Gettin over 40...(mph)

[Bauer]

Hey all.

Got a carb question for the guru's.

The 80 Standard we have in our garage had some carburator issues that were hammered out by me just before xmas, The bike sat for 5+ years after my dad determined it was too expensive to fix the diaphragms. They had developed some pinholes and small cracks, nothing too major, but enough to cause vacuum problems. Thanks to yamabond I was able to fix the carbs, clean them thoroughly (taught by a certified technician friend that grew up around these carbs) and sync them on the bike and give it to my dad for a xmas present. Due to the cold weather here in Nodak, I was unable to take the bike out for a cruise until this spring. This is where the problem comes into play....

The bike fires off, but doesnt really seem to want to, my non-expert diagnosis is that it is extremely lean at this point. HOWEVER once running, she purrs like a kitten. You can sit on the bike, not moving, and run the crap out of it all day throttle wise and she never seems to have an issue. But once its out on the road, getting past 40 is impossible. The effect is comparable to bad pickup coil wires (for those of you that know what im talking about) you can give it all the throttle you want, but not go anywhere.

A recheck of the diaphragms show no holes or possible leak points. So a vacuum leak is likely out.

Bike has stock airbox with K&N filter, factory jetting, 4-1 exhaust (brand unknown)

What are my options????

Thanks for the help.

[TopCatGr58]

Back to the basics.

Hey Bauer,

Sounds electrical to me. Start with the basics, when running are ALL 4 pipes hot, or do you have some that are cold? Which ones in what pairing, 1-2, 3-4 combo...likely fuel, or 1-4 and 2-3, likely ignition...PU coils, Ignition coils, TCI?

Plugs, wet, dry??

You could always pull the carbs off of your SG and put them on for a test, if still same, then ruled out carbs!
T.C.

[Bauer]

TC,

Thought about the carb swap, but im running 120 mains on my bike for the exhaust and pod filters. Would the added richness cause problems?


Will do the ignition check otherwise


Thanks

[Ken Talbot]

I think you nailed it with "effect is comparable to bad pickup coil wires". Remove the cover, fire it up, and start yanking those wires. You will know right away.

[Bauer]

pickup coils were fixed approx. 15000 miles ago.

Just did the fix on my special this week, I couldnt get past 2000rpms in any gear, so making it to 40 was definately out.

Im working on boxing some stuff up to move out of my apartment by mid may, later tonight I am going to go swap the carbs onto my bike (all ready had them off the standard) at least this way Ill be able to tell if its fuel or electrical related.

[Bauer]

30 minutes after starting (gotta love pods) I was able to swap, drive, fill gas, and re swap the carbs. Almost cried at the 3.019 price for premium gas. Gettin to be too expensive for my college arse to ride the bike, I cant wait till ive got a full time job. ANYWAYS, heres the fidings.....


Definately not eletrical related, something internal to the carbs. Bike runs smoothly and accelerates smoothly up to about 38mph, at this point, it seems to be starved of gas. It doesnt seem to make a difference if its just a gradual roll up, or hard on the throttle. All cylinders are hot enough to take away your fingerprints for life.

Now what??? Could it still possibly be a vacuum problem, not raising the slides far enough? or more likely a fuel setting problem (air/fuel screws??)

[TopCatGr58]

Okay,
If I understand you, you put your dad's rebuilt/repaired carbs on your SG, and it exhibited the same symptoms as your dads G!?

Back to the beginning, you repaired the pinholes in the diaphragms. Have you checked to make sure the vacuum slides actually still move?

I was playing with my bike some time back after working on the carbs, and doing some test video recording, and had the filters off so I could see down the carb intake throats. Sitting there in neutral, no load on the engine, I was able to rev it to 7Krpm and the vacuum slides barely raised....this was SLOWLY rolling on the throttle. But when I would crack them open from idle developing a lot more vacuum and the slides would pop and jump up considerably until the rpms raised, and the vacuum equalized, and then the slides would lower again.

I don't remember folks recommending fixing them with Yamabond? It's a good gasket sealant, but not necessarily a good adhesive? Using some liquid rubber cement, with some pieces of rubber gloves or such is what I remember, but haven't reviewed them for a while?
T.C.

[Bauer]

A while back when I was researching ways to repair the diaphragms, I came across a thread on here recommending the use of yamabond 5 to repair cracks/pinholes. It worked quite well and still retains its flexibilty.

Same symptoms and carbs, different bikes.

The slides not moving is an option, one we were leaning towards as well.

I was playing with my bike some time back after working on the carbs, and doing some test video recording, and had the filters off so I could see down the carb intake throats. Sitting there in neutral, no load on the engine, I was able to rev it to 7Krpm and the vacuum slides barely raised....this was SLOWLY rolling on the throttle. But when I would crack them open from idle developing a lot more vacuum and the slides would pop and jump up considerably until the rpms raised, and the vacuum equalized, and then the slides would lower again.

Now please take note that all I know about carburators is the parts, and how to clean said parts.

If what knowledge I do have is correct. the slides should rise, hold and fall, by throttle position (open, hold, close respectively)????

[TopCatGr58]

Sorry Bauer,

But with the OLDER or Manual type carbs that have the slides connected to the throttle cable, then YES, it will rise and fall as you turn the throttle. BUT, ours are vacuum controlled, and so depending on the load of the engine, the amount of vacuum varies, and so the pull on the slides varies as the vacuum and needs of the engine varies. While cruising, there is very little load on the engine, carbs, and so the slides are actually not riding very high at all, but when you want to accellerate, you crack the throttle, which opens the butterflies, this creates a vacuum differential and draws the slides up which raises the slide needle, letting in more fuel with the increased air, but as the engine responds, and the vacuum evens out, the slides will drop down "some". They will be higher than at idle, but not near as high as when under heavy load and large throttle input!
T.C.

[Ken Talbot]

Bauer, have you tried testing the diaphragms by removing the pods, then lifting each slide with a finger? Lift up a slide, remove your finger, and see how fast the slide falls back down. I won't hint at the answer - try it yourself and come back and tell us what you see.

[fredintoon]

alignment?

Hi Bauer,
if this is your first go-around with vacuum-operated carbs you might not have noticed. On the outer edge of the diaphragm there is a small half-circle bulge in the rubber. In the groove in the top of the carb body where the diaphragm is located there is a matching cut-out. When the diaphragm goes back in the bulge on it's edge has to fit in the cut-out. If it ain't, the diaphragm piston will be rotated from it's proper orientation and the diaphragm will not seal. This will for sure not let the bike run right.
Fred Hill, S'toon.

[Bauer]

sorry for the delay, was busy cleaning...

TC, my error, wasnt using the noggin. I actually knew the answer to that, just didnt think it through past the fact that we use vacuum.

Ken, Hey, I do know one trick haha. The slides rise with slight tension(against the spring) and fall slowly as well(equlizing the pressure) They dont drop like you were hinting at.

Could the equalization tube between the diaphragms and the float bowls possibly be plugged??? Thus causing the massive inflow of air when on the throttle, but no equalization (lower than atmospheric air pressure) between the dia's and the bowl???

You'll have to excuse my lack of terminolgy.

[Bauer]

Fred, I was aware of the half moons on the dia's and they are all positioned correctly.


Im not a virgin, but I dont have many years of experience either

[Dennyz]

Low float settings can cause a similar problem.

[fredintoon]

It takes a delicate touch

Bauer sez:-
Fred, I was aware of the half moons on the dia's and they are all positioned correctly.
Hi Bauer, um, yes, but,
you gotta be real careful fitting the covers back on or the slightly fat rim around the diaphragm won't be properly trapped in it's groove to make the proper seal even if the half-moon is in the right place. Over the years (and those things are older than you are fer chrissake) the rubber has changed shape just enough that it don't quite fit nice any more. I smear them with hydraulic seal installation grease to initially stick them in the grooves then slowly & sensuously slither the covers on to feel them touch the carb body all round then hold the cover down while I put the screws in.
Fred Hill, S'toon.