discouraged & desperate! need help.

[mason s]

getting desperate & really need help. my bike is driving me up the walls. I've been wrenching on it for a couple months now. upgraded to a hughs pma after my rotor went tits up. ever since I've had a tough time. left side coil went out not long after. which I replaced, & am now just having such a hard time tuning things. carbs have been off five times already, & are clean as all hell. my setup is a 1976, points, bs38s with unis & cocktail shakers.

my problem is this.. the left side of my bike seems impossible to tune. I took it on a ride yesterday & it was running decent, but bogging off idle until I gave it enough gas to pick up. so I tried going up 1 on the pilots, & it seemed okay until I started getting white smoke out of the left exhaust. something I've never seen on my bike. pulled the plugs, right side looks perfect, left is dark & wet (oil fouled?) put a new plug in & it's popping on the left & wouldn't idle well. why is my right side so resilient but the left is so damn stubborn? no matter what jetting I do the left side seems to struggle, but it's getting great spark.. sprayed carb cleaner on the intakes to see if I have an air leak but I can't really tell or see anything unusual. though I've never done that sort of test...
any help would be so greatly appreciated. thanks!

 

[azman857]

Float levels set? Synced? Dirt can show up at anytime to keep floats down and keep gas flowing into the bowels. Are the floats free to swing? Float needles in spec and not damaged? Float seats in spec and not grooved? jetting the same?
Is the coil getting 12V? Timed to spec? Plug wire up to snuff. Spark plug cap OK

 

[scabber]

Did you sync the carbs ?

 

[mason s]

carbs are synced, float height set, & functioning properly with needle & seat. new plugs & wires, coil testing well, I tried switching the floats & needles to see if problem switched to right side but continues on left. I have the carbs back off now, needle & seat look good, no grooves or imperfections & needle working properly. bike is timed & tuned otherwise. do you think maybe a slide isn't working properly? it seems to with the carb off... or maybe it got out of time somehow? it fires right up but can't seem to get it jetted or mixed right. it's been a tough one for me. thanks for the replies guys. hope that helps narrow things

 

[mason s]

okay so I think I may have finally figured out what's going on. may be hard to explain but the needle with clip on my left side carb didnt seem to be sitting as far down as the right side. pulled it apart & the clips are both in the middle position, The slides both seem to function okay, but with the carb upside down the problematic side doesn't seem to respond quickly when I push the needle down. itll settle at the half way point. where as the right bounces right back. sorry if this is at all confusing. this is a new one for me.

 

[TwoManyXS1Bs]

I'd try an isolation test.

Pull left plug, unplug left point.
Run the idle screw up a bit.
Start and set idle. You're now running a 325cc single (right side).
Ride it around a bit, see how it runs.

Now, reverse the scenario.
Pull right plug, unplug right point.
Put the leftside stuff back in place.
Fire it up, ride it around, see what's different...

 

[TwoManyXS1Bs]

okay so I think I may have finally figured out what's going on. may be hard to explain but the needle with clip on my left side carb doesn't seem to be sitting as high (with carb upside down) as the right side. pulled it apart & the clips are both in the middle position, The slides both seem to function well, though that needle is acting as if it is in the leanest most position, if not beyond that. a few mm difference in height for sure

Check the markings on both needles. Then cross check with the needle numbers in the carb guide...

 

[mason s]

they both say 4m1 on them which is to spec for a 76. the left side needle just wants to settle lower than the right. (again, carbs are upside down.) I can pull up on the needle and it rises s hair but settles back down a couple mm. right holds its place well. if that makes sense.

 

[peanut]

if the problem is bogging off of idle or poor throttle response off idle,... then that doesn't involve the needles . The needles don't come into play until 1/4 throttle onwards.

Bogging off idle is usually caused by a rapid increase in air and a slight lag in fuel delivery due to the huge vacuum created when you yank the throttle open. To compensate for this ,the slides on a CV carb rise slowly, creating a strong vacuum which in turn pulls the additional fuel through that is required .

You need to look at the pilot circuit. if the pilot jets are correctly sized and clean and both the air mixture screws are set correctly and the pilot air intake is cleaned and not blocked by the air filter (mouth of venturi ) then you need to look at the diaphrams.

Make sure the diaphram air equalisation vent (top vent, mouth of venturi ) is not being blocked by your air filter rim.

Lift both slides, block the diaphram vents with your finger then let the slides drop. The slides should stay where they are or drop very slowly.
If either of the slides drop smartly then you have an air leak either where the diaphram surrounds your needle or around the edge of the diaphram where it seals or a small hole or tear in the diaphram.

My diaphrams were old and stiff so I smeared a little vasoline around the edge of the diaphrams before replacing the caps and that sealed mine perfectly.

Remember .....the air mixture screw to set the idle allows a miniscule amount of air in and even a 1/2 turn of the screw can effect the idle dramatically so that......... tiny amount of air leak is all that is needed to completely screw your carb mixture settings

 

[mason s]

makes good sense, thanks peanut. appreciate the help. after all I've been through with the carbs & had a feeling it may be some sort of air leak/diaphragm issue. which would make sense of this mess. I'll do the couple tests & make sure all is sealing well in the morning, & report back. thanks again for the detailed response.

 

[weekendrider]

peanut if the slides are not closing maybe it does affect the idle?
The off idle bog does it have to be the fuel catching up to the amount of air?
Maybe with one slide not closing it could be a flood bog, too much fuel without enough air?

OP didn't you mention somewhere that you also have excess (leaking) fuel on one side?
If so is it the same side as the slide problem? Have you compared slide spring length?

 

[peanut]

peanut if the slides are not closing maybe it does affect the idle?
The off idle bog does it have to be the fuel catching up to the amount of air?
Maybe with one slide not closing it could be a flood bog, too much fuel without enough air?

yes it could be due to a slide/s sticking... they may have been swopped between carbs during rebuilding and sticking but I wouldn't expect the engine to run at all if they were.
I should have asked if the engine still bogged if the throttles were opened slowly or if the revs stay high and don't return to idle smartly

All engines face the same problem when opening up the throttle from an idle situation. The engine suddenly draws a huge amount of air which depresses the vacuum and reduces the amount of fuel drawn into the carb venturi.
CV carbs compensate with the diaphrams keeping the slides from rising too fast which maintains the vacuum and effectively gives the extra shot of fuel needed.

Flat slide carbs don't have diaphrams so you can't take them WOT off idle without bogging. Thats why later flat slide carbs have pump valves to inject extra fuel at that point .

It sounds like there are several issues and the carbs probably need to be set up again from scratch.
I don't really understand what mason s means by the left side needle wants to settle lower than the right when upside down ?
Is it this that makes you think one of the slides might be sticking ?

 

[mason s]

peanut if the slides are not closing maybe it does affect the idle?
The off idle bog does it have to be the fuel catching up to the amount of air?
Maybe with one slide not closing it could be a flood bog, too much fuel without enough air?

OP didn't you mention somewhere that you also have excess (leaking) fuel on one side?
If so is it the same side as the slide problem? Have you compared slide spring length?

yeah it was hard to tell on my ride the other day whether the bog was a too rich or too lean type of problem. I am leaking gas on the other side, actually. can't seem to get that to go away either. floats & needles & seats all work perfectly fine. I don't get it.

 

[mason s]

yes it could be due to a slide/s sticking... they may have been swopped between carbs during rebuilding and sticking but I wouldn't expect the engine to run at all if they were.
I should have asked if the engine still bogged if the throttles were opened slowly or if the revs stay high and don't return to idle smartly

All engines face the same problem when opening up the throttle from an idle situation. The engine suddenly draws a huge amount of air which depresses the vacuum and reduces the amount of fuel drawn into the carb venturi.
CV carbs compensate with the diaphrams keeping the slides from rising too fast which maintains the vacuum and effectively gives the extra shot of fuel needed.

Flat slide carbs don't have diaphrams so you can't take them WOT off idle without bogging. Thats why later flat slide carbs have pump valves to inject extra fuel at that point .

It sounds like there are several issues and the carbs probably need to be set up again from scratch.
I don't really understand what mason s means by the left side needle wants to settle lower than the right when upside down ?
Is it this that makes you think one of the slides might be sticking ?

the bog was prevalent when throttle was opened slowly. just from a dead stop to a slower take off. almost as if I was starting in 2nd gear.
what I mean is the slide & slide needle dont return to their normal seated position. It stops just shy of that. but functions properly & smoothly otherwise. i tried posting a photo of it but it doesn't seem to want to let me. I'm going to head out to the shop today & try to see if there is a problem with the diaphragm

 

[peanut]

ok good luck ...keep us posted

 

[mason s]

weekendrider, I just had my carbs back apart & one of the springs looks a hair smaller, couple mm's, not much but is noticeable to the eye. got the slides to move nicely, & Vaseline'd the diaphrams to get a better seal. as well as replaced the gaskets on the main nozzle/needle jets. putting it back on the bike now...

 

[weekendrider]

Is it the one from the slide that doesn't drop fully? If they are the same amount of coils you might try stretching it?

 

[mason s]

it was, got it stretched just a hair & the seem nice & even. the gaskets I got for the needle jet are barely too fat & don't want to seat well so im stuck there till i track down a better size.

 

[TwoManyXS1Bs]

Try a forum Google custom search on "Needle jet oring"...

 

[mason s]

found it thank you. I got a 1.5 x 4 I'll hunt down the 1 x 4