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He says he's Australian but he has a Canadian accent, a ?
 

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Discussion Starter · #11 · (Edited)
Well seems I do have problems after all, but back to the bike if any of you guys can help I would be most grateful.

Having some problems with my new bevel ss, backfires on deceleration since I bought it (but didn’t think that much of it). After a couple of decent rides (2nd ride not running fantastic) I went out on the highway gave it a skinful and it started running really bad backfiring constantly even while cruising /accelerating.
It was almost dark and I could see the backfiring was coming from the front cylinder (right hand pipe popping flames out). Upon arriving home I did notice my fuel line was empty to my front carb but when I took the line from the carb off and turned the tap on, fuel ran freely.
Put the line back on and turned the tap on but fuel did not run onto the line ? now I’m confused as when I turn the rear fuel tap on I can clearly see movement of fuel filling the line.

Makes sense I thought front cylinder backfiring, no fuel in line , running lean , yes of course that’s the problem!
The previous owner did have a problem with blasting media in the gas tank after having it stripped and repainted, could this still be blocking the fuel supply?
But if the tap is blocked why does fuel flow out the tap through the line no problems but soon as the line is hooked up to the carb it doesn’t seem to flow freely at all (not sure what to think).

Started the bike the next morning, still running shit, filled up the front fuel line using a syringe, started it and still ran shit, eventually I took out he spark plugs and cleaned them and swapped them around, bike started and ran fairly well (but still backfiring on deceleration)

Another thing of note was that when I undid the float bowl emptied it and put back on, turn on the fuel tap and fuel immediately filled the carb and the whole fuel line? fuel did not fill the fuel line until I emptied the float bowl.
:confused:
PS: Satansfist, I'm not allowed to say banana
 

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From my experience with my SS with 40mm carbs it's often the front one that plays up. As well, the fuel flow to that carb can sometimes seem to be a mystery. Do you have both taps on? Does the tickler on the front carb flood it whenever you press it? Have you checked the float level? Does the float move freely? Have you cleaned out the various jets, air passages and filters?

Bruce
 

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Discussion Starter · #13 ·
From my experience with my SS with 40mm carbs it's often the front one that plays up. As well, the fuel flow to that carb can sometimes seem to be a mystery. Do you have both taps on? Does the tickler on the front carb flood it whenever you press it? Have you checked the float level? Does the float move freely? Have you cleaned out the various jets, air passages and filters?

Bruce
Hi Bruce, Yes both taps are on, it doesn't have a tickler I have a 1982 model with a choke, haven't checked the float or float level, haven't cleaned out the various jets ,wouldn't really know where to start (i'll have to get a workshop manual).
cleaned out the little filter behind the attachment where the fuel line enters the carb (it was about a quarter full of blasting media, silica I think)
was thinking float level was my next target but don't know how to check.
Was also going to get some more fuel line and hook up the carbs to the opposite taps to see if fuel will run freely into the front carb., 2ndly maybe swap carbs around to see if the rear cyl. played up instead.
cheers Greg
 

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I suspect that the fuel pipe issue might be a red herring, normally the two fuel taps are linked with a cross pipe under the tank, so the left-hand tap may provide the fuel until the level drops, then the right hand feeds fuel. Anyhow, what you describe could be ignition or carburation and it is very hard to separate the two. The ignition cables in the engine break down over time, so this is a possibility, but it is easier to eliminate the carbs as the culprits.

The first thing that I would suspect is that the manifold rubbers between the manifold and inlet port are split, allowing in air, this is very common and even a small amount of air will cause popping and banging; CHECK THESE FIRST!

Are the plugs looking black and sooty? If so, one possibility is that the choke cables are too tight, which will stop the choke plungers fully seating, and allowing the choke to leak fuel through. Check that there is free play on the choke cables.

The carbs are very simple and I would suggest that you remove each one from the cables, take off the float bowls and using an exploded diagram, unscrew each jet and blow through it, bolt everything back on and retry. If there is still no cure, then try to get the carbs ultrasonically cleaned. If the bike has been standing for even a short time, gum can build up in the pilot air drillings and cause the symptoms that you describe. I don't think that the float level would cause misfiring.
 

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Cheers Greg,

The Dellorto tuning guide at the bottom of this website will pretty much tell you anything you need to know about these carbs. It is downloadable. I'm inclined to believe you have a fuel delivery problem rather than an electrical one - I've been there. Having said that the pick-up wires should be replaced as a matter of course if they haven't been already because this is a notorious trouble spot that affects all these bikes.

https://www.ducatimeccanica.com/

Bruce
 

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Could be some crap in the float needle or the tap for the horiz.cyl. If the needle and seat is blocked or stuck, fuel won't flow in the line. Once the float bowl is full and the level is correct the fuel in the line won't move until fuel is used. Depending on the curve in the line it may not appear the line is full back to the tap but fuel will flow as the level in the carb drops. I would suggest you inspect the float needle and seat and clean the pilot jet and passages. Then go on to the pickup wiring, you can check it somewhat with an ohmmeter [pickup resistance and shorting to ground] or pull the primary cover to see if the insulation is cracking/falling off. The Bosch ign. boxes, once considered eternal are starting to prove otherwise, causing misfires or not advancing the timing. Remember, most carb problems are electrical and vice versa.
 

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Cheers Greg,

The Dellorto tuning guide at the bottom of this website will pretty much tell you anything you need to know about these carbs. It is downloadable. I'm inclined to believe you have a fuel delivery problem rather than an electrical one - I've been there. Having said that the pick-up wires should be replaced as a matter of course if they haven't been already because this is a notorious trouble spot that affects all these bikes.

https://www.ducatimeccanica.com/

Bruce
I would normally check the carbs first as well, though you did mention it started to run better when cleaning and swapping the spark plugs. Like someone else said, the boots can get cracked and let air in as well so check those (if you have any suspicions, use electrical tape and wrap them to test [not usually a smiled upon long term solution, but easy to verify and easy to remove]). I would check the float height in the carbs, it looks like the link Roadstar gave you is a great starting point for the whole carbs in general

float height: https://www.ducatimeccanica.com/float_levels.html

When you were out cruising and it wasn't running so well, was it losing power at any point or just backfiring? Were you able to get an idea of how long the bike sat idle before you bought it? That would give you a good starting point to look at too (carbs and gas tank are almost always culprit on a bike that's sat for any good amount of time--especially if it ran well before it was put away).

There's a great youtube video by "common motor" on a honda twin carb, its 3 parts but it's a great starting point if you just need to wrap your head around the whole process, though it's not specific to your bike.

P.S. thanks for that link Bruce, bookmarking that
 

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Discussion Starter · #18 · (Edited)
Hi Duccout, I did have an earlier ss years ago that did have fuel taps linked with a cross pipe, this 1982 model I have doesn’t have that cross pipe just the line direct from tap to carb.
Just thinking with the ignition problem would it do anything if I changed the spark plug leads around to opposing cylinders (would it change which cyl. Played up if it’s ignition problem?) or do those wires in in the case more determine which cylinder would play up?

I’ll definitely check those manifold rubbers first, the choke cables (thanks Duccout), the plugs do look a bit black and sooty, all I did was wash the front one with some wax and grease remover (similar to a white spirits) and the front cyl. Suddenly started to come back to life with a lot of spicking and spacking backfiring that’s when I took out the rear one and cleaned that too and swapped them around and it ran much better.

Tyr, good tip with the electrical tape , “When you were out cruising and it wasn't running so well, was it losing power at any point or just backfiring” yeah lack of power as well it was practically running on one cyl. I think?
“Were you able to get an idea of how long the bike sat idle before you bought it” yeah it was sitting idle for a couple of years (but used to start it periodically), I asked the owner when I first went to look at it when was the last time he started it and he said about six months ago (he stored with an empty tank tank)
I’m not even sure whether the carbs have been set up that well or when it had a carby tune, though it starts easy and idles fairly well just occasionally snuffing (I think when it kind of gets a little backfire or spit from that front cyl.?)

Just thinking back before I cleaned the plugs I noticed the front carb was not exactly vertical (probably at 80 or even 70 degree lean on it, if 90 degree in straight up and down) when I moved it to the vertical position and started it it started spitting out the carby and I moved it back to close to the original position and it stopped the spitting from the carb. That’s what got me thinking about the float position.

Anyhow thanks for all the tips (much appreciated) and the links Bruce and Tyr and Wdietz and Duccout I’ll try those other checks if the simpler things don’t work.

Well busy day ahead
 

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Discussion Starter · #19 ·
Well didn’t get a real lot done today, checked the choke cables had some play, put some tap around the manifold.
Took the bike out for a run, bike was running really good to my surprise (but still some backfiring on deceleration) took the tape off the manifold and still running good , put tape back on, still running good, took it back off still running good
Also idling real well, no snuffing at all.
Did notice at all times today my front carb fuel hose was full up. So thinking there was some kind of blockage that has come good, but would that cause my plug to foul up like it was running rich? I wouldn’t have thought so
But maybe there is a couple of problems? All I know for sure is I’m confused.
If it’s still running great next weekend I will take off the exhaust and put new header pipe gaskets in and put some muffler sealant on all the joins to see if that effects the backfiring (personally I don’t think it will make a difference but I want to rule it out)
 

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Back-firing is due to weakness in the carburation, or a leak in the exhaust system, which you are checking out anyway. Are the exhaust ring nuts tight?

It may be that the carbs are gummed up after the bike has been sitting, and it may clear itself with use. A few years ago I couldn't get out on my 900 for about three months due to the winter weather; normally I would have drained the float bowls, but as I expected each weekend to be going for a ride, before the weather intervened, I didn't. In the spring when I could get out, the bike ran horribly, but each time I went out it got better until it cleared completely.
 
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