestowed upon me - I ordered everything and rebuild my carburetors.

In the rain / snow with a pretty serious cough / cold I got the bike back together and it actually fired right up.

I installed all new o-rings in carbs, adjusted things just as they had come out, and carbs are perfectly in-sync with one another. I installed a new OEM petcock, and made a feeble attempt at adjusting my throttle cables. Sealed my air-box with weather stripping, and replaced missing filter with OEM filter element.

After the bike started up (pretty much immediately) I let it run on choke for a minute or two, then turned the choke off and set the idle around 1,200 rpms. Everything idles ok minus a slight pinging sound but I'm not sure if the engine did that previously or not.

When I rev the throttle slowly, all is well. If I go wide open throttle immediately it bogs and or stalls immediately. A few popping sounds while holding the throttle steady at any rpms.

Please tell me I don't need to remove my carbs to mess with anything inside them...

Any suggestions as to what may be the bogging / popping / pinging?

[hampshirehog]

That bogging is a classic sign of the carbs running weak. Have you put the vacuum tube back on correctly? Plus did you set float height? Or it might be as simple that the motor need to warm up some more.

[79FiveFifty]

Yeah, I only let it warm up for 1 minute.. and vacuum tube is snug at both ends.

It does seem like I didn't warm it up enough though, as my carbureted truck does the same thing if it's not completely warm.

Oh, and yes I set the float heights to 24mm

The popping sound went away for the most part as the bike got warmer also, could it be just from the the "fresh" install of the carbs?

[hampshirehog]

If it goes away when it gets warmer the you're not far off. When you did the synch was it just a bench (by eye) synch? The 550s in particular are sensitive to proper synchronisation with gauges.

[79FiveFifty]

Bench, but i ended up not having to move anything very much because the measurements were very accurate to start with, the bikes pretty young (7K miles.)

I did use a few different measuring tools and a laser to help confirm since you are right, going by eye is tricky. I am pretty sure I have all 4 with in hundreths of an inch of each other.

I forgot to mention, when I rebuilt the carbs, I left the slide arms intact, I didn't take them apart purposely to preserve the original state of tune. Once back together however I made tiny adjustments.

[almarconi]

Even if you get the float heights the same, you need to measure the fuel level in the bowls. Float height might get you close but you really need to measure the fuel level. You want the same level in each bowl. Very small changes in the tang on the float can make your fuel level too high or too low. Porous floats, worn fuel needles can change your fuel level even if the float height is the same. You still need to vacuum sync the carbs, a bench sync is only a rough setting. Did you change the boots from carb to the manifold as well as the manifold o-rings. More than likely you have an air leak somewhere.

[79FiveFifty]

Changed intake pipe o-rings, but not the rubber boots on the intake side. Couldn't find them but If I come across them I will order a set of those. I wish I had ordered new floats and float needles.. maybe I will order some of those too.

I'll try the starter fluid around manifold trick to see if the idle jumps to find any leaks.

Is there any tuning to be done using the air screws on the side of the carbs while installed on the bike or no?

[almarconi]

I'll try the starter fluid around manifold trick to see if the idle jumps to find any leaks.

Carb cleaner or wd40 would be a better choice.

there any tuning to be done using the air screws on the side of the carbs while installed on the bike or no?

I'm not that familiar with tuning the VM carbs but yes the fuel screw on bottom and the air screws on side should be set. A good starting point is fuel screws 3/4-1 turn out and air screws 1.5 turns out.

[79FiveFifty]

fuel @ 1 and air at 1.5.. guess I'll have to just read the plugs and see what I'm getting to know what needs to be changed.

[79FiveFifty]

i took the bike for a test drive, warmed it up, to gas station, got 93 octane in there.. everything was running / driving just fine.

Then.. I go up a fairly steep mountain road, and the rpms die immediately in 3rd gear, the bike stalls.

I turn it around, fires right up.. go down the mountain.. (popping from exhaust while engine braking) the bike will not accelerate what so ever. stalls as soon as you give it throttle if the choke is not on. won't go over 3,000 rpms / 25 mph and if you hit the throttle at all it will die..

The only way I managed to get it home was adjusting the choke back on to allow me to even move it the 6 miles home..

What on earth could be wrong now? I guess I'm running super lean? but why did i make it that far with out a problem.. only on a hill did it die and not recover thereafter.

[Steve]

What on earth could be wrong now?

My guess would be the 93 octane. Get that stuff out of there before you have to burn it out.

Higher octane does NOT mean it's better gas. Higher octane is a band-aid to keep the mixture from lighting with the extra heat of higher compression. The compression in your stock bike is not high enough to heat the mixture enough to light it before the spark, so you don't need higher octane. Higher-octane gas burns slower than lower-octane gas, so the spark needs to be advanced to compensate. Even after you advance the spark to get the mixture fully-burned by the proper time, you will still have less energy available, because higher-octane fuel actually has fewer BTUs per gallon. Any additional power in an engine is because of higher compression, not higher octane or advanced spark.

.

[79FiveFifty]

The reason I put 93 in the bike was because the manual says it recommends 90-95 octane - I figure premium was right there in the middle I guess our bikes don't like it?


Other than that though it should still have run, I don't think it would flat out die like it did with higher octane would it?

[hampshirehog]

It's not the octane rating that's making it do that - you're lean. If you're sure on float height and your carbs are clean I'd have a blo*dy good look at that fuel tap. If it's got a prime position give it a go on that setting - maybe the diaphragm isn't moving far enough. Plus check the filter isn't clogged or the fuel pipe kinked.

[79FiveFifty]

I just dumped my whole tank of gas into the truck, and refilled with 87 octane from a gas can.. no dice.

petcock is brand new, but there is a scew to the bottom right of the level.. does that do anything? the stock one didnt have that, this was supposed to be oem replaced.. and it is oem.. just has a screw for some adjustment my old one didnt have.. no prime position though.

carb heights were all set to 24mm, but come to think of it my float needles did sag about 1mm each.. so im probably somewhere near 22.5/23 could that cause me to run way to lean to ride?

brand new oem air filter, and also no kink in fuel hose.. messed with that about 3 times. (including just now removing the tank.)

listening to my exhaust the left exhaust is fine, the right exhaust sounds to have some sort of metallic clicking sound going on with the engine rpms.

I guess the carbs have to come back out and install all new floats, and float needles huh?

[79FiveFifty]

ordered new float needles.. new floats are 30 dollars a piece at the bandit.. yeah thats making away like a bandit alright..

could the fact that I only turned my pilot fuel screws out about 1 turn be causing me to run lean?

(sorry for all the stupid questions this is my first bike / first time so .. I'm just trying to learn.)